In Vitro Characterization of Mems Based Piezoelctrically Actuated Drug Delivery Device for Biomedical Applications

In Vitro Characterization of Mems Based Piezoelctrically Actuated Drug Delivery Device for Biomedical Applications

Abstract

Implantable devices that detect and treat diseases without any intervention required from the patient are expected to be the trend of the future. This paper presents a peizo electrically controlled MEMS drug delivery device for on-demand release of defined quantities of drug in a sustained and controlled manner. A drug-loaded polymer based micro reservoir (600μm ×550μm) is sealed by a Polydimethylsiloxane (PDMS) membrane placed over the drug reservoir on which the piezoelectric material is deposited. On application of voltage across this piezoelectric material, the membrane deflects allowing the fluid to fill into the chamber that will mix with the drug and due to concentration variation; the drug would come off the reservoir or vice versa. A 0.3μm-thick PZT material is deposited on 20μm PDMS membrane. Discharge of the drug solution and the release rates were controlled by an external electric field. Characterization of the devices was implemented in-vitro using the colored water solution. The reservoir was capable of delivering 20μl drug on application of 10V.

Keywords: Polydimethylsiloxan; Drug Delivery; PZT Materialy

Introduction

In recent years, one of the most exciting progresses in MEMS application is the rapid evolution of Biological-Microelectromechanical systems (BIOMEMS). The BIOMEMS has gained its attention due to the microfabrication technology which has been applied to the successful development of a variety of health care related products. The research on microfabricated devices for medical application is gaining more attention. The microfabricated drug delivery system and its utility in the medical application have become a major topic of research [1-4]. In addition to basic components, such as micro channels, microvalves, micropumps, micro mixers and micro-reactors for flow management at microscopic volumes, various novel sensor and detection platforms have been reported in the micro-fluid and BIO-MEMS fields. Many of the so-called micro total analysis systems (μ-TAS) or lab-on-a-chip systems have also been reported and will offer new paradigms in biomedicine and biology, in particular, the ability to perform point-of-care measurements [5-6]. A microchip delivery system consists of a substrate which consists of fabricated reservoirs capable of holding chemicals in the solid, liquid, or gel form. The microfabrication of these devices includes numerous techniques such as lithography, thin film deposition, etching, and so on [7]. The Microfabrication technology for drug delivery system has many advantages over the traditional drug delivery approach which uses spherical drug delivery principle [8]. The use of micro technology offers a number of advantages which may modernize the field of controlled release. Microfabrication also offers precise control over shape, size, and geometry of delivery devices which in turn can increase the drug loading capacities and provide better control over drug release. Single microfabricated devices can integrate multiple reservoirs with different drug or bio-molecules and can be filled in with Pico to nanoliters of the solution, this offers a significant advantage of releasing the drug in a multi-directional way which makes it unique from the unidirectional spherical drug delivery system [9-11].

There is extensive work being carried out to use Polydimethylsiloxane (PDMS) which is considered to be bio compatible, less expensive as the main material for different drug delivery systems for cancer treatment, HIV treatment etc. PDMS based drug delivery systems can be used to achieve prolonged release profiles [12]. The drug that will be loaded into the PDMS structures can be sustained for months. The drug delivery is controlled by different actuation techniques such as diffusion or magnetic actuation [13-15]. The developed device is capable of delivering a required quantity of drug to the targeted site using piezoelectric actuation technique. The device was actuated using piezoelectric actuation technique. This non-invasive fabricated device provides reusability, precise control and can enable the patient or a physician to actively administrate the drug as and when required.

Device Fabrication

The molds for the micro reservoirs, were made using photolithography by SU-8 2150; (MicroChem Corp., MA, USA) negative photoresist was spin-coated on a glass substrate and patterned. Cured PDMS [Sylgard 184 Silicone Elastomer, Dow Corning Corp oration] was then molded using the SU8 pattern (Figure 1). Also a 20μm thick PDMS membrane was prepared by spin coating the PDMS on the glass substrate. These reservoirs and the membrane are then treated with argon-induced plasma for 15mins and test liquid was filled in the reservoir as a sample drug. The treated membrane was then metalized (aluminium) followed by the sputtering of 0.3μm PZT layer and later evaporated for aluminium electrode using masks. The membrane was irreversibly bonded to the reservoir layer. Next, an aperture of 100*100μm 2 was drilled with a UV laser (254 nm wavelength). The bellow diagram describes the flow of the fabrication of PZT-Electrodes.

Figure 1: The membrane fabrication.

Results and Discussion

Unlike the conventional drug delivery devices, the fabricated Piezoelctrically actuated device can be used to deliver the drug to a specific target [16-18]. The PDMS membrane and the reservoir are made hydrophilic by argon plasma treatment, in order to prevent the adsorption of the drug on the PDMS surface. This surface modification is also required to have a uniform deposition of the PZT material. The fabricated device is shown in Figure 2. The device was fabricated with different membrane thickness with 5μm, 10μm and 20μm thickness. The actuation test was also carried out varying the deposition thickness of PZT for different membrane thickness. It was observed that increase in PZT thickness with constant membrane thickness results in less voltage application which is an advantage of this present device. The table shown in the below Table 1 summarizes the voltage required to actuate the device with different thickness.

Actuation Test

The actuation of the PZT membrane was achieved by applying variable voltages across the PZT electrodes. The device with test liquid was immersed in water. The voltage across the electrodes was slowly increased in steps. It was observed that there was permeation of the test liquid with respect to the increased voltage. it was further proven using the microscopic testing of the obtained sample with changed colour. The release of the drug is due to the deflection of the PZT membrane. The rate of drug flow was controlled by the actuation voltage. The direction of deflection of the membrane can be controlled by the direction in which electric field is applied across the electrodes. The graph in Figure 3 shows the flow of drug Vs the applied voltage. The maximum amount of the test liquid delivered was found to be 20μL. The volume of drug loaded can be varied by changing the size of the reservoirs. The purpose of this drug delivery device was to measure the drug release as a function of external actuation and not for the characterization of the drug. The percentage of cumulative drug release was calculated considering the device of PZT thickness 0.5μm and it was calculated by the below equation

(%) = × 100

Conclusion

Advances in drug delivery systems have brought better control rates and increased efficacy. The developed DDS can be used for both the liquid and solid drugs. The device finds many applications where targeted and controlled delivery is required, such as protein delivery, insulin delivery, chemotherapy etc. The actuation method of the device was verified along with all the unit steps and it is concluded that increasing voltage across PZT increases the deflection of the membrane which ultimately will be used to deliver the drug into the target source. Different PZT materials with differed properties such as relative permittivity, density, can be used as electrodes for the actuation.

