Unencapsulated Cells Research Articles

Improved efficiency and stability of inverted polymer solar cells with a solution-processed BPhen interlayer and polystyrene beads

We demonstrate improved power conversion efficiency (PCE) and strongly enhanced stability of inverted organic solar cells (OSCs) with Cs halides by solution casting BPhen (4,7-di(phenyl)-1,10-phenanthroline) on the halide layer and ∼100nm polystyrene beads (PSB) on the blank side of the OSC’s substrate. The PCE of ITO/CsCl/P3HT:PCBM/MoO3/Al (where P3HT is poly 3-hexylthiophene and PCBM is [6,6]-phenyl-C60-butyric acid methyl ester) improves by up to 46%, from 2.5% to ∼3.7%, by adding a solution-processed BPhen layer between the CsCl and the active layer. For such cells with CsI (PCE ∼3.3–3.4%) the increase was only 6–9%, to 3.5–3.7%. The PCE of cells devoid of the halides but with BPhen was ∼3.3%. The cells were optimized by varying the BPhen concentration in a chlorobenzene solution. The results are consistent with reduced charge recombination at the ITO interface in the presence of the hole blocking BPhen interlayer. The use of hole blocking BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline), as a substitute for BPhen, also showed an enhancement (though lower due to its lower electron mobility), verifying the effect of these materials as hole blocking interlayers. Interestingly, the stability of such non-encapsulated devices with CsCl/BPhen or CsI/BPhen improved significantly. For example, the PCE of unencapsulated cells with CsCl/BPhen kept in the dark under ambient conditions dropped by less than 2% after more than 3weeks; the PCE of similar cells devoid of the BPhen layer dropped by ∼60% during the same period. The PCE of the cell with CsCl/BPhen dropped by ∼16% after 2months. High humidity, as expected, resulted in faster deterioration in cell performance. The PCE, however, was restored to within ∼10% of the original value for 2week old cells by solution–application of a PSB layer on the blank side of the cell’s glass substrate. These beads direct and scatter the light to enhance absorption in the active layer. The results demonstrate that a simple approach such as casting a film of ∼100nm diameter PSB from an aqueous suspension on the blank side of the OSC substrate can improve long-term performance, and that spin coating BPhen is a low-cost and easy approach to reduce charge recombination at the cathode in inverted structures for increased PCE and stability.

Stability of sub‐micron‐thick CdTe solar cells

ABSTRACTSputtered CdS/CdTe cells with only 0.75 µm of CdTe have reached AM1.5 efficiencies over 12.5%. But the use of very thin absorber layers of CdTe raises questions about the possible impact on long‐term stability when the back contact is very close to the main junction. In this study, we have performed accelerated life testing (ALT) on unencapsulated CdTe dot cells with absorber thickness ranging from 0.7 to 2.1 µm. After 900 h of ALT at 85°C under continuous one‐sun illumination, with open circuit biasing and no encapsulation, we find that any decrease in stability as CdTe thickness decreases is within the ~10% statistical uncertainty shown by the sample sets of more than 20 cells each. Cells of all thicknesses exhibited some decrease in performance under these stress conditions, and open‐circuit voltage appears to be the key factor in decreased efficiency. These changes in performance under ALT at 85°C are found to be consistent with a projected field lifetime of about 40 years in typical conditions. Secondary ion mass spectroscopy depth profiles of several elements including Cu showed no evidence of ALT‐driven diffusion in these sputtered CdTe cells. Copyright © 2013 John Wiley & Sons, Ltd.

