Biomedical Engineering Reference
In-Depth Information
level of adhesion to the surface with an unordered pattern than to that of both planar
surfaces and ordered surfaces. The surfaces with the ordered patterns had even
lower levels of adhesion than fl at surfaces. It is clear from studies such as this that
not only must size and shape of the features be considered by the bioengineer when
designing a scaffold but also the technology used must be carefully considered.
What follows is a review of several applications of engineered cellular environ-
ments that are designed to either recreate native tissue architecture or control the
environment of cells so they may better survive in vivo transplantation. In all of
these cases, the engineering of the environment is used to allow cells to grow and
function in a manner that they would in vivo. Micro- and nanotechnology play an
important role in the fabrication of all of these environments. The techniques
employed either provide the cells with a natural ECM environment so the cells can
interact with it yet control the organization of this environment to force cells to take
on natural tissue patterns, or they create nanoscale conduits (pores) to control the
movement of molecules in and out of the cells' environment.
2
Nanoporous Alumina Membranes for Bone
Tissue Engineering
The success of orthopedic implants depends on the native bone tissue making and
retaining stable fi xation to the implant. A better understanding of the events that
take place at the bone-material interface is needed in order to engineer materials
that will promote an interfacial layer between tissue and implant with adequate
healing and biomechanical properties. Materials that promote osseointegration can
help speed the healing process and strengthen the bone-implant interface.
Alumina, a synthetically produced amphoteric aluminum oxide Al
2
O
3
, is a scaf-
fold material that is biocompatible and has current applications in orthopedic and
dental implants. Nanoscale features in bone have led to taking materials such as alu-
mina and patterning them with features of the same size scale. It is hoped that this
may lead to better integration into the host bone as well as improved biocompatibil-
ity. Nanoporous alumina has received much attention for its use in bone tissue engi-
neering. The use of nanoporous alumina stems from the idea that the feature size
matches that of the inorganic particles in bone. Swan, et al. have produced porous
alumina membranes with pore sizes ranging from 30 to 80 nm created using a two-
step anodization process (Fig.
1
) (Swan et al.
2005a
). These membranes were fabri-
cated from aluminum sheeting with a process adapted from Gong et al. (
2003
) . The
aluminum is coated on one side with butyl acetate. This acts as a protective barrier
during the anodization process (Fig.
1a
). The fi rst step in making the pores is the
creation of dimples on the uncoated surface of the aluminum. Anodization occurs in
a glass chamber where the aluminum sheet acts as the anode and platinum foil acts
as the cathode. Both the aluminum sheet and the platinum are suspended from elec-
tronic leads into a bath of 0.25 M oxalic acid, which acts as the electrolyte. This step
creates an oxide layer on the aluminum surface. The resultant pore size can be