Titanium Plate Cranioplasty Induced Intravascular Papillary Endothelial Tumor: Case Report and Review of the Literature - https://biomedres01.blogspot.com/2020/03/titanium-plate-cranioplasty-induced.html

 

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Current Recommendations on Treatment of Acute Diverticulitis -Mini Review

Current Recommendations on Treatment of Acute Diverticulitis -Mini Review

Introduction

Diverticulosis is a common disease in Western world and is associated with a Western lifestyle with low fiber diet, smoking, constipation. It is quite rare in the East, however its incidence is growing also in the Eastern countries. Diverticula are a small outpouching of the colonic wall and are harmless, unless they became inflammed or cause other symptoms. Colonic diverticula can occur anywhere in the colon or rectum, but they most often occur in the descending and sigmoid colon [1]. The majority of individuals (80-85%) with colonic diverticula remain asymptomatic, 10-15% of people with colonic diverticulosis develop abdominal symptoms, such as abdominal pain, bloating or changes in bowel habits. Those symptoms, without macroscopical changes within diverticula, we describe as a symptomatic uncomplicated diverticular disease (SUDD). The other complications ot diverticular disease are acute inflammation of the one or more diverticula (acute diverticulitis), bleeding, fistulas with other organs, intestinal obstruction. The lifetime risk of developing acute diverticulitis in people with colonic diverticulosis is about 4% [2]. This mini-review article summarizes some latest guidelines and suggestions regarding treatment of acute divericulitis, which were proposed mainly by the World Society of Emergency Surgeons (WSES) [3].

Mini Review

Diverticulum is the protrusion of the inner layer of the intestinal wall (mucosa and submucosa) through the weak points in the muscular layer of the intestinal wall, forming small pouches (diverticula) that bulge out the large bowel. Inflammation of diverticula is defined as diverticulitis and is most sommon in the sigmoid colon [4]. Acute diverticulitis can be simply classified as uncomplicated and complicated. In uncomplicated acute diverticulitis the inflammation is limited to the bowel wall and does not spread beyond the visceral peritoneum. Complicated diverticulitis is, when the inflammation spreads beyond the bowel wall with formation of pericolic or distant abscesses or perforation in to the abdominal cavity with consequent diffuse purulent or stercoral peritonitis [5]. The most simple and understandable classification of complicated diverticulitis was proposed by Hinchey, which classifies complicated diverticulitis in to four stages. Stage 1 is a acute diverticulitis with a pericolic abscess, stage 2 is acute diverticulitis with a distant intra-abdominal abscess, pelvic abscess or retroperitoneal abscess. Hinchey stage 3 describes complicated acute diverticulitis with diffuse purulent peritonitis and stage 4 with diffuse stercoral peritonitis. Hinchey classification helps us to decide, whether to treat patients conservatively or more invasively with percutaneous drainage or surgery. Uncomplicated acute diverticulitis can be managed conservatively with antibiotics. Some authors believe, that mild cases of uncomplicated acute diverticulitis are self-limited and don’t need antibiotic therapy. Mild cases of uncomplicated acute diverticulitis don’t need admission to hospital but need to be carefully followed-up [6].

Approximately 15-20% of patients have complicated acute diverticulitis and have an abscess on CT scan, when they are admitted to hospital. Patients with smaller diverticular abscesses (less than 4-5 cm) may be treated by antibiotics alone. Patients with larger abscesses (more than 4-5 cm) can best be treated by percutaneous drainage combined with antibiotic therapy. Whenever percutaneous drainage of the abscess is not feasible or not available, based on the clinical conditions patients with large abscesses can be initially treated by antibiotic therapy alone. However, careful clinical monitoring is mandatory [3].

In Hinchey stage 3 and 4 acute diverticulitis surgical management is mandatory. Some authors recommend minimally invasive procedure with only laparoscopic lavage and drainage of the abdominal cavity in Hinchey stage 3, when there is present purulent peritonitis without evident hole in the colon. However, further studies need to be done to elucidate the role of minimally invasive surgery in complicated diverticulitis. The other option, which is currently the gold standard for treatment of a perforated acute diverticulitis with diffuse peritonitis, is standard open surgery with removal of the diseased colon and formation of terminal colostomy (Hartmann’s procedure), irrigation and drainage of the abdominal cavity [3,4,6]. The colostomy can be temporary or permanent, depending on the patient’s age, general condition, comorbidities and also on patient’s desire to reconstruct the large bowel. In young and healthy patients with acute perforated diverticulitis some authors recommend one stage procedure with primary anastomosis, however there is a risk of anastomotic dehiscence and another operation with formation of the terminal colostomy [3]. Even in young and healthy patients with massive peritoneal contamination it is the best option to perform two-stage procedure with Hartmann’s procedure first and terminal colostomy closure later [3-6].

Conclusion

Acute diverticulitis is a complication of diverticulosis. It can be uncomplicated or complicated. Uncomplicated forms of acute diverticulitis can usually be managed conservatively. Complicated acute diverticulitis can also be managed concervatively with antibiotics or in combination with percutaneous drainage. Surgical management must be employed for advanced forms of complicated acute diverticulitis with perforation and peritonitis.

A Note on the Application of Advanced Statistical Methods in Medical Research - https://biomedres01.blogspot.com/2020/03/a-note-on-application-of-advanced.html

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A Note on the Application of Advanced Statistical Methods in Medical Research

A Note on the Application of Advanced Statistical Methods in Medical Research

Introduction

The data on many aspect of life science are both categorical and numerically measured values. Some of these data are observed from controlled and/or random experiments. Whatever be the source of data, the analysis of these helps the researchers to infer about the characteristics of the population from which the data are collected. The researchers in the field of medical science often face the problem in doing analysis of the collected data due to lack of knowledge of proper statistical techniques suitable for a particular data. For proper conclusion about the parameter of the population, it needs the application of the proper analytical techniques. Once a technique is identified, the analysis can be performed using any of the Statistical Packages. The main aspect of the data in bioscience is related to public health and main aspect of analysis is to suggest ways and means to control the disease and to suggest the methods so that premature death can be reduced, specially the child and infant death. For some countries, the failure of birth control is also a health hazard. Thus, the health planners need the proper analytical findings in the field of medical science and in the field of other aspects of bioscience.

The empirical analysis in the field of health science needs data related to health hazard collected from several units suffering from any health problem or expect to suffer from some communicable or non-communicable diseases. Any unit under study may provide different types of information (information of values of variable). As the values of the variables are collected from each member of the investigated units, the variables are expected to be correlated. We usually recognize these collected data as Multivariate Data. There are different methods to handle these Multivariate Data. In this note, application of some of the multivariate techniques are discussed. The multivariate analysis has two main aspects, viz.

a)Dependence analysis, and

b)Interdependence analysis

The multivariate regression analysis including logistic regression analysis, discriminant analysis, and multivariate analysis of variance are the topics of dependence analysis. The interdependence analysis, also known as data reduction technique, deals with principle component analysis, factor analysis, cluster analysis and canonical correlation analysis. The data, multivariate or uni-variate, are collected according to some pre-determined objectives. The analytical plan is also pre-determined so that proper conclusion can be drawn according to the objectives. The whole activities along with statistical interpretation are presented concisely. This presentation of analytical results is known as reporting writing. However, the presentation of analytical results along with different activities of the research work varies from work to work and it also varies with the variation of objective of the research. Let us now discuss some of the application of the multivariate analysis using a part of the real data collected by Urmi and Bhuyan [1]. They have already done some analysis and presented in some of the research papers published in home and abroad [2].

