title: The impact of critical point drying with liquid carbon dioxide on collagen-hydroxyapatite composite scaffolds.
abstract: Collagen-hydroxyapatite composites for bone tissue engineering are usually made by freezing an aqueous dispersion of these components and then freeze-drying. This method creates a foamed matrix which may not be optimum for growing cell colonies larger than a few hundred micrometres due to the limited diffusion of nutrients and oxygen, and the limited removal of waste metabolites. Incorporating a network of microchannels in the interior of the scaffold which may permit the flow of nutrient-rich media has been proposed as a method to overcome these diffusion constraints. A novel three-dimensional printing and critical point drying technique previously used to make collagen scaffolds has been modified to create collagen-hydroxyapatite scaffolds. This study investigates the properties of collagen and collagen-hydroxyapatite scaffolds and whether subjecting collagen and hydroxyapatite to critical point drying with liquid carbon dioxide results in any changes to the individual components. Specifically, the hydroxyapatite component was characterized before and after processing using wavelength-dispersive X-ray spectroscopy, X-ray diffraction and infrared spectroscopy. Critical point drying did not induce elemental, crystallographic or molecular changes in the hydroxyapatite. The quaternary structure of collagen was characterized using transmission electron microscopy and the quarter-staggered array characteristic of native collagen remained after processing. Microstructural characterization of the composites using scanning electron microscopy showed the hydroxyapatite particles were mechanically interlocked in the collagen matrix. The in vitro biological response of MG63 osteogenic cells to the composite scaffolds were characterized using the Alamar Blue, PicoGreen, alkaline phosphate and Live/Dead assays, and revealed that the critical point dried scaffolds were non-cytotoxic.
authors.affiliation: Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK. sachlos@seas.harvard.edu
authors.forename: Eleftherios
authors.initials: E
authors.lastname: Sachlos
authors.forename: Denys A
authors.initials: DA
authors.lastname: Wahl
authors.forename: James T
authors.initials: JT
authors.lastname: Triffitt
authors.forename: Jan T
authors.initials: JT
authors.lastname: Czernuszka
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry / Q000494:pharmacology; D018786:Bone Substitutes / Q000737:chemistry* / Q000494:pharmacology*; D002245:Carbon Dioxide / Q000737:chemistry*; D002460:Cell Line; D003094:Collagen / Q000737:chemistry* / Q000494:pharmacology*; D003890:Desiccation; D017886:Durapatite / Q000737:chemistry* / Q000494:pharmacology*; D019544:Equipment Failure Analysis; D006801:Humans; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects*; D012996:Solutions; D013499:Surface Properties
chemical_list: D001672:Biocompatible Materials; D018786:Bone Substitutes; D012996:Solutions; D002245:Carbon Dioxide; D003094:Collagen; D017886:Durapatite