Strong calcium phosphate cement-chitosan-mesh construct containing cell-encapsulating hydrogel beads for bone tissue...

Calcium phosphate cement (CPC) is known for its ability to conform to irregular shapes and harden in situ to form hydroxyapatite, a material compatible with bone. However, CPC's setting reaction can be harmful to cells, limiting its use in tissue engineering. Prior research has shown that CPC alone can support bone regeneration but lacks sufficient mechanical strength for load-bearing applications. Encapsulation of cells in protective hydrogels has been proposed to mitigate CPC's cytotoxic effects. Chitosan and fiber mesh reinforcement have been explored separately to improve CPC's mechanical properties. This gap motivated the development of a composite CPC construct that integrates cell-encapsulating hydrogel beads with chitosan and mesh reinforcement. No prior work had resolved how to combine these elements effectively. The need to protect cells while enhancing mechanical strength remains unmet. CPC-based composites have not yet achieved the strength required for moderate stress-bearing bone repair. This study addresses these limitations by introducing a novel CPC construct.

The study aimed to develop a CPC-based composite that protects encapsulated cells during the setting process while enhancing mechanical strength. The researchers tested whether alginate hydrogel beads could shield MC3T3-E1 osteoblast cells from CPC's cytotoxic effects. They also evaluated how chitosan and fiber mesh reinforcement could improve CPC's mechanical properties. The specific problem addressed was the lack of a CPC construct that maintains cell viability and achieves sufficient strength for bone tissue engineering. The motivation stemmed from the need for in situ hardening materials that support moderate stress-bearing applications. CPC's setting reaction is known to harm cells, so a protective strategy was necessary. The study sought to determine if combining CPC with chitosan and mesh could achieve both cell viability and mechanical strength. The researchers hypothesized that the composite would perform better than conventional CPC.

The researchers encapsulated MC3T3-E1 osteoblast cells in alginate hydrogel beads to protect them from CPC's setting reaction. They prepared three CPC composites: conventional CPC, CPC-chitosan, and CPC-chitosan-mesh. The composites were mixed with the cell-encapsulating beads and allowed to set. Cell viability was assessed using a Wst-1 colorimetric assay to measure mitochondrial dehydrogenase activity. Flexural strength was tested using mechanical assays. The study compared absorbance values and flexural strength across the three composite types. The researchers also compared the results to a control group with cells in beads in culture medium without CPC. The CPC-chitosan-mesh composite included one or three fiber mesh layers to evaluate reinforcement effects. The study used Tukey's test to analyze statistical significance at p = 0.05.

Cell viability was similar across all CPC composites and the control group. Absorbance values at 450 nm were 1.36 ± 0.41 for conventional CPC, 1.29 ± 0.24 for CPC-chitosan, and 0.73 ± 0.22 for CPC-chitosan-mesh, all comparable to the control's 1.00 ± 0.14. The CPC-chitosan composite showed a 77% increase in flexural strength compared to conventional CPC (1.3 MPa vs. 2.3 MPa). Adding fiber mesh further improved strength: 4.3 MPa with one mesh layer and 9.5 MPa with three mesh layers. These strengths matched reported values for sintered porous hydroxyapatite implants and cancellous bone. The CPC-chitosan-mesh composite reached the highest flexural strength. The study found that chitosan and mesh reinforcement progressively enhanced mechanical properties. The cell-encapsulated CPC constructs showed favorable viability and strength for bone tissue engineering.

The study demonstrated that alginate hydrogel beads effectively protected MC3T3-E1 cells during CPC setting. Cell viability was maintained across all composites and matched the control group. Chitosan and fiber mesh reinforcement significantly improved CPC's mechanical strength. The CPC-chitosan-mesh composite achieved 9.5 MPa, comparable to cancellous bone and hydroxyapatite implants. The authors propose that this construct could be suitable for moderate stress-bearing bone tissue engineering applications. The results suggest that CPC-based composites can be tailored for both cell viability and mechanical performance. The study's findings support the potential of CPC-chitosan-mesh composites for bone repair. The authors conclude that their approach offers a promising strategy for in situ hardening bone cements.