Inverted Polymer Solar Cells with Annealing-Free Solution-Processable NiO.

Nickel oxide (NiO) offers intrinsic p-type behavior and high thermal and chemical stability, making it promising as a hole transport layer (HTL) material in inverted organic solar cells. However, its use in this application has been rare because of a wettability problem caused by use of water as base solvent and high-temperature annealing requirements. In the present work, an annealing-free solution-processable method for NiO deposition is developed and applied in both conventional and inverted non-fullerene polymer solar cells. To overcome the wettability problem, the typical DI water solvent is replaced with a mixed solvent of DI water and isopropyl alcohol with a small amount of 2-butanol additive. This allows a NiO nanoparticle suspension (s-NiO) to be deposited on a hydrophobic active layer surface. An inverted non-fullerene solar cell based on a blend of p-type polymer PTB7-Th and non-fullerene acceptor IEICO-4F exhibits the high efficiency of 11.23% with an s-NiO HTL, comparable to the efficiency of an inverted solar cell with a MoOx HTL deposited by thermal evaporation. Conventionally structured devices including this s-NiO layer show efficiency comparable to that of a conventional device with a PEDOT:PSS HTL.

Freestanding Oxide Membranes for Epitaxial Ferroelectric Heterojunctions.

Since facile routes to fabricate freestanding oxide membranes were previously established, tremendous efforts have been made to further improve their crystallinity, and fascinating physical properties have been also reported in heterointegrated freestanding membranes. Here, we demonstrate our synthetic recipe to manufacture highly crystalline perovskite SrRuO3 freestanding membranes using new infinite-layer perovskite SrCuO2 sacrificial layers. To accomplish this, SrRuO3/SrCuO2 bilayer thin films are epitaxially grown on SrTiO3 (001) substrates, and the topmost SrRuO3 layer is chemically exfoliated by etching the SrCuO2 template layer. The as-exfoliated SrRuO3 membranes are mechanically transferred to various nonoxide substrates for the subsequent BaTiO3 film growth. Finally, freestanding heteroepitaxial junctions of ferroelectric BaTiO3 and metallic SrRuO3 are realized, exhibiting robust ferroelectricity. Intriguingly, the enhancement of piezoelectric responses is identified in freestanding BaTiO3/SrRuO3 heterojunctions with mixed ferroelectric domain states. Our approaches will offer more opportunities to develop heteroepitaxial freestanding oxide membranes with high crystallinity and enhanced functionality.

Template Engineering of Metal-to-Insulator Transitions in Epitaxial Bilayer Nickelate Thin Films.

Understanding metal-to-insulator phase transitions in solids has been a keystone not only for discovering novel physical phenomena in condensed matter physics but also for achieving scientific breakthroughs in materials science. In this work, we demonstrate that the transport properties (i.e., resistivity and transition temperature) in the metal-to-insulator transitions of perovskite nickelates are tunable via the epitaxial heterojunctions of LaNiO3 and NdNiO3 thin films. A mismatch in the oxygen coordination environment and interfacial octahedral coupling at the oxide heterointerface allows us to realize an exotic phase that is unattainable in the parent compound. With oxygen vacancy formation for strain accommodation, the topmost LaNiO3 layer in LaNiO3/NdNiO3 bilayer thin films is structurally engineered and it electrically undergoes a metal-to-insulator transition that does not appear in metallic LaNiO3. Modification of the NdNiO3 template layer thickness provides an additional knob for tailoring the tilting angles of corner-connected NiO6 octahedra and the linked transport characteristics further. Our approaches can be harnessed to tune physical properties in complex oxides and to realize exotic physical phenomena through oxide thin-film heterostructuring.

The influence of electrospun aligned poly(epsilon-caprolactone)/collagen nanofiber meshes on the formation of self-aligned skeletal muscle myotubes.

