Poly(glycerol sebacate) (PGS) has been used successfully as a scaffolding material for soft tissue engineering. PGS scaffolds, however, are usually mechanically isotropic, which may restrict their use in tissue repairs as many soft tissues in the body have anisotropic mechanical behaviors. Although various methods have been used to fabricate anisotropic scaffolds, it remains challenging to make anisotropic scaffolds from thermoset PGS. Here a new, simple method to fabricate an anisotropic PGS membrane which can then be used to construct thicker three-dimensional anisotropic scaffolds was developed. First, an aligned sacrificial poly(vinyl alcohol) fibrous membrane was prepared by electrospinning. The fibrous membrane was then partially immersed in PGS prepolymer solution, resulting in a composite membrane upon drying. After curing, the sacrificial fibers within the membrane were removed by water, supposedly leaving aligned cylindrical pores in the membrane. Both SEM and AFM illustrated aligned grooves on the surface of the resultant PGS membrane, indicating the successful removal of sacrificial fibers. The PGS membrane was validated to be mechanically anisotropic using uniaxial tensile testing along and perpendicular to the predominant pore direction. The in vitro cytocompatibility of the PGS membrane was confirmed. As a demonstration of its potential application in vascular tissue engineering, a tubular scaffold was constructed by wrapping a stack of two axisymmetric pieces of the anisotropic PGS membranes on a mandrel. The compliance of the scaffold was found to depend on the pitch angle of its double helical structure, imitating the anisotropic mechanical behavior of the arterial media. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 760-770, 2018.

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Most tissues, including those to be decellularized for tissue engineering applications, are frozen for long term preservation. Such conventional cryopreservation has been shown to alter the structure and mechanical properties of tissues. Little is known, however, how freezing affects decellularization of tissues. The purpose of this study was two-fold: to examine the effects of freezing on decellularization of human umbilical arteries (HUAs), which represent a potential scaffolding material for small-diameter tissue-engineered vascular grafts, and to examine how decellularization affects the mechanical properties of frozen HUAs. Among many decellularization methods, hypotonic sodium dodecyl sulfate solution was selected as the decellularizing agent and tested on fresh HUAs to optimize decellularization conditions. The efficiency of decellularization was evaluated by DNA assay and histology every 12 up to 48 h. The optimized decellularization protocol was then performed on frozen HUAs. The stiffness, burst pressure, and suture retention strength of fresh HUAs and frozen HUAs before and after decellularization were also examined. It appeared that freezing decreased the efficiency of decellularization, which may be attributed to the condensed extracellular matrix caused by freezing. While the stiffness of fresh HUAs did not change significantly after decellularization, decellularization reduced the compliance of frozen HUAs. Interestingly, the stiffness of decellularized frozen HUAs was similar to that of decellularized fresh HUAs. Although little difference in stiffness was observed, we suggest avoiding freezing if more efficient and complete decellularization is desired.

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We synthesized a biodegradable, elastomeric, and functionalizable polyurethane (PU) that can be electrospun for use as a scaffold in soft tissue engineering. The PU was synthesized from polycaprolactone diol, hexamethylene diisocyanate, and dimethylolpropionic acid (DMPA) chain extender using two-step polymerization and designated as PU-DMPA. A control PU using 1,4-butanediol (1,4-BDO) as a chain extender was synthesized similarly and designated as PU-BDO. The chemical structure of the two PUs was verified by FT-IR and 1H-NMR. The PU-DMPA had a lower molecular weight than the PU-BDO (~16,700 Da vs. ~78,600 Da). The melting enthalpy of the PU-DMPA was greater than that of the PU-BDO. Both the PUs exhibited elastomeric behaviors with a comparable elongation at break (λ=L/L0= 13.2). The PU-DMPA had a higher initial modulus (19.8 MPa vs. 8.7 MPa) and a lower linear modulus (0.7 MPa vs. 1.2 MPa) and ultimate strength (9.5 MPa vs. 13.8 MPa) than the PU-BDO. The PU-DMPA had better hydrophilicity than the PU-BDO. Both the PUs displayed no cytotoxicity, although the adhesion of human umbilical artery smooth muscle cells on the PU-DMPA surface was better. Bead free electrospun PU-DMPA membranes with a narrow fiber diameter distribution were successfully fabricated. As a demonstration of its functionalizability, gelatin was conjugated to the electrospun PU-DMPA membrane using carbodiimide chemistry. Moreover, hyaluronic acid was immobilized on the amino-functionalized PU-DMPA. In conclusion, the PU-DMPA has the potential to be used as a scaffold material for soft tissue engineering.