The investigation of ZnO/ poly(vinylidene) fluoride nanocomposites for orthopedic applications with improved mechanical, piezoelectric, and antimicrobial properties

Abstract

Many studies have shown that piezoelectric materials can be used as bioactively charged surfaces to enhance cell functions and result in tissue regeneration (such as nerve injury repair, bone formation, wound healing, and more). Poly(vinylidene) fluoride (PVDF) and zinc oxide (ZnO) are regarded as potential bone tissue engineering materials because of their many attractive properties including biocompatibility, high piezoelectricity and good mechanical properties. ZnO nanoparticles (NPs) are also well known for their antibacterial properties, in which infection is a growing concern in orthopedics. In this study, PVDF scaffolds doped with crystalline ZnO NPs (termed ZnO/PVDF) were prepared by electrospinning, followed by chemical characterization via Fourier Transform Infrared Microscopy (FTIR). Additionally, their piezoelectric and mechanical properties were also evaluated. In vitro osteoblast (or bone forming cells) assays were performed to determine material cytotoxicity and bone regrowth potential. Staphylococcus aureus (SA), Methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli) bacteria were also seeded and counted to evaluate scaffold antimicrobial properties. Results of this study showed for the first time significantly reduced E. coli, SA and MRSA density on ZnO/PVDF scaffolds when using 2 or 1 mg/ml of ZnO in PVDF composites compared to pure PVDF scaffolds (controls) in 6 hours culture. Compared to controls and non-piezo excited samples, osteoblast density was 30% greater when scaffolds were piezo-excited in 1 and 3 days cell culture. Significantly decreased bacteria (E. coli, SA and MRSA) density and increased osteoblast density on the piezoelectric stimulated ZnO/PVDF scaffolds demonstrated that these scaffolds have a strong potential for antibacterial orthopedic applications, especially considering that bacteria growth was minimized without using antibiotics and, thus, this approach does not contribute to the growing problem of antibiotic-resistance bacteria troubling medicine today. Moreover, with an increased β phase ratio in PVDF, enhanced mechanical properties also indicated that the ZnO/PVDF scaffolds can be considered as an orthopedic implant material or used for other mechanical and electrical applications with greater efficiency than what may be presently available.