Current treatment options for restoring large skeletal muscle tissue defects due to trauma or tumor ablation are limited by the host muscle tissue availability and donor site morbidity of muscle flap implantation. Creation of implantable functional muscle tissue that could restore muscle defects may bea possible solution. To engineer functional muscle tissue for reconstruction, scaffolds that mimic native fibers need to be developed. In this study we examined the feasibility of using poly(epsilon-caprolactone) (PCL)/collagen based nanofibers using electrospinning as a scaffold system for implantable engineered muscle. We investigated whether electrospun nanofibers could guide morphogenesis of skeletal muscle cells and enhance cellular organization. Nanofibers with different fiber orientations were fabricated by electrospinning with a blend of PCL and collagen. Human skeletal muscle cells (hSkMCs) were seeded onto the electrospun PCL/collagen nanofiber meshes and analyzed for cell adhesion, proliferation and organization. Our results show that unidirectionally oriented nanofibers significantly induced muscle cell alignment and myotube formation as compared to randomly oriented nanofibers. The aligned composite nanofiber scaffolds seeded with skeletal muscle cells may provide implantable functional muscle tissues for patients with large muscle defects.

In Situ Tissue Regeneration of Renal Tissue Induced by Collagen Hydrogel Injection.

Host stem/progenitor cells can be mobilized and recruited to a target location using biomaterials, and these cells may be used for in situ tissue regeneration. The objective of this study was to investigate whether host biologic resources could be used to regenerate renal tissue in situ. Collagen hydrogel was injected into the kidneys of normal mice, and rat kidneys that had sustained ischemia/reperfusion injury. After injection, the kidneys of both animal models were examined up to 4 weeks for host tissue response. The infiltrating host cells present within the injection regions expressed renal stem/progenitor cell markers, PAX-2, CD24, and CD133, as well as mesenchymal stem cell marker, CD44. The regenerated renal structures were identified by immunohistochemistry for renal cell specific markers, including synaptopodin and CD31 for glomeruli and cytokeratin and neprilysin for tubules. Quantitatively, the number of glomeruli found in the injected regions was significantly higher when compared to normal regions of renal cortex. This phenomenon occurred in normal and ischemic injured kidneys. Furthermore, the renal function after ischemia/reperfusion injury was recovered after collagen hydrogel injection. These results demonstrate that introduction of biomaterials into the kidney is able to facilitate the regeneration of glomerular and tubular structures in normal and injured kidneys. Such an approach has the potential to become a simple and effective treatment for patients with renal failure. Stem Cells Translational Medicine 2018;7:241-250.

Bioengineered multilayered human corneas from discarded human corneal tissue.

Corneal transplantation has become a common procedure to improve visual acuity by replacing the opaque or distorted host tissue with clear healthy donor corneal tissue. However, globally its wide spread clinical utility is limited due to a lack of supply of high quality corneas. Bioengineered neo-corneas using discarded human corneas to isolate corneal endothelial and epithelial cells, as well as corneal stroma as a scaffolding material, could help address this shortage. The objective of this study was to fabricate multilayered corneal equivalents that could be suitable for full thickness cornea transplantation. To achieve this goal human corneal endothelial cells (hCEC) and human limbal epithelial cells (hLEC) were isolated from discarded human corneas and expanded in vitro, maintaining their phenotype for at least 3 passages. We used our previously described process of human cornea decellularization to create corneal scaffolds that preserve the native extracellular matrix of the corneal stroma. The corneal scaffolds were seeded with hCEC and hLEC, using a special apparatus that enabled seeding both sides of the scaffold. The cell-seeded corneal constructs supported hCEC and hLEC growth and multi-cellular organization for 2 weeks in vitro. Immunohistochemical analysis showed expression of typical hCEC and hLEC markers on their corresponding sides. Importantly, the cell-seeded corneal constructs were more transparent than non-seeded corneal scaffolds. Taken together, this study demonstrates the feasibility of creating multilayered cornea equivalents, exclusively from human donor-derived materials. These constructs may be suitable for corneal transplantation, and as a short-term application, may serve for ophthalmological drug testing purposes.

Response of MG63 osteoblast-like cells onto polycarbonate membrane surfaces with different micropore sizes.

