Resorbable polymers mechanical properties

The idea of using polymers as binders for particulate bioceramics to prepare biocomposites with improved processing and retention characteristics and to overcome the problem of poor mechanical properties was reported. Poly(rac-lactide) (PDLLA) is a thermoplastic biodegradable, resorbable, and biocompatible aliphatic polyester, which in recent years received significant attention in the biomedical research field. It was also generally viewed as a polymer of the future because... 

ProLastin polymers are a family of protein-based materials w hose resorption rate in vivo can be controlled by adjusting the sequence and not just the composition of the polymer (Cappello et al, 1995). These adjustments can be made so as to cause little change in the formulation characteristics of the materials, their physical forms, or their mechanical properties. They have good mechanical integrity with no need for chemical crosslinking. They degrade by enzymatic proteolysis and are presumed to resorb by surface erosion. Their breakdowm products are peptides or amino acids w hich are electroneutral at physiological pH and cause no undue inflammation or tissue response. 

One limitation of the broad use of these resorbable implants in bone fracture treatment relates to their relatively poor mechanical properties [1]. Therefore, different techniques have been apphed to produce resorbable internal fixation devices with enhanced mechanical performance [2]. However, many problems with these techniques, hke delamination between the matrix and the reinforcing component or high crystallinity of the polymer, have not been solved yet. 

Various enzymatically resorbable polymers are currently under in vitro and in vivo investigation with a view to applying them to clinical practice for different biomedical applications due to their unique advantages. However, their limited mechanical properties restrict their use. Most of these biopolymers are used in the form of hydrogels, nanofibers, or thin films. With some modifications, some of these biopolymers have the potential to be spun into fibers for biomedical textile applications. This section deals with the major enzymatically resorbable biopolymers. Table 6.2 shows the classification of enzymatically resorbable polymers that have been studied and/or are used for various biomedical applications [1,2,4]. 

PLA is a biodegradable, bioresorbable polymer fiiat can be assimilated by the body and has important applications in sustained-release drug delivery systems. The mechanical properties and absorbability of PLA make it an ideal candidate for implants in bone and soft tissue and for resorbable sutures. 

Table 8 summarises the mechanical properties of self-reinforced polymer composites based on resorbable polymers. Although the exact processing routes and the stif iesses of these composites are not often reported, Tormala et al. reported the creation of unidirectionally reinforced PGA-based self-reinforced polymer composites by sintering together commercial PGA sutures [107]. These composites were reported to have a longitudinal flexural stiffness of 12 GPa and a longitudinal flexural strength of 365 MPa. 

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