Fast setting calcium phosphate cement-chitosan composite: mechanical properties and dissolution rates.

Calcium phosphate cement (CPC) can self-harden in vivo to form hydroxyapatite (HA) with excellent osteoconductivity. In recent studies, CPC-chitosan composites are developed with high mechanical strength and washout resistance. The objectives of the present study are to optimize the setting time and mechanical properties of a CPC-chitosan composite by tailoring the chitosan content, and to evaluate the bioresorbability by using an in vitro dissolution model. Six chitosan mass fractions are tested: 0, 10, 15, 20, 25, and 30%. Specimens are immersed in solutions with pH ranging from 3.5 to 5 to simulate the acidic environments produced by osteoclasts in vivo. Dissolution is measured as the fraction of mass loss versus immersion time from 7d to 28d. The CPC-chitosan composite with 20% by mass chitosan has a setting time (mean+/-SD; n=4) of 13 1 min, significantly less than 87 7 min for CPC control without chitosan (p<0.05). The composite flexural strength (mean+/-SD; n 1/4 6) was 14 2 MPa, significantly higher than 4 1 MPa of CPC control (p<0.05). At an intermediate pH of 4.5, the fraction of mass loss for CPC with 20% chitosan and CPC control without chitosan are not significantly different (p>0.1). The dissolution rates (fraction of mass loss per day,%/d) were 1.05 for CPC control and 1.08 for CPC-chitosan. In summary, a CPC-chitosan composite is developed with fast-setting and a flexural strength three-fold of that of CPC control without chitosan. Both materials are soluble in acidic environments, indicating that adding chitosan did not compromise the bioresorbability of CPC. The strong and resorbable CPC-chitosan composite may be useful in moderate stress-bearing craniofacial and orthopedic repairs.