Strong, macroporous, and in situ-setting calcium phosphate cement-layered structures

Calcium phosphate cement (CPC) is valued for its osteoconductive properties and in situ-setting behavior. However, its limited mechanical strength restricts clinical use to non-load-bearing applications. Prior research has shown that increasing porosity in CPC scaffolds reduces mechanical strength, creating a conflict between tissue integration and structural integrity. This gap motivated the development of a functionally graded CPC structure. No prior work had resolved how to balance macroporosity with sufficient strength for bone replacement. Existing CPC formulations lack the ability to meet both mechanical and biological requirements simultaneously. The need for CPC scaffolds that can support tissue growth while maintaining structural stability remains unmet. This study aimed to address that limitation by combining two CPC layers with distinct properties. The challenge lies in integrating a macroporous layer for tissue ingrowth with a strong layer for mechanical support.

This study aimed to develop a layered CPC structure that combines macroporosity and mechanical strength. The specific problem addressed is the inability of traditional CPC scaffolds to meet both tissue integration and load-bearing requirements. The motivation stems from the clinical need for CPC implants that can support bone regeneration under moderate stress. The research proposed a dual-layer design to overcome the limitations of single-phase CPC. One layer was designed for tissue ingrowth, while the other provided structural support. The design incorporated a biopolymer to enhance mechanical properties. The goal was to evaluate how porosity and layer thickness ratios affect scaffold performance. This approach sought to enable CPC implants for broader clinical applications.

The study combined a macroporous CPC layer with a fiber-reinforced strong CPC layer to create a functionally graded structure. A biopolymer, chitosan, was added to both layers to improve mechanical properties. Flexural strength was measured using a three-point bending test on six specimens per condition. Porosity was quantified using microcomputed tomography and image analysis techniques. Macropore length was determined from histological sections of the scaffold. Nano-sized hydroxyapatite crystal formation was analyzed using scanning electron microscopy. The relationship between flexural strength and the strong layer thickness-to-specimen thickness ratio was modeled mathematically. The study evaluated how varying porosity and layer thickness ratios influenced mechanical performance.

Flexural strength decreased from 9.7 MPa to 1.8 MPa as porosity increased from 44.6% to 66.2%. With strong-layer reinforcement, strength increased to 25.2 MPa and 10.0 MPa at these porosities. These values exceeded those of sintered porous hydroxyapatite implants and cancellous bone. The strong layer thickness-to-specimen thickness ratio correlated with flexural strength via the equation S = 17.6(a/h) + 3.2 MPa. Macropores averaged 183 micrometers in length, suitable for cell infiltration and tissue ingrowth. Nano-sized hydroxyapatite crystals formed the scaffold matrix in CPC with chitosan. The layered structure enabled simultaneous high strength and macroporosity. These findings suggest the design meets both mechanical and biological requirements.

The study developed a functionally graded CPC scaffold with a macroporous layer and a strong layer. The design achieved a balance between mechanical strength and tissue integration. The strong layer provided early strength, while the macroporous layer supported tissue ingrowth. The addition of chitosan enhanced the mechanical properties of both layers. The mathematical relationship between strength and layer thickness ratio was validated experimentally. The scaffold met or exceeded the mechanical performance of existing CPC implants. The macropores were suitable for cell infiltration and tissue ingrowth. The authors propose that this design could be useful in moderate stress-bearing applications.