Modification of calcium phosphate cement with poly (γ-glutamic acid) and its strontium salt for kyphoplasty application

- New injectable apatite bone cements were developed.
- The new cements had greatly enhanced mechanical strengths compared to CPC.
- The new cements were demonstrated to be promising for kyphoplasty application.

To meet the requirements of minimally invasive surgical treatments for osteoporotic vertebral compression fracture, various strategies have been proposed to enhance the properties of calcium phosphate cement (CPC). Here, a new strategy was developed by incorporating poly (γ-glutamic acid) (γ-PGA) and its strontium salt into the formulation of alpha tricalcium phosphate (α-TCP)-based CPC. Effects of γ-PGA on the injectability, cohesion, setting times, mechanical compressive strengths and cytocompatibility were systematically studied. Results showed that the injectability, cohesion and setting times were considerably improved by introducing γ-PGA into the CPC. Moreover, after setting for 7 days, the compressive strengths increased from 14.6 ± 1.4 MPa for pure CPC to 35.3 ± 1.7 MPa for CPC with 8.9 wt% γ-PGA and further to 61.2 ± 5.4 MPa for CPC with 8.9 wt% γ-PGA combined with its strontium salt. In vitro osteoblast proliferation tests showed that the group of CPC modified by γ-PGA and its strontium salt had better cytocompatibility than the pure CPC group. All results suggest that optimal properties were obtained for the cement with 8.9 wt% γ-PGA added to its solid phases and using strontium salt as the reactive liquid phase, making it as a promising candidate for application in kyphoplasty.