Bio-Instructive Bone Implants

Biomaterials for bone substitutes are used to fill in bone loss and in many surgical procedures in maxillofacial medicine, dentistry, orthopaedics, oncology and reconstruction, and more. In addition to an in-depth knowledge of the human body, designing these implants involves both the fields of materials and mechanical engineering. Today, bone reconstruction operations are designed to optimize implant integration into the host bone and to participate in bone regeneration. David Marchat, materials researcher at the Centre Ingénierie et Santé (CIS) at Mines Saint-Étienne, in France, in partnership with Osseomatix, a company specializing in bone reconstruction, developed a custom-designed biomaterial for bone implant that promotes bone growth. According to Marchat, “Our research is focused on the need for a bio-instructive implant, in other words, an implant that can tell cells how to rebuild bone and promote vascularization.”

The substitute created by the CIS team is calcium phosphate-based, a biocompatible material currently used in healing lesions measuring less than 1 cm3. The new intelligent implant is used when a bone defect is more extensive and cannot be repaired by the body. In this case, the use of synthetic biomaterials avoids the risks associated with autografts or allografts, implants derived from the patient or a donor, respectively. 

Layered Beehive Structure

Thanks to its architecture and chemical composition, the implant developed by Marchat and his team will contribute to the natural remodeling process in bone defects. At the beginning of the process, cells surrounding the damaged area recede, clearing the bone reconstruction surface. This surface is then excavated by osteoclasts in order to reach the bone growth factors. The osteoblasts then rest on the exhumed surface, releasing collagen and alkaline phosphatase, elements that fill the hollowed-out cavity of the lesion. During the process, bone tissue is vascularized in order to supply nutrients required by the cells. The following video details the steps in bone formation.

To participate in this process, the implant must accommodate the vascularized bone cells and tissues. To address this constraint, the CIS team created a layered honeycomb material. The function of this architecture is to direct circulation of activated micro-organisms in the process. The largest pores of this structure then allow bone cells and blood vessels to penetrate the implant, while the smaller pores are responsible for housing the bone-regenerating cells. The chemical elements that make up the implant also take part in the bone-filling process. The implant should degrade as the bone regenerates. While Marchat and his team succeeded in modelling the material from a 3D-printed mould, they must now work on the biodegradability of the bone substitute. This task is not easy as the implant’s degradation time must be managed to prevent it from either disappearing before completing the filling process, or from lingering, which could hinder bone regeneration. This undertaking combining biomaterials engineering and medicine is ongoing, the test phase being another challenge. The team is interested in developing a 3D bioreactor using human cells. The artificial bio-medium will make it possible to test a bone implant under physiological conditions that mimic those of the human body. This project will provide the team with a device for in vitro experimentation, thus avoiding animal testing.