title: Frozen delivery of brushite calcium phosphate cements.
abstract: Calcium phosphate cements typically harden following the combination of a calcium phosphate powder component with an aqueous solution to form a matrix consisting of hydroxyapatite or brushite. The mixing process can be very important to the mechanical properties exhibited by cement materials and consequently when used clinically, since they are usually hand-mixed their mechanical properties are prone to operator-induced variability. It is possible to reduce this variability by pre-mixing the cement, e.g. by replacing the aqueous liquid component with non-reactive glycerol. Here, for the first time, we report the formation of three different pre-mixed brushite cement formulations formed by freezing the cement pastes following combination of the powder and liquid components. When frozen and stored at -80 degrees C or less, significant degradation in compression strength did not occur for the duration of the study (28 days). Interestingly, in the case of the brushite cement formed from the combination of beta-tricalcium phosphate with 2 M orthophosphoric acid solution, freezing the cement paste had the effect of increasing mean compressive strength fivefold (from 4 to 20 MPa). The increase in compression strength was accompanied by a reduction in the setting rate of the cement. As no differences in porosity or degree of reaction were observed, strength improvement was attributed to a modification of crystal morphology and a reduction in damage caused to the cement matrix during manipulation.
authors.affiliation: Chemical Engineering, School of Engineering, University of Birmingham, Edgbaston, Birmingham, West Midlands B15 2TT, UK. l.m.grover@bham.ac.uk
authors.forename: Liam M
authors.initials: LM
authors.lastname: Grover
authors.forename: Michael P
authors.initials: MP
authors.lastname: Hofmann
authors.forename: Uwe
authors.initials: U
authors.lastname: Gbureck
authors.forename: Balamurgan
authors.initials: B
authors.lastname: Kumarasami
authors.forename: Jake E
authors.initials: JE
authors.lastname: Barralet
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry*; D002130:Calcium Phosphates / Q000737:chemistry*; D019245:Compressive Strength; D016503:Drug Delivery Systems; D017886:Durapatite / Q000737:chemistry; D017102:Fracture Healing; D005615:Freezing; D005990:Glycerol / Q000737:chemistry; D006801:Humans; D016062:Porosity; D011208:Powders; D013696:Temperature; D014961:X-Ray Diffraction
chemical_list: D001672:Biocompatible Materials; D002130:Calcium Phosphates; D011208:Powders; C485817:beta-tricalcium phosphate; D017886:Durapatite; C020243:calcium phosphate; C494366:calcium phosphate, dibasic, dihydrate; D005990:Glycerol