Biomedical applications synthetic materials

Polyvinyl alcohol (PVA), which is a water soluble polyhidroxy polymer, is one of the widely used synthetic polymers for a variety of medical applications [197] because of easy preparation, excellent chemical resistance, and physical properties. [198] But it has poor stability in water because of its highly hydrophilic character. Therefore, to overcome this problem PVA should be insolubilized by copolymerization [43], grafting [199], crosslinking [200], and blending [201], These processes may lead a decrease in the hydrophilic character of PVA. Because of this reason these processes should be carried out in the presence of hydrophilic polymers. Polyfyinyl pyrrolidone), PVP, is one of the hydrophilic, biocompatible polymer and it is used in many biomedical applications [202] and separation processes to increase the hydrophilic character of the blended polymeric materials [203,204], An important factor in the development of new materials based on polymeric blends is the miscibility between the polymers in the mixture, because the degree of miscibility is directly related to the final properties of polymeric blends [205],... 

Significant developments have occurred in recent years in the fields of biopolymers and biomaterials. New synthetic materials have been synthesized and tested for a variety of biomedical and related applications from linings for artifical hearts to artifical pancreas devices and from intraocular lenses to drug delivery systems. Of particular interest in the future is the development of intelligent polymers or materials with special functional groups that can be used either for specialty medical applications or as templates or scaffolds for tissue regeneration. 

Finally, collagen can form a variety of collagen composites with other water-soluble materials. Ions, peptides, proteins, and polysaccharides can all be uniformly incorporated into a collagen matrix. The methods of composite formation include ionic and covalent bonding, entrapment, entanglement, and co-precipitation. A two-phase composite can be formed between collagen, ceramics, and synthetic polymers for specific biomedical applications. 

As mentioned above, the preparation of nanogels by addition reactions of functional macromolecular precursors is mainly used for biomedical applications. Thus, the choice of synthetic precursors for microgel formation is restricted to biocompatible materials. Moreover, as most applications are in drug delivery, the molecular weight of the gel precursors should be below the threshold for renal clearance, a value that depends on the molecular architecture and chemical nature of the polymer but that is usually smaller than 30kDa, which is set as the limit for linear PEG [97], Polymers that are mostly used and thus presented in more detail here are PEG, poly(glycidol) (PG), and polyethylene imine) (PEI). 

Peptide-poly(ethylene glycol) (PEG) block copolymers are ofparticiflar interest, both from a structural and a functional point of view. Poly(ethylene glycol) is also often referred to as poly(ethylene oxide) (PEG). Throughout this article, however, this polyether will be referred to as PEG. In contrast to the hybrid block copolymers discussed in the previous paragraphs, which were based on amorphous synthetic polymers, PEG is a semi-crystalline polymer. In addition to microphase separation and the tendency of the peptide blocks towards aggregation, crystallization of PEG introduces an additional factor that can influence the structure formation of these hybrid block copolymers, furthermore, PEG is an FDA approved biocompatible polymer, which makes peptide-PEG hybrid block copolymers potentially interesting materials for biomedical applications. 

A wide variety of chemical catalysts is nowadays available to polymerize monomers into well-defined polymers and polymer architectures that are applicable in advanced materials for example, as biomedical applications and nanotechnology. However, synthetic polymers rarely possess well-defined stereochemistries in their backbones. This sharply contrasts with the polymers made by nature where perfect stereocontrol is the norm. An interesting exception is poly-L-lactide, a polyester that is used in a variety of biomedical applications [1]. By simply playing with the stereochemistry of the backbone, properties ranging from a semicrystalline, high melting polymer (poly-L-lactide) to an amorphous high Tg polymer (poly-meso-lactide) have been achieved [2]. 

Biomimetics is a distinct and rapidly growing discipline that provides insight into the secrets of how Nature s biological pathways work, how they are manifest in diverse aspects of chemistry, physics and engineering, and in which way they can be emulated to provide materials and objects useful for biomedical applications. According to the Oxford Dictionary, the term biomimetics means relating to or denoting synthetic methods which mimic biochemical processes . 

Interest in biomedical applications of polymers dates back over 50 years. This interest is due in part to the fact that most biomaterials present in the human body are macromolecules (proteins, nucleic acids, etc.). When tissues or organs containing such materials need complete or partial replacement, it is logical to replace them with synthetic polymeric materials whenever natural replacement materials are not readily available. Although ceramics and metals can be used in certain cases, most biomedical applications require the use of some synthetic polymer or a modified natural macromolecule. Several recent books describe the range of biomedical applications of polymers (2-12). 

The first reported biomedical applications of pLA polymers involved use as sutures and prosthetics [8]. American Cyanamid developed synthetic, degradable sutures composed of pGA in the 1960s [9], while Ethicon developed similar materials involving pGA and pLA [10, 11]. 

Natural and synthetic zeolites as well as other mesoporous and microporous solids are used in many industrial and household applications. However, it is less known that in recent years these exciting materials are increasingly being used in biomedical applications. In this review different current and possible future biomedical applications, together with our own research results obtained from studies of such materials, are critically described. Current needs for synthesis and characterization of novel mesoporous and microporous materials which would be better suited for biomedical applications are also described. 

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