Infection burden and immunological responses are equivalent for polymeric and metallic implant materials in vitro and in a murine model of fracture-related infection.

The development of an infection is a major complication for some patients with implanted biomaterials. Whether the material or surface composition of the used biomaterial influences infection has not been directly compared for key biomaterials currently in use in human patients. We conducted a thorough in vitro and in vivo investigation using titanium (Ti) and polyether-ether-ketone (PEEK) as both commercially available and as modified equivalents (surface polished Ti, and oxygen plasma treated PEEK). Complement activation and cytokine secretion of cell of the immune system was assessed in vitro for all materials in the absence and presence of bacterial stimulants. In a follow-up in vivo study, we monitored bacterial infection associated with clinically available and standard Ti and PEEK inoculated with Staphylococcus aureus. Complement activation was affected by material choice in the absence of bacterial stimulation, although the material based differences were largely lost upon bacterial stimulation. In the in vivo study, the bacterial burden, histological response and cytokine secretion suggests that there is no significant difference between both PEEK and Ti. In conclusion, the underlying material has a certain impact in the absence of bacterial stimulation, however, in the presence of bacterial stimulation, bacteria seem to dictate the responses in a manner that overshadows the influence of material surface properties. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 1095-1106, 2019.

An in vitro investigation of bacteria-osteoblast competition on oxygen plasma-modified PEEK.

Polyetheretherketone (PEEK) films were oxygen plasma treated to increase surface free energy and characterized by X-ray photoelectron microscopy, atomic force microscopy, and water contact angles. A parallel plate flow chamber was used to measure Staphylococcus epidermidis, Staphylococcus aureus, and U-2 OS osteosarcomal cell-line adhesion to the PEEK films in separate monocultures. In addition, bacteria and U-2 OS cells were cocultured to model competition between osteoblasts and contaminating bacteria for the test surfaces. Plasma treatment of the surfaces increased surface oxygen content and decreased the hydrophobicity of the materials, but did not lead to a significant difference in bacterial or U-2 OS cell adhesion in the monocultures. In the S. epidermidis coculture experiments, the U-2 OS cells adhered in greater numbers on the treated surfaces compared to the untreated PEEK and spread to a similar extent. However, in the presence of S. aureus, cell death of the U-2 OS occurred within 10 h on all surfaces. The results of this study suggest that oxygen plasma treatment of PEEK may maintain the ability of osteoblast-like cells to adhere and spread, even in the presence of S. epidermidis contamination, without increasing the risk of preoperative bacterial adhesion. Therefore, oxygen plasma-treated PEEK remains a promising method to improve implant surface free energy for osseointegration.

Osseointegration of machined, injection moulded and oxygen plasma modified PEEK implants in a sheep model.

Machined and injection moulded polyetheretherketone (PEEK) implants with and without an oxygen plasma modification were prepared and implanted in sheep cancellous and cortical bone. After 4, 12 and 26 weeks, osseointegration was evaluated through mechanical push-out tests and histomorphometry. In the cancellous bone, push-out force increased with time, a trend toward higher force was observed for machined compared to moulded, and oxygen plasma modified compared to unmodified. On-going remodelling of the bone was detected in the periphery of the implants at 4 weeks. Minimal or no inflammation was observed with all the implants at all locations and time-points. Bone-implant contact (BIC) was quantified at all-time points and locations for all the four PEEK implant surfaces. The BIC values ranged from 15 to 75% with an average of 29 ± 13% in the cancellous bone and 25-65% with an average of 50 ± 12% in the cortical bone. In the cortical bone the BIC increased significantly from 4 to 26 weeks. This in vivo study has identified that surface topography of PEEK implants influences osseointegration. In addition, oxygen plasma has the potential to increase bone-implant interface stability. This study provides a unique reference for further modifications and in vivo assessment of PEEK implants.

Attachment of human primary osteoblast cells to modified polyethylene surfaces.

Ultra-high-molecular-weight polyethylene (UHMWPE) has a long history of use in medical devices, primarily for articulating surfaces due to its inherent low surface energy which limits tissue integration. To widen the applications of UHMWPE, the surface energy can be increased. The increase in surface energy would improve the adsorption of proteins and attachment of cells to allow tissue integration, thereby allowing UHMWPE to potentially be used for a wider range of implants. The attachment and function of human primary osteoblast-like (HOB) cells to surfaces of UHMWPE with various levels of incorporated surface oxygen have been investigated. The surface modification of the UHMWPE was produced by exposure to a UV/ozone treatment. The resulting surface chemistry was studied using X-ray photoelectron spectroscopy (XPS), and the topography and surface structure were probed by atomic force microscopy (AFM) and scanning electron microscopy (SEM), which showed an increase in surface oxygen from 11 to 26 atom % with no significant change to the surface topography. The absolute root mean square roughness of both untreated and UV/ozone-treated surfaces was within 350-450 nm, and the water contact angles decreased with increasing oxygen incorporation, i.e., showing an increase in surface hydrophilicity. Cell attachment and functionality were assessed over a 21 day period for each cell-surface combination studied; these were performed using SEM and the alamarBlue assay to study cell attachment and proliferation and energy-dispersive X-ray (EDX) analysis to confirm extracellular mineral deposits, and total protein assay to examine the intra- and extracellular protein expressed by the cells. HOB cells cultured for 21 days on the modified UHMWPE surfaces with 19 and 26 atom % oxygen incorporated showed significantly higher cell densities compared to cells cultured on tissue culture polystyrene (TCPS) from day 3 onward. This indicated that the cells attached and proliferated more readily on the UV/ozone-treated UHMWPE surfaces than on untreated UHMWPE and TCPS surfaces. Contact guidance of the cells was observed on the UHMWPE surfaces by both SEM and AFM. Scanning electron micrographs showed that the cells were confluent on the modified UHMWPE surfaces by day 10, which led to visible layering of the cells by day 21, an indicator of nodule formation. In vitro mineralization of the extracellular matrix expressed by the HOB cells on the modified UHMWPE surfaces was confirmed by SEM and EDX analysis; spherulite structures were observed near cell protrusions by day 21. EDX analysis confirmed the spherulites to contain calcium and phosphorus, the major constituents in calcium phosphate apatite, the mineral phase of bone. Overall cell attachment, functionality, and mineralization were found to be enhanced on the UV/ozone-modified UHMWPE surfaces, demonstrating the importance of optimizing the surface chemistry for primary HOB cells.