A synthetic
mimic of mussel adhesive protein, dopamine-modified
four-armed poly(ethylene glycol) (PEG-D4), was combined with a synthetic
nanosilicate, Laponite (Na0.7+(Mg5.5Li0.3Si8)O20(OH)4)0.7–), to form an injectable naoncomposite tissue adhesive hydrogel.
Incorporation of up to 2 wt % Laponite significantly reduced the cure
time while enhancing the bulk mechanical and adhesive properties of
the adhesive due to strong interfacial binding between dopamine and
Laponite. The addition of Laponite did not alter the degradation rate
and cytocompatibility of PEG-D4 adhesive. On the basis of subcutaneous
implantation in rat, PEG-D4 nanocomposite hydrogels elicited minimal
inflammatory response and exhibited an enhanced level of cellular
infiltration as compared to Laponite-free samples. The addition of
Laponite is potentially a simple and effective method for promoting
bioactivity in a bioinert, synthetic PEG-based adhesive while simultaneously
enhancing its mechanical and adhesive properties.
Due to the increasing needs for organ transplantation and a universal shortage of donated tissues, tissue engineering emerges as a useful approach to engineer functional tissues. Although different synthetic materials have been used to fabricate tissue engineering scaffolds, they have many limitations such as the biocompatibility concerns, the inability to support cell attachment, and undesirable degradation rate. Fibrin gel, a biopolymeric material, provides numerous advantages over synthetic materials in functioning as a tissue engineering scaffold and a cell carrier. Fibrin gel exhibits excellent biocompatibility, promotes cell attachment, and can degrade in a controllable manner. Additionally, fibrin gel mimics the natural blood-clotting process and self-assembles into a polymer network. The ability for fibrin to cure in situ has been exploited to develop injectable scaffolds for the repair of damaged cardiac and cartilage tissues. Additionally, fibrin gel has been utilized as a cell carrier to protect cells from the forces during the application and cell delivery processes while enhancing the cell viability and tissue regeneration. Here, we review the recent advancement in developing fibrin-based biomaterials for the development of injectable tissue engineering scaffold and cell carriers.
The
remarkable underwater adhesion strategy employed by mussels
has inspired bioadhesives that have demonstrated promise in connective
tissue repair, wound closure, and local delivery of therapeutic cells
and drugs. While the pH of oxygenated blood and internal tissues is
typically around 7.4, skin and tumor tissues are significantly more
acidic. Additionally, blood loss during surgery and ischemia can lead
to dysoxia, which lowers pH levels of internal tissues and organs.
Using 4-armed PEG end-capped with dopamine (PEG-D) as a model adhesive
polymer, the effect of pH on the rate of intermolecular cross-linking
and adhesion to biological substrates of catechol-containing adhesives
was determined. Adhesive formulated at an acidic pH (pH 5.7–6.7)
demonstrated reduced curing rate, mechanical properties, and adhesive
performance to pericardium tissues. Although a faster curing rate
was observed at pH 8, these adhesives also demonstrated reduced mechanical
and bioadhesive properties when compared to adhesives buffered at
pH 7.4. Adhesives formulated at pH 7.4 demonstrated a good balance
of fast curing rate, elevated mechanical properties and interfacial
binding ability. UV–vis spectroscopy evaluation revealed that
the stability of the transient oxidation intermediate of dopamine
was increased under acidic conditions, which likely reduced the rate
of intermolecular cross-linking and bulk cohesive properties for hydrogels
formulated at these pH levels. At pH 8, competing cross-linking reaction
mechanisms and reduced concentration of dopamine catechol due to auto-oxidation
likely reduced the degree of dopamine polymerization and adhesive
strength for these hydrogels. pH plays an important role in the adhesive
performance of mussel-inspired bioadhesives and the pH of the adhesive
formulation needs to be adjusted for the intended application.
A simple strategy is provided to construct novel supramolecular hydrogels with both self-healing and shape memory properties. Starting from achieving self-healable hydrogel based on the dynamic interactions of phenylboronic acid modified sodium alginate (Alg-PBA) and poly(vinyl alcohol) (PVA), further formation of a complex of alginate with Ca(2+) renders this hydrogel with the capability of shape memory at the macro-/microscopic scales.
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