Cross-linking methods of electrospun fibrinogen scaffolds for tissue engineering applications

Electrospinning adipose tissue-derived extracellular matrix for adipose stem cell culture

Basement membrane-rich extracellular matrices, particularly murine sarcoma-derived Matrigel, play important roles in regenerative medicine research, exhibiting marked cellular responses in vitro and in vivo, although with limited clinical applications. We find that a human-derived matrix from lipoaspirate fat, a tissue rich in basement membrane components, can be fabricated by electrospinning and used to support cell culture. We describe practical applications and purification of extracellular matrix (ECM) from adipose tissue (At-ECM) and its use in electrospinning scaffolds and adipose stem cell (ASC) culture. The matrix composition of this purified and electrospun At-ECM was assessed histochemically for basement membrane, connective tissue, collagen, elastic fibers/elastin, glycoprotein, and proteoglycans. Each histochemical stain was positive in fat tissue, purified At-ECM, and electrospun At-ECM, and to some extent positive in a 10:90 blend with polydioxanone (PDO). We also show that electrospun At-ECM, alone and blended with PDO, supports ASC attachment and growth, suggesting that electrospun At-ECM scaffolds support ASC cultivation. These studies show that At-ECM can be isolated and electrospun as a basement membrane-rich tissue engineering matrix capable of supporting stem cells, providing the groundwork for an array of future regenerative medicine advances.

Development and long-term in vivo evaluation of a biodegradable urethane-doped polyester elastomer

We have recently reported upon the development of crosslinked urethane-doped polyester (CUPE) network elastomers, which was motivated by the desire to overcome the drawbacks presented by crosslinked network polyesters and biodegradable polyurethanes for soft tissue engineering applications. Although the effect of the isocyanate content and post-polymerization conditions on the material structure-property relationship was examined in detail, the ability of the diol component to modulate the material properties was only studied briefly. Herein, we present a detailed report on the development of CUPE polymers synthesized using diols 4, 6, 8, 10, or 12 methylene units in length in order to investigate what role the diol component plays on the resulting material's physical properties, and assess their long-term biological performance in vivo. An increase in the diol length was shown to affect the physical properties of the CUPE polymers primarily through lowered polymeric crosslinking densities and elevated material hydrophobicity. The use of longer chain diols resulted in CUPE polymers with increased molecular weights resulting in higher tensile strength and elasticity, while also increasing the material hydrophobicity to lower bulk swelling and prolong the polymer degradation rates. Although the number of methylene units largely affected the physical properties of CUPE, the choice of diol did not affect the overall polymer cell/tissue-compatibility both in vitro and in vivo. In conclusion, we have established the diol component as an important parameter in controlling the structure-property relationship of the polymer in addition to diisocyanate concentration and post-polymerization conditions. Expanding the family of CUPE polymers increases the choices of biodegradable elastomers for tissue engineering applications.

A smart bilayer scaffold of elastin-like recombinamer and collagen for soft tissue engineering

Elastin-like recombinamers (ELRs) are smart, protein-based polymers designed with desired peptide sequences using recombinant DNA technology. The aim of the present study was to produce improved tissue engineering scaffolds from collagen and an elastin-like protein tailored to contain the cell adhesion peptide RGD, and to investigate the structural and mechanical capacities of the resulting scaffolds (foams, fibers and foam-fiber bilayer scaffolds). The results of the scanning electron microscopy, mercury porosimetry and mechanical testing indicated that incorporation of ELR into the scaffolds improved the uniformity and continuity of the pore network, decreased the pore size (from 200 to 20 μm) and the fiber diameter (from 1.179 μm to 306 nm), broadened the pore size distribution (from 70-200 to 4-200 μm) and increased their flexibility (from 0.007 to 0.011 kPa⁻¹). Culture of human fibroblasts and epithelial cells in ELR-collagen scaffolds showed the positive contribution of ELR on proliferation of both types of cells.

Beaded plasma clot: a potent sustained-release, drug-delivery system

Aim: The aim of the study was to prepare a drug-entrapped, beaded form of blood plasma for possible sustained drug delivery. Method: Blood plasma mixed with various drugs was enriched with CaCl2 and transferred in the form of small droplets on to a glass slide covered with parafilm. Clot formation was induced by incubation at 37°C. Results: Plasma-bead entrapped tetracycline, amphotericin B and daunorubicin were released gradually in vitro. Crosslinking of the beads with glutaraldehyde decreased the release rate of drugs remarkably. The plasma bead-entrapped cefotaxime administered subcutaneously in mice was released in a slow and sustained fashion and remained in circulation for a longer duration than the antibiotic administered in the free form. Conclusion: The plasma beads have potential for the sustained delivery of drugs in vivo, since their preparation does not require additional thrombin or other proteins and can be readily accomplished by using autologous plasma, thereby minimizing the risk of immunological complications.

