SILICON NITRIDE FOR ORTHOPEDIC IMPLANTS
Silicon nitride is an ideal material for medical implants. Its wear rate is extremely low, and the wear particles are soluble and can be cleared from the body. Silicon nitride is chemically resistant, and it has a high dielectric constant, which confers resistance to fretting corrosion.
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WHAT MAKES SILICON NITRIDE SO EFFECTIVE FOR ORTHOPEDIC IMPLANTS?
SURFACE TOPOGRAPHY
Surface chemistry is a major factor in the success of any implantable device. Compared to polymer polyetheretherketone (PEEK) or titanium, silicon nitride is hydrophilic, i.e., it attracts body fluids containing proteins and bone-forming cells that are critical to bone healing. Simple manufacturing variations, such as glazing or heating in a nitrogen or oxidizing atmosphere, can modify implant surface chemistry, which allows tailoring of implant chemistry to specific biomedical applications.
BONE HEALING
Silicon nitride turns on osteoblasts (bone-forming cells) and suppresses osteoclasts (bone resorbing cells). A manufacturing change called “nitrogen-annealing” results in a near 200% increase in bone formation by cells exposed to silicon nitride¹³. This finding has excellent implications for speeding up bone healing, bone fusion, and implant integration into the skeleton. Furthermore, silicon nitride has demonstrated superior osseointegration capabilities when compared to titanium and PEEK⁴ implant materials.
SUPERIOR IMAGING
On X-ray images, plastic implants are invisible while metals obscure the visibility of bone. CT scans and MRI images are also distorted by metal implants. Implants made of silicon nitride are visible on X-ray images without obscuring the underlying bone details. Also, silicon nitride implants allow for distortion- and artifact-free MRI and CT images, thus giving a clear assessment of the implant, bone, and surrounding areas.
BIOCOMPATIBILITY
A study showed a near-200% increase in bone formation by cells exposed to silicon nitride⁸, which indicates that, when used as a dental implant, the material may speed up bone healing, bone fusion, and implant integration into the skeleton⁹. Several other studies have demonstrated enhanced bone formation in in-vitro and in animal models¹⁰⁻¹⁵.
BACTERIAL RESISTANCE
Bacterial infection of any biomaterial implant is a serious clinical problem. Silicon nitride is inherently resistant to bacteria and biofilm formation⁵⁴,⁵⁶. The antibacterial behavior of silicon nitride is probably multifactorial, and relates to surface chemistry, surface pH, texture, and electrical charge⁷. Optimizing these surface properties for specific implants is a clear advantage of the material.
HYPOALLERGENIC/METAL-ION FREE
While titanium is the “gold standard” for the fabrication of dental implants, ceramics are making inroads. Ceramic implants are metal-free, eliminating allergy concerns for patients. Silicon nitride has been thoroughly tested to ISO 10993-01 standards. It is metal free and has no corrosion, no galvanism effect, no metallic taste, and no electronic disturbances.
ORTHOPEDIC APPLICATIONS
MEDICAL-GRADE SILICON NITRIDE
DENTAL IMPLANTS
Dental implants are another biomedical application where ceramics are making significant inroads. Silicon nitride shows great promise for use in dental implants due to its ability to turn on bone-forming cells (osteoblasts) and suppress bone resorbing cells. Even more exciting is its bacterial resistance.
FOOT OSTEOTOMY & FUSION
Foot osteotomy and fusion procedures are performed to address fractures, bunions, hammertoe, or flat foot conditions. In these procedures, bone is cut and reshaped to alleviate pain, and implant materials such as PEEK and titanium are currently used to facilitate bone fusion. Silicon nitride’s osteogenic characteristics⁴, ⁵, ⁵⁰, combined with its antibacterial properties⁴, ⁵, ¹¹, ⁵⁰, make it a strong consideration as an implant material in this market.
SPINAL IMPLANTS
WHY IS SILICON NITRIDE AN IDEAL FOR SPINAL IMPLANTS?
When used to make spinal fusion implants, silicon nitride has the flexibility of a dense, porous, or combined architecture that can mimic the cortical-cancellous structure of bone¹,². Cumulative silicon nitride implantations through 2018 total about 35,000. Of these, fewer than 30 FDA-reportable adverse events manifested, with no implant-related infections relative to an industry standard of 3–10%.
CRANIOMAXILLOFACIAL IMPLANTS
WHY IS SILICON NITRIDE AN IDEAL FOR CRANIOMAXILLOFACIAL IMPLANTS?
Each year, more than 235,000 Americans undergo reconstructive surgery to repair CMF damage due to injury or disease³,⁴. Pre-shaped metal, polymer, or bioactive ceramic implants are used in cases that require bone repair or replacement; however, those materials have an average failure rate of 5.5% (12% to 37% in the orbital region)⁵. Failures due to poor osseointegration; prosthetic infections; and material corrosion, degradation, and fracture6 often lead to revision surgery, hardware removal, debridement, long-term antibiotic use, and implant replacement. A better material is needed to overcome these problems.
Silicon nitride has the essential physical, mechanical, and biological characteristics to fill this gap. It has been shown to accelerate bone healing, reduce the incidence of infection, eliminate metal toxicity, enhance radiographic imaging, lessen patient pain and disability, and decrease the overall health-care burden associated with failed or failing implants, as compared to current materials².
PARTNER WITH SINTX
Work with us as an OEM partner to develop products utilizing our FleX-SN line of products for orthopedic applications. Our leading R&D and manufacturing teams can collaborate on specialized and niche application development for your company. SINTX can help you develop the most effective way to utilize FleX-SN for maximum efficacy and lowest cost for medical-grade OEM components.