Polymer optoelectronic structures for retinal prosthesis

This commentary highlights the effectiveness of optoelectronic properties of polymer semiconductors based on recent results emerging from our laboratory, where these materials are explored as artificial receptors for interfacing with the visual systems. Organic semiconductors based polymer layers in contact with physiological media exhibit interesting photophysical features, which mimic certain natural photoreceptors, including those in the retina. The availability of such optoelectronic materials opens up a gateway to utilize these structures as neuronal interfaces for stimulating retinal ganglion cells. In a recently reported work entitled “A polymer optoelectronic interface provides visual cues to a blind retina,” we utilized a specific configuration of a polymer semiconductor device structure to elicit neuronal activity in a blind retina upon photoexcitation. The elicited neuronal signals were found to have several features that followed the optoelectronic response of the polymer film. More importantly, the polymer-induced retinal response resembled the natural response of the retina to photoexcitation. These observations open up a promising material alternative for artificial retina applications.     

Hyperbaric oxygen therapy treatment for the fixation of implant prosthesis in oncology patients irradiated

doi: 10.1111/j.1741‐2358.2012.00636.x Hyperbaric oxygen therapy treatment for the fixation of implant prosthesis in oncology patients irradiated Objectives: This study aimed to present a clinical report of an irradiated oncologic patient who underwent hyperbaric oxygen therapy to be rehabilitated with implant‐supported prosthesis. Materials and Methods: A 67‐year‐old man was admitted at Oral Oncology Center (FOA‐UNESP) presenting a lesion on the mouth floor. After clinical evaluation, incisional biopsy and histopathological exam, a grade II squamous cell carcinoma was diagnosed. The patient was subjected to surgery to remove the lesion and partial glossectomy. Afterwards, the radiotherapy, in the left/right cervicofacial area of the supraclavicular fossa, was conducted. After 3 years of the surgery, the patient was submitted to hyperbaric oxygen therapy. Then, four implants were installed in patient’s mandible. Five months later, an upper conventional complete denture and lower full‐arch implant‐supported prosthesis were fabricated. Conclusion: The treatment resulted in several benefits such as improving his chewing efficiency, swallowing and speech, less denture trauma on the mucosa and improving his self‐esteem.     

Carbon Dangling Bonds in Photodegraded Polymer:Fullerene Solar Cells

Intrinsic photodegradation of organic solar cells, theoretically attributed to C? H bond rearrangement/breaking, remains a key commercialization barrier. This work presents, via dark electron paramagnetic resonance (EPR), the first experimental evidence for metastable C dangling bonds (DBs) formed by blue/UV irradiation of polymer:fullerene blend films in nitrogen. The DB density increases with irradiation and decreases ≈4‐fold after 2 weeks in the dark. The dark EPR also shows increased densities of other spin‐active sites in photodegraded polymer, fullerene, and polymer:fullerene blend films, consistent with broad electronic measurements of fundamental properties, including defect/gap state densities. The EPR and electronic measurements enable identification of defect states, whether in the polymer, fullerene, or at the donor/acceptor (D/A) interface. Importantly, the EPR results indicate that the DBs are at the D/A interface, as they were present only in the blend films. The role of polarons in interface DB formation is also discussed.     

A role for polyamines in retinal ganglion cell excitotoxic death

Neuronal death due to excessive activation of N -methyl- d -aspartate (NMDA) receptors is a hallmark of neurodegenerative diseases. The polyamines: putrescine, spermine, and spermidine, bind to specific sites on the NMDA receptor and promote its activation, but their role in NMDA-induced neuronal death is ill defined. In this study, we characterized the role of polyamines in excitotoxic death of retinal ganglion cells (RGCs), a population of central neurons susceptible to NMDA-induced damage. Our data show that endogenous arginase I, the rate limiting enzyme for polyamine biosynthesis, is expressed in the intact, adult retina. Intraocular injection of NMDA visibly increased arginase I expression in Müller cells, the predominant glial cell-type in the mammalian retina. Inhibition of polyamine synthesis using di-fluoro-methyl-ornithine (DFMO) was markedly neuroprotective, while injection of exogenous polyamines in conjunction with NMDA exacerbated RGC death. Blockade of the polyamine binding sites on NMDA receptors using the non-competitive antagonist ifenprodil was neuroprotective, suggesting that polyamines contribute to excitotoxic death, at least partly, by binding to NMDA receptors. Importantly, we also demonstrate that NMDA leads to activation of both the Erk1/2 and PI3 K/Akt pathways, but only the PI3 K/Akt kinase was required for di-fluoro-methyl-ornithine-induced RGC survival. In summary, our study reveals that polyamines modulate neuronal death in the retina via different mechanisms that potentiate NMDA-triggered excitotoxicity.     