Application of the Multivariate Analysis

Multiple Regression Analysis

For regression analysis the general consideration is that when n sample units are investigated to collect information on several variables, it may happen that some of the variables are interrelated. For example, prevalence of diabetes [ yes= 1, no = 0] and level of BMI (kg /m2) are interrelated along with other variables, viz. age, income, residence, level of education, marital status, occupation, gender, smoking habit, physical labor, food habit, habituated in processed food, restaurant food, etc. These factors mentioned here are interrelated and some the factors depend on income. Again, income depends on level of education and profession. If it is expected that blood sugar level (y mmol /l ) of any person, children or adolescent or adult depends on age (x₁ years ) , height (x₂ meter ), weight (x₃ kg ) food habit ( x₄, taking more protein = 3, more rice = 2 more sugar product = 1 and healthy food = 0 ) and family income (x₅ in thousand taka ), multiple regression analysis of y on x₁ , x₂ , x₃ , x₄ and x₅ can be performed , where the multiple regression model is given by

y = B₀+B₁x₁+ B₂x₂+……….. + B₅x₅+ e

In general y depends on k (= 5) explanatory variables x’s, e is a random component which is inserted in the model to study the impacts of other variables which are not included in the model. The objective of the study is to estimate the parameters Bi’s and to test the significance of these parameters. Under usual assumptions, the analysis can be done. Using a part of the data of Atika and Bhuyan [1] the analytical results of regression were shown in Tables 1 & 2. The analysis was done using 125 observations. It was observed that blood sugar level significantly dependent on income. Here for the conclusion made was dependent on the assumption that the explanatory variables (x’s) were independent and the random component (e) was normally and independently distributed with mean zero and with common variance (Tables 1 & 2).

Logistic Regression Analysis

Let us consider that the prevalence of diabetes (y = 1 for diabetic patient, y = 0 non-diabetic person) depends on some of the variables discussed above. Here dependent variable is a binary variable (indicator variable) instead of a continuous variable. Thus, usual multiple regression analysis is not suitable to study the effect of explanatory variables on the dependent variable. To overcome the problem, Logistic regression analysis is to be done. As an example, using the same set of data as mentioned above, the logistic regression analysis was performed, and the results were presented in Table 3. This analysis also indicated that the income and height of the respondent had significant impacts on prevalence of diabetes (Table 3). As a further example of logistic regression, let us consider the analytical results of data on smoking habit of students of American International University - Bangladesh [3,4], where smoking habit [yes=1, no=0 ] was considered as dependent variable and age of students, father’s education, mother’s education, family income, residential origin and knowledge of health hazard of students were considered as dependent variable. The analytical results were shown in Table 4. The analytical results showed that smoking habit was significantly influenced due to the variable age of students, residential origin and knowledge regarding health hazard of tobacco smoking. The example is a case of binary logistic regression, where dependent variable is classified into two classes. The dependent variable can also be classified into several classes and we can do the similar analysis.

Canonical Correlation Analysis

In a separate study [5] it was observed that smoking habit and awareness regarding health hazard of tobacco smoking were significantly associated. Again, these two variables were related with other socioeconomic characteristics. Hence, Bhuyan and Urmi (2018) decided to observe the joint relationship of the variable’s awareness of the health hazard of tobacco smoking with other socioeconomic variables. This was done by Canonical Correlation analysis, which is also a component of multivariate analysis (Table 5).

Factor Analysis

It is a multivariate technique to reduce the data. For example, a diabetic patient came to a doctor for treatment. Before start of treatment, doctor needs to know about the height, weight, BMI, along with other characteristics. But BMI depends on height and weight. Here BMI is a common factor. Thus, instead of observing height, weight and BMI, it is better to observe only BMI and BMI will help to provide a conclusive decision regarding decision the prevalence of diabetes. Here instead of studying many variables, some common factors can be identified for conclusion. The technique of selection of few factors for further analysis known as Factor analysis and it is a data reduction technique. The factors are selected in such a way that most (around 90%) of the variability of the data set is explained by the selected factors. One of the selection procedure is Principle Analysis and principle component analysis is another technique of interdependence analysis. As an example of the factor analysis, the data mentioned above had been used to select some the important factors to study the prevalence of diabetes. The factor analysis provided two important factors to study the variability in the data set of the prevalence of diabetes. The two factors explained 65% inherent variation in the data set. The first component indicated that the prevalence of diabetes was mainly for body weight followed by age and height. The analytical results were presented in the following Table 6.

Discriminant Analysis

It is also a multivariate technique in which a set of data can be classified into several classes according to some indicator variable and mathematical method is applied to discriminate the sample units so that some important variables are identified for the discrimination of the group of observations. For example, let us consider that the sample units are classified as diabetic and nondiabetic. It was observed in some studies that [5,6] diabetic and nondiabetic people were significantly different due to socioeconomic variables and some variables were very important to discriminate the two groups. Bhuyan et al [6] have done such an analysis to discriminate the students of public and private universities in respect of some social characters. There are different mathematical steps to estimate the discriminant scores for the students. Later on the correlation coefficients of each variable and the discriminant scores are calculated to identify the important factors for two groups of students are discriminated. The correlation coefficients between variables and discriminate scores are shown in Table 7.The analysis provides information that public and private university students were significantly different in respect of their social background. Education of parent was very much influencing in discriminating the students of public and private universities. The second important factor is the residential origin followed by age of students. More urban students and students of higher ages are admitted in private universities. Smoking habit was not significantly different between two groups of students (r = 0.002) (Table 7). As a further example of discriminant analysis, the analysis presented by Fardus and Bhuyan [7] may be mentioned. In that paper, the diabetic patients of some urban and rural areas in Bangladesh were discriminated by the types of diabetes. Including one unknown type, the patients were classified into 4 types of diabetes and 3 significantly different discriminant functions were derived. The major cause of discrimination of the patients were studied by the correlation coefficients of the variables and the discriminant scores. The significant correlation coefficients were presented in the following Table 8. The first function discriminated well among the groups of patients and the variables age and education followed by residence were important to discriminate among patients of different types of diabetes. The second function discriminated well among the patients of different groups and the important variables age, income followed by education were identified for discrimination.The third function discriminated well among the patients of different types of diabetes and the variables age and residence were identified very important for discrimination. Further statistical analysis in Medical Science are investigation of association of two characteristics and hence to study more prevalence of a particular characteristic. As an example, let us consider the data of used by Urmi and Bhuyan [1], where the association of level of obesity and prevalence of diabetes were studied. The results are shown below. It was observed that the prevalence of diabetes and level of obesity were significantly associated (p-value =0.033). Form the study of odd ratio it was observed that the overweight and obese group had 69% more chance to be affected by diabetes than the non-obese group. The risk ratio for this group is 1.47 (Table 9). In the above analysis both the variables used are qualitative in nature. These variables do not follow normal distribution. Most of the test statistics are based on the assumption of normalty of the data. But the test is valid as it is a non-parametric test. Other non-parametric test are also used in the analysis of data of medical science. The study of health hazard and survival analysis are other two aspects of analysis of data related to medical science. In this note a short review of multivariate analysis was presented. For further analysis one can go through the books on applied multivariate analysis [8].

