Do crosslinking and vitamin E stabilization influence microbial adhesions on UHMWPE-based biomaterials?

Abstract

Background: Microorganism adhesion on polyethylene for total joint arthroplasty is a concern. Many studies have focused on vitamin E-stabilized ultrahigh-molecular-weight polyethylene (UHMWPE), whereas first-generation, highly crosslinked UHMWPE, which is the most commonly used in clinical practice, has been scarcely evaluated.

Questions/purposes: We aimed (1) to compare the adherence of Staphylococcus epidermidis, Staphylococcus aureus, Escherichia coli, and Candida albicans with virgin (untreated) UHMWPE (PE) and crosslinked UHMWPE (XLPE); (2) to correlate the results with the biomaterial surface properties; and (3) to determine whether the decreased adhesion on vitamin E-stabilized UHMWPE (VE-PE) previously recorded for bacteria can also be confirmed for C albicans.

Methods: Microbial adhesion of biofilm-producing American Type Culture Collection (ATCC) and clinical strains on XLPE and VE-PE were compared with PE at 3, 7, 24, and 48 hours of incubation and quantified, as colony forming units (CFU)/mL, using a sonication protocol. Sample surfaces were characterized by scanning electron microscopy, roughness and contact angle measurements, attenuated total reflection-Fourier transform infrared spectroscopy, and x-ray photoelectron spectroscopy (XPS) to reveal qualitative differences in surface composition and topography that could influence the microbial adhesion. The results were analyzed by descriptive statistics and tested by unpaired t-tests.

Results: All microorganisms, both ATCC and clinical strains, showed lower adhesion (p < 0.05) on XLPE with adhesion percentages ranging from 18% to 25%, compared with PE with adhesion percentages ranging from 51% to 55%, after 48 hours. Only the ATCC S epidermidis showed a reduced adhesion profile even at 3 hours (adhesion ratio of 14% on XLPE versus 50% on PE) and 24 hours (19% on XLPE versus 55% on PE) of incubation. ATCC and clinical C albicans were less adherent to XLPE than to PE (p < 0.05) showing even at the earlier incubation time points adhesion values always of 10(3) CFU/mL and 10(4) CFU/mL, respectively. Roughness and contact angle were 0.8 ± 0.2 μm and 92° ± 3°, respectively, with no differences among samples. Qualitative differences in the surface chemical composition were revealed by XPS only. A confirmation of the decreased adhesion on VE-PE respect to PE was also registered here for C albicans strains (p < 0.05).

Conclusions: Vitamin E stabilization and crosslinking of UHMWPE are capable of reducing microbial adhesion. Further studies are needed to fully elucidate the mechanisms of modulation of microbial adhesion to medical-grade UHMWPE.

Clinical relevance: Our results suggest that VE-PE and XLPE may have an added benefit of being more resistant to bacterial adhesion, even fungal strains.

Fig. 1A–C

SEM micrographs representative of the surface topography of the three materials before microbial adhesion assay are shown: (A) PE, (B) XLPE, and (C) VE-PE. Each material type had a comparable surface topography.

Fig. 2

Representative ATR-FTIR spectra from each of the three materials after immersion in TSB for 24 hours are shown: PE (blue), VE-PE (red) and XLPE (green). The inset shows weak traces of proteins adsorbed on the surfaces: weak absorption bands at 1645, 1578, and 1542 cm⁻¹ [2].

Fig. 3A–C

Representative XPS spectra of the three materials are shown: (A) PE, (B) XLPE, and (C) VE-PE. The deconvolution of the C1s peak envelope showed the presence of chemically shifted peaks at 286.5 eV and 288 eV indicating the presence of alcohols/ethers (C-OH/C-OR) and carbonyl groups (C=O), respectively. An additional shoulder at 283.5 eV, whose attribution is still unclear, appeared in the spectrum of VE-PE.