International researchers continue the trend toward overcoming challenges in bone regeneration, sharing the results of their study in the recently published “Tough magnesium phosphate-based 3D-printed implants induce bone regeneration in an equine defect model.” When doctors take on the task of rebuilding human bone, there is usually a need for material that can not only mimic human tissue but is also biodegradable, making it suitable for use with implants. Such materials must possess the proper mechanical properties, presenting further difficulty in many cases.
With current data pointing toward an annual increase of 10% for bone grafting procedures, medical scientists and researchers are more motivated than ever to develop new techniques and experiment with new materials—usually related to scaffolding. Typical scaffolds are composed of materials that can degrade like:
- Ceramics like hydroxyapatite, tricalcium phosphate, or bioglass
- Polmer-based materials like polycaprolactone, pollactide-co-glycolide
A variety of different traditional techniques are generally used, leaving researchers still to deal with obstacles like inferior structures, constrictions related to mechanical properties, and challenges in creating scaffolds for defects above 10mm. In this study, the researchers turned to extrusion-based 3D printing with ceramics, while exploring previous work in 3D printing with bioceramics with hydroxyapatite and polycaprolactone or poly(lactic-co-glycolic acid).
Previous materials may have presented challenges due to a lack of load-bearing properties, leading the researchers to explore polymer-ceramic composites due to better mechanical properties; however, there can be issues with decreased osteoinductivity because of polymer masking and lower solubility. Magnesium phosphate cement (MPC) and metal ions in calcium phosphate (CPC) show better potential for bone regeneration though:
“Recently, magnesium phosphate (MgP) materials have captured increasing attention due to their high in vivo solubility and low tendency to transform into lower soluble CaP phases at physiological conditions,” stated the researchers.
Other ions like Sr2+, into CaP and MgP. materials may also allow for regeneration. In this study, the authors were able to 3D print scaffolds made from magnesium phosphate, controlling the necessary properties with the use of PCL, a common thermoplastic material used in bone regeneration. They also added small amounts of biologically active Sr2+ ions, evaluating the materials first in a basal and osteogenic medium (in vitro) and then in an equine tuber coxae defect model (in vivo).
The researchers used a 3D Discovery printer for extruding paste through a 22G conical nozzle, with dispensing pressure of 0.9 bar for continuous printing at room temperature. Cylindrical and rectangular samples of varying sizes were 3D printed for the study.
Ultimately, MgPSr and PCL were found to substantially improve osteogenic response for the in vitro culture, and noted as “capable of effectively repairing a critical sized bone defect,” with the implant inside the equine tuber coxae models for six months. The 30 wt% PCL eliminated cracks and premature failure, a benefit of using ceramics in the presence of load-bearing sites. One of the most successful points of this study, however, was compressive mechanical properties of the MgPSr-PCL30 composites acting “in the range of native cancellous bone.”
Even after noted and rapid degradation in vitro, the implants exhibited suitable load bearing capacity. The scaffolding was found to be both osteoconductive and osteoinductive, supporting bone regeneration around the implant, while also “bridging” the bone defect.
“Interestingly, EDX analysis of the newly formed bone revealed a mineral composition and Ca to P ratio similar to the native equine bone, which confirmed the osteopromotive properties of the develop scaffold materials,” stated the researchers.
The results reflected strong, stable scaffolds and a viable system for tissue engineering and bone regeneration. Many other studies have been promising too—despite difficulties in bone regeneration activity—from research targeting areas like the jaw bone for regeneration, using other materials like titanium, and fabricating other complex scaffolds.[Source / Images: “Tough magnesium phosphate-based 3D-printed implants induce bone regeneration in an equine defect model”]
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