Synthesis and characterization of hydroxyl-terminated polybutadiene modified low temperature adaptive self-matting waterborne polyurethane.

Hydroxyl-terminated polybutadiene (HTPB) is a flexible telechelic compound with a main chain containing a slightly cross-linked activated carbon-carbon double bond and a hydroxyl group at the end. Therefore, in this paper, HTPB was used as a terminal diol prepolymer, and sulfonate AAS and carboxylic acid DMPA were used as hydrophilic chain extenders to prepare low-temperature adaptive self-matting waterborne polyurethane (WPU). Due to the fact that the non-polar butene chain in the HTPB prepolymer cannot form a hydrogen bond with the urethane group, and the solubility parameter difference between the hard segment formed by the urethane group is large, the gap of T g between the soft and hard segments of the WPU increases by nearly 10 °C, with more obvious microphase separation. At the same time, by adjusting the HTPB content, WPU emulsions with different particle sizes can be obtained, thereby obtaining WPU emulsions with good extinction properties and mechanical properties. The results show that HTPB-based WPU with a certain degree of microphase separation and roughness obtained by introducing a large number of non-polar carbon chains has good extinction ability, and the 60° glossiness can be as low as 0.4 GU. Meanwhile, the introduction of HTPB can improve the mechanical properties and low temperature flexibility of WPU. The T g,s (the glass transition temperature of soft segment) of WPU modified by the HTPB block decreased by 5.82 °C, and the ΔT g increased by 21.04 °C, indicating that the degree of microphase separation increased. At -50 °C, the elongation at break and tensile strength of WPU modified by HTPB can still maintain 785.2% and 76.7 MPa, which are 1.82 times and 2.91 times those of WPU with only PTMG as soft segment, respectively. The self-matting WPU coating prepared in this paper can meet the requirements of severe cold weather and has potential application prospects in the field of finishing.

Hydrogel-complexed small-diameter vascular graft loaded with tissue-specific vascular extracellular matrix components used for tissue engineering.

Tissue engineering is thought to the most promising strategy to develop successful small diameter vascular grafts (SDVG) to meet clinical demand. The introduction of natural substances into the SDVG made from synthetic biomaterials can improve the biocompatibility to promote the regeneration of SDVG in vivo. Due to that natural materials from different sources may have property deviation, it is vital to determine the source of natural materials to optimize SDVG fabrication for tissue engineering applications. In this study, bioactive SDVGs were prepared via coating of heparin-modified poly-(ε-caprolactone) scaffolds with a precursor solution containing vascular extracellular matrix (VECM) components and subsequent in situ gelation. The mechanical properties, degradation behaviors, and morphologies of the SDVGs were thoroughly characterized and evaluated. Cell experiments demonstrated the in vitro tissue specificity of the VECM that could promote the proliferation of endothelial cells better than skin-derived collagen. Furthermore, three types of SDVGs, SDVGs with blank hydrogel, SDVGs with skin-derived collagen, and SDVGs with vascular extracellular matrix (VECM-SDVGs), were implanted into the abdominal aorta of rats for one month. The explanted SDVGs were then comprehensively evaluated using hematoxylin and eosin, Masson, von Kossa staining, and immunohistochemical staining for CD31, α-SMA, and MHC. The results showed that the VECM-SDVGs showed the best endothelium regeneration, appropriate intima regeneration, and no calcification, indicating the in vivo specificity of the fabricated VECM-SDVGs. Thus, long-term implantation of VECM-SDVGs was performed. The results showed that a complete endothelial layer formed after 6 months of implantation, and the amount of contractile SMCs in the regenerative smooth muscle layer approached the amount of native aorta at the 12th month. Consequently, relying on vascular tissue specificity, VECM-SDVGs can modulate the regenerative behavior of the implanted SDVGs in vivo to achieve satisfactory vascular regeneration both in short- and long-term implantation.

The performance of heparin modified poly(ε-caprolactone) small diameter tissue engineering vascular graft in canine-A long-term pilot experiment in vivo.

