International Materials Reviews

Bone is a remarkable living material that comes in two forms with different porosities and different macrostructure, but with the same highly organised microstructure and nanostructure. As bone accumulates damage, it is removed and replaced. When the mechanical demands on bone increase the bone mass increases, while reductions in the loading leads to the removal of bone, thus bone can be considered a ‘smart material’. The ongoing replacement of old bone tissue by new bone tissue is called remodelling. Bone formation, repair and remodelling is controlled and produced by four types of cell, namely osteoblasts, osteoclasts, osteocytes and bone lining cells. Bone remodelling is regulated by signals to these cells generated by mechanical loading. Exactly how loads are transferred into bone, how the bone cells sense these loads and how the signals are translated into bone formation or removal is unknown. In this review, the structure of bone and the cells responsible for maintaining bone are described. The mechanisms that cause bone to adapt to mechanical loading have been investigated. The methods that have been employed in attempts to determine this mechanism are considered.

Biological studies indicate that numerous materials present in living tissues owe their success to an optimal combination of properties and adaptive structures, rather than to extreme properties per se. Through studying natural tissues and by biomimesis, new polymer and composite materials may be designed to emulate the structural and functional responses of bone. These materials must ensure biochemical affinity with host tissue through judicious mixing of specific chemical cues. Also, they must mimic the response under load exhibited by natural bone through complex organisation of material phases, i.e. embedding of collagen fibres in the extracellular substance. Fibre and particulate reinforced polymers are increasingly significant in the development of new biomedical materials, since they can be engineered more accurately than monolithic structures. Meanwhile, design of nanocomposites with specific morphological and chemical signals is emerging as a powerful approach to the mimesis of extracellular matrix of natural bone. In both cases, the manipulation of the main materials features at the micro- and nano-metric scale offers an intriguing strategy for improvement of biological and mechanical response. Several biodegradable and bioresorbable materials, as well as technologies and scaffold designs, will be critically reviewed, illustrating the potential of bio-inspired composites and multicomponent platforms for bone tissue engineering.

Marine organisms are constituted by materials with a vast range of properties and characteristics that may justify their potential application within the biomedical field. Moreover, assuring the sustainable exploitation of natural marine resources, the valorisation of residues from marine origin, like those obtained from food processing, constitutes a highly interesting platform for development of novel biomaterials, with both economic and environmental benefits. In this perspective, an increasing number of different types of compounds are being isolated from aquatic organisms and transformed into profitable products for health applications, including controlled drug delivery and tissue engineering devices. This report reviews the work that is being developed on the isolation and characterisation of some polysaccharides, proteins, glycosaminoglycans and ceramics from marine raw materials. Emphasis is given to agar, alginates, carrageenans, chitin and chitosan, among other polysaccharides, collagen, glycosaminoglycans such as chondroitin sulphate, heparin and hyaluronic acid, calcium phosphorous compounds and biosilica. Finally, this report ends by reviewing the application of the previously mentioned materials on specific biomedical applications, in particular their participation on the development of controlled drug delivery systems and tissue engineering scaffolds.