Synthetic biodegradable polymer matrices

Nanofibrous Matrix. Collagen (qv) is a major natural extracellular matrix component and possesses a fibrous structure with fiber bimdles varying in diameter from 50 to 500 nm (62,114). To mimic the nanofibrous architecture of collagen and to overcome the concerns over materials from a natural source such as pathogen transmission and immune rejection, a novel phase separation technique has been developed in our laboratory to fabricate nanofibrous matrices from synthetic biodegradable polymers (112). For example, PLLA solutions are cooled to induce phase separation and gelation. The solvent is directly sublimated or first exchanged with a different solvent and then sublimated. Several solvents and solvent mixtures have been utilized to fabricate the desired nanofibrous matrices in our laboratory (Fig. 13) (112). 

Solvent casting and particulate leaching (SC/PL) is a simple and commonly used method for fabricating scaffolds for tissue engineering. With an appropriate thermal treatment, porous constructs of synthetic biodegradable polymers can be prepared with specific porosity, surfaceivolume ratio, pore size and crystallinity for different applications. This method involves mixing water-soluble salt (e.g. sodium chloride, sodium citrate) particles into a polymer solution. The mixture is then cast into the mould of the desired shape. After the solvent is removed by evaporation or lyophilization, the salt particles are leached out to obtain a porous structure with the pore shape limited to the cubic crystal shape of the salt. Removal of soluble particles from the interior of a polymer matrix is difficult and limits the thickness of the films prepared to ca. 2 mm [293]. 

In recent years starch, the polysaccharide of cereals, legumes and tubers, has acquired relevance as a biodegradable polymer and is becoming increasingly important as an industrial material (Fritz Aichholzer, 1995). Starch is a thermoplastic polymer and it can therefore be extruded or injection moulded (Balta Calleja et al, 1999). It can also be processed by application of pressure and heat. Starch has been used successfully as a matrix in composites of natural fibres (flax, jute, etc.). The use of starch in these composites could be of value in applications such as automobile interiors. An advantage of this biopolymer is that its preparation as well as its destruction do not act negatively upon the environment. A further advantage of starch is its low price as compared with conventional synthetic thermoplastics (PE, PP). 

Stankus JJ et al (2008) Hybrid nanofibrous scaffolds from electrospinning of a synthetic biodegradable elastomer and urinary bladder matrix. J Biomater Sci Polym Ed 19(5) 635-652... 

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