(220a) Nanostructured Vapor Deposited Surface Treatments Improve Bone-Anchored Hearing Aid Integration

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.