A quick protocol for the preparation of mouse retinal cryosections for immunohistochemistry

Immunohistochemistry (IHC) using mouse retinal cryosections is widely used to study the expression and intracellular localization of proteins in mouse retinas. Conventionally, the preparation of retinal cryosections from mice involves tissue fixation, cryoprotection, the removal of the cornea and lens, embedding and sectioning. The procedure takes 1–2 days to complete. Recently, we developed a new technique for the preparation of murine retinal cryosections by coating the sclera with a layer of Super Glue. This enables us to remove the cornea and extract the lens from the unfixed murine eye without causing the eyecup to collapse. In the present study, based on this new technique, we move a step forward to modify the conventional protocol. Unlike in the conventional protocol, in this method, we first coat the unfixed mouse eyeball on the sclera with Super Glue and then remove the cornea and lens. The eyecup is then fixed, cryoprotected and sectioned. This new protocol for the preparation of retinal cryosections reduces the time for the procedure to as little as 2 h. Importantly, the new protocol consistently improves the morphology of retinal sections as well as the image quality of IHC. Thus, this new quick protocol will be greatly beneficial to the community of visual sciences by expediting research progress and improving the results of IHC.     

A retinal circuit model accounting for wide-field amacrine cells

In previous experimental studies on the visual processing in vertebrates, higher-order visual functions such as the object segregation from background were found even in the retinal stage. Previously, the “linear–nonlinear” (LN) cascade models have been applied to the retinal circuit, and succeeded to describe the input-output dynamics for certain parts of the circuit, e.g., the receptive field of the outer retinal neurons. And recently, some abstract models composed of LN cascades as the circuit elements could explain the higher-order retinal functions. However, in such a model, each class of retinal neurons is mostly omitted and thus, how those neurons play roles in the visual computations cannot be explored. Here, we present a spatio-temporal computational model of the vertebrate retina, based on the response function for each class of retinal neurons and on the anatomical inter-cellular connections. This model was capable of not only reproducing the spatio-temporal filtering properties of the outer retinal neurons, but also realizing the object segregation mechanism in the inner retinal circuit involving the “wide-field” amacrine cells. Moreover, the first-order Wiener kernels calculated for the neurons in our model showed a reasonable fit to the kernels previously measured in the real retinal neuron in situ.     

Neural cell differentiation from retinal pigment epithelial cells of the newt: An organ culture model for the urodele retinal regeneration

Transdifferentiation from retinal pigment epithelium (RPE) to neural retina (NR) was studied under a new culture system as an experimental model for newt retinal regeneration. Adult newt RPEs were organ cultured with surrounding connective tissues, such as the choroid and sclera, on a filter membrane. Around day 7 in vitro, lightly pigmented “neuron‐like cells” with neuritic processes were found migrating out from the explant onto the filter membrane. Their number gradually increased day by day. BrdU‐labeling study showed that RPE cells initiated to proliferate under the culture condition on day 4 in vitro, temporally correlating to the time course of retinal regeneration in vivo. Histological observations of cultured explants showed that proliferating RPE cells did not form the stratified structure typically observed in the NR but they rather migrated out from the explants. Neuronal differentiation was examined by immunohistochemical detection of various neuron‐specific proteins; HPC‐1 (syntaxin), GABA, serotonin, rhodopsin, and acetylated tubulin. Immunoreactive cells for these proteins always possessed fine and long neurite‐like processes. Numerous lightly pigmented cells with neuron‐like morphology showed HPC‐1 immunoreactivity. Fibroblast growth factor‐2 (FGF‐2), known as a potent factor for the transdifferentiation of ocular tissues in various vertebrates, substantially increased the numbers of both neuron‐like cells and HPC‐1‐like immunoreactive cells in a dose‐dependent manner. These results indicate that our culture method ensures neural differentiation of newt RPE cells in vitro and provides, for the first time, a suitable in vitro experimental model system for studying tissue‐intrinsic factors responsible for newt retinal regeneration. © 2002 Wiley Periodicals, Inc. J Neurobiol 50: 209–220, 2002; DOI 10.1002/neu.10031     

