Bone scaffolds with controllable porosity

• Main Author: Winnett, James
• Published: University of Warwick 2015
• Subjects: 617.4; RD Surgery
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.682845

The Adaptive Foam Reticulation (AFR) technique, a combination of foam reticulation and freeze casting, has been investigated for producing bone repair bioscaffolds from hydroxyapatite (HA), titanium (Ti) and titanium-aluminium-vanadium (Ti-6Al-4V). Scaffolds have a network of macropores of diameter between 94 and 546 mm, with struts 20 to 118 mm thick. The structure was dependent on the template from which structures were produced, the number of coats of slurry applied to the template and the sintering temperature. The struts contained numerous micropores, the size of which was increased from 2-5 to 20-30 mm by decreasing the freezing temperature. Whilst the size of individual micropores was independent of the amount of porogen in the slurry, there was some coalescence at higher percentages. Scaffolds exhibited porosities of between 76 and 96%, with porosity consistently decreased by increasing the number of coats from one to five. The mechanical strength of all samples was determined theoretically by the novel incorporation of a shape factor conventially used for microporous structures into an existing equation used to calculate the yield stress of porous structures. In most cases this agreed with the experimentally obtained yield stress. With compressive yield stresses of 0.002 to 0.18MPa and 0.002 to 1.8 MPa respectively, HA and Ti structures are only suitable in non-load bearing situations. However Ti-6Al-4V scaffolds had yield stresses of 0.21-13.7 MPa, within the range of cancellous bone. AFR-fabricated HA scaffold offered greater in-vitro cell viability than a commercially available porous HA disc. Including a porogen offered no improvement in viability compared to structures fabricated without porogen, except at the highest inclusion where a statistically significant increase was observed. The weak compressive strength of scaffolds needs improving, and fabrications require in-vivo analyses. However, AFR could offer a viable alternative to other manufacturing techniques.