Biomedical Engineering Reference
In-Depth Information
osteoblast lineage [129]. In addition, cells from the monocyte lineage can give rise to osteo-
clastic, bone resorbing cells [130]. Osteoclasts have been shown to be phagocytose particles
and to remain bone resorbing cells at the same time [131,132]. RBMC culture is suitable to
investigate the effects of particle exposure on the formation and consequent function of
osteoblastic and osteoclastic cells.
The cellular response of RBMC on a-C:H(Ti) coatings [133] and a-C:H(Ti) film fragments
[134] were investigated. Increased proliferation and reduced osteoclast-like cell activity
could be obtained on the a-C:H(Ti) coatings, while these reactions were not seen on pure
a-C:H films or on glass control samples [133]. The results on the film particles showed that
plain a-C:H and a-C:H(Ti) particles were inert. Both kinds of particles did not significantly
stimulate the osteoclast-related enzyme tartrate-resistant acid phosphatase [134].
Neuronal cells
. The potential for a-C to be used as biomaterials for the central nervous sys-
tem was investigated [135]. The growth and survival of the N2a maurine neuroblastoma
cell line and primary cortal neurons on a-C, surface-oxidized a-C and phosphorus-doped
a-C films were studied. The results conclusively show that a-C is not cytotoxic to neurons
or neural-like (N2a) cells. Cell adhesion and growth of neurons is greatly enhanced by
either surface oxidation of the a-C or incorporation of phosphorus within the a-C matrix
(up to 20 at.%). It is perhaps interesting to note that a-C(P) has the lowest water contact
angle, followed by surface-oxidized a-C and then a-C. In this case, the adhesion and
growth are better on surfaces with higher surface energy (hydrophilic). Furthermore, the
different surface properties of a-C(P)/a-C can be exploited to generate spatially directed
neuron growth via patterned deposition of these materials.
Endocrine cells
. Cells release transmitters in discrete packets, a process called
quantal exo-
cytosis
, as intracellular vesicles fuse with the cell membrane and release their contents.
Electrochemical measurement of transmitter or hormone release from individual cells
on microchips has applications both in basic science and drug screening. The ability of
candidate electrode materials to promote the attachment of two hormone-secreting cell
types (bovine adrenal chromaffin cell and insulin-secreting INS-1 cell line) was investi-
gated [136]. From the result, nitrogen-doped a-C is better than several other commonly
used electrochemical electrode materials for promoting cell attachment of endocrine cells.
This is probably due to the optimal surface energy of a-C(N) as compared to the other
candidates.
In Vivo Studies
An in vivo test performed by inserting 12-mm-long, 4-mm-diameter stainless steel cylin-
ders coated with a-C:H into the cortical bone and muscular tissue of sheep [104]. Several
implants were evaluated after 4 weeks and others after 12 weeks. It was found that the
a-C:H coatings had no macroscopic adverse effects on the bone or muscle tissue. In another
in vivo study, a-C:H coated cobalt-chromium (CoCr) cylinders were implanted in intra-
muscular locations in rats and in transcortical sites in sheep (Figure 2.37). The specimens
were retrieved 90 days after surgery, and their histological analysis showed that the a-C:H-
coated specimens were tolerated well in both body sites [112].
The in vivo tissue response of a-C:H-coated titanium was investigated [137]. The mate-
rials were implanted in the paravertebral muscles along both sides of the spine of New
Zealand rabbits. Preparation of materials, methods used, and evaluation of the tissue
response conformed to ASTM F981-93 (1999) standards. The parameters studied included
evidence of necrosis, presence of inflammatory cells, fatty infiltration, calcification, and
edema. Tissue-cell reaction studied on the samples explanted after 1, 3, 6, and 12 months