Response of different types of cells on materials is important for the applications of tissue engineering and regenerative medicine. It is recognized that the behavior of the cell adhesion, proliferation, and differentiation on materials depends largely on surface characteristics such as wettability, chemistry, charge, rigidity, and roughness. In this study, we examined the behavior of MG63 osteoblast-like cells cultured on a polycarbonate (PC) membrane surfaces with different micropore sizes (0.2-8.0 microm in diameter). Cell adhesion and proliferation to the PC membrane surfaces were determined by cell counting and MTT assay. The effect of surface micropore on the MG63 cells was evaluated by cell morphology, protein content, and alkaline phosphatase (ALP) specific activity. It seems that the cell adhesion and proliferation were progressively inhibited as the PC membranes had micropores with increasing size, probably due to surface discontinuities produced by track-etched pores. Increasing micropore size of the PC membrane results in improved protein synthesis and ALP specific activity in isolated cells. There was a statistically significant difference (P<0.05) between different micropore sizes. The MG63 cells also maintained their phenotype under conditions that support a round cell shape. RT-PCR analysis further confirmed the osteogenic phenotype of the MG63 cells onto the PC membranes with different micropore sizes. In results, as micropore size is getting larger, cell number is reduced and cell differentiation and matrix production is increased. This study demonstrated that the surface topography plays an important role for phenotypic expression of the MG63 osteoblast-like cells.

Heparin-modified gelatin scaffolds for human corneal endothelial cell transplantation.

Although one of the most transplanted tissues, a shortage of cadaveric corneas for transplantation still exists in the western society and elsewhere. The goal of this study was to develop a biological scaffold to support transfer of cultured human corneal endothelial cells (HCECs) into the anterior chamber of the eye, potentially a replacement for cadaveric donor tissue. A series of transparent scaffolds were fabricated from gelatin and modified with heparin. Mechanical parameters of the scaffolds, such as stiffness, affected cell proliferation, phenotype and cell surface marker expression were determined. The heparin-modified scaffolds had a greater capacity to absorb basic fibroblast growth factor (bFGF) and showed better release kinetics for up to 20 days. The release of bFGF from the scaffolds improved HCECs survival and reduced cellular loss. The scaffolds were flexible and could be folded and implanted in rabbits' eyes, through a small incision in the cornea. The scaffolds adhered to the inner surface of the corneal stroma and gradually integrated with the surrounding tissue. These results indicate that gelatin based corneal scaffolds modified to absorb and release growth factors and seeded with HCECs, might be a suitable alternative for cadaveric cornea transplantation.

Factors affecting successful isolation of human corneal endothelial cells for clinical use.

Corneal transplantation is a common transplant procedure used to improve visual acuity by replacing the opaque or distorted host tissue with clear healthy donor tissue. However, its clinical utility is limited due to a lack of donor supply of high-quality corneas. Bioengineered neocorneas, created using an expandable population of human donor-derived corneal endothelial cells (HCECs), could address this shortage. Thus, the objective of this study was to evaluate HCEC sourcing with various isolation methods, including enzymatic digestion, culture medium components, and adhesive proteins. HCECs were obtained from corneas obtained from various aged donors after endothelial keratoplasty. Under a dissection microscope, the Descemet's membrane, including the attached corneal endothelium, was stripped from the stroma, and the cells were isolated and expanded by explant culture or by enzymatic digestion with enzymes such as collagenase II, dispase, or trypsin. In order to improve the initial cell attachment, tissue culture plates were coated with collagen IV, fibronectin, or fibronectin-collagen combination coating mix (FNC) before cell plating. We were able to successfully obtain HCECs from 32% (86/269) of donor corneas. Donor age and isolation method influenced the characteristics of the resulting in vitro HCEC culture. Under all conditions tested, FNC-coated plates showed higher quality cultures than the other coatings tested. These results suggest that donor age and HCEC isolation methodology are the two factors that most directly affect the quality of the resulting HCEC culture in vitro. These factors should guide the methodological development for the clinical expansion of HCECs for the generation of bioengineered neocorneas.

In vitro evaluation of the interactions between human corneal endothelial cells and extracellular matrix proteins.

