Medical implants are devices created to replace, help, or improve a failing biological structure. Often, they are produced as prosthetics to replace missing limbs and body parts. Another common use of implants is for the delivery of medication, the monitoring of various bodily functions, and providing support to tissues and organs. Around 7 million Americans have artificial joints, meaning that at least 2% of people in the US have a medical implant.
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Medical implants are placed inside the body or onto its surface, therefore, the way they interact with the living tissue is vital to the way they function. The composition and surface roughness of a medical implant greatly impacts the rate of osseointegration (bone ingrowth into a metal implant). Studies have shown that rough surfaces provide favorable conditions for osseointegration, supporting biological activities with biomechanical stability.
Here, we discuss in detail how the surface roughness of medical implants affects their functionality.
Studies Show that Surface Roughness of Medical Implants Improves Osseointegration
Over the years, numerous studies have demonstrated how implants with surface roughness in comparison to those with smooth surfaces promote greater levels of osseointegration. In one such study, researchers compared the bone remodeling activity on two different kinds of titanium implants, one with a machined smooth surface and another with a plasma-sprayed rough surface.
The team used a confocal laser scanning microscope (CLSM) to measure the levels of direct bone-implant contact and bone volume after the implants were embedded into the femurs of rabbits.
The results showed that the rough-surfaced titanium implants promoted greater percentages of direct bone-implant contact and bone volume in comparison with the smooth-surfaced titanium implants. They also found evidence to suggest that this increased bone volume observed in rabbits who had the rough-surfaced titanium implants was due to less remodeling activity during the early stages following implantation in comparison with the smooth-surfaced implants. The team concluded that the surface roughness of titanium plays a significant role in determining the delicate balance between the formation of new bone and the resorption of remodeling at the interface of the implants.
In more recent years, scientists have attempted to further improve the success of medical implants. Research into medical implants has begun to pay special attention to the efficacy of implants with ‘micro rough’ surfaces. Implants that utilize micro rough titanium surfaces have gained attention and their use in medical implants has increased over the past few decades.
Implants with micro rough titanium surfaces are commonly created via reducing techniques, including grit-blasting with Al2O3 or TiO2 particles, a combination of sandblasting and acid-etching, or acid-etching alone. Various in-vivo studies using different animal models have tested the impact of these surfaces on the implant’s efficacy at promoting osteointegration.
In reviewing multiple studies that investigate this newer medical implant material, it can be concluded that implants with micro rough surfaces induce gone integration in shorter timeframes and achieve a higher percentage of bone-implant contact, as well as a higher level of resistance to shear in comparison with implants that have a smooth surface.
Scientists have explored the underlying mechanisms that allow surface roughness to modulate these effects. Recent in-vitro experimental studies have shed some light on this by investigating responses at the cellular level to implant surface topography. The data collected from these studies has revealed that osteoblasts (cells responsible for the formation of new bone tissue) are sensitive to surface roughness. Osteoblasts exposed to surface roughness exhibit decreased proliferation alongside a more differentiated phenotype.
In addition, PGE2 production has been shown to be augmented on rough surfaces, as is TGF beta 1 production. This data demonstrates that surface roughness may be able to mediate the autocrine and paracrine regulation of osteogenesis. Finally, studies have shown that surface roughness can effectively modulate the effect of systemic hormones, such as 1,25-(OH)2D3, on osteoblasts.
Clinical trials have also shown the benefits of producing medical implants with rough surfaces rather than smooth ones. Clinical trials in humans have demonstrated that roughened titanium implants require a reduced healing timeframe before loading (6-8 weeks as opposed to the usual 12 weeks). Shorter healing times carry many clinical advantages, such as shorter hospital stays and reduced distress/impact on life for the patient.
Data has shown that the surface roughness of implants can mean that shorter sizes can be used (6-8 mm) than those conventionally accepted. The use of shorter implants offers the benefit of avoiding the need for more extensive surgical procedures such as sinus grafting in the maxilla and nerve lateralization in the mandible.
While more research and data are needed to allow us to fully comprehend the maximum potential of using rough surfaces on medical implants, the research currently points to the numerous benefits of surface roughness particularly for the induction of osseointegration.
References and Further Reading
FDA. (2019) Implants and Prosthetics. [Online] Available at: https://www.fda.gov/medical-devices/products-and-medical-procedures/implants-and-prosthetics
Le Guéhennec, L., Soueidan, A., Layrolle, P. and Amouriq, Y. (2007) Surface treatments of titanium dental implants for rapid osseointegration. Dental Materials, 23(7), pp.844-854. https://pubmed.ncbi.nlm.nih.gov/16904738/
Suzuki, K., Aoki, K. and Ohya, K. (1997) Effects of surface roughness of titanium implants on bone remodeling activity of femur in rabbits. Bone, 21(6), pp.507-514. https://pubmed.ncbi.nlm.nih.gov/9430240/
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