Injectable biphasic calcium phosphate bone cements (BCPCs) composed of β-tricalcium phosphate (β-TCP) and hydroxyapatite (HA) have been intensively investigated because of their high rate of biodegradation, bioactivity and osteoconductivity, which can be adjusted by changing the ratio between β-TCP and HA phases after setting. The aim of this study was to evaluate the performance of 1 wt% chitosan fiber additive with biphasic calcium phosphate as an injectable bone cement both in vitro and in vivo. In vitro evaluation of compressive strength, degradation rate, morphology, and cell and alkaline phosphatase activities was done by comparison with bone cement without β-TCP. The in vivo results for micro-CT scanning and histological examinations for three groups (control, BCPC and commercial biphasic calcium phosphate granules) were characterized and compared. After the addition of 20 wt% β-TCP to calcium phosphate cement, the initial and final setting times of the sample were 3.92 min and 11.46 min, respectively, which were not significantly different from cement without β-TCP. The degradation time of the BCPC material was longer than that of calcium phosphate cement alone. The healing process was significantly faster for BCPC than for the control and commercial product groups. Therefore, this is the first evidence that BCPC is an attractive option for bone surgery due to its faster stimulation of healing and faster degradation rate.

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This study has investigated the effect of combination of new liquid phase mixture of disodium hydrogen phosphate (Na 2 HPO 4 ) and polyacrylic acid (PAA) on the compressive strength, setting time, bioactivity, and cytotoxicity of biphasic calcium phosphate cement. The PAA was known as one of water-soluble and biocompatible polymers to improve the mechanical performances of the bone cement, but it usually inhibits the phase conversion to hydroxyapatite after the cement has already set.The aim of this work was to evaluate the incorporation of the mixture of PAA and Na 2 HPO 4 into biphasic cement. We have found the crucial concentration for adding PAA/Na 2 HPO 4 at 30:70 v/v% to enhance the mechanical strength, cell viability, and maintain bioactivity. The phase composition and crosslinking reaction between PAA and alpha-tricalcium phosphate (α-TCP) powder were detected by XRD and FTIR techniques. The beta-tricalcium phosphate (β-TCP) was added in the formula to achieve the biphasic cement, which composed of β-TCP and apatite/calcium deficient-hydroxyapatite (CD-HA) in the final product. The biphasic granule commercial product was used as comparison in the cell viability test. This work had been confirmed that the cement was a nontoxic material. Therefore, our results suggest that the PAA/Na 2 HPO 4 could be beneficial for further clinical applications. K E Y W O R D Sbiopolymer, bone cement, calcium phosphate cement, polyacrylic acid, polymeric cement

In this work, three different modified cements, control apatite/beta-tricalcium phosphate cement (CPC), polymeric CPC (p-CPC), and bioactive glass added polymeric cement (p-CPC/BG) were evaluated regarding their physical properties and the responses of primary human osteoblast cells (HObs) and mesenchymal stem cells (MSCs). Although polyacrylic acid (PAA) increased compressive strength and Young's modulus of the cement, it could cause poor apatite phase formation, a prolonged setting time, and a lower degradation rate. Consequently, bioactive glass (BG) was added to PAA/cement to improve its physical properties, such as compressive strength, Young's modulus, setting time, and degradation. For in vitro testing, HObs viability was assessed under two culture systems with cement-preconditioned medium (indirect) and with cement (direct). HObs viability was examined in direct contact with cements treated by different prewashing conditions. HObs presented a more well spread morphology on cement soaked in medium overnight, as compared to other cements with no treatment and washing in PBS. In addition, the proliferation, differentiation, and total collagen production of both HObs and MSCs adhered to the cement were detected. Cells showed excellent proliferation on PAA/cement and PAA/BG/cement. Furthermore, the higher released Si ion and lower acidosis of PAA/BG/cementconditioned medium resulted in an increase in osteogenic differentiation (HObs and MSCs) and enhanced collagen production (HObs in osteogenic medium and MSCs in control medium). Therefore, our findings suggest that BG incorporated PAA/apatite/ β-TCP cement could be a promising formula for bone repair applications.apatite bone cement, bioactive glass, calcium phosphate cement, osteoblast, polyacrylic acid, polymeric calcium phosphate cement, stem cells | INTRODUCTIONOsteoporosis, one of the common diseases of the aging population, is one orthopedic issue that frequently requires treatment with a bone replacement material. 1 Synthetic bone graft substitutes are attractive due to the limited availability of autografts and their associated costs. 2,3 Calcium phosphate cements (CPCs) are one of the most promising biomaterials for bone grafting applications due to their

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