Characterization of polyurethane scaffold surface functionalization with diamines and heparin.

Polyurethane scaffolds (PUs) have a good biocompatibility but lack cell recognition sites. In this study, we functionalized the surface of a PU, P(D/L)LA and PCL (50:50) containing urethane segments, with heparin. The first step in this functionalization, aminolysis, lead to free amine groups on the surface of the PU. Free amine content was determined to be 6.4 nmol/mL/mg scaffold, a significant increase of 230%. Subsequently, heparin was crosslinked. Immunohistochemistry demonstrated the presence of heparin homogeneous throughout the 3D porous scaffold. Young's modulus decreased significantly till 50% of the native stiffness after aminolysis and did not change after heparin crosslinking. Contact angle on PU films significantly decreased from 82.7° to 64.3° after heparin crosslinking, indicating a more hydrophilic surface. This functionalization beholds great potential for tissue engineering purposes. When used in a load-bearing environment, caution is necessary due to reduction in mechanical stiffness.

Effect of load on the repair of osteochondral defects using a porous polymer scaffold.

The aim of the present study was to evaluate if a porous polymer scaffold, currently used for partial meniscal replacement in clinical practice, could initiate regeneration and repair of osteochondral defects, and if regeneration and repair were related to mechanical stimulation. Two equally sized osteochondral defects were created bilaterally in each trochlear groove of 16 adult female New Zealand White rabbits. The defects were filled with polycaprolactone-polyurethane scaffolds of either 3 or 4 mm in height. Regeneration and repair of the defects were evaluated after 8 (n = 8) and 14 weeks (n = 8). After 8 weeks of implantation, both the 3- and 4-mm scaffolds were flush with the native cartilage. The amount of cartilaginous tissue was similar in both scaffold types. Pores located in the more central zones of the scaffolds contained less cartilaginous tissue when compared with pores located in the more superficial zones. After 14 weeks, significantly more cartilaginous tissue was present in 4 mm scaffolds when compared with the 3-mm scaffolds (p = 0.03). In the 4-mm scaffolds, progression of cartilaginous tissue from the surface of the scaffold toward the center was observed over time, whereas in the 3-mm scaffold, the percentage of cartilaginous tissue in the central zones was not different from the situation after 8 weeks. Osteochondral defects might be treated using porous polymer scaffolds currently used for partial meniscus replacement, although several limitations need yet to be overcome. The results suggest that mechanical forces may not have to be applied over long periods of time to accelerate tissue formation and increase cartilage repair longevity.

Enzymatic mineralization of hydrogels for bone tissue engineering by incorporation of alkaline phosphatase.

Alkaline phosphatase (ALP), an enzyme involved in mineralization of bone, is incorporated into three hydrogel biomaterials to induce their mineralization with calcium phosphate (CaP). These are collagen type I, a mussel-protein-inspired adhesive consisting of PEG substituted with catechol groups, cPEG, and the PEG/fumaric acid copolymer OPF. After incubation in Ca-GP solution, FTIR, EDS, SEM, XRD, SAED, ICP-OES, and von Kossa staining confirm CaP formation. The amount of mineral formed decreases in the order cPEG > collagen > OPF. The mineral:polymer ratio decreases in the order collagen > cPEG > OPF. Mineralization increases Young's modulus, most profoundly for cPEG. Such enzymatically mineralized hydrogel/CaP composites may find application as bone regeneration materials.

Improving the cell distribution in collagen-coated poly-caprolactone knittings.

Adequate cellular in-growth into biomaterials is one of the fundamental requirements of scaffolds used in regenerative medicine. Type I collagen is the most commonly used material for soft tissue engineering, because it is nonimmunogenic and a highly porous network for cellular support can be produced. However, in general, adequate cell in-growth and cell seeding has been suboptimal. In this study we prepared collagen scaffolds of different collagen densities and investigated the cellular distribution. We also prepared a hybrid polymer-collagen scaffold to achieve an optimal cellular distribution as well as sufficient mechanical strength. Collagen scaffolds [ranging from 0.3% to 0.8% (w/v)] with and without a mechanically stable polymer knitting [poly-caprolactone (PCL)] were prepared. The porous structure of collagen scaffolds was characterized using scanning electron microscopy and hematoxylin-eosin staining. The mechanical strength of hybrid scaffolds (collagen with or without PCL) was determined using tensile strength analysis. Cellular in-growth and interconnectivity were evaluated using fluorescent bead distribution and human bladder smooth muscle cells and human urothelium seeding. The lower density collagen scaffolds showed remarkably deeper cellular penetration and by combining it with PCL knitting the tensile strength was enhanced. This study indicated that a hybrid scaffold prepared from 0.4% collagen strengthened with knitting achieved the best cellular distribution.