Self-assembled monolayer as an interfacial modification material for highly efficient and air-stable inverted organic solar cells

Organic solar cells with inverted structures can greatly improve photovoltaic stability. This paper reports a method to lower the work function of indium tin oxide (ITO) in inverted organic solar cells by modification with ultrathin 3-aminopropyltriethoxysilane (APTES) monolayers. The device studies showed that the resulting photovoltaic efficiencies were significantly increased from 0.64% to 4.83% with the use of the APTES monolayer, which could be attributed to the dramatic enhancement in the open-circuit voltage and fill factor. The effective electron selectivity in the case of the APTES-modified ITO could be attributed to the reduction of the work function of ITO as a result of the electron-donating nature of the amine groups in the APTES monolayer. The power conversion efficiency of the unencapsulated inverted organic solar cells with APTES-modified ITO remained above 80% of their original values even after storage in air for thirty days. Our results provide a promising approach to improve the performance of highly efficient and air-stable inverted organic solar cells.

Titanium–Aluminum Bilayer Cathode for Small-Molecular Organic Solar Cells with Prolonged Life upon Exposure to Air

The in-air stability of unencapsulated small-molecular organic solar cells (OSCs) was improved by 3 orders of magnitude by using a Ti (inner)–Al (exposed to air) bilayer cathode, in comparison with that of Al-monolayer-cathode OSCs. The stability of the unencapsulated bilayer-cathode OSCs (AlTi-OSCs) was comparable to that of encapsulated ones. These devices were degradation-free in air for more than 3 months. Under weathering tests, the unencapsulated AlTi-OSCs recovered their performance in the idle periods. This provides us with an effective and economical approach to prevent degradation of the extensively studied aluminum-cathode OSCs.

A new method to improve the lifetime stability of small molecule bilayer heterojunction organic solar cells

Unencapsulated small molecular solar cells with a layer of carboxylated copper phthalocyanine (CuPc⁎) introduced between the donor copper phthalocyanine (CuPc) and acceptor 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDI), and using ITO and Ag as the cathode and anode were investigated for 35 days. The performance and stability were compared between traditional ITO/PEDOT:PSS/CuPc/PTCDI/Ag cells and the new ITO/PEDOT:PSS/CuPc/CuPc*/PTCDI/Ag cells. The comparison shows that the modified cell has an enhanced stability compared to traditional cells. The improvement of the lifetime is likely due to the CuPc* layer working as buffer layer to prevent humidity and oxygen from diffusing into the active layer. Different thicknesses of CuPc were investigated to study the effects of CuPc layer thickness on the electrical properties of these devices. It was found that the properties of the cell with 20nm thickness of CuPc were the best.

Enhancing Insemination Performance in Pigs Through Controlled Release of Encapsulated Spermatozoa

Encapsulation of boar semen is a novel technique that allows insemination to be performed as a single intervention without the need to dilute the semen. The research reviewed in this paper shows that spermatozoa encapsulated in alginate are able to achieve the same fertility as two or three inseminations per oestrus using standard techniques and unencapsulated cells. The use of encapsulated spermatozoa is currently limited by the need for longer semen processing time and wastage of disposable material (catheters, plastic bottles, etc.). In this review, the advantages, the drawbacks and the future possibilities for artificial insemination with encapsulated spermatozoa in the sow are discussed, with the aim of applying this promising new methodology for the optimization of sow reproductive performance.

Microencapsulation of Lactobacillus plantarum (mtcc 5422) by spray-freeze-drying method and evaluation of survival in simulated gastrointestinal conditions

Spray-drying (SD) and freeze-drying (FD) are widely used methods for microencapsulation of heat-sensitive materials like probiotics for long-term preservation and transport. Spray-freeze-drying (SFD) is relatively a new technique that involves spraying a solution into a cold medium and removal of solvent (water) by conventional vacuum FD method. In this study, the SFD microencapsulated Lactobacillus plantarum powder (1:1 and 1:1.5 core-to-wall ratios of whey protein) is compared with the microencapsulated powders produced by FD and SD methods. The SFD and FD processed microencapsulated powder show 20% higher cell viability than the SD samples. In simulated gastrointestinal conditions, the SFD and FD cells show up to 4 h better tolerance than SD samples and unencapsulated cells in acidic and pepsin condition. The morphology of SFD samples shows particles almost in spherical shape with numerous fine pores, which in turn results in good rehydration behaviour of the powdered product.

