gms | German Medical Science

Objectives: The development of a biodegradable and biocompatible bone adhesive (BA) has the potential to revolutionize the treatment of bone fractures, enabling fixation even for small bone fragments [1]. However, as of now, there is no BA available.

Functionalized calcium phosphate (CaP) nanoparticles are a promising starting point for a functional bone adhesive [2]. This project aims to explore the impact of an experimental CaP-nanoparticle-based BA on various aspects of bone healing processes using in vitro, ex vivo, and in vivo models.

Methods: BA discs were made by pressing freeze-dried calcium phosphate-carboxymethylcellulose-silica nanoparticles (CaP/CMC/SiO2) into discs with 10 mm diameter. The bone adhesive paste was prepared by mixing 2 wt% aqueous alginate solution with freeze-dried CaP/CMC/SiO2 at a mass ratio of 3.6:1, resulting in a pasty consistency.

Influence of BA on bone formation was tested by differentiating hBMSCs SCP1 cells into osteoblasts on the BA discs surface. After complete differentiation, cells were fixed and stained with Sirius red to visualize osteoblast-deposited extracellular matrix.

The BA’s impact on angiogenesis was tested in chicken embryos. Fertile eggs were incubated at 37.5 °C. On day 5, a 3 mm bone adhesive paste cylinder was placed on the chorio allantoic membrane (CAM). After 4 days, the implanted material was removed, fixed, and cryo-embedded. Histological sections were stained with MEP21 antibodies, a marker for chicken blood endothelial cells.

The animal model was designed to allow BA testing in vivo. Femurs of 3-month-old rats were unilaterally osteotomized and the fracture was stabilized with an intramedullary nail. Bone healing was monitored by weekly in vivo CT.

Results and conclusion: Sirius red staining indicated comparable collagen deposition by osteoblasts on both BA (55 ± 16%) and control surfaces (38 ± 8%), suggesting no impact on differentiation or matrix formation (unpaired t test: p = 0.059).

After 4 days of incubation on CAM, a dense network of blood vessels tightly surrounded the implant. MEP21 immuno-fluorescent staining confirmed peri-implant angiogenesis. Microscopic analysis indicated positive angiogenesis, suggesting no obstruction by BA.

In vivo CTs showed sufficient stabilization by intramedullary nail for bone healing. Bone volume at the fracture area increased weekly with wide variation among rats. The established animal model for BA testing showed a healing pattern that suggests borderline stabilization. This provides a suitable model for testing BAs, since additional stabilization by the BA should lead to a more uniform and faster healing.

Initial findings indicate that the BA has no adverse impact on crucial aspects of bone healing, such as osteoblast differentiation and angiogenesis. Subsequent experiments will focus on testing BA effect on bone healing in vivo, using the established animal model. Furthermore, the BA's influence on osteoclast differentiation will be evaluated.