Long-term in vivo observation in large animal model is critical for evaluating the potential of small diameter tissue engineering vascular graft (SDTEVG) in clinical application, but is rarely reported. In this study, a SDTEVG is fabricated by the electrospinning of poly(ε-caprolactone) and subsequent heparin modification. SDTEVG is implanted into canine's abdominal aorta for 511 days in order to investigate its clinical feasibility. An active and robust remodeling process was characterized by a confluent endothelium, macrophage infiltrate, extracellular matrix deposition and remodeling on the explanted graft. The immunohistochemical and immunofluorescence analysis further exhibit the regeneration of endothelium and smooth muscle layer on tunica intima and tunica media, respectively. Thus, long-term follow-up reveals viable neovessel formation beyond graft degradation. Furthermore, the von Kossa staining exhibits no occurrence of calcification. However, although no TEVG failure or rupture happens during the follow-up, the aneurysm is found by both Doppler ultrasonic and gross observation. Consequently, as-prepared TEVG shows promising potential in vascular tissue engineering if it can be appropriately strengthened to prevent the occurrence of aneurysm.

Hydrogel Complex Electrospun Scaffolds and Their Multiple Functions in In Situ Vascular Tissue Engineering.

Hydrogel complex scaffolds (hydrogel scaffolds) are prepared by coating precursor solutions onto heparin-modified poly(ε-caprolactone) (PCLH) scaffolds followed by subsequent in situ gelation. Here, we show that hydrogel complexation can significantly strengthen the scaffold and slow its degradation. The hydrogel scaffold was implanted into the abdominal aorta of a rat model, and the aneurysm incidence rate of the hydrogel scaffolds sharply decreased compared with that of the hydrogel-free scaffolds. Histological and immunohistological analyses showed that the implanted grafts had good vascular regeneration. The absence of calcification and occurrence of contractile smooth muscle cells (SMCs) at the first month was found in the hydrogel-free PCLH scaffold due to the presence of surface-modified heparin, whereas the hydrogel scaffold exhibited mild calcification and later occurrence of contractile SMCs as the complexed hydrogel covered the fibers and blocked the interaction between heparin and cells. Heparin was further physically encapsulated into the hydrogel before gelation, and its sustainable release was demonstrated by an in vitro release test. A pilot implantation in a rabbit carotid model showed that the encapsulated heparin modulated the scaffold characteristics including anticoagulation, anticalcification, and the early occurrence of contractile SMCs in vivo. Consequently, hydrogel complexation can significantly improve the in vivo regeneration property of the scaffold due to its multiple beneficial characteristics.

In situ hydrogel dressing loaded with heparin and basic fibroblast growth factor for accelerating wound healing in rat.

In order to accelerate the healing of chronic wound, a hydrogel dressing encapsulating with heparin and basic fibroblast growth factor is prepared by the Michael addition of 4-arm acrylated polyethylene glycol and dithiothreitol. As-prepared hydrogel dressing can combine the advantages of wet healing theory and exogenous growth factor supplement. Furthermore, the encapsulated heparin can play a role in diminishing inflammation and accelerating wound healing in addition to its well-known function of stabilizing basic fibroblast growth factor. In vitro release test shows the hydrogel network is able to sustainably release basic fibroblast growth factor within 10 days by the regulation of heparin, while released growth factor can significantly promote fibroblast's proliferation in vitro. Moreover, the wound healing in rat shows that as-prepared hydrogel dressing could accelerate wound healing in vivo much more effectively compared with blank hydrogel dressing and negative control. Hematoxylin-eosin and Masson's Trichrome staining exhibit the formation of complete and uniform epidermis. Immunohistochemical staining exhibits heparin can help hydrogel dressing to possess low inflammation in early stage, which is beneficial for accelerating wound healing as well as preventing the production of scar tissue. The enzyme-linked immunosorbent assay results demonstrate the exogenous bFGF in hydrogel can significantly upgrade the expressing of vascular endothelial growth factor and transforming growth factor-ß in wound site, which indicate better angiogenesis, and better on-site cell proliferation in wound site, respectively. Those results are further demonstrated by immunohistochemical and immunofluorescence staining. Consequently, as-prepared hydrogel dressing shows promising potential to perform better therapy efficacy in clinic for accelerating wound healing.