Fabrication of porous bioceramics with porosity gradients similar to the bimodal structure of cortical and cancellous bone

Abstract

The aim of this study was to fabricate porous implant materials with graded pore structures similar to the bimodal structure of cortical and cancellous bone. Porous hydroxyapatite/tricalcium phosphate (HA/TCP) bioceramics with interconnected porosity and controlled pore sizes required to simulate natural bone tissue morphology were fabricated by a novel technique of vacuum impregnation of reticulated polymeric foams with ceramic slip. Functionally gradient materials (FGMs) with porosity gradients were made by joining different pore per inch (ppi) foams together by either stitching or pressfitting to form templates. Post production, no defects could be seen at the interface between the two different porosity sections. The macropore sizes of the HA/TCP bioceramics were larger than 100 mum which is appropriate for bone ingrowth. A sample with a graded porous structure which is close to the human bone morphology was also developed. The two component structures were conspicuously different but joined together firmly. Four point bend testing of FGM samples showed them to have similar mechanical properties to homogeneous ceramics based on foam templates with uniform pore sizes, with no evidence of interfacial weakness. Many potential biomedical applications could be developed utilising graded porous structures. The ease of processing will make it possible to fabricate a range of complex shapes for different applications.

Biocomposites and hybrid biomaterials based on calcium orthophosphates

“…For example, many studies have been performed to fabricate porosity-graded calcium orthophosphate bioceramics in attempts to mimic the porous structure of bones. [1099][1100][1101][1102] This is a structural approach to fabricating FGM. Besides that, there is a compositional approach.…”

Calcium orthophosphate bioceramics

“…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 [574]. To finalize the production topic, creation of the desired porosity in CaPO 4 bioceramics is a rather complicated engineering task and the interested readers are referred to the additional publications on the subject [343,446,544,[575][576][577][578][579][580][581][582][583].…”

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“…Functionally graded bioceramics consisting of calcium orthophosphates only [575] have been developed [411,482,484,[578][579][580][581][582][583][584][585][586][587]. For example, dense sintered bodies with gradual compositional changes from α-TCP to HA were prepared by sintering a diamond-coated HA compacts at 1280 °C under a reduced pressure, followed by heating under the atmospheric conditions [578].…”

“…Thus, in various attempts to mimic the porous structure of bones, calcium orthophosphate bioceramics with graded porosity have been fabricated [375,411,482,484,[578][579][580][581][582][583][584][585]588]. For example, graded porous calcium orthophosphate bioceramics can be produced by means of tape casting and lamination (Fig.…”