Cds and Cdse Quantum Dot Solar Cells Production and Improving Efficiency of the Cells by Ion-Doped Quantum Points Cds Holmium - https://biomedres01.blogspot.com/2020/03/cds-and-cdse-quantum-dot-solar-cells.html

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Titanium Plate Cranioplasty Induced Intravascular Papillary Endothelial Tumor: Case Report and Review of the Literature

Titanium Plate Cranioplasty Induced Intravascular Papillary Endothelial Tumor: Case Report and Review of the Literature

Abstract

Intravascular Papillary Endothelial Hyperplasia (IPEH) or Masson’s tumor are non-specific vascular lesions which enclose reactive proliferation of endothelial cells that arise in an organizing thrombus. These tumors are an extremely rare intracranial entity, with few cases in the literature reported.

Case Report: The authors present a 66-year-old male who underwent decompressive craniectomy and a titanium plate cranioplasty due to a warfare injury 40 years ago. Recently, he presented to our institution with a lesion which has started to grow several years prior to his admission, growing on the patient’s titanium plate underneath the skin. He underwent surgery with complete removal of the tumor and made a complete recovery. The tumor turned out to be an Intravascular Papillary Endothelial Hyperplasia (IPEH) tumor. The authors present a case report involving an intracranial IPEH tumor and current intracranial treatment modalities for this type of tumor.

Abbreviations: IPEH: Intravascular Papillary Endothelial Hyperplasia; CT: Computed Tomography; IPEHT: IPEH Tumors; MRI: Magnetic Resonance Imaging

Case Report

The authors present a craniotomy for removal of a left frontal lesion growing on a titanium cranioplasty. This 66-year-old doctor was injured in the Ararb-Israeli 1973 War. He was a tank driver and his tank were the last tank to suffer a direct hit from a mortar bomb shell during the war. He underwent urgent surgery and a right frontal craniectomy in Egypt, leaving a titanium plate as a bone graft instead of his frontal bone which was removed during surgery. 4 years prior to this admission, a frontal subcutaneous bossing on the patent’s frontal bone appeared. It was indolent until 2 years prior to admission when it demonstrated continued growth. The tumor’s last dimensions prior to surgery were measured at 9cm width over 5cm length. This 66-year-old male sustained a head injury in 1973. However, he continued to live a normal, fulfilling life. Being the first student in his class to graduate medical school after being in a rehab institution for combat soldiers. The patient was recently admitted to our service to undergo surgery for removal of a superficial subcutaneous lesion which presented as a cosmetic problem. The patient denied headaches, seizures or any other neurological complaint, however the appearance greatly disturbed him, enough to undergo surgery and removal of the lesion. Prior to surgery, the patient underwent a Computed Tomography (CT) scan which demonstrated an extra-axial lesion adherent to the patient’s titanium plate (Figures 1 & 2).

During surgery, the patient was laid in the supine position (Figures 3 & 4) and an incision on the skin immediately superior to where the tumor was palpated was made. The tumor was quickly visualized with a gross total excision of the tumor via an approachable and well-defined plain achieved (Figures 5 & 6). The titanium plate inserted during his first operation was made visible during surgery (Figure 7). Suturing of the scar with complete closure was done and a temporary drain left subcutaneously (Figure 8). The patient was extubated in the operating room with no immediate neurological deficit. After surgery, the patient underwent a swift recovery. He was discharged after several days with no neurological deficits, and in an elated spirit after removal of this subcutaneous lesion. The pathology report turned out to be of an Intravascular Papillary Endothelial Hyperplasia (IPEH) type defined as a Masson tumor.

Discussion

IPEH tumors were first described by Masson in 192310-12. Papillary endothelial hyperplasia tumors are a benign, non-specific vascular lesion which enclose reactive proliferation of endothelial cells that arise in an organizing thrombus [1]. The term IPEH suggests that thrombosis happens prior to papillary proliferation and that this proliferation is aided by the thrombotic material’s matrix [2]. IPEH Tumors (IPEHT) are most commonly seen in the skin’s sub-cutaneous tissue with intracranial lesions being rare, with a bit over 30 cases which have hitherto been reported. On Computed Tomography (CT) imaging, these tumors pose a diagnostic challenge, with difficulty telling apart these tumors and eosinophilic granulomas or other skull tumors. In addition, on CT scans hemorrhage is commonly present [3], however no hemorrhagic signs were seen on this patient’s CT scan. In addition, Magnetic Resonance Imaging (MRI) scans can demonstrate the extremely vascular and hyperdense nature of IPEHTs93. Imaging can be misleading, however, as Ong et al. report on a 37-yearold male which underwent surgery for resection of a WHO grade III anaplastic astrocytoma 10. 5 years into follow-up, the patient’s imaging showed progressive enlargement of the lesion into the resection cavity, radiographically consistent with tumor recurrence. Chemotherapy was considered, but eventually the patient underwent surgical excision with gross total resection and the pathology was consistent with an IPEHT.

Cagli and colleagues reported about 4 intracranial cases of PEHs which were treated surgically. They report complete removal of only 2 of the lesions, however all 4 cases involved cranial nerve deficits [4]. Furthermore, surgical removal, when complete seems to be enough treatment [3,5,6]. It is important to completely remove the tumor as recurrence or progression may be seen. As an example, for difficult to treat tumors of this type, Avellino et al. report of a Masson tumor in the cerebellopontine angle of a 75-year-old woman. The patient underwent preoperative embolization, subtotal resection and postoperative radiotherapy. The patient was symptomatic 9 years later and had to undergo a repeat embolization and near gross total resection. 15months after her first recurrence, a second recurrence was seen to which she underwent stereotactic gamma knife surgery, leaving a residual and stable looking tumor on follow up of 2.75 years. Indeed, Hastruk et al. also reported on an IPEH tumor mimicking a recurrence in a 56-year-old male which was operated for a left posterior convexity meningioma and which was thought to have a recurrence [7]. In cases where the surgical approach is challenging, unlike in our case, Gamma Knife radiosurgery can be employed. Ohshima et al. report of a successful treatment of a superior orbital fissure PEHT after incomplete resection of the tumor as an alternative therapeutic modality [8], however due to a small cohort and few cases reported of radiosurgery treatment, it is difficult to draw conclusions about the efficacy of adjuvant treatment [3].

