Composite matrices containing ceramics and absorbable polymers have been proposed as scaffolding materials for bone regeneration in order to combine the osteoconductive properties of the ceramics and the mechanical resiliency of the polymers. """"""""Biomimetic"""""""" mineralization involves the nucleation and growth of apatite crystals in a super-saturated ionic environment. Apatite coating of even inherently non-osteoconductive polymers have greatly improved osteoconductivity. Although this apatite- coating technique has been reported with a wide range or polymers, most of the published results involve simple, non-porous substrates. The creation of uniform apatite coating throughout thick (>1 cm) porous polymeric structures has not been reported. Porous scaffolds involve much higher surface-to-volume ratios than non-porous substrates, and the delivery of ions to satisfy the large surface area may be transport-limited in thick scaffolds (>1 cm) of clinically relevant dimensions. We hypothesized that by affecting the availability of essential ions for nucleation and growth, transport limitations govern the kinetics and distribution of apatite nucleation and growth within the interconnected pores of large, complex (>1 cm) tissue engineering scaffolds. This hypothesis will be tested experimentally by controlling several relevant parameters (fluid flow rate, transport length-scale, and resistance to flow) that directly affect transport behavior. Fluid flow rate controls the availability of ions per unit time, and is easily controlled by adjusting the pump speed. Transport length-scale determines the spatial uniformity of ionic delivery, and can be controlled by incorporating channels of varying dimensions throughout the thick scaffolds. Flow resistance can be controlled by varying pore size. Smaller pores result in larger flow resistance, and also produce larger surface areas. Porous multichannel devices with varying channel diameter and microporosity will be constructed by a novel computer-based manufacturing technology, which 'has been used successfully to fabricate large polymeric scaffolds possessing complex macroscopic shape (>1 cm), oriented channels (<1 cm), and interconnected porosity (0.01 - 0.1 mm). Samples will be subjected to various transport conditions, sectioned at specified strategic locations, and characterized microstructurally and chemically to determine the effects of transport parameters on coating uniformity.
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