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Dendritic Polymers for the Repair of Tissues
Published in Delphine Felder-Flesch, Dendrimers in Nanomedicine, 2016
Cynthia Ghobril, Mark W. Grinstaff
For example, Grinstaff and co-workers explored the crosslinking of amine terminated-G1-peptide dendrons A and NHS-PEG-NHS B (Fig. 3.6.1, Section 3.2) to form A:B hydrogel sealants for the repair of scleral incisions used in pars plana vitrectomy procedures.27 Vitrectomy is the surgical removal of the vitreous gel from the middle of the eye to correct the vision, and is usually conducted when there is retinal detachment, macular holes or vitreous hemorrhage. The surgeon makes small slits (usually three, less than 2 mm) in the side of the eye (pars plana area), in order to (1) suck out the vitreous gel, and repair the retina by removing subretinal fluids, scar tissues, and fixing macular holes, (2) insert an infusion line to replace the fluid and maintain the normal IOP, and (3) insert a light source for optical illumination. At the end of the procedure, the surgeon refills the eye with a saline solution and closes the incisions with sutures until the wound is healed. To determine whether the A:B hydrogels were more efficient in sealing 1.4 mm scleral wounds than sutures, a set of experiments were conducted on ex vivo enucleated pig eyes, where hydrogel precursors were first mixed at 18 wt% and quickly applied on the wounds, and the LPs were then measured after gelation and compared to 7-0 vicryl suture-treated eyes. The wounds treated with sutures had LPs of 140 ± 68 mmHg, whereas the ones treated with the bioadhesive hydrogels attained pressures higher than 250 mmHg without leakage. The hydrogel completely adhered to the tissue and prevented the wound from leaking even at high pressures. This high adhesion strength was likely due to the formation of an interpenetrating network between the gel and the host tissue, as suggested by the authors, reinforced by the possible reaction of residual NHS units of the hydrogel with amino groups of proteins presented in the extracellular matrix (ECM) of the tissue.
Phase retrieval for studying the structure of vitreous floaters simulated in a model eye
Published in Journal of Modern Optics, 2021
Varis Karitans, Sergejs Fomins, Maris Ozolinsh
Vitreous floaters belong to a class of entoptic phenomena and are experienced by most people as chains, bubbles, cobwebs and other structures floating in the field of view. Vitreous floaters are transparent phase objects, i.e. cells, fibrils, clumps of proteins floating in a liquified vitreous body [1,2]. Typical size of the elements causing vitreous floaters lies in the range from a few to few tens of micrometers [3]. Vitreous floaters manifest themselves as diffraction patterns due to the mismatch between the refractive indices of the floating elements and the surrounding media [4,5]. In most cases, vitreous floaters cause merely visual discomfort and do not indicate any serious ocular condition, however, a sudden increase in the number of vitreous floaters may point to retinal detachment, inflammation, hemorrhage, or other pathologies. In most cases, people are able to adapt to vitreous floaters, however, if vitreous floaters become symptomatic, patients may want to remove them. Currently, vitreolysis and vitrectomy are the most efficient treatment options [6], however, both options are associated with high risks (retinal detachment, tears, hemorrhage, burns and others) and their necessity must be carefully considered. In order to neutralize vitreous floaters safely, a non-invasive method is preferred. A reasonable and safe method how to cancel or reduce the effects of vitreous floaters can be based on spatial modulation of the light entering the eye. In order to know the required modulation of the incoming light, the structure of the elements causing vitreous floaters must be determined. Once the structure of these elements has been determined, the shape of a wavefront modulator can be adjusted so that the phase distortions caused by the floating elements can be eliminated. Currently, optical coherence tomography (OCT) [7] and ultrasonography [8] can be used to determine the structure of elements floating in a liquified vitreous body. These methods, however, can be difficult to be incorporated into an optical system performing the dual task, i.e. analysing the structure of the floating elements and compensating the phase distortions.