The use of titanium cranioplasties for calvarial defects is still seen today [9], with long term outcomes of patients undergoing secondary cranioplasty after decompressive craniectomy for trauma or infraction being the material of choice. However, there are no reports of lesions growing on top of titanium cranioplasties. In a prospective trial from July 2018, comparing long term outcomes of cranioplasty with the use of an autologous cranioplasty and custom-made titanium bones in patients after craniectomies, custom-made titanium skulls had fewer bone resorption [10] . However, complications are seen with the use of this material. Hill et al. [11] retrospectively examined all titanium cranioplasties in his institution between 2007-2011, with 95 patients included in the study. 29 of these patients developed one or more post-cranioplasty complications, with a complication rate of 31.5%. The following complications were noted: subdural hematoma, extradural hematoma, CSF leak, seizures, intracerebral hemorrhage [12], subgaleal collection and pain. Of these 29 cases, 9 required cranioplasty removal and 10 required a further surgical procedure, with infection being the most common complication. In another retrospective study of titanium cranioplasties involving 174 patients, Mukherjee et al. had a complication rate of 26.4% and 10.3% rate of plate removal [13,14]. In neither studies were there any abnormal lesions growing on the plate.

Conclusion

To the best of our knowledge, this is the first case of an IPEH tumor occurring after secondary cranioplasty due to combatinduced craniectomy. IPEH tumors are a rare intracranial entity, which may also cause dire cosmetic consequences. These tumors, however, when located on the superficial brain, can be successfully fully removed. In cases of incomplete intracranial removal or where cranial nerves are involved, one may use additional treatment modalities such as radiosurgery after a surgical attempt. Further research with larger cohorts of patients are needed in-order to understand the role of adjuvant therapy in these rare intracranial tumors.

Modified Mortars with the Polymers Addition for Thermal Insulation Systems of Polystyrene - https://biomedres01.blogspot.com/2020/03/modified-mortars-with-polymers-addition.html

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Modified Mortars with the Polymers Addition for Thermal Insulation Systems of Polystyrene

Modified Mortars with the Polymers Addition for Thermal Insulation Systems of Polystyrene

Abstract

At the time of the increasing shortage of fossil fuels and their rising prices, energy saving is the main topic. For example, in Germany in the housing sector 75% of the total energy is consumed for the air conditioning in the household, mainly for heating. Today, all new buildings must meet the standards for energy efficiency. The fastest and most efficient way to save energy for heating and improving the climate inside the building is thermal insulation of external walls of the building. In this paper, polymer-cementitious adhesive for bonding and reinforcing, its composition, characteristics and mechanism of binding to the substrate was processed. The influence of the dispersed polymer on the characteristics of polymer-cement mortar for external thermal insulation has been examined in details.

Keywords: Redispersible Polymers; Polymer-Cement Mortar; Polymer-Cementitious Adhesive for Bonding and Reinforcing

Abbreviations: EPS: Expanded Polystyrene; PC: Portland Cement; PPC: Portland Pozzolanic Cement; HAC: High Alumina Cement; MC: Methyl Cellulose; MHEC: Methyl Hydroxyethyl Cellulose; MHPC: Methyl Hydroxypropyl Cellulose

Introduction

A typical system of external thermal insulation consists a polymer-cement adhesive for bonding of insulation material, insulation plates of expanded polystyrene (EPS) or stone wool, then polymer-cement base layer for mounting and reinforcing of facade mesh, fixing components (insulation wedges), one or more finishing layers of polymer-cement adhesive [1]. Components of external insulation system shown in Figure 1. A parameter that characterizes thermal losses through walls is the coefficient of thermal conductivity, This is the amount of heat the building element loses in one second per m² surface at a temperature difference of 1 K, expressed in W/m²K. Lower coefficient of heat conductivity means better thermal protection of the building. The most desirable insulation material is stone wool because it is a good insulator and has the ability to diffuse vapor, and styrofoam is located on second place [2,3] (Figure 1).

Application of Polymer-Cement Adhesive

The first discovery is the development of a powdery redisperse polymer. The polymers added to cement-based adhesives to improve their elasticity and adhesion to the substrate. With the advent of this technology allows the construction chemical industry to present dry polymer-modified adhesives for a variety of purposes:Adhesives based on ceramic bonding cement,

a) Mortars based on gypsum or cement,

b) Cementitious adhesives for thermal insulation,

c) Grout mass,

d) Self-healing mass,

e) Repair mortars,

f) Mortar for masonry,

g) Cementitious waterproofing

Today’s dry polymer-cement adhesives contain numerous additives to improve applicability (open time, consistency, etc.) as well as bonding to the substrate (water retention, elasticity). As the production process is automated and computer controlled, products are produced of precisely defined and uniform quality as well as precisely defined properties with a high degree of reliability in application [1]. When installing an external thermal insulation system, two types of adhesive are required:

A. Adhesive for bonding insulating material to a concrete wall or brick wall (good adhesion to the wall and insulation material as well as good flexibility to handle different coefficients of thermal expansion of the substrate).

B. Adhesive for reinforcement. It should cover the insulation material and to form the base wear-resistant layer for decorative plaster. The reinforcement adhesive requirements are slightly different from the adhesive bonding requirements. Good adhesion to the insulation material, long open time, easy handling, good impact resistance and low water absorption are also important properties of reinforcement adhesives. It is often a compromise and the same material is used for bonding and for reinforcing.

Connective Tissue

The main tasks of the binder are to form a firm bond with the substrate and the material for thermal insulation (adhesion), as well as to link the aggregate grains (cohesion). Today, there are three main types of cement used in the polymer-cement based adhesives: Portland cement (PC), Portland Pozzolanic Cement (PPC) and aluminate cement (High Alumina Cement, HAC) [1]. Portland cement is a hydraulic binder that is obtained by fine grinding portland cement clinker with a specific addition of gypsum, which binds and cures in air and under water. The raw material for the production of portland cement consists of limestone and clay minerals, whereby this ratio is usually 75-80% limestone and 20- 25% clay minerals. The binding speed is regulated by adding 3-5% of the gypsum or anhydrite [4].

Aggregates

Generally, aggregates mean material loosening structures formed in the form of assemblies of more or less identical particles, i.e. material relatively homogeneous in the sense of substancebuilders. Aggregates contain unbound particles (granules) of a certain size. In the narrow sense, aggregates are all grainy (inert) materials that, together with certain bonding materials (cement, lime, bitumen, polymers), are used to obtain various types of mortar and concrete, therefore, materials that are defined by the general term composite materials. Generally, aggregates are classified as natural or artificial [5,6]. In this paper, two natural, inorganic aggregates, ie quartz sand, particle size up to 0.8 mm, and stone dust (so-called filler) were used, particle size up to 0.1 mm. Thus, in this case, a combination of aggregates of different particle sizes is used to ensure a better packing, where smaller particles fill the vacuums between larger particles.

