Elastase-sensitive elastomeric scaffolds with variable anisotropy for soft tissue engineering

Abstract

Purpose: To develop elastase-sensitive polyurethane scaffolds that would be applicable to the engineering of mechanically active soft tissues.

Methods: A polyurethane containing an elastase-sensitive peptide sequence was processed into scaffolds by thermally induced phase separation. Processing conditions were manipulated to alter scaffold properties and anisotropy. The scaffold's mechanical properties, degradation, and cytocompatibility using muscle-derived stem cells were characterized. Scaffold in vivo degradation was evaluated by subcutaneous implantation.

Results: When heat transfer was multidirectional, scaffolds had randomly oriented pores. Imposition of a heat transfer gradient resulted in oriented pores. Both scaffolds were flexible and relatively strong with mechanical properties dependent upon fabrication conditions such as solvent type, polymer concentration and quenching temperature. Oriented scaffolds exhibited anisotropic mechanical properties with greater tensile strength in the orientation direction. These scaffolds also supported muscle-derived stem cell growth more effectively than random scaffolds. The scaffolds expressed over 40% weight loss after 56 days in elastase containing buffer. Elastase-sensitive scaffolds were complete degraded after 8 weeks subcutaneous implantation in rats, markedly faster than similar polyurethanes that did not contain the peptide sequence.

Conclusion: The elastase-sensitive polyurethane scaffolds showed promise for application in soft tissue engineering where controlling scaffold mechanical properties and pore architecture are desirable.

Fig. 1

Scaffolds fabricated under variable conditions that were not designed to induce oriented pore formation (abbreviations are those from Table I). A PU380D, B PU380, C PU880, D PU1080, E PU320D, F PU320, G PU820 and H PU1020. Scale bars are 200 um.

Fig. 2

Scaffolds fabricated under variable conditions with thermal gradients that were designed to induce oriented pore formation (abbreviations are those from Table II). A GPU520 longitudinal, B GPU520 transverse, C GPU820 longitudinal, D GPU820 transverse, E GPU1020 longitudinal, F GPU1020 transverse, G GPU1080 longitudinal, and H GPU1080 transverse. Scale bars are 500 um.

Fig. 3

Typical stress–strain curves for the random scaffold PU1080, and the longitudinal and transverse directions of the oriented scaffold GPU1080.

Fig. 4

Mechanical properties of random scaffolds.

Fig. 5

Mechanical properties of oriented scaffolds. Left Effect of polymer concentration; right effect of quenching temperature.

Fig. 6

Weight loss of PU1080 scaffolds in PBS with or without elastase.

Fig. 7

Relative number of muscle derived stem cell in random (PU1080) and orientated (GPU1080) scaffolds after 3 and 7 days of culture. The cell number in oriented scaffolds was higher than random scaffolds at both time points (p<0.05). Oriented scaffolds cut transversely were used for cell culture.

Fig. 8

H & E staining of random PU1080 (A) and oriented GPU1080 (B) scaffolds after 7 days of culture with muscle derived stem cells. Oriented scaffolds cut transversely were used for cell culture.

Fig. 9

Overview of subcutaneous implantation of PEUU scaffolds (A and B) and PU1080 scaffolds (C and D) after 4 (A and C) and 8 (B and D) weeks of implantation. Blue and black arrows denote sutures and scaffold edge respectively.

Fig. 10

H & E staining of PEUU scaffolds (A and B) and PU1080 scaffolds (C and D) after 4 (A and C) and 8 (B and D) weeks of implantation. Blue and black arrows denote sutures and scaffold edge respectively.