REVIEW A. Tampieri G. Celotti E. Landi From biomimetic apatites to biologically inspired composites Received: 7 June 2004 / Revised: 25 October 2004 / Accepted: 27 October 2004 / Published online: 5 February 2005 Ó Springer-Verlag 2005 Abstract Hydroxyapatite is an elective material for bone substitution. In this outline of our recent activity the crucial role of nanostructured ceramics in the design and preparation of ceramic scaffolds will be described, focussing on our more recent interest in biomimetic apatites, in particular apatites containing HPO 4 2 CO 3 2 and Mg 2+ which are similar to the mineral component of bone. The paper describes such nanostructured products and, in particular, innovative synthetic tech- niques capable of yielding powders with higher reactivity and bioactivity. However, so far the characteristics of artificial bone tissues have been shown to be very dif- ferent from those of natural bone, mainly because of the absence of the peculiar self-organizing interaction be- tween apatites and the protein component. This causes modification of the structure of apatites and of the fea- tures of the overall composite forming human bone tissue. Therefore, attempts to mimic the features and structure of natural bone tissue, leading toward so-called bio-inspired materials, will be speculated upon. New techniques used to reproduce a composite in which a nanosize blade-like crystal of hydroxyapatite (HA) grows in contact with self-assembling fibres of natural polymer will be presented. In this specific case, the amazing ability of biological systems to store and pro- cess information at the molecular level, nucleating nanosize apatites (bio-inspired material), is exploited. Keywords Bone substitute Biomimetic apatites Biohybrid composite Biologically inspired synthesis Biomimetic apatites With the ageing of the population and the prolonging of active life, there is an increasing demand for materials that can potentially replace, repair or even regenerate injured or diseased bone. Bone is, in fact, among the most frequently transplanted tissues. The enormous need for bone grafts and recent progress in biomaterial science have stimulated the rapid growth and expansion of a new field: bone tissue engineering [1–3]. For that reason in the last decade technological re- search has moved toward the synthesis of new substi- tuting materials mimicking natural bone tissues [4–8] and the development of in-vitro autologous bone start- ing from cultured cells and biomaterials. The alloplastic materials most utilized in recent years are ceramic materials: the role of biological ceramics during reconstructive bone surgery is fundamentally osteoconductive. An ideal bone substitute must be able to function as a scaffold and to participate in formation of new bone. Besides being biologically compatible it must also be bioreabsorbable so that it may be com- pletely substituted by newly formed bone. To meet these requirements biologically compatible materials, calcium phosphate-based bioactives and glass-based bioactives, have been researched and designed. Recently an increase in our knowledge has helped us to more clearly define the real composition of natural bone tissue as a dynamic system made of many inter- acting agents in a complex environment and the func- tionality of the active groups contained therein; one consequence of this has been the study and development of new biomimetic apatites. Bioreabsorbability is strictly related to solubility in physiological fluids (SBF). The solubility of hydroxy- apatite (HA) under physiological conditions can be in- creased by modifying the crystallinity grade of the powders and by adding doping groups which substitute those present in the apatite to vary the characteristics of the apatite itself without destroying the unit cell. Preparation of low-grade-crystallinity powders can be realized by implementation of innovative synthesis with a nanodimensional control. Powders obtained by sol–gel or spray-drying processes, etc., [9, 10] are char- acterized by very small particles with high specific sur- A. Tampieri (&) G. Celotti E. Landi Istituto di Scienza e Tecnologia dei Materiali Ceramici, ISTEC-CNR, Via Granarolo 64, 48018 Faenza, Italy E-mail: tampieri@istec.cnr.it Anal Bioanal Chem (2005) 381: 568–576 DOI 10.1007/s00216-004-2943-0