Bionanocomposites are a novel class of nanosized materials. They contain the constituent of biological origin and particles with at least one dimension in the range of 1–100 nm. There are similarities with nanocomposites but also fundamental differences in the methods of preparation, properties, functionalities, biodegradability, biocompatibility, and applications. The article includes two parts. Bionanocomposite definition and classification along with nanoparticles, biomaterials, and methods of their preparation are initially reviewed. Then, novel approaches developed by our team are presented. The first approach concerns the preparation of bionanocomposites from chitosan and nanoparticles. It is based on the regulated charging of polysaccharide by the gradual shift of solution pH. When charges appear, the biomacromolecules come into the electrostatic interactions with negatively charged nanoparticles that cause the jellification of solutions. It is also applied to form films. They have a nacre-like structure from stacked planar nanoparticles separated by aligned biomacromolecules. The second approach deals with the biomimicking mineralization of biopolymers by using a novel silica precursor. Its advantage over the current sol-gel processing is in the compatibility and regulation of processes and structure of generated silica. Another example of the mineralization is presented by titania. Syntheses are performed in anhydrous ethylene glycol. Processes and structure of bionanocomposites are regulated by water that is added in an amount to only hydrate functional groups in the carbohydrate macromolecule.

Hydrogels are prepared by means of progressive acidification of xanthan solution containing dispersed chitosan particles in noncharged state at pH a little larger than pK_a of this polysaccharide. The following pH shift causes gradual charging of chitosan macromolecules that are involved into electrostatic interactions with oppositely charged xanthan. This triggered self-regulating processes of polysaccharide self-organization into supramolecular structures. Fibrillation or capsulation was observed that depended on the charge mixing ratio between chitosan and xanthan. The jellification of solutions took place in a case of fibrillar morphology. The strongest hydrogels were found where a fine and dense network of aligning fibrils of mean diameter of around 30 nm were generated. Where oppositely charged polysaccharides self-organized into capsules, the hydrogel was not formed because of the absence of cross-links between particles that could reach few mm in diameter and had mechanically strong shell.