Biomedical Engineering Reference
In-Depth Information
depends upon both the susceptible bonds as well as the enzymatic concentra-
tion in the scaffold environment.
Lutolf et al. created a synthetic scaffold for bone grafts based on the bi-
ological recognition principle [48, 267]. Here, the authors have synthesized
a PEG-based hydrogel scaffold using a matrix metalloproteinase (MMP) la-
bile bi-functional peptide as a crosslinker, which is susceptible to cell-triggered
proteolysis, i.e. the hydrogel degrades into soluble products upon exposure to
cell-secreted MMPs. In this case, the crosslinker determines the hydrogel ma-
terial properties by responding to the cell-secreted MMPs. In another study,
Halstenberg et al. designed PEG-protein based biomaterial by grafting PEGDA
onto an artificial protein created by a recombinant DNA approach [266]. Here,
the protein was designed so as to perform cell-mediated degradation, while the
PEGDA were used to create the network via photopolymerization.
Minimally Invasive Strategies
Advances in polymeric materials engineering offer new opportunities for
minimally invasive surgeries (MIS), aimed at minimizing patient trauma and
speeding up recovery. Many research and clinical studies have indeed focused
on tissue engineering systems that can be injected in a noninvasive man-
ner for use in arthroscopic surgery [66, 101, 268]. One attractive method to
reduce the implantation invasiveness is to create hydrogels within the body
via in situ polymerization. The advantage of in situ polymerization is that
the functionalized oligomers (containing both insoluble and soluble bioac-
tive molecules) can be injected into the defect site through small incisions
and their subsequent polymerization enables a homogenous encapsulation of
cells within the hydrogel. Since the fluidic precursors of the cell-hydrogel sys-
tem can fill any irregular defect shapes, hydrogel-based scaffolds are highly
suitable for treating defects which are not easily accessible, unless one adopts
an invasive surgical procedure. The in situ polymerization also results in im-
proved contact between the native tissue and hydrogel. The use of hydrogels
also obviates many complications associated with residual toxic solvents since
the hydrogels are water based. To this end, various in situ polymerization
techniques/hydrogels such as photopolymerization, stimuli responsive poly-
mers, shape memory polymers, and self-assembling peptide-based systems
have been widely explored for minimally invasive applications.
In this approach, components of the scaffold along with viable cells are
injected in a fluid state into the defect site arthroscopically, followed by
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