Microengineered hydrogels for tissue engineering
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Hydrogels are presently under investigation as a delivery system for bioactive molecules, because of their similar physical properties as that of living tissue, which is due to their high water content, soft and rubbery consistency, and low interfacial tension with water or biological fluids. Anionic hydrogels are used in the design of intelligent controlled release devices for site-specific drug delivery of therapeutic proteins to the large intestine, where the biological activity of the proteins are prolonged, and cationic hydrogels are studied for the development of self regulated insulin delivery system, which releases the insulin in response to changing glucose concentration. The different methods of preparation of hydrogels, novel methods of crosslinking used in the preparation of hydrogels, the mechanism of water transport through the ionic hydrogels, and the release mechanism of the solute from the hydrogels, are discussed in the present article. The hydrogels, since their discovery by Wichterle and Lim in 1960 of poly(2-hydroxyethyl methacrylate) 1 , have been of great interest to biomedical scientists. Hydrogels are three dimensional hydrophilic polymer networks capable of swelling in water or biological fluids, and retaining a large amount of fluids in the swollen state 2 . Their ability to absorb water is due to the presence of hydrophilic groups such as –OH, –CONH–, –CONH 2 , – COOH, and –SO 3 H 3 . The water content in the hydrogels affect different properties like permeability, mechanical properties, surface properties, and biocompatibility. Hydrogels have similar physical properties as that of living tissue, and this similarity is due to the high water content, soft and rubbery consistency, and low interfacial tension with water or biological fluids 4 . The ability of molecules of different size to diffuse into (drug loading), and out (release drug) of hydrogels, permit the use of hydrogels as delivery systems. Since hydrogels have high permeability for water soluble drugs and proteins, the most common mechanism of drug release in the hydrogel system, is diffusion. Factors like polymer composition, water content, crosslinking density, and crystallinity, can be used to control the release rate and release mechanism from hydrogels 5 .
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Hydrogels have been shown to be very useful in the field of drug delivery due to their high biocompatibility and ability to sustain delivery. Therefore, the tuning of their properties should be the focus of study to optimise their potential. Hydrogels have been generally limited to the delivery of hydrophilic drugs. However, as many of the new drugs coming to market are hydrophobic in nature, new approaches for integrating hydrophobic drugs into hydrogels should be developed. This article discusses the possible new ways to incorporate hydrophobic drugs within hydrogel structures that have been developed through research. This review describes hydrogel-based systems for hydrophobic compound delivery included in the literature. The section covers all the main types of hydrogels, including physical hydrogels and chemical hydrogels. Additionally, reported applications of these hydrogels are described in the subsequent sections.
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Hydrogels are three-dimensional materials that can withstand a great amount of water incorporation while maintaining integrity. This allows hydrogels to be very unique biomedical materials, especially for drug delivery. Much effort has been made to incorporate hydrophilic molecules in hydrogels in the field of drug delivery, while loading of hydrophobic drugs has not been vastly studied. However, in recent years, research has also been conducted on incorporating hydrophobic molecules within hydrogel matrices for achieving a steady release of drugs to treat various ailments. Here, we summarize the types of hydrogels used as drug delivery vehicles, various methods to incorporate hydrophobic molecules in hydrogel matrices, and the potential therapeutic applications of hydrogels in cancer.
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Hydrogels are known as polymer-based networks with the ability to absorb water and other body fluids. Because of this, the hydrogels are used to preserve drugs, proteins, nutrients or cells. Hydrogels possess great biocompatibility, and properties like soft tissue, and networks full of water, which allows oxygen, nutrients, and metabolites to pass. Therefore, hydrogels are extensively employed as scaffolds in tissue engineering. Specifically, hydrogels made of natural polymers are efficient structures for tissue regeneration, because they mimic natural environment which improves the expression of cellular behavior. Producing natural polymer-based hydrogels from collagen, hyaluronic acid (HA), fibrin, alginate, and chitosan is a significant tactic for tissue engineering because it is useful to recognize the interaction between scaffold with a tissue or cell, their cellular reactions, and potential for tissue regeneration. The present review article is focused on injectable hydrogels scaffolds made of biocompatible natural polymers with particular features, the methods that can be employed to engineer injectable hydrogels and their latest applications in tissue regeneration.
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Hydrogels made from a variety of materials may be used as a novel technology in regenerative medicine in the biomedical field. Hydrogels may be made using both chemical and physical processes, depending on the source material. Size, elastic modulus, swelling, and degradation rate are only a few of the many physical parameters that may be used to define hydrogels in experiments. Hydrogels made from natural polymers have been the focus of our review. Due to their remarkable biocompatibility and nontoxicity, simple gelation, and functionalization, hydrogels derived from natural polymers have received extensive attention in recent decades. As a result, natural polymer hydrogels are considered excellent biomaterials that have great potential in the biomedical field. Because carriers play such a large role in determining how far and how fast drugs reach their intended recipients, the need for intelligent drug delivery systems (DDSs) is on the rise. An outstanding goal of this study is to examine the impact that various crosslinking process parameters have on the drug delivery mechanism.
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