INTRODUCTION TO PROCESSING OF BIOMATERIALS - Advanced Biomaterials: Fundamentals, Processing, and Applications - page 262

and poly (lactic acid), Parker et al. demonstrated that application of periodic or
random micro grooves to polymer implants had no benefi cial effect on peri-
implant tissue healing [87]. Although there are some reports on the limited infl u-
ence of surface modifi cation on cell behavior, a large majority of reports support
the fact that surfaces of biomaterial-based implants can signifi cantly infl uence
cell and tissue response. Hence, there have been efforts to understand and
develop improved methods for surface modifi cation. Also, since most of the cell-
biomaterial interactions occur at the micrometer and nanometer length scale,
there has been a strong motivation to understand and develop methods for pro-
cessing as well as for fabrication at these length scales.
8.4.2 Micro/Nano Fabrication [88]
Although fabrication of micro/nanometer scale devices for electronics/electro-
mechanical applications have been extensively reported, their use in biomedical
applications is more recent and is projected to grow exponentially in the near
future. The fabrication techniques at the micro/nanometer scale use either the
top-down or the bottom-up approach to fabricate micro/nano structures. The top-
down approach involves starting with a bulk material/biomaterial and arriving at
the desired length scale by reduction in material content (subtractive process),
whereas the bottom-up approach involves starting at a molecular scale and build-
ing on that to arrive at the desired length scale (additive process). The fabrication
techniques for biomedical devices were initially limited to manufacturing of poly-
meric drug delivery devices but have now been expanded to multiple applications
including fabrication of smart devices such as BIOMEMS and BIONEMS [90].
Micro/nanometer scale fabrication techniques like LENS(r) have found use in
production of implantable devices with controlled surface architecture. These
techniques hold promise in the production of micro/nanometer scale scaffolds
[12, 86] , micro - fl uidics for artifi cial vascularization and, implantable microchips as
self - regulated drug devices.
Broadly, microfabrication techniques can be divided into two types:
• Surface micromachining—is an additive process in which fabrication of
structures is done via deposited thin fi lms.
• Bulk micromachining—is a subtractive process in which fabrication of
structures is done by selective removal of material from the bulk material.
Table 8.5 enlists some of the various micro/nano-meter scale biomedical
structures along with their respective fabrication techniques [23, 89].
After establishing that surface chemistry and topography of biomaterials
can be tailored to provoke a favorable cellular response, this concept has gained
signifi cant importance in the design of advanced biomaterials. As a consequence,
numerous methods have emerged that can precisely tailor biomaterial surface
chemistry and topography. However, it is expected that as our understanding of
cellular responses to surface chemistry and topography improves, the designing