Biomedical Engineering Reference
In-Depth Information
deformation and complete recovery, and elastic properties of the materials [42].
For example, the mechanical characteristics and degradability of shape-memory,
multiblock copolymers can be used for the preparation of smart surgical suture.
Lendlein and Langer fabricated a self-tightenable biodegradable suture from a
biodegradable, elastic shape-memory polymer. The suture can be loosely con-
nected and then heated above critical temperature to trigger the shape recovery
and tighten the suture [11] .
9.5
Elastic Hydrogels for Tissue Expander Applications
A material or device designed to induce skin or tissue expansion for the purpose
of reconstructive and plastic surgeries has been called a tissue expander. Tissue
expanders are temporary infl atable implants that are positioned under the skin to
facilitate the increase of tissue dimensions for reconstruction [43]. As an example,
Figure 9.8 illustrates a schematic diagram of a skin expander using a fl atable
balloon.
An ideal expander should have several characteristics: easily placed through a
small access site, gradually enlarge over a relatively short time, well tolerated over
the long term, avoid uncomfortable infl ation spikes, and resistant to infection [44].
In 1982, Austad and Rose introduced a self-infl ating expander that consisted of a
permeable silicone membrane fi lled with a hypertonic saline solution [45].
However, the expansion of the silicone balloon takes too long (8-14 weeks) and
induces tissue necrosis [46].
The use of hydrogels as tissue expanders in reconstructive surgery was fi rst
developed in 1992 by Downes
et al.
who exploited the osmotically driven expansion
of a biocompatible poly(hydroxylethyl methacrylate) hydrogel [47]. The hydrogels
are placed in their dry, contracted states, and expand gradually to their full size
with over 10-fold increase in volume. Wiese verifi ed that hydrogels are effi cient
materials to induce the tissue expansion using vinyl - 2 - pyrrolidone ( VP )/ methyl
methacrylate (MMA) copolymeric hydrogel and demonstrating their biocompati-
bility and swelling pressure [46]. Once implanted, the VP/MMA absorbs body
fl uids that leads to gradual swelling of the device to a 250-300% in volume as
shown in Figure 9.9. Wiese
et al.
also introduced the innovative self-fi lling device,
using a hydrogel matrix consisting of MMA/VP by replacing the CH
3
groups in
Inflated expander
Injection port
Fill tube
Expanded skin
Skin
Expander
Muscle Tissue
Muscle Tissue
Figure 9.8
Schematic diagram of skin expander using an infl atable balloon.
