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Abstract
Bone is the second most frequently transplanted tissue after blood. Damaged bone needs to be restored in order to protect vital organs and/or restore mobility of the patient. Tissue engineered bone is an attractive alternative to current bone grafts and biomaterial substitutes. It could provide an unlimited supply of immunologically-tolerated biological substitutes that respond to physiological and biochemical stimuli and grow with the patient. Collagen and hydroxyapatite (HA) are the natural extracellular components of bone and arguably the ideal materials to construct bone tissue engineering scaffolds. Collagen and collagen-HA composite scaffolds with predefined internal microchannels and external shape have been developed for bone tissue engineering. Solid freeform fabrication is used to customise the scaffold architecture. The scaffolds are produced by printing a mould using a commercial 3D printer, casting a dispersion of collagen or collagen-HA into the mould, freezing the aqueous dispersant, then liberating the scaffold by dissolving the mould and ice crystals in ethanol and critical point drying with liquid carbon dioxide. Residue of the mould have been detected, leading to the identification of cholesterol as a biologically benign material which can be used to print moulds. The microchannel network can assist in the perfusion of the scaffold and support cell migration and survival deep within the construct. Microchannels greater than 138μm can be produced with this process. Other important scaffold parameters such as pore size can be controlled by the freezing rate and concentration of collagen and HA dispersion to create pores ranging from 4 to 250μm. The in vitro cytotoxicity and biological response of osteosarcoma MG63 cells to collagen and collagen-HA scaffolds were assessed for 14 days and found to perform in an identical manner to freeze-dried collagen scaffolds. These collagen and collagen-HA scaffolds mimic the key structural and compositional components of the natural extracellular matrix of bone, providing a suitable substrate for the growth of this tissue.
