A novel strategy to enhance interfacial adhesion in fiber-reinforced calcium phosphate cement

TLDR: The aim of the present work was to improve the interfacial adhesion between fibers and matrix to obtain tougher biocompatible fiber-reinforced calcium phosphate cements (FRCPCs), which resulted in an increase of the work of fracture (several hundred-fold increase), while the elastic modulus and bending strength were maintained similar to the materials without additives.

Abstract: Calcium phosphate cements (CPCs) are extensively used as synthetic bone grafts, but their poor toughness limits their use to non-load-bearing applications. Reinforcement through introduction of fibers and yarns has been evaluated in various studies but always resulted in a decrease in elastic modulus or bending strength when compared to the CPC matrix. The aim of the present work was to improve the interfacial adhesion between fibers and matrix to obtain tougher biocompatible fiber-reinforced calcium phosphate cements (FRCPCs). This was done by adding a polymer solution to the matrix, with chemical affinity to the reinforcing chitosan fibers, namely trimethyl chitosan (TMC). The improved wettability and chemical affinity of the chitosan fibers with the TMC in the liquid phase led to an enhancement of the interfacial adhesion. This resulted in an increase of the work of fracture (several hundred-fold increase), while the elastic modulus and bending strength were maintained similar to the materials without additives. Additionally the TMC-modified CPCs showed suitable biocompatibility with an osteoblastic cell line.

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Figure 2. Crystalline phases determined by X-ray diffraction of a) initial powder α –TCP, b) sample C 7 days after setting, and c) sample TMC 7 days after setting.

Figure 3. Mechanical properties under bending of unreinforced CPCs (C and TMC) and fiberreinforced CPCs (C-8f, TMC-4f, TMC-8f, TMC-12f): a) Typical load/deflection curves, b) Young’s modulus (E), c) bending strength, and d) work of fracture (WOF). Groups indicated with same symbol do not have statistically significant differences (p > 0.05).

Figure 7. SEM images showing the morphology of cells cultured on C and TMC samples for 7 days.

Figure 6. Live/dead images showing the alive cells (green) and the dead cells (red) on the C and TMC samples surface at different time points (bar = 100 μm)

Figure 5. a) Number of cells adhered on the samples surface at different time points, and b) evolution with time of the pH of the cell culture medium (1 ml) in contact with a cement disc (15 mm diameter x 1.5 mm thickness).

Table 3. Crystalline phases as determined by X-ray diffraction, and specific surface area measured by N2 adsorption of the initial powder and set cements.