The significance of thermal analysis in biomaterials

In any biomaterial application, the composition and structure of a candidate biomaterial relevant to the properties under consideration should be evaluated. Generally, the biomaterial specification is set at the beginning of the design cycle and the properties of the candidate 

The thermal behaviour of materials can also provide important information about the structure and morphology of a material. For example, while most synthetic polymers have a glass transition temperature (Tg) associated with amorphous structure in the material, only polymers with regular chain architecture can crystalhse and so have a melting temperature (IJn). These in turn can have a direct effect on the mechanical performance of the materials since below Tg polymers tend to be glassy and become more rubbery above 7. These thermal properties can also be used to identify or verify the nature of the composition. For example, random copolymers will only exhibit one Tg that will be somewhere in between the 7 s of the individual homopolymers, whereas block copolymers will exhibit 7 s characteristic of each homopolymer but will be slightly shifted due to imperfect phase separations. Similarly this can be applied to polymeric blends, which are essentially two polymeric systems mixed together. 

The following sections will highlight some examples of how thermal analysis techniques have been applied in the characterisation of biomaterials to demonstrate the versatility of these complementary techniques. 

Over the past two decades, DMA has proven to be a useful technique for the characterisation of biomaterials since it not only gives a quantitative assessment of material properties such as stiffness and damping, but also provides structural information. This is because the dynamic mechanical properties of materials are sensitive to aU kinds of transitions, relaxation processes, structural heterogeneity and morphology of multi-phase systems such as crystalline polymers, polyblends and composites. DMA can also pinpoint thermal transitions for example, typical output of tan 8 versus temperature will display a peak at Tg. Above 7, peaks correspond to the crystalline regions and eventually Tm. As a technique, DMA is also sensitive for the characterisation of polymers of similar chemical compositions, as well as detecting the presence of moderate quantities of additives such as plasticisers or leachable materials. For example, PVC is very stiff, however, with the addition of plasticisers it can be made more flexible. 

1 Particulate and/or fibre-filled polymer composites as bone substitutes 

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