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

Spectral Determination of Retinal Oxygen Content in Dog Retina Using Computerized Tomographic Imaging Spectroscopy

Dry age-related macular degeneration (AMD) is the most common cause of blindness in the elderly and is thought to result from dysfunction and loss of retinal pigmented epithelium (RPE) resulting in photoreceptor loss. Replacement of lost RPE cells with stem cell-derived RPE (SC-RPE) in patients with AMD and similar retinal diseases is currently being tested in clinical trials. Subretinal delivery of cell suspensions of SC-RPE is being investigated as a treatment approach. However, there are concerns about long-term survival of these cells and their ability to form a polarized monolayer, which is vital for RPE function. Implantation of SC-RPE cells grown on natural or synthetic bioengineered scaffolds made of biodegradable or nonbiodegradable materials has resulted in promising anatomic and functional outcomes in preclinical studies. Such scaffolds support the survival and function of the RPE monolayer and facilitate manipulation and subretinal implantation. An ideal scaffold should mimic the properties of the natural RPE substrate: Bruch’s membrane. It should have a similar thickness, flexibility, micro- and macromolecule permeability, and the ability to promote survival, polarity, and function of the transplanted SC-RPE.

Scaffolds for Cell Transplantation

Spatiotemporal Analysis of Visually Evoked Potentials in the Cortex of a Blind Subject With a Chronic Intraocular Retinal Prosthesis

High Intensity Focus Ultrasound (HIFU) to Breakdown Lens for Cataract Surgery

Nanophotoswitches (NPSs) offer a new tool for optical
stimulation of neuronal activity, in vitro and also potentially in vivo. Our group previously reported a ruthenium bipyridine (Rubpy)-based NPS that inserts into the plasma membrane and upon visible illumination generates an electrical dipole, triggering action potentials in adrenal chromaffin cells. We have recently demonstrated
that after intravitreal injection of this NPS into the eyes of blind rats, illumination of the eye elicited electrical activity in the contralateral superior colliculus. To better understand the site of action of the NPS in retina, we examined the distribution of the molecules in different
retinal layers after intravitreal injection.

Methods: Rubpy molecules can be visualized by their luminescence (610 nm) upon visible wavelength illumination (460 nm). To resolve the luminescence from different retinal layers, a rapid-scan twophoton imaging system (LaVison) was used (Ti:Sapphire laser tuned to 900 nm). Intravitreal injection (1 mM, 4 μL Rubpy-based NPSs
in BSS), followed by eye removal and retina isolation 2-5 hrs after, was performed on young RCS rats. Luminescence images of the wholemount retina were captured by an EM-CCD camera (Andor). 

Results: At 2 hrs after intravitreal injection and with continuous superfusion of Ames medium, luminescence was confined near the injection site. Luminescence was observed localized to surface membranes of axons and somata of retinal ganglion cells (RGC), demonstrating the impermeability of the cell membrane to the NPS molecules. The outer retina did not show significant luminescence.
After 3 additional hours, luminescence was more diffused within the RGC layer and still did not extend to the outer retina. 

Conclusions: This study shows marked staining of RGC layer by intravitreally injected Rubpy-based NPS molecules, consistent with the hypothesis that the photoactivated NPS molecules induce electrical activity in the superior colliculus by acting on the RGCs that deliver electrical signals to the visual pathway outside the eyes. Distinct from other nano-scale optical cellular modulating approaches using optogenetics or azobenzene-based photoswitches, the NPS approach obviates the need for gene manipulation or toxic UV illumination, highlighting its potential in generating high-acuity prosthetic vision in patients blinded by retinal degenerative diseases.

Mark S. Humayun

Papers

Spectral Determination of Retinal Oxygen Content in Dog Retina Using Computerized Tomographic Imaging Spectroscopy

Scaffolds for Cell Transplantation

Spatiotemporal Analysis of Visually Evoked Potentials in the Cortex of a Blind Subject With a Chronic Intraocular Retinal Prosthesis

High Intensity Focus Ultrasound (HIFU) to Breakdown Lens for Cataract Surgery

Imaging Novel Ruthenium bipyridine-based Nanophotoswitches in Retina