OSSIS Silver-Coated Implant Research Results: the silver lining against implant-associated infections.
OSSIS implants provide surgeons and patients the best one-time solution, whilst preventing infections. The silver coating used by OSSIS on its implants helps ensure consistent osseointegration all the while providing the antibacterial properties of silver.
Surgeons face considerable challenges in the treatment of complicated degenerative defects or tumors in bone. In addition to good surgical technique and decision-making, successful treatment will depend upon robust and reliable implants. In these complex situations, it is ideal to provide patients the best solution in the first instance of treatment.
Having said that, surgical complications threaten the longevity of orthopedic implants. In particular, implant-associated infections can have a devastating impact on patients. Not only do these complications present a new set of clinical problems for the surgeon, but these also create substantial social and economic burden on our patients.
What is the solution for preventing implant-related infections? At OSSIS, the goal is to provide one orthopedic implant for life. In this regard, silver-coated implants are the new frontier in infection prophylaxis.
Partnering with Bio-Gate, OSSIS implants can now be enhanced with HyProtect™ plasma coating, providing one of the best solutions for decreased infection risk and improved implant survivorship.
The devastating burden of infection
Implant-related infections are devastating complications following orthopedic surgery. Apart from the surgical implications of treating infections, the social and economic burdens are costly. In fact, the median cost of treatment for orthopedic trauma patients with surgical site infections is twice as high compared to non-infected patients. (1)
For that reason, interest has shifted to the antibacterial properties of silver for medical implants. Highly reactive silver ions react with bacterial cell membranes inducing cell death as well as impairing important cell functions to eradicate the infection threat. The HyProtect™ silver coating addresses the formation of bacterial “biofilms”, believed to be the root cause of persistent or late-onset infections.
“Bio-Gate developed HyProtect, an ultrathin bioresorbable coating with embedded silver particles to reduce the risk of biofilm formation and help prevent infections on orthopaedic implants. We have compiled a large amount of data and performed several studies that demonstrate the efficacy and safety of our coating technology. This includes the successful application of HyProtect on more than 75.000 veterinary implants with a 10-fold reduction of the infection rate.”
Fig. 1: Histological evaluation of devices inserted into trabecular bone.
All implants were surrounded by a newly formed bony lamella with abundant osteoid formation. (a) Example of histological images of femoral and tibial HyProtect™-coated implants. (b) Example of histological images of femoral and tibial uncoated implants. Giemsa staining. Cells and nuclei are stained in different shades of blue, collagen and osteoid in pale blue, cartilage matrix in red to violet and mineralised bone matrix in pink to pale pink. (c) Bone apposition in percentage of implant surface for coated and uncoated implants in the trabecular bone. Bone apposition was the most for the devices implanted under non-loaded conditions at the femoral condyle. The silver coating did not significantly influence bone apposition at any implant location, as there was no difference between coated and uncoated implants. Median and individual values; a p ≤ 0.05. Source: Stein et al.(3)
OSSIS and Bio-Gate: a winning collaboration
The use of silver for medical devices has a pristine track record in lowering infection rates. The same can be said for their application in orthopedic implants. As much as a 50% decrease in infection rates can be appreciated when using silver-coated endoprosthesis over conventional implants following extensive tumor surgeries (2). The problem, however, lies in its tendency to impair the osseointegration at the bone-implant interface. Failure of osseointegration may compromise long-term stability.
The key lies in the design and application of the silver. At OSSIS, the products undergo high-quality processes and procedures to create our market-leading versions of these coated medical devices. In partnering with Bio-Gate, OSSIS implants make optimal use of the HyProtect™ Antimicrobial Plasma Coating for the silver-coating enhancements.
OSSIS Technical Engineer Manager, Bethany Oates, clarifies why OSSIS’ implementation of the HyProtect™ coating does not compromise osseointegration while at the same time limits systemic silver to a non-toxic dose.
“HyProtect has silver particles embedded between layers of siloxane. This means the silver never comes into contact directly with the bone and allows the bone to grow onto the implant. Additionally, the silver will diffuse into the body over 90 days. Because of the vapor deposition onto the implant surface, the patient receives a low, non-toxic dose of silver.”
Not all silver-coated implants are created equal
With the correct implementation of silver coating, osseointegration between implant and bone can reliably occur. It is all a matter of correct implementation of design and understanding of how silver interacts with the bone and the surrounding organic tissues.
