Introduction: Loss of one's sense of hearing can be very detrimental to a person's quality of life with significant limitation in communication. 360 million people in the world have disabling hearing loss, with a rate of 347 per 100,000. Bone-anchored hearing aids (BAHA) are bone-conduction-based hearing aids with titanium implants embedded in the skull. Up to 17% of patients with percutaneous BAHAs have adverse skin reactions around the implant despite strict hygiene practices and antibiotic regimens. This is particularly problematic in children, whose speech/language development is in a critical stage, there are failure rates up to 37%, with 25% requiring explantation. To address this, we investigated the use of nano-featured surfacing for these implants to both reduce infection and inflammatory responses while improving osseointegration. Nanomaterials have been found to have a profound effect upon cell-material interactions, including prevention of bacterial proliferation as well as heightened mammalian cell growth for tissue regeneration. With varied deposition parameters we have demonstrated topographical control of these surfaces and observed changes in bacterial and osteoblast adhesion and integration.
Materials and Methods: Uniform titanium thin films were deposited onto the surfaces of titanium coupons. Changes in vapor deposition parameters allowed us to obtain nano-featured coatings and control the surface topography and extent of nano-roughening. This in turn allowed us to modify surface energy and resulting cellular interactions. Bacterial studies were performed with S. aureus, S. epidermidis and P. aeruginosa, and seeded at approximately 20,000 bacteria per sample. After 24 hours of incubation, bacteria were removed and counted using a colony-forming unit (CFU) assay as well as a live/dead assay. For osteoblast adhesion and proliferation studies, hFOB human osteoblasts (ATCC) were seeded at 10,000 cells/mm2 and quantified via MTS after 4 hrs and 1, 4 and 7 days. All experiments were completed in triplicate and repeated at least three different times.
Results and Discussion: Treated Ti coupons had clear changes in visible appearance and in nano-scale topography. When imaged by atomic force microscopy (AFM), 100-nm scale peaks were formed after treatment (Fig 1) with a greater roughness (Rq = 23 nm, 59 nm) as ion beam intensity increased than untreated Ti (Rq = 4 nm). In addition to increasing measured roughness, the topography of the samples could be tuned for peak morphology (spiky vs rounded) as well as frequency (larger singular peaks surrounded by smaller features or evenly-distributed peaks at high concentrations). Ti coated surfaces had much less adherent bacteria (S. aureus) after 24 than plain Ti, supporting past observations with other nano-rough materials.
Figure 1. Atomic force microscopy of untreated (left), and samples treated with low and high (middle and right) ion beam energy.
Conclusions: Vapor deposited titanium coatings on Ti can impart controllable nano-scale texturing. Here, we demonstrated antibacterial and pro-osteoblast properties of the resulting nano-rough surfaces.
Acknowledgements: The authors thank Northeastern University and the College of Engineering for funding.
See more of this Group/Topical: Topical Conference: Chemical Engineers in Medicine