Additives

Additives are substances usually of organic origin, which are added in small amounts to a dry mix, modifying the properties of fresh or hardened glue, mortar or paste. The content of these supplements is usually below 1%. Only redisperse polymers are added in higher percentages. Additives for the production of dry mortar may be added to the mixture solely in powder form. If several different accessories are used, they must be compatible with each other.

Redispersible Polymers

Redispersible polymers are organic polymeric materials produced from aqueous dispersions by spraying technology, as shown in Figure 2. Water dispersions are two-phase systems in which the dispersant is water. Redispersible polymers provide the following properties in adhesives for thermal insulation:

Figure 2: Simplified process of forming redispersible polymers and forming redispersion [6]. The synthetic polymer is dispersed in water.

a) Better adhesion to the substrate,

b) Impact resistance

c) Less damage during impact,

d) Aging properties (good properties after varying climatic conditions),

e) Hydrophobicity (good water odor).

Dosing of redispersible polymers ranges from 0 to 5%, but it should be noted that the overall product price increases with increasing polymer content so that the content of the polymer needs to be accurate enough to achieve satisfactory results as far as the characteristics of the final product are concerned. The following picture shows the structures of the most commonly used polymer in adhesives for external thermal insulation systems [1] (Figure 3).

Water Retention Additives

The main purpose of the water retention additive is to keep the water in the fresh adhesive for a longer period of time so that the cement has enough available hydration water. Water also acts as a lubricant to improve the freshness of fresh adhesives and is also essential for the hydration process of cement. The loss of water from the adhesive is reduced by the adsorption of waterretaining additives on the substrate and on the bonding particles and by forming a thin layer of low permeability. Other parameters influenced by water retention additives are open time, improved wettability of the particles, and reduced subsidence of the adhesive. High water retention can be achieved by chemically modified methyl cellulose (MC). Methyl cellulose modification is performed with ethylene oxide or propylene oxide. The resulting modification products are methyl hydroxyethyl cellulose (MHEC) having the structure shown in (Figure 4) or methyl hydroxypropyl cellulose (MHPC). The MHEC content in formulations does not exceed values greater than 0.5%. The following illustrations show the solubility of MHEC and MC with increasing temperature and retaining water with the addition of MHEC (Figures 5 & 6).

Influence of Temperature on Bonding of Glue: Thermoplastic polymers are semi-crystalline solids consisting of crystalline and amorphous parts. The ratio of crystalline and amorphous parts depends on the primary structure of the polymer and on the parameters of the production process. The amorphous parts of the solid polymer can be in glass or rubber, depending on the ambient temperature. The temperature at which the transformation from the glass state occurs to the rubber and vice versa is called the glass transition temperature (Tg). Below Tg polymers are rigid and fragile. By heating, they soften and become more elastic, i.e. they go into a rubbery state. Another parameter important for the formation of a polymer film is the minimum temperature of film forming (MTF). MTF is the temperature at which the polymer particles will coalesce and form a continuous unopened film. Therefore, it is the lowest temperature that is necessary to meet the conditions to start the formation of the film. The minimum temperature of the film formation depends on the size of the dispersion particles, the drying time, etc., but mainly depends on the glass transition temperature of the polymer. Polymer dispersions do not form a film at a temperature below the MTF, but only white powder is formed. The polymer dispersions that dry at a temperature slightly below the MTF form a white, opaque low-strength film. Just above the MTF deformation and coalescence of the dispersion particles is strong enough to form a continuous film without cracks. Socalled coalescing additives, plasticizers, solvents can lower the MTF far below the Tg of dry polymer. Thus, the choice of coalescing additives is an interesting field of investigation to ensure that polymer dispersions in adhesives form a film even when used at + 5°C. Examples of coalescing additives are dibutylphthalate (DBF), ethylene glycol ethers and organic solvents (e.g., toluene). The MTFF polymer can be reduced by more than 20 °C [1].

Stabilnost Prema Vodi: After the polymer diffused between adjacent particles, the formed polymer bonds are not soluble in water. However, the film still contains a water-soluble protective colloid that easily absorbs water so that the polymer bonds can hydrate and swell, which can weaken the adhesion strength of the hardened adhesive. Depending on the nature of the polymer, there is a possibility of reacting (saponification) (Figure 11). Poly (ethylene-vinyl acetate) hydrolyzed (saponified) in the presence of alkali in an alcohol and polyvinyl acetate. Alkalinity (pH>12) is present in cementitious adhesives when they come into contact with water. High alkalinity catalyzes EVA hydrolysis (Figure 12). Water solubility can be increased to the extent that the polymer can be washed out of the cement matrix by rain. Polymers containing nonpolar monomers (ethene, butadiene, styrene ...) are not susceptible to saponification [1].

Experiment

We examined the characteristics of the adhesive depending on the share of the redispersion polymers in it:

a) Testing the consistency of fresh adhesive,

b) Testing the adhesion of adhesive to the surface

c) Testing bending strength of hardened adhesive,

d) Testing compressive strength of hardened adhesive,

e) Testing capillary water absorption of hardened adhesive

f) Testing the volume mass of hardened adhesive.

Test results are presented in tables and diagrams, along with photos of the samples and a short description of the test.

Technical characteristics of the components for making the adhesives used in the practical part of the work

Cement: As a cement binder in our experiments we used Portland cement with the addition of fly ash CEM II / B-W 42.5 N, manufactured by Kakanj cement. Cement meets all the prescribed requirements and it is suitable for the preparation of adhesives for sticking EPS plates and adhesives for reinforcement. Additional testing of cement is not required. Proportion of cement in the formulations was 33.1%. The chemical composition of Portland cement CEM II / B-W 42.5 N is shown in Table 4 [8]. Cement producer Kakanj cement is shown in Table 5.

Conclusion

The results of tests carried out in the context of practical part show that the addition of the redispersed polymer directly affects all investigated properties, except the consistency of fresh adhesive where there have been no significant changes with increase of the share of redispersed polymer. The adhesion of adhesive on the surface is increased with the increase of the share of redispersed polymer, because of the occurrence of formation of polymer bond in the cement matrix that additionally binds adhesive on substrate. Adhesion is also the main characteristic of adhesives for external thermal insulation together with the capillary water absorption, so that the redispersed polymer is added in order to increase adhesion of mortar of the substrate and to reduce the capillary water absorption.

The results show decrease of the flexural and compressive strength of the adhesive with the increasing share of redispersed polymer, because of the type of the redispersed polymer used, ie. redispersible polymer used belongs to the class of redisperse soft polymers because of the low glass transition temperature (-6°C). Increase of the share of dispersed polymer leads to decrease of volume mass, primarily because of reduced share of aggregate which has higher specific weight than the specific weight of the polymer dispersion. In practice, we add 1 to 35 of the redispersion polymer. We add 1 to 2% of redispersible polymer in the adhesive for gluing EPS panels, while the adhesive for the reinforcement contains 2 to 3%. It should be noted that the redispersion polymers are most expensive components in adhesives for external thermal insulation, so that with these proportions satisfactory properties of adhesive are achieved and by this competitive product is provided.