A review of histomorphometric analysis techniques for assessing implant-soft tissue interface

Abstract

The success of dental implant treatment depends on the healing of both hard and soft tissues. While osseointegration provides initial success, the biological seal of the peri-implant soft tissue is crucial for maintaining the long term success of implants. Most studies of the biological seal of peri-implant tissues are based on animal or monolayer cell culture models. To understand the mechanisms of soft tissue attachment and the factors affecting the integrity of the soft tissue around the implants, it is essential to obtain good quality histological sections for microscopic examination. The nature of the specimens, however, which consist of both metal implant and soft peri-implant tissues, poses difficulties in preparing the specimens for histomorphometric analysis of the implant-soft tissue interface. We review various methods that have been used for the implant-tissue interface investigation with particular focus on the soft tissue. The different methods are classified and the advantages and limitations of the different techniques are highlighted.     

A role for CK2 upon interkinetic nuclear migration in the cell cycle of retinal progenitor cells

In developing retina, the nucleus of the elongated neuroepithelial cells undergoes interkinetic nuclear migration (INM), that is it migrates back and forth across the proliferative layer during the cell cycle. S-phase occurs at the basal side, while M-phase occurs at the apical margin of the retinal progenitors. G1 and G2-phases occur along the nuclear migration pathway. We tested whether this feature of the retinal cell cycle is controlled by CK2, which, among its many substrates, phosphorylates both molecular motors and cytoskeletal components. Double immunolabeling showed that CK2 is contained in BrdU-labeled retinal progenitors. INM was examined after pulse labeling the retina of newborn rats with BrdU, by plotting nuclear movement from basal to apical sides of the retinal progenitors during G2. The CK2 specific inhibitor 4,5,6,7-tetrabromobenzotriazole inhibited the activity of rat retinal CK2, and blocked nuclear movement proper in a dose-dependent way. No apoptosis was detected, and total numbers of BrdU-labeled nuclei remained constant following treatment. Immunohistochemistry showed that, following inhibition of CK2, the tubulin cytoskeleton is disorganized, with reduced acetylated and increased tyrosinated tubulin. This indicates a reduction in stable microtubules, with accumulation of free tubulin dimers. The results show that CK2 activity is required for INM in retinal progenitor cells.     

Polymer conformation: 3. Rapid methods for seeking contact-free double helices

A methodology for mapping helix constraint surfaces and contact-free molecular structures, as introduced in parts 1 and 2 of the series^1,2, has been developed and extended to include investigation of stability and stereochemical feasibility of double helices. The motivation for this development was prompted by practical considerations concerning the interpretation of new X-ray fibre diffraction patterns obtained from the gelling polysaccharide agarose³, in the light of previous interpretations⁴ favouring a double helix model for this biopolymer. The method may be of use for objectively scrutinizing double helix structures the interpretation of a number of which, e.g. carrageenan^5,6, poly(methyl methacrylate)^7,10, isotactic polystyrene^11,12, xanthan gum^13,16, appear to be controversial issues.     