Influence of cathode oxidation via the hole extraction layer in polymer:fullerene solar cells

In this paper, we elucidate the role of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) in the degradation of polymer:PCBM ((6,6)-phenyl C 61-butyric acid methyl ester) solar cells. The study is done on unencapsulated cells exposed to ambient conditions in dark. The cell degradation results from reduced carrier extraction, and an investigation of the various interfaces within the cell allows us to correlate this to oxidation of the low work function metal cathode. We further show that this oxidation is caused by water vapor diffusion from the edges through the hygroscopic PEDOT:PSS layer. We demonstrate that only the hygroscopic nature of PEDOT:PSS, and not its acidity, has a detrimental impact. The oxidation of the cathode progresses in synchrony with the water ingress into the PEDOT:PSS layer from the edges of the device towards the central part, and results in a progressive constriction of the active area. When the PEDOT:PSS layer is replaced by an evaporated layer of MoO 3, the device lifetime is improved considerably even with highly reactive metal cathodes. Finally, we provide a quantitative relationship between device lifetime and the level of humidity in the ambient, thus establishing a suitable accelerated shelf-life test for organic solar cells and their encapsulation.

Correction of Hyperglycemia in Type 1 Diabetic Models by Transplantation of Encapsulated Insulin-producing Cells Derived from Mouse Embryo Progenitor

Shortage of cadaveric pancreata and requirement of immune suppression are two major obstacles in transplantation therapy of type 1 diabetes. Here, we investigate whether i.p. transplantation of alginate-encapsulated insulin-producing cells from the embryo-derived mouse embryo progenitor-derived insulin-producing-1 (MEPI-1) line could lower hyperglycemia in immune-competent, allogeneic diabetic mice. Within days after transplantation, hyperglycemia was reversed followed by about 2.5 months of normo- to moderate hypoglycemia before relapsing. Mice transplanted with unencapsulated MEPI cells relapsed within 2 weeks. Removal of the transplanted capsules by washing of the peritoneal cavity caused an immediate relapse of hyperglycemia that could be reversed with a second transplantation. The removed capsules had fibrotic overgrowth but remained permeable to 70 kDa dextrans and displayed glucose-stimulated insulin secretion. Following transplantation, the number of cells in capsules increased initially, before decreasing to below the starting cell number at 75 days. Histological examination showed that beyond day 40 post-transplantation, encapsulated cell clusters exhibited proliferating cells with a necrotic core. Blood glucose, insulin levels, and oral glucose tolerance test in the transplanted animals correlated directly with the number of viable cells remaining in the capsules. Our study demonstrated that encapsulation could effectively protect MEPI cells from the host immune system without compromising their ability to correct hyperglycemia in immune-competent diabetic mice for 2.5 months, thereby providing proof that immunoisolation of expansible but immune-incompatible stem cell-derived surrogate β-cells by encapsulation is a viable diabetes therapy.

Transplantation of microencapsulated umbilical-cord-blood-derived hepatic-like cells for treatment of hepatic failure

