Combination with Natural Polymers

In this section, examples of scaffolds made primarily of HA as cell (chondrocytes, MSC) delivery vehicles to stimulate cartilage regeneration are provided. 

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Formulations for particleboard and plywood adhesives based on combinations of diisocyanates and compounds from renewable resources like tannins, starch, and proteins have been developed and tested at the Fraunhofer-Institute. All in all, the results of gluing tests indicated the potential for using diisocyanates combined with natural polymers for adhesive purposes where each natural product used alone will fail. More attempts will be necessary to find precise mixtures to produce successful adhesives for panel products. The development of adequate particleboard and plywood glue formulations based on diisocyanates and natural polymers has to be accompanied by more sophisticated technologies than those used in conventional production processes. The results presented here may give some hints on how these technologies can evolve. 

In every living cell there are found nucleoproteins substances made up of proteins combined with natural polymers of another kind, the nucleic acids. Of all fields of chemistry, the study of the nucleic acids is perhaps the most exciting, for these compounds are the substance of heredity. Let us look very briefly at the structure of nucleic acids and, then, in the next section, see how this structure may be related to their literally vital role in heredity. 

Generally speaking, synthetic polymers have better mechanical strength than natural polymers. They allow researchers more flexibihty in the design and development of new products, but challenge them with the difficult task of minimising cytotoxicity in such products. As a result, they are usually used in combination with natural polymers or are modified or functionalised to improve their biocompatibUity. 

To study the hemocompatible of PURs in combination with natural polymers, Xu et al. [101] have synthesized copolymers of PUR with hyaluronic add. The presence of hyaluronic acid could incorporate non thrombogenic nature to the PURs due to the presence of hyalmonic acid in biofluid. Hyaluronic acid when used as a chain extender for PUR... 

Nanostructured composites, where both the reinforcement and the matrix are biobased, are discussed in the book by Oksman and Sain (2006). Cellulose combined with natural polymers led to the development of a class of biodegradable and envi-ronmentally-friendly bionanocomposites. This family of nanocomposites is expected to remarkably improve material properties when compared with the matrix polymers or conventional micro- and macro-composite materials. Such improvements in properties typically include a higher modulus and strength, improved barrier properties, and increased heat distortion temperature [4]. 

This chapter will introduce polymer systems containing either naturally occurring maaomolecules (polysaccharides, proteins, DNA) or their subunits (bioanalogous molecules, amino acids, short peptides and peptide derivatives, polypeptides, polynucleotides), respectively. The natural building blocks can be connected by covalent bonds or by self-assembly and either can be used alone (see, e.g.. Section 5.4) or in combination with synthetic polymer units (biohybrids). Alternatively the building block itself may be a hybrid of a natural and synthetic molecule (bioconjugate cf. Section 3.5), as, for instance, a PEG-peptide conjugate. 

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