Biomedical Engineering Reference
In-Depth Information
TowardBiomedicalApplications
PEM-Coated Implantable Biomaterials
For applications in the fields of implantable biomaterials and tissue engineering, films
are used as surface coatings with the aim of providing an additional functionality for
the original materials or engineered tissue. Several aspects therefore appear particularly
important, as discussed in the following paragraphs.
For coating the surfaces of biomaterials (metals, synthetic or natural polymers, ceram-
ics), it is first important to characterize the coating of the film on the materials and then to
investigate the behavior of specific cell types, depending on the planned application. Very
interestingly, several type of materials have been modified by LbL films (Figure 8.11 and
Table 8.1). Table 8.1 summarizes all the studies performed in vitro on various materials as
initial substrates. They are classified according to the type of application: bone, vascular
tissue, dental tissue, neuronal tissue, pancreas, tracheal prostheses, and general engineer-
ing applications. It appears that bone and vascular tissue engineering are the fields that
have attracted the greatest number of studies. This is not surprising as these two fields
represent the largest markets of implantable biomaterials.
For applications in the field of orthopedics, osteoblasts are usually investigated. One
of the most studied materials is titanium because of its large application for orthopedic
implants (Geetha et al. 2009). New types of nano- and microporous scaffolds as future
tissue engineered constructs are also currently being investigated, including electro-
spun fibers (Li et al. 2008) and polymer-based scaffolds (Liu et al. 2005b). As first step, cell
adhesion, proliferation, and viability are quantified. The film coating has to allow cells to
adhere.
In the vascular engineering field, the most used materials are stainless steels (standard
material for stents) and synthetic polymers such as polyethylene terephtalate (PET), poly-
caprolactone, and polytetrafluoroethylene (or PTFE, Teflon®). These later ones are cur-
rently employed as vascular grafts. As the film-coated materials are going to be in contact
with blood and with the vascular wall, studies often concern endothelial cells, platelets,
or inflammatory cells such as macrophages. In this context, natural polyelectrolytes can
potentially be used in multilayer films because of their intrinsic bioactivity. DEX and HEP
can be used for their antithrombogenicity. HA can be used for its high water retention
capacity. CHI/DEX films were found to exhibit anticoagulant properties only when dex-
tran was the outermost layer of the film and when the films were built in 0.5 M NaCl or
1 M NaCl (Serizawa et al. 2002). On the other hand, CHI/HEP films built in 1 M NaCl
also exhibited strong anticoagulant activity regardless of the outermost surface of the film
(Serizawa et al. 2002). This type of multilayer film thus has good potential for the sur-
face modification of medical implants in contact with blood. The thromboresistance of a
(CHI/HA) 4 -coated NiTi substrate was also demonstrated by Thierry et al. (2003). These
films were found to significantly reduce platelet adhesion by 38% after 1 h of exposure
to platelet-rich plasma. On the contrary, the adhesion of polymorphonuclear neutrophils
onto the coated surface increased slightly, compared to bare metal.
Applications in the field of dentistry are also foreseen, with titanium being again one of
the materials of choice due to its biocompatibility.
The design of the surfaces with a targeted functionality is a considerable challenge for
future applications in tissue engineering and biomaterials. It is possible that adhesive pep-
tides or ECM proteins may enhance specific cell adhesion (see Section 8.3.4). The growth
 
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