Surface Control and Cellular Response of Biomaterials Treated by Accelerated Neutral Atom Beam
Joseph Khoury, Michael Walsh, Sean Kirkpatrick
Exogenesis Corporation, Billerica, MA 01821, USA
Email: [email protected], Web site: http://www.exogenesis.us
While many materials have desired features such as elasticity and radiolucency, few have the cellular
characteristics to make them good biomaterials. Not only is there a desire for cells to attach to a surface and
differentiate into the appropriate tissue, there is also a need to decrease the ability of bacteria to attach to a
material and create a biofilm. Many have attempted chemical treatment, plasma modification, and composite
preparation to enhance these materials with limited success. Here we describe a surface modification technology
that results in significantly enhanced cell attachment and differentiation while decreasing the ability of bacterial
cells from attaching. Accelerated neutral atom beam (ANAB) 1, is a first of its kind beam that initiates from the
acceleration of argon (Ar) gas cluster ions (GCIB) 2 that are then broken apart to generate truly neutral atoms
that have been accelerated towards a surface. The resulting collisions with the surface produces a physical
rearrangement of the top 1 to 3 nanometers (nm) of the surface without leaving any residual gas components on
or in the surface. ANAB surface modifications of the materials are characterized as having a nanotopography
with peak to peak features in the 20-50 nm range (Figure 1A) and enhanced wettability, both of which are
understood to be important in eukaryotic cell attachment, proliferation, and differentiation. However,
prokaryotic cells, typically in the 1-3 µm diameter range as opposed to 50-100 µm of eukaryotic cells, have a
decreased ability to attach to this texture. The use of polyetheretherketone (PEEK) is rapidly growing in the
biomaterials space due to its favorable features such as its similar elasticity to bone and radiolucency which
allows visualization of fusion by CT scans or MRI. Being an inert material, PEEK fails to integrate with
adjoining bone without the use of an additive, however, rapid bacterial attachment and biofilm formation has
been documented in the literature 3. In this study, we treated 1 cm round PEEK coupons with ANAB at a dose
of 2.5x1016 Ar atoms/cm2 and measured their ability to increase attachment of hFOB osteoblast cells while
decreasing the ability of either Gram-negative P. aeruginosa or Gram-positive S. aureus bacteria to attach.
Following initial seeding of 2,000 hFOB cells on either control or ANAB-treated PEEK (n=3), cells on ANAB
surfaces rapidly attached and proliferated to 7,830 ± 700 by day 10 as compared to 2,675 ± 278 on control
(p<0.0024; Figure 1B). For bacterial studies, equal concentrations of bacteria as measured by optical density
for either species were seeded on control or ANAB-treated PEEK coupons for 3 hours. Coupons were then
rinsed, fixed in 2.5% glutaraldehyde followed by 1% OsO4, and imaged by scanning electron microscopy. While
bacteria were rapidly growing and colonizing on control PEEK, ANAB treatment of the surface resulted in
noticeably fewer bacteria (Figure 1C). This study demonstrates the ability to control biomaterial surfaces to
enhance cellular attachment and integration while decreasing ability of bacteria to create biofilms.
Figure 1. A) Atomic force microscope imaging of control (upper) and ANAB-treated PEEK (lower) reveals a nanotopography
modification of the surface. B) Cell assay shows enhanced hFOB proliferation over time on ANAB-treated PEEK (green) as compared
to controls (red; * p<0.05). C) Scanning electron microscopy reveals decreased bacterial cell attachment on ANAB-treated PEEK (right)
as compared to control (left), bars=50 µm.
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Presentation Method: Invited Oral