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Cds and Cdse Quantum Dot Solar Cells Production and Improving Efficiency of the Cells by Ion-Doped Quantum Points Cds Holmium

Cds and Cdse Quantum Dot Solar Cells Production and Improving Efficiency of the Cells by Ion-Doped Quantum Points Cds Holmium

Abstract

This project aims to improve the efficiency of solar cells doped by CdS quantum dot and Ho⁺³ ion. Successive Ionic Layer Absorption and Reaction (SILAR) and Chemical Bath Deposition method (CBD), were used to deposit a CdS/CdSe layer on TiO₂ film. According to J-V diagram, it is concluded that adding holmium ions (Ho³⁺) will enhance the efficiency of quantum dot sensitized solar cells up to 2.53%.

Keywords: Solar Cells; Quantum Dots; Holmium

Abbrevations: QD: Quantum Dots; SILAR: Successive Ionic Layer Absorption and Reaction; CBD: Chemical Bath Deposition Method; MEG: Multiple Excitation Generation; EIS: Electrochemical Impedance Spectroscopy; XRD: X-ray Diffraction; FTO: Fluorine Doped Tin Oxide

Introduction

Nowadays, energy issues have been challenged as the most important human necessities. In the meantime solar or photovoltaic cells have been attended in order to transferring of solar energy to electricity in which solar energy has been used as a clean, unexpansive and available energy source [1-3]. Solar cells are divided into different types such as dye sensitized, silicone solar cells, molecular, GaAs and quantum dots (QD) [4, 5]. Recently, QD solar cells have attracted great attention because of their low cost, high surface area and more quantum yield [6-8]. In QDs, Multiple excitation generation properties (MEG) cause a few electron transfers from valance band to conductive band by incident of just one photon which increases absorption in solar cell and finely leads to high performance of solar cell [9]. Some QDs are used in preparation of solar cells such as: InAs, CdTe, PbS, InPO₄, CdS, CdSe, etc. Using CdS and CdSe simultaneously has a good effect on emission of light because of increasing of band gap via a synergic effect [10-12]. There are some methods for deposition of QDs onto TiO₂ like chemical bath deposition (CBD), SILAR and hot injection growth method. In cathode electrode, Pt or Cu₂S is used which because of high cost of Pt using the Cu₂S is more popular and common [13,14]. In order to increase electron injection from QD to TiO₂, coating a layer of ZnS has a great effect via omitting surface-nods made on TiO₂ that this layer improves quality and efficiency of solar cells. In many inves tigations, I-/I₃- solution is used as electrolyte. However, because of corrosion of solar cells by this redox complex solution, polysulfide solution S²-/Sx²- is used as a substitute electrolyte.

A new method for improving the solar cell performance is introducing some metals such as Mn, Ni, Ag, Cd etc to cells [15-18]. In this work existence of Ho³⁺ ion in QDSCS cells was used for the first time in order to improvement in photovoltaic performance of QDSCS (Figure 1).

Figure 1: Schematic of the FTO TiO₂/CdS: Ho/CdSe electronic structure. Direct arrows indicate the electron hole photogeneration. Dashed arrow indicates the electron transfer from CdS CB to the midgap electronic states and direct curved arrows are related to electron transfer from CdSe to CdS QDs and from CdS trap states to TiO₂ CB.

Figure 1: Schematic of the FTO TiO₂/CdS: Ho/CdSe electronic structure. Direct arrows indicate the electron hole photogeneration. Dashed arrow indicates the electron transfer from CdS CB to the midgap electronic states and direct curved arrows are related to electron transfer from CdSe to CdS QDs and from CdS trap states to TiO₂ CB.

Experimental Section

Apparatus: SEM-EDX model Irost was applied for. Solar simulator model SIM800. Bath-Ultrasonic model (Sonica). Water purification system model No. F3JN94307E. Electrochemical Impedance Spectroscopy (EIS) was performed on IM6ex Electrochemical Workstation (ZAHNER) over a frequency range of (1×105–1×10−1) Hz with 10 mV ac amplitude under forward bias of (-0.6) V in the dark. Formation of cells by ion-doped quantum points CdS holmium were analyzed by means of a Philips X-ray diffraction (XRD) equipfped. The XRD data were collected in the scale of 2Ɵ = 10–80˚ a scanning speed of 3˚ min-1.

Materials: Cadmium nitrate tetrahydrate (Cd(NO₃)₂.4H₂O, Alfa Aesar, 98.5%), Sodium sulfide nonahydrate (Na₂S.9H₂O, aladdin, ≥98.0%), Nitriloacetic acid (N(CH₂COO)₃, sigmaaldrich, ≥99.0%), Copper(II) sulfate pentahydrate (CuSO₄.5H₂O, sigmaaldrich, 99.99%), Holmium (III) hexahydrate (HoCl₃.6H₂O, sigmaaldrich, 99.9%), Sodium hydroxide (NaOH, Merck, 99.0%), Sodium sulphite (Na₂SO₃, sigmaaldrich, ≥98.0%), Zinc acetate (Zn (CH₃COO)₂.2H₂O, Merck, 99.5%), Selenium powder (Se, Acros, 99.5%), Copper (II) nitrate (Cu(NO3)2.3H₂O) and Sulphur powder (S, VWR Chemicals, 99.5%), Fluorine doped tin oxide (FTO) glass, TiO₂ nanoparticle. All reagents and solvents were purchased from commercial sources and were used without further purification.

Preparation of CdS/CdSe/Ho³⁺ Solar Cells: First, we deposited a thin film of TiO₂ on FTO transparent conductive layer According to doctor blade method. Secondly, the electrode was heated up to 125 °C for 6 minutes and then cool down to 25 °C. This process was repeated until a desired thickness was achieved. To prepare X electrode, TiO₂ photoanodes were placed in a 10mL of cadmium nitrate solution (1.17g in water) for 5 minutes and then were washed with distilled water. Then, TiO₂ photoanodes were immersed in a 10mL solution containing 2.14g sodium sulfide for 5 minutes. This cycle was repeated for three times. The resulting electrode was used as the control electrode. To prepare Y photoanode, plunge a photoanode was immersed in a 10mL of solution with 1.17g of dissolved cadmium nitrate and 0.284g Ho³⁺ for 5 minutes, and then the sample was dried. The sample is added to the solution of 2.4g of Na₂S per 10mL H₂O. This cycle was repeated for 3 times. The electrodes were dried at room temperature. Based on reported synthesis by Samadpour et al. [19]. In order to prepare CdSe, 1.26g of sodium sulfite and 0.315g of selenium powder was refluxed in 50mL of distilled water under nitrogen gas for 5 hours at a temperature of 80-85 °C at 400-500rpm.