To investigate intraperitoneal transplantation of microencapsulated hepatic-like cells from human umbilical cord blood for treatment of hepatic failure in rats. CD34+ cells in umbilical cord blood cells were isolated by magnetic cell sorting. In the in vitro experiment, sorted CD34+ cells were amplified and induced into hepatic-like cells by culturing with a combination of fibroblast growth factor 4 and hepatocyte growth factor. Cultures without growth factor addition served as controls. mRNA and protein levels for hepatic-like cells were analyzed by reverse transcription-polymerase chain reaction, immunohistochemistry and immunofluorescence. In the in vivo experiment, the hepatic-like cells were encapsulated and transplanted into the abdominal cavity of acute hepatic failure (AHF) rats at 48 h after D-galactosamine induction of acute hepatic failure. Transplantation with PBS and unencapsulated hepatic-like cells served as controls. The mortality rate, hepatic pathological changes and serum biochemical indexes were determined. The morphology and structure of microcapsules in the greater omentum were observed. Human albumin, alpha-fetoprotein and GATA-4 mRNA and albumin protein positive cells were found among cultured cells after 16 d. Albumin level in culture medium was significantly increased after culturing with growth factors in comparison with culturing without growth factor addition (P < 0.01). Compared with the unencapsulated group, the mortality rate of the encapsulated hepatic-like cell-transplanted group was significantly lower (P < 0.05). Serum biochemical parameters, alanine aminotransferase, aspartate aminotransferase and total bilirubin in the encapsulated group were significantly improvement compared with the PBS control group (P < 0.01). Pathological staining further supported these findings. At 1-2 wk post-transplantation, free microcapsules with a round clear structure and a smooth surface were observed in peritoneal lavage fluid, surviving cells inside microcapsules were found by trypan blue staining, but some fibrous tissue around microcapsules was also detected in the greater omentum of encapsulated group by hematoxylin and eosin staining. Transplantation of microencapsulated hepatic-like cells derived from umbilical cord blood cells could preliminarily alleviate the symptoms of AHF rats.

Hydrogel Microsphere Encapsulation of a Cell-Based Gene Therapy System Increases Cell Survival of Injected Cells, Transgene Expression, and Bone Volume in a Model of Heterotopic Ossification

Bone morphogenetic proteins (BMPs) are well known for their osteoinductive activity, yet harnessing this capacity remains a high-priority research focus. We present a novel technology that delivers high BMP-2 levels at targeted locations for rapid endochondral bone formation, enhancing our preexisting cell-based gene therapy system by microencapsulating adenovirus-transduced cells in nondegradable poly(ethylene glycol) diacrylate (PEGDA) hydrogels before intramuscular delivery. This study evaluates the in vitro and in vivo viability, gene expression, and bone formation from transgenic fibroblasts encapsulated in PEGDA microspheres. Fluorescent viability and cytotoxicity assays demonstrated >95% viability in microencapsulated cells. ELISA and alkaline phosphatase assays established that BMP-2 secretion and specific activity from microencapsulated AdBMP2-transduced fibroblasts were not statistically different from monolayer. Longitudinal transgene expression studies of AdDsRed-transduced fibroblasts, followed through live animal optical fluorescent imaging, showed that microencapsulated cells expressed longer than unencapsulated cells. When comparable numbers of microencapsulated AdBMP2-transduced cells were intramuscularly injected into mice, microcomputed tomography evaluation demonstrated that the resultant heterotopic bone formation was approximately twice the volume of unencapsulated cells. The data suggest that microencapsulation protects cells and prolongs and spatially distributes transgene expression. Thus, incorporation of PEGDA hydrogels significantly advances current gene therapy bone repair approaches.

Enhancement of photovoltaic cell response due to high-refractive-index encapsulants

This study compares the electrical output of photovoltaic (PV) cells encapsulated with silicones having different refractive indices to unencapsulated PV cells. It is demonstrated that the optical concentration ratio of dome-shaped concentrator PV systems can be increased by using a higher refractive-index encapsulant. The short-circuit photocurrent of the PV cell having high-refractive-index encapsulation (n=1.57) is 71% higher than that of the PV cell having a low-refractive-index encapsulation (n=1.41), and 316% higher than that of the unencapsulated PV cell. These experimental concentration-ratio enhancements are consistent with the theoretical estimates of concentration ratio dependence on the refractive index of the PV concentrator.

Interfacial processes in small molecule organic solar cells

This paper presents an overview of the recent progress of small molecule organic solar cells mainly based on the previous works of our group. We will mainly focus on the interfacial processes in the cells. The dissociation of excitons at electrode/organic and organic/organic interfaces can be directly observed by transient photovoltage measurements. A simple model including dissociation of excitons at the interface and drift of free carriers in the built-in field is proposed to explain the observed signals of transient photovoltage. Besides exciton-blocking and preventing damage due to cathode evaporation, blocking permeation of oxygen and/or water molecules and modulating the built-in field are proposed as functions of the buffer layer between C60 and Al. By the use of the inverted structure, a shelf lifetime of over 1500 h is achieved for unencapsulated small-molecule organic solar cells.