Kinetic constants for the inhibition of camel retinal acetylcholinesterase by the carbamate insecticide lannate

We have designed this study to determine various kinetic parameters of camel retinal membrane‐bound acetylcholinesterase (AChE; EC 3.1.1.7) inhibition by carbamate insecticide lannate [methyl N‐{{(methylamino)carbonyl}oxy} ethanimidothioate]. All these kinetic constants were derived by simple graphical methods. The value of kinetic parameters was estimated as follows: 0.061 (μM)⁻¹, 1.14 (μM)⁻¹, 0.216 μM, 0.016 min⁻¹, 0.0741 (μM min)⁻¹, 0.746 μM, and 4.42 μM for velocity constant (K_v), new inhibition constant (K_nic), dissociation constant (K_d), carbamylation rate constant (k_2c), overall carbamylation rate constant (k′2 ), 50% inhibition constant (K_I50), and 99% inhibition constant (K_I99), respectively. These unique methods may be used to estimate such kinetic parameters for time‐dependent inhibition of enzymes by variety of chemicals, insecticides, herbicides, and drugs. © 1998 John Wiley & Sons, Inc. J Biochem Toxicol 13: 41–46, 1999     

Polymer microarrays for high throughput discovery of biomaterials

The discovery of novel biomaterials that are optimized for a specific biological application is readily achieved using polymer microarrays, which allows a combinatorial library of materials to be screened in a parallel, high throughput format (1). Herein is described the formation and characterization of a polymer microarray using an on-chip photopolymerization technique (2). This involves mixing monomers at varied ratios to produce a library of monomer solutions, transferring the solution to a glass slide format using a robotic printing device and curing with UV irradiation. This format is readily amenable to many biological assays, including stem cell attachment and proliferation, cell sorting and low bacterial adhesion, allowing the ready identification of 'hit' materials that fulfill a specific biological criterion (3-5). Furthermore, the use of high throughput surface characterization (HTSC) allows the biological performance to be correlated with physio-chemical properties, hence elucidating the biological-material interaction (6). HTSC makes use of water contact angle (WCA) measurements, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). In particular, ToF-SIMS provides a chemically rich analysis of the sample that can be used to correlate the cell response with a molecular moiety. In some cases, the biological performance can be predicted from the ToF-SIMS spectra, demonstrating the chemical dependence of a biological-material interaction, and informing the development of hit materials (5,3).     

Neuroprotective role of Nrf2 for retinal ganglion cells in ischemia‐reperfusion

Retinal ischemia plays a critical role in multiple vision‐threatening diseases and leads to death of retinal neurons, particularly ganglion cells. Oxidative stress plays an important role in this ganglion cell loss. Nrf2 (NF‐E2‐related factor 2) is a major regulator of the antioxidant response, and its role in the retina is increasingly appreciated. We investigated the potential retinal neuroprotective function of Nrf2 after ischemia‐reperfusion (I/R) injury. In an experimental model of retinal I/R, Nrf2 knockout mice exhibited much greater loss of neuronal cells in the ganglion cell layer than wild‐type mice. Primary retinal ganglion cells isolated from Nrf2 knockout mice exhibited decreased cell viability compared to wild‐type retinal ganglion cells, demonstrating the cell‐intrinsic protective role of Nrf2. The retinal neuronal cell line 661W exhibited reduced cell viability following siRNA‐mediated knockdown of Nrf2 under conditions of oxidative stress, and this was associated with exacerbation of increase in reactive oxygen species. The synthetic triterpenoid CDDO‐Im (2‐Cyano‐3,12‐dioxooleana‐1,9‐dien‐28‐imidazolide), a potent Nrf2 activator, inhibited reactive oxygen species increase in cultured 661W under oxidative stress conditions and increased neuronal cell survival after I/R injury in wild‐type, but not Nrf2 knockout mice. Our findings indicate that Nrf2 exhibits a retinal neuroprotective function in I/R and suggest that pharmacologic activation of Nrf2 could be a therapeutic strategy.

     

Energy substrate requirements for survival of rat retinal cells in culture: the importance of glucose and monocarboxylates

The process of metabolic coupling has been described as a means of providing additional fuel for neurons during periods of intense activity. This process has been suggested to occur in the mammalian retina, but whether retinal neurons can metabolise glial-derived monocarboxylates remains uncertain. The present study therefore sought to define the preferred energy substrates for maintenance of different retinal cells in culture, in order to clarify whether metabolic coupling can potentially occur in this tissue. All cells in rat retinal cultures were detrimentally affected by glucose deprivation. The effect on some neurons, however, could be partially reversed by 5 mm pyruvate or lactate. Furthermore, the glycolytic inhibitor, iodoacetic acid, caused a dose-dependent loss of all retinal cells in culture, whereas the mitochondrial inhibitor, 2,4-dinitrophenol, only led to a decrease in the number of neurons. Finally, inhibition of transporters for glucose or monocarboxylates caused the respective loss of glia or neurons from cultures. These data together demonstrate that, although cells do preferentially metabolise glucose, monocarboxylates such as lactate or pyruvate do play an important role in neuronal maintenance. These data therefore give partial support to the notion that metabolic coupling may occur in the retina.     