An animal study using titanium-vanadium (Ti6AI4V) devices with the HyProtect™ silver coating has shown favorable results (3). Sixteen adult Merino sheep were randomly assigned to two surgical groups: sheep in one group were implanted with the silver-coated implants while sheep in the other group were implanted with uncoated implants. Biomechanical evaluation using the pull-out test, histological examination, and tissue silver content were evaluated after the sheep bones were examined after 6 months.
Did silver coating affect osseointegration? No, it did not. Closer histologic investigation revealed that the silver coating did not significantly alter bone apposition in different implant locations in the femur and tibia. Furthermore, the implants had excellent osseointegration as the pull-out force exceeded the capacity of the 10kN load cell used to measure the shear strength. Only mechanical loading inversely affected shear strength, regardless of whether implants were coated or uncoated. Additionally, there were non-toxic levels of silver in the blood.
“The HyProtect coating on OSSIS implants does not have a negative effect on osseointegration as the silver particles applied between the polysiloxane layers allows the bone to directly contact the implant surface.”
From these study results, Ti6AI4V implants appear to show good osseointegration, both with and without HyProtect™ silver coating while not showing any negative aspects. Surgeons can have confidence in the implant design to achieve stability while taking advantage of the antibacterial properties of silver.
But, not all silver-coated implants are created equal. Another animal study investigated the osseointegration of galvanic silver-coated titanium cementless stems in a beagle model (4). Twenty beagles (~18kg and 3.5 years) were included in the study and their implant-femur specimens were extracted after 12 months for biomechanical and histological evaluation.
Were the results similar to those in the Ti6AI4V implants study? They were not. Of the ten implanted femora with the silver-coated prostheses, none showed osseointegration in any case. Furthermore, it was shown that the titanium prostheses of the control group had direct contact with the femur with adequate osseointegration. Therefore, the study did not recommend coating areas of the implants that are in direct contact to the bone with this technology. Otherwise a revision after about 12 months to an uncoated implant might be necessary. The study also mentions that surgeons in compassionate care cases using this galvanic silver coating technology have confirmed these results of loosing patterns.
Silver is believed to reduce osseointegration due to its negative effects on osteoblast function. When directly interacting with bone, silver may decrease osteoblast formation and inhibit bony ingrowth. A possible explanation for these results is due to the direct contact of the bone to the silver using this galvanic technology. The HyProtect™ technology that is used on OSSIS implants has been especially designed to achieve a high efficacy against bacterial infections while maintaining a good osseointegration.
Fig. 2: Osseointegration of devices inserted into the cortical bone.
(a) Shear strength in N/mm2 of cylindrical implants inserted into the tibial diaphysis. There was no difference between coated and uncoated implants. (b) Bone apposition in percentage of implant surface of the coated and uncoated devices implanted in the tibial diaphysis. Bone apposition to the implants was not influenced by the silver coating as there was no difference between coated and uncoated devices. Median and individual values. Source: Stein et al.(3)
Conclusion
Implant-associated infections are a risk in any orthopaedic surgery. It goes against the philosophy of providing one orthopaedic implant for life and exacts a heavy toll on patients.
OSSIS implants provide surgeons and patients the best, one-time solution in preventing infections. With a robust implementation of Bio-Gate’s HyProtect™ Silver Coating, these implants have consistent osseointegration all the while providing the antibacterial properties of silver. Overall, when using OSSIS custom implants with HyProtect™ coating, surgeons can have confidence in good long-term outcomes for their patients.
References
Thakore RV, Greenberg SE, Shi H, Foxx AM, Francois EL, Prablek MA, et al. Surgical site infection in orthopedic trauma: A case-control study evaluating risk factors and cost. J Clin Orthop Trauma. 2015 Dec;6(4):220–6.
Wafa H, Grimer RJ, Reddy K, Jeys L, Abudu A, Carter SR, et al. Retrospective evaluation of the incidence of early periprosthetic infection with silver-treated endoprostheses in high-risk patients: case-control study. Bone Joint J. 2015 Feb;97-B(2):252–7.
Stein, S et al. “Osseointegration of titanium implants with a novel silver coating under dynamic loading.” European cells & materials vol. 39 249-259. 30 Jun. 2020, doi:10.22203/eCM.v039a16.
Schorn, D “Beurteilung der Osseointegration einer Silberbeschichtung von Hüftendoprothesen bei Hunden anhand mikroskopischer Techniken“, INAUGURAL-DISSERTATION zur Erlangung des doctor medicinae dentium der Medizinischen Fakultät der Westfälischen Wilhelms-Universität Münster vorgelegt von Welz, Christian aus Neubeckum, 2008.