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Abstract

Hydroxyapatite has been considered for use in the repair of osseous defects for the last 20 years. Recent developments have led to interest in the potential of porous hydroxyapatite as a synthetic bone graft. However, despite considerable activity in this field, regarding assessment of the biological response to such materials, the basic materials characterization is often inadequate. This paper documents the characterization of the chemical composition, mechanical integrity, macro- and microstructure of a porous hydroxyapatite, Endobon (E. Merck GmbH), intended for the bone-graft market. Specimens possesed a range of apparent densities from 0.35 to 1.44 g cm(-3). Chemical analysis demonstrated that the natural apatite precursor of Endobon was not converted to pure hydroxyapatite, but retained many of the ionic substituents found in bone mineral, notably carbonate, sodium and magnesium ions. Investigation of the microstructure illustrated that the struts of the material were not fully dense, but had retained some traces of the network of osteocyte lacunae. Macrostructural analysis demonstrated the complex inter-relationship between the structural features of an open pore structure. Both pore size and connectivity were found to be inversely dependent on apparent density. Furthermore, measurement of pore aspect ratio and orientation demonstrated a relationship between apparent density and the degree of macrostructural anisotropy within the specimens, while, it was also noted that pore connectivity was sensitive to anisotropy. Compression testing demonstrated the effect of apparent density and macrostructural anisotropy on the mechanical properties. An increase in apparent density from 0.38 to 1.25 g cm(-3) resulted in increases in ultimate compressive stress and compressive modulus of 1 to 11 MPa and 0.2 to 3.1 GPa, respectively. Furthermore, anisotropic high density (> 0.9 g cm(-3)) specimens were found to possess lower compressive moduli than isotropic specimens with equivalent apparent densities. These results underline the importance of full structural and mechanical characterization of porous ceramic implant materials.

Calcium orthophosphate-based biocomposites and hybrid biomaterials

“…Even so, the major limitations to use calcium orthophosphates as load-bearing biomaterials are their mechanical properties; namely, they are brittle with poor fatigue resistance [26][27][28]. The poor mechanical behavior is even more evident for highly porous ceramics and scaffolds because porosity[100 lm is considered as the requirement for proper vascularization and bone cell colonization [84][85][86], i.e., why, in biomedical applications calcium orthophosphates are used primarily as fillers and coatings [23].…”

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“…Furthermore, dimensions of open pores are directly related to bone formation, since such pores grant both the surface and space for cell adhesion and bone ingrowth. On the other hand, pore interconnection provides the ways for cell distribution and migration, as well as it allows an efficient in vivo blood vessel formation suitable for sustaining bone tissue neo-formation and possibly remodeling [155,[376][377][378][379][380][381][382][383][384][385]. Namely, porous HA bioceramics can be colonized by bone tissues [381,[386][387][388][389][390][391][392][393][394][395][396].…”

“…In the case of coralline HA or bovine-derived apatites, the porosity of the original biologic material (coral or bovine bone) is usually preserved during processing [94]. To conclude this topic, creation of the desired http://ccaasmag.org/BIO porosity in calcium orthophosphate bioceramics is a rather complicated engineering task and the interested readers are referred to other publications on this subject [112,377,402,416,.…”

“…(Table 3) currently are either in use or under a consideration in many areas of dentistry and orthopedics, with even more in development. For example, bulk materials, available in dense and porous forms, are used for alveolar ridge augmentation, immediate tooth replacement and maxillofacial reconstruction [64,377]. Other examples include burrhole buttons [505], orbital implants (Bio-Eye ® ) [506][507][508][509], other ophthalmic applications [510,511], increment of the hearing ossicles, spine fusion and repair of bone defects [512,513].…”

Novel Bamboo-Like Fibrous, Micro-Channeled and Functional Gradient Microstructure Control of Ceramics

“…17,18) The suitable pore size for bio-ceramics was reported to be approximately 100-300 mm in diameter. 18,19) Recently, an innovative fibrous monolithic process was adapted to impart desirable mechanical properties as well as continuously porous ceramic composites. 20,21) This newly designed fibrous monolithic process is an effective way to control the bio-mimetic bamboo-like fibrous microstructure.…”