The result is the formation of sodium selenosulphate (Solution of a). According to Figure 2, different solutions with different volumes were prepared. 1.2g of cadmium sulphate were dissolved in 50mL of distilled water. Separately, 1.40g of sodium hydroxide was dissolved in 10mm of distilled water. Moreover, 1.65g nitriloacetic acid was dissolved in 40mL of distilled water in a round-bottom flask and then three samples were mixed and finally added to the b solution (Figure 2). The final products of a and b was placed in a beaker of 200mL. The synthesized electrodes were kept away from sunlight for 15 to 18 hours at 2 to 3 °C, Ultimatelly, the electrodes were washed with distilled water (Figure 3). The electrode immersed in a solution consist of 0.219g of zinc acetate, 10mL of distilled water and 0.24g sodium sulfide Na₂S. This cycle was repeated three times. FTO glass was immersed in an aqueous solution of 1.2g copper nitrate in 10mL of distilled water for 30 seconds and then was washed with ethanol. This cycle was repeated for 5 times. Finally a black thin layer of CuS appeared on FTO. Three aqueous solutions containing 1.2g Na₂S, 0.16g S, 0.2g NaOH were prepared separately and 5mL of each solution was mixed in a round-bottom flask for 90 minutes at the room temperature.

Figure 2: Preparation of a solution (sodium sulfite+ selenium powder) and b solution (cadmium sulphate+ sodium hydroxide+ nitriloacetic acid).

Figure 3: X (blank) and Y (Ho doped on X) electrodes in solution of a+ b.

Results and Discussion

SEM

To determine the particle sizes in anodic sub-layer coated by a layer of TiO₂ (20-40nm) and to measure the thikness of the layer’s SEM-EDX analysis was performed. (Figure 4a) shows SEM image of TiO₂ layers (20 to 400nm) that indicates a porous surface and uniform particle size. The diameters of first and second layers are estimated to be 3.77μm (TiO₂-400nm) and 4.72μm (TiO₂-200 nm) respectively. SEM images in Figure 4b shows that surface morphology has been changed in the presence of CdS/CdSe quantum dotes and shiny dots with 500nm size is appeared that can be related to CdS/CdSe quantum dotes. The diameter of first and second layers have changed to 4.03μm and 4.27μm, respectively. Finally, the thicknesses of TiO₂ layers are shown to be 4.04μm and 6.32μm for first and second layers in Figure 4c, respectively.

Electrochemical Impedance Spectroscopy (EIS)

Figure 7 shows the electrochemical impedance spectra (EIS) of the CdS/CdSe and CdS/CdSe/Ho. Nyquist curves obtained from EIS measurements were fitted with equivalent circuit model as shown in Figure 7. Recombination resistance (Rre) of CdS/CdSe and CdS/ CdSe/Ho samples are 263.30Ω and 628.23Ω, respectively, which means the electrons and holes recombination in the Ho-doped CdS/CdSe solar cells are less than that of CdS devices. Thus, the less charge recombination can be observed in CdS/CdSe/Ho.

Conclusion

Doping of few amounts of Ho³⁺ ions improves electronic and photo-physical properties of quantum dots and creates an electronic level at the middle gap area. This electronic state changes charge separation and reduces electron-hole recombination. Changing in the type and amount of impurity causes different electronic and photonic properties of nanocrystal semiconductors. In this work, quantum dot solar cells were fabricated, and some investigations were performed on their structure and it was indicated that quantum yield increased from 0.87% to 2.53% by adding Ho³⁺ metal ion. Using Ho³⁺ for surface modification leads to increase in yield of solar cells which it can be concluded that adding lanthanides ions increase the performance of quantum dots because of electron transportation properties and these cases may increase quantum yield of nanoparticle solar cells.

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The Drive to Succeed: The Instructional Leader

The Drive to Succeed: The Instructional Leader

Opinion

Instructional leaders spend countless hours contemplating how to increase teacher efficacy that will influence directly to student achievement in the classroom. The rise of greater accountability in today’s K-12 assessment model empowers instructional leaders to look beyond their scope to see endless possibilities for both teachers and students. To identify the possibilities for teachers and students, an instructional leader must take a deeper look to identify barriers that hinder success. Leaders often find themselves engrossed in the day-to-day work, which distracts their focus and efforts to bring about effective change. Digging deeper into the root cause requires the instructional leader to create a shared purpose for teaching and learning. Precisely, one that fosters a community of trust, respect, and teamwork. As a result, the instructional leader holds significant influence to bring about change for campus and student success. The road is not always easy but if the instructional leaders decide to look deeper, the journey to success is clear. It is through this lens that guides the leader to inspire all stakeholders to become a part of the process of change. How this drives teacher and student success, one may ask? The following elements help and shape the plan for success:

a) Effective communication the vision and mission;

b) Allow feedback on the vision and mission;

c) Redefine the vision, mission, and implementation based upon the feedback;

d) Host community forums about the new direction;

e) Solicit feedback from the community forums;

f) Implement the change initiative;

g) Monitor and adjust;

h) Evaluate progress;

Change is only actualized in the mindset of the instructional leader, which activates the will and vision for success. By doing this, the voice of all stakeholders is heard and, in turn, brings a solution focus initiative for academic success. Moreover, buy-in creates a space and opportunity for the vision to take root in many different forms. Those forms are the undercurrent of student success by which teachers and community leaders assign practices that will assist in creating skillful educators and academically engaged students for success. The instructional leader creates the community of practice to bridge the work of collaboration and instructional feedback. This is as an integral part of the instructional culture - a culture that models itself around the continuous improvement model. Specifically, this model centers around outcome-based professional development practices that empowers, enforces, and activates teacher effectiveness based on sound instructional practices, instructional delivery, and assessment. According to Hook (2017), the Teacher Professional Development (TPD) model is a continuous cycle of improvement that is characterized by the following:

a) Exploration - giving teachers an opportunity to explore instructional strategies to drive student success.

b) Reflection - allow teachers an opportunity to reflect on instructional practices and delivery through an effective coaching model. Utilizing a well-development campus walkthrough tool to adequate support the area of challenges and promises.

c) Discussion - allowing time for collaboration and discussion of best practices that work with colleagues to activate a by-product of a highly engaged culture of instructional feedback and practice.

d) Application - providing an opportunity and space for teachers to apply instructional practices learned. Diving into assessment data that charts student success.

e) Monitor and Adjust - allowing teachers the time to monitor and adjust their instructional delivery to match student weakness while supporting student strengths.

All of these elements of TPD provide a rich environment for teacher collaboration, instructional feedback, and improved teacher practices. Furthermore, it allows teachers to grow professionally and their students to grow deeper academically (Hooker, 2017).

The quality of the investment in teacher development brings about a greater community of practice. As a result, it bridges the gap between teacher skill deficit and building a teaching and learning community that thrives in the classroom.

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