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      Vitreous Substitutes: The Present and the Future

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          Abstract

          Vitreoretinal surgery has advanced in numerous directions during recent years. The removal of the vitreous body is one of the main characteristics of this surgical procedure. Several molecules have been tested in the past to fill the vitreous cavity and to mimic its functions. We here review the currently available vitreous substitutes, focusing on their molecular properties and functions, together with their adverse effects. Afterwards we describe the characteristics of the ideal vitreous substitute. The challenges facing every ophthalmology researcher are to reach a long-term intraocular permanence of vitreous substitute with total inertness of the molecule injected and the control of inflammatory reactions. We report new polymers with gelification characteristics and smart hydrogels representing the future of vitreoretinal surgery. Finally, we describe the current studies on vitreous regeneration and cell cultures to create new intraocular gels with optimal biocompatibility and rheological properties.

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          A novel pH-sensitive hydrogel composed of N,O-carboxymethyl chitosan and alginate cross-linked by genipin for protein drug delivery.

          Sung-Ching Chen, Yung-Chih Wu, Fwu-Long Mi … (2004)
          A novel pH-sensitive hydrogel system composed of a water-soluble chitosan derivative (N,O-carboxymethyl chitosan, NOCC) and alginate blended with genipin was developed for controlling protein drug delivery. Genipin, a naturally occurring cross-linking agent, is significantly less cytotoxic than glutaraldehyde and may provide a less extent of cross-linking to form a semiinterpenetrating polymeric network (semi-IPN) within the developed hydrogel system. The drug-loading process used in the study was simple and mild. All procedures used were performed in aqueous medium at neutral environment. In the study, preparation of the NOCC/alginate-based hydrogels was reported. Swelling characteristics of these hydrogels as a function of pH values were investigated. Additionally, release profiles of a model protein drug (bovine serum albumin, BSA) from test hydrogels were studied in simulated gastric and intestinal media. The semi-IPN formation of the genipin-cross-linked NOCC/alginate hydrogel was confirmed by means of the scanning electron microscopy-energy dispersive X-ray spectrometer (SEM-EDS) and the ninhydrin assays. The percentage of decrease of free amino groups and cross-linking density for the NOCC/alginate hydrogel cross-linked with 0.75 mM genipin were 18% and 26 mol/m(3), respectively. At pH 1.2, the swelling ratio of the genipin-cross-linked NOCC/alginate hydrogel was limited (2.5) due to formation of hydrogen bonds between NOCC and alginate. At pH 7.4, the carboxylic acid groups on the genipin-cross-linked NOCC/alginate hydrogel became progressively ionized. In this case, the hydrogel swelled more significantly (6.5) due to a large swelling force created by the electrostatic repulsion between the ionized acid groups. The amount of BSA released at pH 1.2 was relatively low (20%), while that released at pH 7.4 increased significantly (80%). The results clearly suggested that the genipin-cross-linked NOCC/alginate hydrogel could be a suitable polymeric carrier for site-specific protein drug delivery in the intestine.
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            Smart Polymeric Gels: Redefining the Limits of Biomedical Devices.

            Il Kwon, Somali Chaterji, Kinam Park (2007)
            This review describes recent progresses in the development and applications of smart polymeric gels, especially in the context of biomedical devices. The review has been organized into three separate sections: defining the basis of smart properties in polymeric gels; describing representative stimuli to which these gels respond; and illustrating a sample application area, namely, microfluidics. One of the major limitations in the use of hydrogels in stimuli-responsive applications is the diffusion rate limited transduction of signals. This can be obviated by engineering interconnected pores in the polymer structure to form capillary networks in the matrix and by downscaling the size of hydrogels to significantly decrease diffusion paths. Reducing the lag time in the induction of smart responses can be highly useful in biomedical devices, such as sensors and actuators. This review also describes molecular imprinting techniques to fabricate hydrogels for specific molecular recognition of target analytes. Additionally, it describes the significant advances in bottom-up nanofabrication strategies, involving supramolecular chemistry. Learning to assemble supramolecular structures from nature has led to the rapid prototyping of functional supramolecular devices. In essence, the barriers in the current performance potential of biomedical devices can be lowered or removed by the rapid convergence of interdisciplinary technologies.
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              Adult vitreous structure and postnatal changes.

              Richard Bishop, J-M Bras (2008)
              This review will focus on the molecular organisation of the adult vitreous and how it undergoes ageing changes throughout life that result in vitreous liquefaction and a predisposition towards posterior vitreous detachment and retinal break formation. At birth, the vitreous humour is in a gel state due to the presence of a network of fine collagen fibrils. With ageing, these collagen fibrils progressively aggregate due to a loss of type IX collagen from their surfaces. The aggregation of collagen fibrils may cause vitreous liquefaction which, when combined with an age-related weakening of postbasal vitreoretinal adhesion, predisposes to posterior vitreous detachment. Throughout postnatal life, the posterior border of the vitreous base migrates posteriorly from the ora serrata into the peripheral retina. This is due to new collagen synthesis by the peripheral retina. This new collagen intertwines with pre-existing cortical vitreous collagen to create new adhesions and thereby extends the vitreous base posteriorly. If irregularities in the posterior border of the vitreous base arise from this process, there is a predisposition towards retinal break formation during posterior vitreous detachment and subsequent rhegmatogenous retinal detachment.
              Article 0 comments Cited 78 times – based on 0 reviews     Review now
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                Author and article information

                Journal
                Journal ID (nlm-ta): Biomed Res Int
                Journal ID (iso-abbrev): Biomed Res Int
                Journal ID (publisher-id): BMRI
                Title: BioMed Research International
                Publisher: Hindawi Publishing Corporation
                ISSN (Print): 2314-6133
                ISSN (Electronic): 2314-6141
                Publication date (Print): 2014
                Publication date (Electronic): 4 May 2014
                Volume: 2014
                Electronic Location Identifier: 351804
                Affiliations
                1Department of Surgical and Morphological Sciences, Section of Ophthalmology, School of Medicine, University of Insubria, Via Guicciardini 9, 21100 Varese, Italy
                2Endocrine Unit, Department of Clinical and Experimental Medicine, School of Medicine, University of Insubria, 21100 Varese, Italy
                3Eye Clinic, Multidisciplinary Department of Medical, Surgical and Dental Sciences, Second University of Naples, 80121 Naples, Italy
                4Department of Ophthalmology, Polytechnic University of Ancona, 60121 Ancona, Italy
                5Genetic Laboratory, Department of Surgical and Morphological Sciences, School of Medicine, University of Insubria, 21100 Varese, Italy
                Author notes

                Academic Editor: Mario R. Romano

                Author information
                http://orcid.org/0000-0002-6920-7021
                http://orcid.org/0000-0002-2280-9981
                http://orcid.org/0000-0002-1334-0974
                Article
                DOI: 10.1155/2014/351804
                PMC ID: 4024399
                PubMed ID: 24877085
                SO-VID: 4995f3e7-249f-4144-8958-692442ff62ab
                Copyright © Copyright © 2014 Simone Donati et al.
                License:

                This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                Date received : 19 February 2014
                Date revision received : 15 April 2014
                Date accepted : 16 April 2014
                Categories
                Subject: Review Article

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