The differences cited above are achieved in biocomposites by nature's use of processing techniques that can be entirely different from those that have been used for synthetic composites. Until recently, in the methods used for synthetic composites, the two or more phases have generally been prepared separately and then combined into the composite structure. Occasionally, some chemistry is involved, but it is, typically, relatively unsophisticated, for example, the curing of resin in a fiberglass composite.
More intelligent approaches are now being used to design materials, particularly those required to have multifunctional uses. In particular, the types of chemical methods that predominate in the construction of biocomposites are being used increasingly by materials scientists. These syntheses are carried out in situ, with either the two phases being generated simultaneously or the second phase being generated within the first. The generation of particles or fibers within a polymer matrix can avoid the difficulties associated with blending agglomerated species into a high-molecular-weight, high-viscosity polymer. The dispersed phase can be present to much greater extents, and much work could be done on the problem of using the polymeric matrix to control its growth. It may also be possible to avoid geometric problems, such as the alignment of fibrous molecules packed to high densities either because of their response to flow patterns or because of their inherent symmetry. Such anisotropy can be disadvantageous in that it leads to strengthening the material in some directions, but at the cost of weakening it in others. When such molecules are grown within an already formed matrix, however, essentially random isotropic packing can be obtained. The shell of the macademia nut is an excellent example of this type of reinforcement. In it, bundles of cellulose fibers are present in structures having considerable alignment. The composite is, thus, random and isotropic at larger scale, and this is the source of its celebrated toughness. Similar arrangements occur in some liquid crystalline polymers, but there is little correlation between the axes of different domains, and nothing has been done yet to mimic this type of composite material. In the case of chemically based methods, the competition between the kinetics of the chemical reactions and the rates of diffusion of reactants and products can also be used to advantage, for example, in the formation of permanent gradients. This approach is yet another opportunity to exploit nature's ideas.
The above exciting areas involve considerable overlap between biomaterials and polymer science. Polymers and biopolymers have a number of common elements, including the problems of understanding molecular conformations as the basis of underlying chemical events, the subtle driving forces, often largely entropic, and considerable overlap in the experimental and theoretical methodologies. Despite the considerable overlap in problems and methodologies in polymer