Chapter Ten
Characterization of Biomaterials
Haishan Zeng
Cancer Imaging Department, British Columbi a Cancer Research Centre,
675 West 10th Avenue, Vancouver, BC, V5Z 1L3, Canada
E-mail: hzeng@bccrc.ca
This chapter starts with an introduction of the issues related to biomaterials charac-
terization and the overall strategies of performing three levels of tests: initial tests
for defining the general properties of a biomaterial and for quality assurance; level
II tests for defining the properties closely related to the end-use applications in-
cluding testing of retrieved materials afterin vitro or in vivo exposure to the host bi-
ological environment; level III tests for evaluating the biological responses of blood
or tissue to the implanted biomaterial. The methods for biomaterial bulk property
analysis are then reviewed with discussions focused on two new technologies:
X-ray micro-computed tomography(μCT) and X-ray microdiffraction. The rest
of this chapter provides detailed reviews on selected surface analysis techniques
including microscopy methods: transmission electron microscopy (TEM), scan-
ning electron microscopy (SEM), scanning tunneling microscopy (STM), atomic
force microscopy (AFM), confocal laser scanning microscopy (CLSM); spectroscopy
methods: X-ray photoelectron spectroscopy (XPS), second ion mass spectrometry
(SIMS), Infrared spectroscopy; microspectroscopy and spectral imaging methods:IR
microspectroscopic imaging, Raman microspectroscopic imaging; thermodynamic
methods: contact angle analysis; and emerging optical methods for in vivo analysis:
rapid Raman spectroscopy, multi-photon excitation (MPE) microscopy, optical
coherence tomography (OCT). The chapter ends by emphasizing the importance
of combing multiple analysis methods for a comprehensive solution of biomaterial
characterization for specific applications.
10.1 INTRODUCTION
The rigorous characterization of biomaterials offers the baseline information upon
which the performance of an MEMS device in the biological host setting can
Biomaterials for MEMS, Edited b y M. Chiao and J.-C. Chiao
Copyright © 2011 by Pan Stanford Publishing Pte. Ltd.
www.panstanford.com
978-981-4241-46-5
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224 H. Zeng
be related. This includes characterization of both the bulk and the surface
properties of biomaterials. Lyman has summarized the required characterization
into three different levels.
1
The first level (initial) tests are used to define the
general properties of a candidate biomaterial and can also be used for quality
assurance on new materials. These include determination of chemical composition
and contaminants as well as tests of basic mechanical properties, such as tensile
strength, elongation, elastic modulus, hardness, density, surface roughness and
surface energy. The results obtained from these tests should be used in guiding the
preliminary selection of potential biomaterials.
The second level of characterization defines the properties that are directly
related to the intended applications of the biomaterial, and thus can help to
refine the selection of candidate materials. Tests should be done on materials
which have been processed in a manner similar to that used in the fabrication
of the final MEMS device (including sterilization) since these processings could
alter both the bulk and the surface properties of the biomaterial. Example
tests include bulk measurements of porosity, creep, stress relaxation, fatigue and
wear testing, as well as surface measurements using techniques such as contact
angle, X-ray photoelectron spectroscopy (XPS), second ion mass spectrometry
(SIMS), attenuated total reflectance Fourier transform infrared spectroscopy (ATR-
FTIR), and scanning electron microscopy (SEM). If the biomaterial is melt formed
polymer or is subjected to heat in any processing or sterilization steps, then
thermal property measurements, such as differential thermal analysis (DTA) and
dynamic-mechanical-thermal analysis (DMTA), will also provide useful structural
information since the morphology and the crystallinity of a polymer material may
be affected during these steps. Additionally, information on protein adsorption
and biomaterial responses to solvents (water, saline, lipids, etc.), which may affect
the biomaterial surface and even the bulk structure), may also be important in
assessing the interaction of the biomaterial with its final biological environment.
Retrieved materials should also be retested after in vitro and/or in vivo exposure
to the host biological environment to determine if any changes have occurred in
the material that may adversely affect its long-term performances.
The third level of testing involves measuring the histological response of
blood and tissue to the presence of the implanted biomaterial using both standard
histological test methods for specific applications (soft and hard tissue, blood,
etc.) as well as molecular biology analyses for the presence of specific cell
typesandmoleculessuchasmatrixproteins, growth factors. In this regard, the
emerging optical techniques such as rapid Raman spectroscopy, optical coherence
tomography (OCT), and multi-photon excitation (MPE) microscopy may play a
more importatnt role and eventually replace some of the histolgy tests with non-
invasive in vivo imaging and analyses. These test results help in understanding the
mechanisms of blood and tissue compatibility, aid in development of new bioma-
terials, and assist in the modification of implant design. Level III testing can also
involve more dedicated techniques, such as STM (scanning tunneling microscopy)
and AFM (atomic force microscopy). These surface characterizations, which allow
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