Biomedical Engineering Reference
In-Depth Information
When treating biomedical materials and components, hybrid processes incorporating gaseous
and metal ion plasma implantation are sometimes more effective. In light of this and other require-
ments, researchers in Plasma Technology Limited and City University of Hong Kong designed and
constructed a third-generation plasma immersion ion implanter for biomedical materials and engi-
neering, and the design is fl exible enough to enable other applications (Figure 19.8). In this chapter,
we introduce the process and effects of PIIID to activate the surface of biomedical titanium alloys
and silicon, mitigate Ni release of the biomedical NiTi alloys, improve the blood compatibility of
blood-contacting materials, and improve the antibacterial property of biopolymers.
19.3 SURFACE ACTIVATION OF BIOMATERIALS
It is very important that biomaterials implanted into human bodies must have excellent bioactive
surfaces. However, many biomaterials, such as titanium and its alloys, silicon, and some ceram-
ics, are bioinert, thereby limiting their application in the clinical fi eld. Therefore, it is a key issue
in the fi eld of biomaterials to improve the surface bioactivity of implanted materials. The bioac-
tivity of titanium alloys, silicon, and titania coatings has been improved by plasma implantation
of hydrogen, calcium, sodium, and other elements. The work on the surface activation of bioma-
terials by PIII conducted in City University of Hong Kong and Shanghai Institute of Ceramics
are described here.
19.3.1 H
YDROGEN
PIII
19.3.1.1
Improvement of Bioactivity on Silicon
In the past three decades, silicon has gradually been recognized as an essential trace element in the
normal metabolism of higher animals, and the role of silicon in the human body has aroused inter-
est in the biomedical community [37-41]. More silicon-containing materials are being investigated
as potential materials in biomedical devices and medical implants. Both silicon-based microelec-
tronics and biosensors have undergone tremendous technical development, but the bioactivity and
biocompatibility of silicon are relatively not well understood. In fact, the surface biocompatibility
of silicon is usually poor, and the interaction between silicon-based biosensors or micro electro
mechanical system (MEMS) and the human body may not be desirable [42,43]. Long-term prob-
lems associated with the packaging and biocompatibility of Si chips have been identifi ed to be major
issues [44]. Therefore, it is necessary to improve the bioactivity and biocompatibility of silicon-
based microelectronics and biosensors to meet the need of clinical applications.
Some attempts have been made to improve the bioactivity and biocompatibility of silicon wafers.
For instance, Canham reported that apatite could be induced to form on the surface of microporous
silicon fi lms obtained by wet etching [45]. Dahmen et al. have shown that surface functionaliza-
tion of amorphous hydrogenated silicon (a-Si:H) and amorphous silicon suboxide fi lms (a-SiO
x
:H)
produced by a hydrosilylation reaction are largely biocompatible [46]. This feature suggests that
Si “biochips” might be developed to bond directly with both living tissue and bone by surface
modifi cation. The ability to form apatite on materials soaked in a simulated body fl uid (SBF) is
commonly used by biomedical researchers to evaluate its bioactivity. The active Si
OH groups on
the surface of silicon-based materials were thought to be effective to induce apatite precipitation on
the surface of materials in SBF [47]. Our works have revealed that the bioactivity of silicon could
indeed be enhanced by hydrogen PIII. An a-Si:H
x
layer can be formed on the surface of the hydro-
gen-implanted silicon wafer. After immersion in SBFs for a certain period, apatite could nucleate
and grow on hydrogen plasma-implanted silicon wafers. The improvement of the bioactivity of
silicon wafer was considered to result from the formation of the functional group, such as Si
-
-
H and
Si
-
OH, on its surface.
