Biomedical Engineering Reference
In-Depth Information
biodegradable polyesters, gels such as gelatin and polyvinyl alcohol, and proteins (the range of
possible polymers is much wider than any of the RP methods reported in Table 4.1). Furthermore,
the method is also highly tunable, in the sense that fi ber diameter and quality is dependent on sev-
eral parameters, for example, viscosity, dipole moment, conductivity, and applied potential. Several
designs and confi gurations of needle tips have been also proposed, such as multiple tips and coaxial
tips, which allow the strands to be deposited as hollow fi bers. Interested readers are encouraged to
consult the excellent review by Pham et al. [22].
At present the collector system where fi bers are laid is very simple, but we envisage more
sophisticated and fast moving collection systems, which could enable site-specifi c fi ber deposition
and orientation and render the electrospinning method RP. We predict that its manufacturing effi -
ciency in terms of RTM ratio is likely to be astonishingly high, possibly a degree of magnitude over
that of FDM because of the high speed with which the polymer jet is ejected from the needle tip and
the high surface to volume ratio produced by very thin fi bers.
4.8 INTEGRATION OF RP METHODS
None of the techniques so far developed can meet the requirements of resolution, RTM ratio, or
fl exibility of materials for the realization of a multifunctional scaffold for tissue engineering. An
emerging trend now is to use the combination of technologies to integrate features at different
scales. In an earlier work, we integrated the PAM technique with site-specifi c surface modifi cation
[23]. Ideally this approach should also combine one or more RP methods. At present, electrospin-
ning, although not strictly RP, is most commonly integrated with other processing methods to pro-
duce microscale networks with higher order networks. An example of this method is the integration
of fi ber bonding with electrospinning. The resulting 3-D scaffolds comprise a macro and a nanofi -
brillar network, which is able to support cell viability and differentiation into bone cells [24]. The
electrospinning technique has also been combined with a wet-spun macrofi brillar network to create
structure-mimicking vessels [25].
Zhang et al. [26] have recently proposed a technique to fabricate scaffold or cell constructs for
tissue engineering by the assembly of microscopic building blocks, realized with different methods
such as bioplotter and FDM techniques in order to mimic the original topology of tissues.
We are certain that this new trend will bring about improvements in design and production
capacity of RP scaffolds.
4.9 COMMERCIAL RP SYSTEMS FOR TISSUE ENGINEERING SCAFFOLDS
RP systems appear to be fairly expensive and bulky, but this is not always the case particularly as far
as fabrication of tissue engineering products is concerned. The maximum size of scaffold desired is
usually no larger than a few centimetres squared, and the fabrication costs are actually only a small
fraction of the total cost of a cell-based 3-D structure, not to mention that of future preclinical and
clinical trails. Some of the RP systems and products described in this chapter are available com-
mercially, but at present these devices and the scaffolds are still very much a niche product used
more for research than for medical applications.
Therics Inc. is a company that produces a line of beta-TCP (β-TCP) products as bone fi llers
using a patented technology, Theriform (www.therics.com). Theriform technology is based on the
3-DP method, which was the fi rst RP technology to be applied for tissue engineering. The company
currently has eight products, two of which are FDA approved with positive clinical results.
PAM-fabricated scaffolds are marketed by Biodigit (www.biodigit.it) for use in cardiac tissue
engineering and are mainly employed for research purposes. They are available in a variety of
materials from biodegradable polyesters to polyurethanes as well as alginates.
