Abstract
Phosphoserine modified cements (PMC) exhibit unique properties, including strong adhesion to tissues and biomaterials. While TTCP-PMCs remodel into bone in vivo, little is known regarding the bioactivity and physiochemical changes that occur during resorption. In the present study, changes in the mechanical strength and composition were evaluated for 28 days, for three formulations of αTCP based PMCs. PMCs were significantly stronger than unmodified cement (38–49 MPa vs. 10 MPa). Inclusion of wollastonite in PMCs appeared to accelerate the conversion to hydroxyapatite, coincident with slight decrease in strength. In non-wollastonite PMCs the initial compressive strength did not change after 28 days in PBS (p > 0.99). Dissolution/degradation of PMC was evaluated in acidic (pH 2.7, pH 4.0), and supersaturated fluids (simulated body fluid (SBF)). PMCs exhibited comparable mass loss (<15%) after 14 days, regardless of pH and ionic concentration. Electron microscopy, infrared spectroscopy, and X-ray analysis revealed that significant amounts of brushite, octacalcium phosphate, and hydroxyapatite reprecipitated, following dissolution in acidic conditions (pH 2.7), while amorphous calcium phosphate formed in SBF. In conclusion, PMC surfaces remodel into metastable precursors to hydroxyapatite, in both acidic and neutral environments. By tuning the composition of PMCs, durable strength in fluids, and rapid transformation can be obtained.
Highlights
Calcium phosphate cements have favorable tissue compatibility, inflammation, healing, and remodeling responses when implanted in hard tissues, due to having a similar surface chemistry as the mineral phase of bone [1,2,3]
In formulation 2, 1.2% mole% of αTCP was substituted with Portland cement because we have previously observed that minor amounts of Portland cement improve the adhesive strength [68,69,70]
Phosphoserine-modified cements retained the benefits of crystalline cements, while presenting amorphous calcium phosphate and metastable αTCP at the cement surface, during dissolution
Summary
Calcium phosphate cements have favorable tissue compatibility, inflammation, healing, and remodeling responses when implanted in hard tissues, due to having a similar surface chemistry as the mineral phase of bone (hydroxyapatite) [1,2,3]. The most common cement additives are calcium chelators, including organic acids (i.e., citric acid) and inorganic polyphosphates (i.e., pyrophosphate) [12,13]. These chelators improve the mechanical strength by reducing the crystal size, and extending the working/setting time. Chelators produce a monomeric organic phase that binds to the mineral surface [16,17,18,19,20], rather than a molecularly intermixed composite [6,10] with macroscale interactions (i.e., polymeric or crosslinking) [21,22,23,24]
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