Review Article Bioinert, biodegradable and injectable polymeric matrix composites for hard tissue replacement: state of the art and recent developments Joa˜o F. Mano a,b , Rui A. Sousa a,b , Luciano F. Boesel a,b , Nuno M. Neves a,b , Rui L. Reis a,b, * a Department of Polymer Engineering, University of Minho, Campus de Azure ´m, 4800-058 Guimara ˜es, Portugal b 3B’s Research Group, Biomaterials, Biodegradables and Biomimetics, University of Minho, Campus de Gualtar, 4710-057 Braga, Portugal Abstract The present review paper examines the use of different types of polymeric matrix composites in hard tissue replacement applica- tions. The review presents the actual state of the art in the fields of bioinert composites for permanent applications, biodegradable matrix composites for temporary applications and the emerging area of injectable composites. In all cases some recent develop- ments are also discussed. The paper starts with an introduction to locate the reader. Bone–analogue composites are then extensively discussed. Several other systems based on an inert polymeric matrix are described, focusing on their proposed applications. A great emphasis is afterwards given to biodegradable matrix systems. The most widely used synthetic bioresorbable systems are analysed and compared with an example of natural origin degradable composites–starch based composites. Finally, composite systems that are non-processable by melt based routes and in many cases injectable are discussed in detail, including several recent developments on this emerging area of research. # 2003 Published by Elsevier Ltd. Keywords: Biomaterials; A. Polymer matrix composites; B. Mechanical properties; B. Microstructure; E. Injection moulding 0266-3538/$ - see front matter # 2003 Published by Elsevier Ltd. doi:10.1016/j.compscitech.2003.09.001 Composites Science and Technology 64 (2004) 789–817 www.elsevier.com/locate/compscitech Contents 1. Introduction ............................................................................................................................................................................... 790 2. Bioinert composites for permanent applications ........................................................................................................................ 791 2.1. Polyethylene-based composites .......................................................................................................................................... 791 2.1.1. The bone analogue concept ................................................................................................................................... 792 2.1.2. Mechanical behaviour dependence on interfacial interaction and HA particle characteristics ............................. 792 2.1.3. Processing routes for the inducement of anisotropy: Hydrostatic Extrusion vs. Shear Controlled Orientation in Injection Moulding (SCORIM) ..................................................................................................... 792 2.1.4. Hybrid composites based on HDPE/HA composites ............................................................................................ 793 2.2. Other inert polymer composite systems in hard tissue substitution .................................................................................. 794 2.2.1. Polymer composite systems ................................................................................................................................... 794 2.2.2. Internal fixation of bone fractures......................................................................................................................... 795 3. Biodegradable composites .......................................................................................................................................................... 797 3.1. Synthetic bioabsorbable polymers ..................................................................................................................................... 797 3.1.1. Degradation of Poly(a-hydroxy esters) ................................................................................................................. 798 3.1.2. SR-composites from Poly(a-hydroxy esters) ......................................................................................................... 798 3.1.3. Poly(e-caprolactone) .............................................................................................................................................. 799 3.1.4. Polyactive TM ....................................................................................................................................................... 799 3.1.5. Bioactive composites ............................................................................................................................................. 800 * Corresponding author. Tel.: +351-253-604781/2; fax: +351-253-604492. E-mail address: rgreis@dep.uminho.pt (R.L. Reis).