Dual Delivery of Placental Growth Factor and Vascular Endothelial Growth Factor from Poly(Hydroxyethyl Methacrylate-Co-Methyl Methacrylate) Microcapsules Containing Doubly Transfected Luciferase-Expressing L929 Cells

Placental growth factor (PlGF) combined with vascular endothelial growth factor (VEGF(164)) did not result in greater luciferase expression of a microencapsulated genetically transfected mouse fibroblast cell line (L929 cells) implanted subcutaneously in nominally syngeneic C3H/HeJ mice than in a control without growth factors. The intent had been to increase the maturity status of VEGF-generated vessels in the implant site by co-delivery of PlGF and thereby to effect an improvement in the persistence of luciferase expression, a marker of encapsulated cell viability. L929 cells were doubly transfected with luciferase and PlGF or luciferase and VEGF. Two hundred microcapsules containing a 1:1 mixture of the two transfected cells were implanted minimally invasively in Matrigel on one side of the mouse; the other side contained 200 microcapsules containing cells expressing luciferase only. Luciferase expression, reflective of encapsulated cell number, peaked at day 21 in both groups at about three times the value at day 1. In contrast with the immature vessels produced with VEGF alone (as reported earlier), the vessels produced here were more mature at day 14, and there were more such vessels than in the control group, although by day 21, there was a mixture of mature and immature vessels with PlGF, consistent with the premise that the maturity status of new vessels is PlGF dose dependent. Furthermore, anti-L929 antibodies (according to flow cytometry) and CD3-positive cells (according to histology) were detected in mice receiving unencapsulated cells, suggesting that there may be minor MHC (major histocompatibility complex) alloantigens and an adaptive immune response in this animal model. Thus successful modulation of the host response to microencapsulated cells may require enhanced vascularization and manipulation of the immune response, even with nominally syngeneic cells.

Cell encapsulation as a potential nondietary therapy for maternal phenylketonuria

The objective of this work was to determine whether cells overexpressing phenylalanine (Phe) hydroxylase (PAH) can significantly reduce Phe in vitro for potential use as a therapy for preventing maternal phenylketonuria. Human 293T and WRL68 cell lines were transiently and stably transfected to overexpress PAH. Cells were encapsulated within microspheres of sodium alginate. Timed measurements of Phe in media were performed using tandem mass spectrometry. Both nonencapsulated and encapsulated transiently transfected cells overexpressing PAH significantly reduced the Phe concentration in media by approximately 50% in comparison to mock-transfected cells. Cell line clones stably expressing PAH significantly decreased the Phe concentration in the media by up to 85% compared with media alone. Both unencapsulated and encapsulated cells overexpressing PAH significantly reduce Phe in vitro. Studies using phenylketonuria model mice will be important in determining the ability of our therapy to prevent the teratogenic effects of elevated maternal Phe in maternal phenylketonuria.

Real-Time Bioluminescence Imaging of Macroencapsulated Fibroblasts Reveals Allograft Protection in Rhesus Monkeys (Macaca mulatta)

Encapsulation of cells has the potential to eliminate the need for immunosuppression for cellular transplantation. Recently, the TheraCyte device was shown to provide long-term immunoprotection of murine islets in a mouse model of diabetes. In this report, translational studies were undertaken using skin fibroblasts from an unrelated rhesus monkey donor that were transduced with an HIV-1-derived lentiviral vector expressing firefly luciferase permitting the use of bioluminescence imaging (BLI) to monitor cell survival over time and in a noninvasive manner. Encapsulated cells were transplanted subcutaneously (n=2), or cells were injected without encapsulation (n=1) and outcomes compared. BLI was performed to monitor cell survival. The BLI signal from the encapsulated cells remained robust postinsertion and in one animal persisted for up to 1 year. In contrast, the control animal that received unencapsulated cells exhibited a complete loss of cell signal within 14 days. These data demonstrate that TheraCyte encapsulation of allogeneic cells provides robust immune protection in transplanted rhesus monkeys.

