Biomedical Engineering Reference
In-Depth Information
promoted human oral keratinocyte adhesion and spreading, especially when collagen type I
coating was included. Zhang and colleagues carried out a series of studies to investigate the
potential of silk electrospun matrices for accelerating early stages in wound healing [47].
The adhesion and spreading of normal human keratinocytes and fibroblasts on methanol-
treated silk fibroin nanofibers alone or precoated with ECM proteins (collagen type I,
fibronectin, and laminin) was evaluated. It was found that the cytocompatibility, fiber
diameter, and high porosity together make silk a suitable candidate material for scaffolding
technology.
Synthetic Polymer Blends
The field of synthetic polymer blending has expanded tremendously in the last three decades
[48]. The main advantage to synthetic polymer is the ability to tailor mechanical properties
and degradation intervals to suit various applications. Synthetic polymers can be fabricated
into various shapes with desired features conducive to tissue in-growth. Furthermore, poly-
mers can be designed with chemical functional groups that can induce tissue in-growth [49].
However, synthetic polymers are limited by their lack of biological cues to promote cell
adhesion, proliferation, and tissue recovery. To circumvent this problem and to improve the
biological properties of synthetic polymers, blends of natural and synthetic polymers have
been fabricated [50].
Poly(
d
,
l
-lactide-co-glycolic) (PLGA) and its derivatives poly(glycolic acid) (PGA) and
poly(lactic acid) (PLA) are well known synthetic polymers often used in biodegradable
studies. The attractiveness of PGA is its degradation product, glycolic acid, a natural
metabolite. Poly(lactic acid) is more hydrophobic than PGA, and is more resistant to hydro-
lytic attack than PGA. For most applications the
l
-lactic acid (LA) is chosen because it is
preferentially metabolized in the body. Poly(
l
-lactide acid) (PLLA), PLGA, and PGA are
among the few biodegradable polymers with Food and Drug Administration (FDA)
approval for
in vivo
applications, thus they have been the most widely used materials for
tissue-engineering scaffolds [49, 51].
Venugopal and associates used a blend of biodegradable PCL and collagen to mimic
ECM and were able to suggest that PCL-coated collagen matrices are suitable for fibroblast
growth, proliferation, and migration inside the matrices [52]. Lu and company used a
PLLA-collagen hybrid scaffold to explore
in vitro
dermal fibroblast culture and
in vivo
wound-healing assessment. The team found that the subcutaneous implantation of PLLA-
collagen and PLLA-gelatin scaffolds promoted the regeneration of dermal tissue and
epidermis, as well as reduced contraction during the formation of new tissue [53]. The
number of papers published in the area of polymeric blends, due to the advantages of both
natural and synthetic materials, suggests that the blend approach will play a large role in the
future of skin regeneration.
Bioactive Nanofibers
An advantage of natural and synthetic polymeric nanofibers is the ability to incorporate bio-
active factors such as therapeutic drugs, antimicrobial agents, and growth factors. Various
strategies can be taken to add bioactive factors into nanofibers, including physical absorption
[54], coaxial spinning [55], and emulsion [56]. Selection of polymeric materials affects the bio-
active factor release kinetics. Hydrophobic polymers provide a backbone that degrade over a
long period as opposed to hydrophilic polymers, which have a faster degradation time [57].