The corneal endothelium is the innermost cell layer of the cornea and rests on Descemet's membrane consisting of various extracellular matrix (ECM) proteins which can directly affect the cellular behaviors such as cell adhesion, proliferation, polarity, morphogenesis and function. The objective of this study was to investigate the interactions between the ECM environment and human corneal endothelial cells (HCECs), with the ultimate goal to improve cell proliferation and function in vitro. To evaluate the interaction of HCECs with ECM proteins, cells were seeded on ECM-coated tissue culture dishes, including collagen type I (COL I), collagen type IV (COL IV), fibronectin (FN), FNC coating mix (FNC) and laminin (LM). Cell adhesion and proliferation of HCECs on each substratum and expression of CEC markers were studied. The results showed that HCECs plated on the COL I, COL IV, FN and FNC-coated plates had enhanced cell adhesion initially; the number for COL I, COL IV, FN and FNC was significantly higher than the control (P < 0.05). In addition, cells grown on ECM protein-coated dishes showed more compact cellular morphology and CEC marker expression compared to cells seeded on uncoated dishes. Collectively, our results suggest that an adequate ECM protein combination can provide a long-term culture environment for HCECs for corneal endothelium transplantation.

Bioengineering endothelialized neo-corneas using donor-derived corneal endothelial cells and decellularized corneal stroma.

Corneal transplantation is a common transplant procedure performed to improve visual acuity by replacing the opaque or distorted host tissue by clear healthy donor tissue. However, its clinical utility is limited due to a lack of high quality donor corneas. Bioengineered neo-corneas, created using an expandable population of human donor-derived corneal endothelial cells (HCEC), could address this current shortage. The objectives of this study were to establish HCEC isolation and culture protocols and to investigate the feasibility of bioengineering corneal tissue constructs by seeding the cells on decellularized human corneal stroma. HCECs were removed from the discarded corneas of eye donors by enzymatic digestion. Cells were expanded and evaluated for their expression of Na(+)/K(+)-ATPase and zona occludens-1 (ZO-1). Donor corneal stromas were cut to 120-200 microm thickness slices using a microtome and then decellularized. Extracellular matrix components and mechanical properties of the scaffolds were measured after decellularization. To engineer neo-corneas, 130 HCEC/mm(2) were seeded on decellularized human corneal stromas. The resulting constructs were placed in growth medium for 14 days and then analyzed using scanning electron microscopy (SEM), histology, and immunocytochemistry. Seeded cells retain expression of the functional markers Na(+)/K(+)-ATPase and ZO-1 and constructs have biomechanical properties similar to those of normal corneas. These results indicate that construction of neo-corneas, using HCECs derived from discarded donor corneas and decellularized thin-layer corneal stromas, may create a new source of high quality corneal tissue for transplantation.

Bilayered scaffold for engineering cellularized blood vessels.

Vascular scaffolds fabricated by electrospinning poly(epsilon-caprolactone) (PCL) and collagen have been designed to provide adequate structural support as well as a favorable adhesion substrate for vascular cells. However, the presence of small-sized pores limits the efficacy of smooth muscle cells (SMC) seeding, as these cells could not adequately infiltrate into the scaffolds. To overcome this challenge, we developed a bilayered scaffolding system that provides different pore sizes to facilitate adequate cellular interactions. Based on the fact that pore size increases with the increase in fiber diameter, four different fiber diameters (ranging 0.27-4.45 mum) were fabricated by electrospinning with controlled parameters. The fabricated scaffolds were examined by evaluating cellular interactions, and the mechanical properties were measured. Endothelial cells (EC) seeded on nanoscaled fibers showed enhanced cellular orientation and focal adhesion. Conversely, fabrication of a larger fiber diameter improved SMC infiltration into the scaffolds. To incorporate both of these properties into a scaffold, bilayered vascular scaffolds were produced. The inner layer yielded small diameter fibers and the outer layer provided large diameter fibers. We show that the bilayered scaffolds permit EC adhesion on the lumen and SMC infiltration into the outer layer. This study suggests that the use of bilayered scaffolds may lead to improved vessel formation.