The Cell–Surface Interaction - Tissue Engineering: Cell-Surface Interactions for Tissue Culture - page 14

3.2.2 Surface Topography In Vivo
Recent short- and long-term in vivo studies using implant devices with varying
surface topographies have shown that the mechanisms involved in this 'niche' are
possibly more ill-defined than in the in vitro situation and, in some cases, con-
flicting results are reported. For instance, Hayakawa et al. [ 77 ] observed a dif-
ference in bone response to grit-blasted and smooth substrates in rabbit cortical
bone. However, this difference was not reported for the same samples when they
were investigated in a trabecular bone model. Conversely, Pearce et al. [ 78 ]
showed that standard microrough commercially pure titanium and TAN had higher
torque removal in both a trabecular and a cortical sheep bone model compared
with polished samples of the same materials over periods of 6, 12 and 18 weeks.
Interestingly, this study also made evident a distinct difference in peak torque
removal for both bone types.
There are literally hundreds of studies that have focused on enhancing osseo-
integration by controlling surface microroughness in vivo; therefore, here we
would like to focus on other applications. For instance, what if strong, rapid bone
bonding or soft tissue adhesion is an undesirable outcome of implantation? Such
cases would include fracture fixation in the hand or shoulder, where tendons and
connective tissues are required to glide over an implant, the face, where strong
tissue adhesion to the implant may cause irritation and disfiguration, and in pae-
diatric patients, where device implantation is transient and will ultimately require
removal. In instances such as these, the occurrence of direct bone bonding would
be a hindrance for desirable implant function.
Several studies have found that microtopographical manipulation of an implant
surface can provide a degree of resolution for these issues. Under normal cir-
cumstances, direct bonding of bone to an implant is the desired outcome and the
occurrence of a fibrous tissue interface is often viewed as an unwanted, negative
outcome. However, in situations such as fracture fixation of the hand, tissue is
required to glide freely over an implant. The current state of the art describes how
titanium and its alloys have more of a tendency for intratendon inflammation
compared with EPSS. This occurrence can cause painful tendon-implant adhesion
and damage possibly causing limited palmar flexion and even tendon rupture.
Although EPSS is produced for clinics with an innate mirrorlike smooth surface,
there remains a preference for the use of titanium and its alloys because of reduced
artefact production in MRI, superior resistance to corrosion and subsequent metal
sensitivity reactions and superior biocompatibility. With regard to fracture fixation
in paediatric and trauma patients, a similar problem occurs as current commercial
metal implants naturally induce rapid bony overgrowth. This makes implant
removal extremely difficult and fraught with complications.
The AO Foundation group [ 59 , 71 , 78 - 81 ] in particular has produced evidence
that by reducing the microroughness of current clinic metal implants (titanium and
its alloys), one can achieve both implant removal and prevention of tissue adhesion
to hand devices. In both instances the studies used the commercial process of
polishing to reduce the microroughness of the implants. Electropolishing is a