There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

American Society for Testing and Materials

비만아 부모의 돌봄 경험: q 방법론

Unintentional transplantation of autologous retinal pigment epithelium during limited macular translocation.

The artificial percept of light may be created by electrically stimulating the neurons of the retina. While a photolithographed array internal to the retina provides superior resolution, an array external to the retina provides easier implantation and improved manufacturability. Therefore it is advantageous to supply a high-resolution electrode array internal to the sclera, near the fovea and a lower-resolution electrode array eternal to the sclera near the periphery of the retina. It is advantageous to encourage current to flow through the retina by providing a physically separate and distinct electrode array and return electrode. The high-resolution electrode array and lower-resolution electrode array may be return electrodes for the other, or completely separate return electrodes may be provided.

Retinal Prosthesis with Multiple Electrode Arrays for Greater Field of View

Purpose To characterize histologic changes in the optic nerve and the retina of an end-stage retinitis pigmentosa (RP) patient after long-term implantation with the Argus II retinal prosthesis system. Methods Serial cross sections from the patient's both eyes were collected postmortem 6 years after implantation. Optic nerve from both eyes were morphometrically analyzed and compared. Retina underneath and outside the array was analyzed and compared with corresponding regions in the fellow eye. Results Although the optic nerve of the implant eye demonstrated significantly more overall atrophy than the fellow eye (P < 0.01), the temporal quadrant that retinotopically corresponded to the location of the array did not show additional damage. The total neuron count of the macular area was not significantly different between the two eyes, but the tack locations and their adjacent areas showed significantly fewer neurons than other perimacular areas. There was an increased expression of glial fibrillary acidic protein (GFAP) throughout the retina in the implant eye versus the fellow eye, but there was no significant difference in the cellular retinaldehyde-binding protein (CRALBP) expression. Except for the revision tack site, no significant increase of inflammatory reaction was detected in the implant eye. Conclusion Long-term implantation and electrical stimulation with an Argus II retinal prosthesis system did not result in significant tissue damage that could be detected by a morphometric analysis. Translational Relevance This study supports the long-term safety of the Argus II device and encourages further development of bioelectronics devices at the retina-machine interface.

Histopathologic Assessment of Optic Nerves and Retina From a Patient With Chronically Implanted Argus II Retinal Prosthesis System.

The retina is a complex and fragile photosensitive part of the central nervous system which is prone to degenerative diseases leading to permanent vision loss. No proven treatment strategies exist to treat or reverse the degenerative conditions. Recent investigations demonstrate that cell transplantation therapies to replace the dysfunctional retinal pigment epithelial (RPE) cells and or the degenerating photoreceptors (PRs) are viable options to restore vision. Pluripotent stem cells, retinal progenitor cells, and somatic stem cells are the main cell sources used for cell transplantation therapies. The success of retinal transplantation based on cell suspension injection is hindered by limited cell survival and lack of cellular integration. Recent advances in material science helped to develop strategies to grow cells as intact monolayers or as sheets on biomaterial scaffolds for transplantation into the eyes. Such implants are found to be more promising than the bolus injection approach. Tissue engineering techniques are specifically designed to construct biodegradable or non-degradable polymer scaffolds to grow cells as a monolayer and construct implantable grafts. The engineered cell construct along with the extracellular matrix formed, can hold the cells in place to enable easy survival, better integration, and improved visual function. This article reviews the advances in the use of scaffolds for transplantation studies in animal models and their application in current clinical trials.

/pdf/tissue-engineering-strategies-for-retina-regeneration-2ngnajjz02.pdf

Tissue Engineering Strategies for Retina Regeneration

Retinal prosthesis can be utilized for restoring vision to blind patients caused by retinitis pigmentosa or age-related macular degeneration. We proposed a 1025-channel high-density flexible microelectrode array (fMEA) for retinal prosthesis based on two kinds of substrate materials: polyimide (PI) and parylene-C (PA). We designed the fMEA with 25×41 pixels, and the diameter of each stimulating microelectrode was 60 µm with a center-to-center spacing of 160 µm. The fMEA was microfabricated with dual-metal-layer structure based on a simplified fabrication process. Meanwhile, the as-fabricated samples were electroplated with platinum gray, which significantly reduced the electrochemical impedance from 110 kΩ to 16 kΩ at 1 kHz, and also provided much larger charge storage capacity. We expect these results will promote the engineering of high-density fMEA for neural stimulation and recording.

Mark S. Humayun

Papers

Unintentional transplantation of autologous retinal pigment epithelium during limited macular translocation.

Retinal Prosthesis with Multiple Electrode Arrays for Greater Field of View

Histopathologic Assessment of Optic Nerves and Retina From a Patient With Chronically Implanted Argus II Retinal Prosthesis System.

Tissue Engineering Strategies for Retina Regeneration

Design and fabrication of a high-density flexible microelectrode array