Biomimetic Polymer Composite Materials for Bone Repair

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NRC's Industrial Materials Institute (IMI) is developing biomimetic structures based on polymer composites to produce biomedical implants having characteristics close to those of natural bones. The unique features of the polymer composite-based materials make them attractive for bone repair and reconstruction, and orthopaedic applications.

Novel Implantable Materials for Biomimicry

NRC's polymer composite materials for bone replacement/repair systems feature:

• Biomimicry: Implants with bone-matching properties from polymer composites (patent pending)
• Osteoconduction: Novel ceramic coating technology for polymer composites (patent pending)
• Improved fixation: High adhesion engineered ceramic coating for implants
• Applications: Orthopaedic (THR/TKR, shoulder) and maxilo-facial

Stress Shielding and Osteointegration

Their unique structure and mechanical properties provide NRC's polymer composite materials with the bone-matching characteristics essential to reduce stress shielding, while their porous bioactive high adhesion coatings provide them with the osteointegration capacity necessary for long-term implant fixation. The combined low stress shielding and osteointegration are key to extend implantation period due to reduced occurrence of implant loosening and to prevent bone resorption for simplified revision surgeries.

Fabrication Process

Composite Structure - NRC's proprietary fabrication process, combining polymer and long fibre reinforced composites moulding technologies, allows the production of a variety of different structures with tuneable bone-matching properties and long-term reliability.

Coating - NRC has also developed a proprietary coating technology enabling the production of high crystallinity, high strength and high adhesion, ISO 13779-compliant HA coating on the polymer composite structures.

NRC HA-coated polymer composite for hip implant stem		HA-coated polymer composite hip stem
Core Polymer Composite HA Coating

Materials Properties and Characteristics

The elastic modulus of the NRC polymer composite structure lies perfectly in cortical bone's range (see following Table), as opposed to dense metals such as Ti alloys and stainless steel 316L commonly used in orthopaedic applications. Matching the properties of the implants with those of the bones is crucial to avoid stress shielding that lead to bone resorption and may play a role in implant loosening.

Long-term mechanical performance also confirmed that NRC's polymer composite materials do not fail in fatigue under normal physiological conditions. In fact, fatigue failures were only obtained in extreme, non-physiological conditions.

Fatigue life diagram showing failure
above 3 – 5 millions cycles under extreme conditions

	Histological sections of intramedullary pin implants (new-Zealand white rabbit, 49 days implantation).
High crystallinity NRC HA coating on polymer composite	30 µm apatite deposit after Kokubo's simulated body fluid conditioning
Regenerated apatite layer (approx. 20 µm) grown on high crystallinity NRC HA coating (approx. 80 µm) on polymer composites showing bioactivity.

Biocompatibility assessment has been perfomed through:

• In vitro cytotoxicity testing (Alamar Blue, MTT- direct and indirect contact)
• In vitro bioactivity (total protein content, Alkaline Phosphatase, type I collagen and osteocalcin-internalized and medium released)
• In vivo rats and rabbits implantation (histology, histomophometry, standard bone apposition measurement)

Business Opportunities

Opportunities are now available for companies and research centers interested in the development and use of orthopaedic devices and bone repair, and reconstruction systems. Through R&D projects and precompetitive research, NRC-IMI works with companies and helps them in a progressive technology transfer process.

Martin Bureau, Ph.D. Group Leader Advanced Polymer Composites Tel.: 450-641-5179 Fax: 450-641-5105 E-mail: Martin.Bureau@cnrc-nrc.gc.ca
Alexandre Paris, Eng. Business Development Officer Advanced Materials Design Tel.: 450-641-7524 Fax: 450-641-5105 E-mail: Alexandre.Paris@cnrc-nrc.gc.ca

Related Information

Institutes:

• NRC Industrial Materials Institute