Resorption of the calcium phosphate layer on S53P4 bioactive glass by osteoclasts

Abstract

Clinically, S53P4 bioactive glass (BAG) has shown very promising results in bone infection treatment, but it is also known to degrade very slowly in vivo. To evaluate which mechanisms (cellular or dissolution) can play a role in the degradation of S53P4 BAG and S53P4 BAG putty, in vitro degradation experiments at different pH (7.4 and 4.6) were performed. Micro computed tomography showed a rapid dissolution of the synthetic binder in the putty formulation, within 12 h is simulated body fluid (pH = 7.4), leaving behind only loose granules. Therefore the degradation of the loose granules was investigated further. Significant weight loss was observed and ion chromatography showed that Ca 2+ , Na + and PO 4 3− ions were released from S54P4 BAG granules in the two fluids. It was observed that the weight loss and ion release were increased when the pH of the fluid was decreased to 4.6. Osteoclasts are known to create such a low pH when resorbing bone and therefore their capacity to degrade S53P4 surfaces were studied as well. Scanning electron microscopy and energy-dispersive X-ray spectroscopy confirmed that osteoclasts were able to create resorption pits in the calcium phosphate layer on S53P4 BAG surfaces. The silica of the BAG, located underneath the calcium phosphate, seemed to hinder further osteclastic resorption of the material. To our knowledge we were the first to observe actively resorbing osteoclasts on S53P4 bioactive glass surfaces, in vitro. Future research is needed to define the specific role osteoclasts play in the degradation of BAG in vivo.

Treatment of Infection-Related Non-Unions with Bioactive Glass—A Promising Approach or Just Another Method of Dead Space Management?

“…Our results conflicted with the findings in patients, where S53P4 was found to be as good as autologous bone tissue regarding osteointegration [25]. A possible explanation could be the inhibition of osteoclasts by silica, a component of S53P4, which was shown by Van Gestel et al [49]. Another important difference could be the segmental bone defect used in this study in contrast to the cavitary defects S53P4 that were used in patients, as we know that cavitary defects have different local conditions that potentially facilitate the pH-sensitive antimicrobial effect of S53P4 [19].…”

Bioactive Glasses: A Promising Therapeutic Ion Release Strategy for Enhancing Wound Healing

“…As we know, the natural process of bone resorption is primarily related to the presence of osteoclasts, which dissolve hydroxyapatite by creating an acidic pH under their ruffled borders. 325,326 Healthy skin has a slightly acidic pH value of 4.0−6.0, while acute and chronic wounds have neutral and alkaline pH, respectively. 327 With the successful progress through the wound healing phases, a decrease in wound pH occurs to restore the acidic pH of the skin.…”

The Implantation of Bioactive Glass Granules Can Contribute the Load-Bearing Capacity of Bones Weakened by Large Cortical Defects

“…The interface layer was only modelled, tuned, and validated against experimental results in the case of loose granules. Over time, BAG will bond to bone and degrades, which will change the mechanical properties of the mixture [2,3,27]. To evaluate to what extent the mechanical properties are affected over time, it would be needed to monitor the stiffness of bone with BAG mixtures during bone ingrowth.…”