Genipin-crosslinked fibrin hydrogels as a potential adhesive to augment intervertebral disc annulus repair

Treatment of damaged intervertebral discs is a significant clinical problem and, despite advances in the repair and replacement of the nucleus pulposus, there are few effective strategies to restore defects in the annulus fibrosus. An annular repair material should meet three specifications: have a modulus similar to the native annulus tissue, support the growth of disc cells, and maintain adhesion to tissue under physiological strain levels. We hypothesized that a genipin crosslinked fibrin gel could meet these requirements. Our mechanical results showed that genipin crosslinked fibrin gels could be created with a modulus in the range of native annular tissue. We also demonstrated that this material is compatible with the in vitro growth of human disc cells, when genipin:fibrin ratios were 0.25:1 or less, although cell proliferation was slower and cell morphology more rounded than for fibrin alone. Finally, lap tests were performed to evaluate adhesion between fibrin gels and pieces of annular tissue. Specimens created without genipin had poor handling properties and readily delaminated, while genipin crosslinked fibrin gels remained adhered to the tissue pieces at strains exceeding physiological levels and failed at 15-30%. This study demonstrated that genipin crosslinked fibrin gels show promise as a gap-filling adhesive biomaterial with tunable material properties, yet the slow cell proliferation suggests this biomaterial may be best suited as a sealant for small annulus fibrosus defects or as an adhesive to augment large annulus repairs. Future studies will evaluate degradation rate, fatigue behaviors, and long-term biocompatibility.

Electrospinning jets and nanofibrous structures

Electrospinning is a process that creates nanofibers through an electrically charged jet of polymer solution or melt. This technique is applicable to virtually every soluble or fusible polymer and is capable of spinning fibers in a variety of shapes and sizes with a wide range of properties to be used in a broad range of biomedical and industrial applications. Electrospinning requires a very simple and economical setup but is an intricate process that depends on several molecular, processing, and technical parameters. This article reviews information on the three stages of the electrospinning process (i.e., jet initiation, elongation, and solidification). Some of the unique properties of the electrospun structures have also been highlighted. This article also illustrates some recent innovations to modify the electrospinning process. The use of electrospun scaffolds in the field of tissue engineering and regenerative medicine has also been described.

Crosslinking of gelatin-based drug carriers by genipin induces changes in drug kinetic profiles in vitro

Hydrogels are extensively studied as carrier matrices for the controlled release of bioactive molecules. The aim of this study was to design gelatin-based hydrogels crosslinked with genipin and study the impact of crosslinking temperature (5, 15 or 25°C) on gel strength, microstructure, cytocompatibility, swelling and drug release. Gels crosslinked at 25°C exhibited the highest Flory-Rehner crosslink density, lowest swelling ratio and the slowest release of indomethacin (Idn, model anti-inflammatory drug). Diffusional exponents (n) indicated non-Fickian swelling kinetics while drug transport was anomalous. Hydrogel biocompatibility, in vitro cell viability, cell cycle experiments with AH-927 and HaCaT cell lines indicated normal cell proliferation without any effect on cell cycle. Overall, these results substantiated the use of genipin-crosslinked hydrogels as a viable carrier matrix for drug release applications.

Ruthenium-catalyzed photo cross-linking of fibrin-based engineered tissue

Most cross-linking methods utilize chemistry or physical processes that are detrimental to cells and tissue development. Those that are not as harmful often do not provide a level of strength that ultimately meets the required application. The purpose of this work was to investigate the use of a ruthenium-sodium persulfate cross-linking system to form dityrosine in fibrin-based engineered tissue. By utilizing the tyrosine residues inherent to fibrin and cell-deposited proteins, at least 3-fold mechanical strength increases and 10-fold stiffness increases were achieved after cross-linking. This strengthening and stiffening effect was found to increase with culture duration prior to cross-linking such that physiologically relevant properties were obtained. Fibrin was not required for this effect as demonstrated by testing with collagen-based engineered tissue. Cross-linked tissues were implanted subcutaneously and shown to have minimal inflammation after 30 days, similar to non-cross-linked controls. Overall, the method employed is rapid, non-toxic, minimally inflammatory, and is capable of increasing strength and stiffness of engineered tissues to physiological levels.

Insoluble synthetic polypeptide mats from aqueous solution by electrospinning

Water-insoluble nanofiber mats of synthetic polypeptides of defined composition have been prepared by a process involving electrospinning from aqueous solution. L-ornithine is a physiological amino acid. Fibers of poly(L-ornithine) (PLO) were produced at feedstock concentrations above 20% w/v. Applied voltage and needle-to-collector distance were crucial for nanofiber formation. Attractive fibers were obtained at 35-40% w/v. Fiber diameter and mat morphology have been characterized by electron microscopy. Polymer cross-linking with glutaraldehyde (GTA) vapor rendered fiber mats water-insoluble. The study has yielded two advances on previous work in the area: avoidance of an animal source of peptides and avoidance of inorganic solvent.

Electrospinning of collagen/biopolymers for regenerative medicine and cardiovascular tissue engineering

The process of electrospinning has seen a resurgence of interest in the last few decades which has led to a rapid increase in the amount of research devoted to its use in tissue engineering applications. Of this research, the area of cardiovascular tissue engineering makes up a large percentage, with substantial resources going towards the creation of bioresorbable vascular grafts composed of electrospun nanofibers of collagen and other biopolymers. These bioresorbable grafts have compositions that allow for the in situ remodeling of the structure, with the eventual replacement of the graft with completely autologous tissue. This review will highlight some of the work done in the field of electrospinning for cardiovascular applications, with an emphasis on the use of biopolymers such as collagens, elastin, gelatin, fibrinogen, and silk fibroin, as well as biopolymers used in combination with resorbable synthetic polymers.