Influence of Alq 3/Au cathode on stability and efficiency of a layered organic solar cell in air

A relatively long lifetime organic solar cell, containing a thin tris-8-hydroxy-quinolato aluminum (Alq 3) layer under an Au cathode, is described. Half-lifetime of the cell in the darkness is over 7 weeks and 30% of the initial power conversion efficiency ( η ) is obtained after 18 weeks. This represents a substantial increase in lifetime compared to that of the unencapsulated Al-cathode cells. Efficiency is enhanced by 60 times compared to a cell that does not contain Alq 3, being 0.60%. The proposed role of Alq 3/Au cathode in this cell is discussed in detail.

Air-stable inverted flexible polymer solar cells using zinc oxide nanoparticles as an electron selective layer

The performance and stability of unencapsulated inverted bulk-heterojunction solar cells with zinc oxide (ZnO) made by different processes as the electron selective contact are compared to conventional bulk-heterojunction solar cells. The low temperature processed inverted devices using ZnO nanoparticles on indium tin oxide plastic substrates showed high power conversion efficiency of ∼3.3%. This inverted device structure possessed much better stability under ambient conditions retaining over 80% of its original conversion efficiency after 40days while the conventional one showed negligible photovoltaic activity after 4days. This is due to the improved stability at the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/Ag interface.

Transplantation of microencapsulated genetically modified xenogeneic cells augments angiogenesis and improves heart function

Cell-based gene therapy offers an alternative strategy for therapeutic angiogenesis for the management of myocardial infarction (MI). However, immune rejection poses a significant obstacle to the implantation of genetically engineered allogeneic or xenogeneic cells. In the present study, an ex vivo gene therapy approach utilizing cell microencapsulation was employed to deliver vascular endothelial growth factor (VEGF) to ischemic myocardium. Chinese hamster ovary (CHO) cells were genetically modified to secrete VEGF and enveloped into semipermeable microcapsules. In vitro assay indicated that the microencapsulated engineered CHO cells could secrete VEGF as high as 3852 pg ml(-1) per 48 h at day 8 after encapsulation. Then the microencapsulated CHO cells were implanted into the injured myocardium in a rat MI model, while engineered CHO cells, blank microcapsules and serum-free culture media were implanted as controls. The humoral immunity to xenogeneic CHO cells were evaluated and we found that the titer of anti-CHO antibodies was significantly lower in the microencapsulated CHO transplantation group than the group receiving unencapsulated CHO cells at two weeks after implantation. However, 1 week later, there was almost no difference between these groups. Histology and western blotting confirmed that the microencapsulated CHO cells maintained their original structure and VEGF secretion three weeks after implantation. The capillary density in the treatment region was also significantly higher in the microencapsulated CHO cell group than control groups, which was consistent with gross heart functional improvement. These data suggest that microencapsulated xenogeneic cell-based gene therapy might be a novel approach for therapeutic angiogenesis in ischemic heart disease.

Organic photovoltaic cells using hexadecafluorophthalocyaninatocopper (F 16CuPc) as electron acceptor material

We fabricated organic photovoltaic cells by using hexadecafluorophthalocyaninatocopper (F 16CuPc) as electron acceptor material and para-sexiphenyl ( p-6P) as electron donor material. F 16CuPc has wide absorption spectrum from 550 nm to 850 nm, which covers the maximum of solar photo flux. The measurement of their external quantum efficiency (EQE) demonstrated that the photocurrent comes from the excitons created in F 16CuPc, which were separated into free electrons and holes at heterojunction interface of p-6P and F 16CuPc. Moreover, F 16CuPc with excellent air-stability improved the environmental stability of photovoltaic cells, and the unencapsulated cells exhibited the shelf lifetime of exceeding a week.