Research On Preparation And Drug Delivery Of α-TCP/α-CSH Bone Cement Scaffolds With Gelatin Microspheres

Calcium phosphate cement (CPC) has been widely considered as good bone repair materials, which shows excellent biocompatibility and osconductibility, and can be molded to any desirable shape during operation without heat release. However, the mechanical property of CPC is not enough to be used as stress-bearing bone scaffolds, and the lack of macropores and slow degradation hinders its wide clinical applications. As a result the modification on CPC has a very important practical significance.In this paper, gelatin microspheres (GMs) andα-calcium sulfate hemihydrate (α-CSH) were added toα-TCP bone cement powder to prepare macroporous scaffolds, and the hydration reaction was performed in simulated body fluid (SBF) . XRD, FT-IR, SEM, EDS and TEM were used to characterize the phase composition and microstructure of the hydration products. The setting time and mechanical properties were tested. The results showed that the main crystal phase of CPC scaffolds resulted from the dissolution of microspheres after two weeks soaking in SBF was poorly crystalline hydroxyapatite (HAp) , which was the same as that of CPC scaffolds without containing GMs. The scaffold with 10wt% GMs has a porosity of 61% and a compressive strength of 4.5MPa after two weeks soaking in SBF, while with the incorporation of 20wt% GMs into CPC, the porosity was 74% which increased by 21%, and compressive strength was 2.5MPa decreased by 51%. It means that the porosity of the scaffold increased slowly when the content of GMs was more than 10wt%, while the compressive strength decreased greatly. Based on the porosity and compressive strength, 10wt% GMs were selected to add to the CPC powder. With the addition of 10wt%α-CSH, the setting time decreased to 19minutes from 34minutes, and the porosity increased slightly. Microstructure analysis found the hydration product HAp was smaller and grew along C axis to form rod-like grain, which resulted in the increase of the compressive strength and toughness of the setting products. EDS analysis further revealed that the hydration product of the scaffold with 10wt%α-CSH addition was calcium deficient HAp with a calcium to phosphorus molar ratio of 1.60, which was much lower than that of the scaffold withoutα-CSH (1.66) , implying thatα-CSH could promote the degradation of scaffolds.Withα-TCP/α-CSH as matrix materials, GMs with gentamicin sulphate were added in the matrix. The results showed that the loading efficiency of composite bone cement was 1.09%, and its setting time, compressive strength and phase composition didn't change obviously compared with that without drug. In vitro drug release experiment showed this composite bone cement was an excellent drug carrier and the drug release profile was divided into three stages: the burst release of 24 hours, then the constant release within 14 days with the cumulative release amount of 67% and a slow release with the cumulative drug release rate of 28 days was 78%. It was found that the cumulative release rate had an exponential relationship with the square root of time.