Correlating Stiffness,Ductility, and Morphology of Polymer:Fullerene Films for Solar Cell Applications

The development of flexible and physically robust organic solar cells requires detailed knowledge of the mechanical behavior of the heterogeneous material stack. However, in these devices there has been limited research on the mechanical properties of the active organic layer. Here, two critical mechanical properties, stiffness and ductility, of a widely studied organic solar cell active layer, a blend film composed of poly(3‐hexylthiophene) (P3HT) and [6,6]‐phenyl C61‐butyric acid methyl ester (PCBM) are reported. Processing conditions are varied to produce films with differing morphology and correlations are developed between the film morphology, mechanical properties and photovoltaic device performance. The morphology is characterized by fitting the absorption of the P3HT:PCBM films to a weakly interacting H‐aggregate model. The elastic modulus is determined using a buckling metrology approach and the crack onset strain is determined by observing the film under tensile strain using optical microscopy. Both the elastic modulus and crack onset strain are found to vary significantly with processing conditions. Processing methods that result in improved device performance are shown to decrease both the compliance and ductility of the film.     

Construction of CoP/NiCoP Nanotadpoles Heterojunction Interface for Wide pH Hydrogen Evolution Electrocatalysis and Supercapacitor

Constructing well defined nanostructures is promising but still challenging for high‐efficiency catalysts for hydrogen evolution reaction (HER) and energy storage. Herein, utilizing the differences in surface energies between (111) facets of CoP and NiCoP, a novel CoP/NiCoP heterojunction is designed and synthesized with a nanotadpoles (NTs)‐like morphology via a solid‐state phase transformation strategy. By effective interface construction, the disorder in terms of electronic structure and coordination environment at the interface in CoP/NiCoP NTs is created, which leads to dramatically elevated HER performance within a wide pH range. Theoretical calculations prove that an optimized proton chemisorption and H₂O dissociation are achieved by an optimized phosphide polymorph at the interface, accelerating the HER reaction. The CoP/NiCoP NTs are also proved to be excellent candidates for use in supercapacitors (SCs) with a high specific capacitance (1106.2 F g^?1 at 1 A g^?1) and good cycling stability (nearly 100% initial capacity retention after 1000 cycles). An asymmetric supercapacitor shows a high energy density (145 F g^?1 at 1 A g^?1) and good cycling stability (capacitance retention is 95% after 3200 cycles). This work provides new insights into the catalyst design for electrocatalytic and energy storage applications.     

Quantitative Analysis and Visualized Evidence for High Charge Separation Efficiency in a Solid‐Liquid Bulk Heterojunction

In the past few decades, some novel low‐cost nanostructured devices have been explored for converting solar energy into electrical or chemical energy, such as organic photovoltaic cells, photoelectrochemical solar cells, and solar water splitting cells. Generally, higher light absorption and/or charge separation efficiency are considered as the main reasons for improved performance in a nanostructured device versus a planar structure. However, quantitative analysis and definite experimental evidence remain elusive. Here, using BiVO₄ as an example, comparable samples with porous and dense structures have been prepared by a simple method. The porous and dense films are assembled into a solid‐electrolyte bulk and planar heterojunction, respectively. Some quantitative results are obtained by decoupling photon absorption, interfacial charge transfer, and charge separation processes. These results suggest that higher charge separation efficiency is mainly responsible for enhanced performance in a solid‐electrolyte bulk heterojunction. Moreover, we also present visualized evidence to show higher charge separation efficiency comes from a shorter photo‐generated hole diffusion distance in a bulk heterojunction. These results can deepen understanding charge transfer in a bulk heterojunction and offer guidance to design a more efficient low‐cost device for solar conversion and storage.