Application of "Stealthy" Polymer Brush Films As Biofilm-Resistant Orthopedic Implant Coatings
Ong Ethan, Student1; Stephanie Le, BS1; Mithani K. Suhail Kamrudin, MD2; Tyler S. Pidgeon, MD3; Daniel Joh, MD , PhD1; Ashutosh Chilkoti, PhD1
1Duke University, Durham, NC; 2Plastics and Reconstructive Surgery, Duke University Medical Center, Durham, NC; 3Duke University Medical Center, Durham, NC
TITLE: Application of “stealthy” polymer bottlebrush films as biofilm-resistant orthopedic hardware coatings
INTRODUCTION: Traumatized patients with open orthopedic injuries to the upper extremity are at increased risk of hardware-related infection (HRI) given the frequency of wound contamination at presentation. Bacterial colonization of hardware can progress to formation of a biofilm that shields pathogens from the host’s immune defenses and antibiotics. Treatment is challenging, often involving hardware removal, debridement, and prolonged antibiotics, which is associated with considerable morbidity and cost. Our strategy to confront the problem of HRI relies on using surface-initiated polymerization techniques to coat metallic implant surfaces with nanometric “stealth” polymer films pioneered by our laboratory. These polymers are hydrophilic, bottlebrush-shaped constructs with highly anti-biofouling (cell- and protein-resistant) properties, which we hypothesize will be optimal for camouflaging implant surfaces from bacterial adhesion(Fig. 1A).
MATERIALS AND METHODS: PBB films are grown directly from solid substrates via surface-initiated atom transfer radical polymerization (SI-ATRP) from poly(oligo(ethylene glycol) methyl ether methacrylate (POEGMA) (a non-toxic, non-fluorinated material). In brief, stainless-steel substrates undergo a brief wet oxidation with nitric acid, followed by chemical surface functionalization with a brominated polymerization initiator, which is then followed by SI-ATRP of POEGMA to generate PBB films. This strategy enables bottom-up growth of PBBs from a surface, leading to ~50 nanometer thick conformal thin films with reliable uniformity and chemical stability.
RESULTS: Our preliminary experiments thus far have shown that we can reliably coat stainless steel surfaces with PBBs. Analysis of the chemical composition of our surfaces by x-ray photoelectron spectroscopy demonstrates successful growth of conformal POEGMA-based surface coatings on steel (Fig. 1B). Functional characterization with contact angle goniometry shows surface wetting behavior consistent with previously reported values. We observe that while liquid cultures of staphylococcus aureus organisms bind avidly to bare stainless steel substrates, bacterial binding is virtually eliminated on substrates coated with PBBs.
CONCLUSIONS: Our in-vitro experiments indicate that our PBB-coated surfaces are effective in preventing bacterial surface adhesion. Further studies in a preclinical model will further assess this strategy to prevent clinical infection. Successful realization of “stealthy” anti-infective implant coatings will have major impact on improving clinical outcomes, quality of life, and reducing healthcare costs.
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