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A completely confluent endothelial cell (EC) monolayer is required to maintain proper vascular function in small diameter tissue-engineered vascular graft (TEVG). However, the most effective method for EC attachment to the luminal surface and formation of an entire endothelium layer that works in vitro remains a complicated challenge that requires urgent resolution. Although pulsatile flow has been shown to be better suited for the generation of functional endothelium, the optimal frequency setting is unknown. Several pulsatile flow frequencies were used to implant rat bone mesenchymal stem cells (MSC) into the lumen of decellularized porcine carotid arteries. The endothelium's integrity and cell activity were investigated in order to determine the best pulse frequency settings. The results showed that MSC were maximally preserved and exhibited maximal morphological changes with improved endothelialization performance in response to increased pulse stimulation frequency. Increased pulse frequency stimulation stimulates the expression of mechanoreceptor markers, cytoskeleton reorganization in the direction of blood flow, denser skeletal proteins fibronectin, and stronger intercellular connections when compared to constant pulse frequency stimulation. MSC eventually develops an intact endothelial layer with anti-thrombotic properties on the inner wall of the decellularized tubular lumen. Conclusion: The decellularized vessels retain the three-dimensional structure of the vasculature, have a surface topography suitable for MSC growth, and have good mechanical properties. By increasing the frequency of pulsed stimulation, MSC endothelialize the lumen of the decellularized vasculature. It is expected to have anti-thrombotic and anti-neointimal hyperplasia properties after implantation, ultimately improving the patency of TEVG.

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.

A novel drug eluting retrievable vena cava filter (RVCF) with a heparin-modified poly(ε-caprolactone) (hPCL) coating containing rapamycin was prepared by electrospraying. The in vitro drug release pattern showed that the encapsulated rapamycin in the coating can be sustainably released within one month, whereas activated partial thromboplastin time (APTT) and in vitro cell culture showed that the drug eluting RVCF can effectively extend blood clotting time and inhibit smooth muscle cell (SMC) and endothelial cell (EC) proliferation, respectively. The as-prepared drug eluting RVCF and corresponding commercial RVCF were implanted into the vena cava of sheep. The retrieval operation at a predetermined time point showed that the drug eluting RVCF had a much higher retrieval rate than the commercial RVCF. Comprehensive investigations, including histological, immunohistological and immunofluorescence analyses, on explanted veins were carried out. The results demonstrated that the as-prepared RVCF possessed excellent antihyperplasia properties in vivo, significantly improving the retrieval rate and extending the in vivo dwelling time in sheep. Consequently, the drug eluting RVCF has promising potential for application in the clinic to improve RVCF retrieval rates.

A polyrotaxane-containing triblock copolymer (PRTBP) was synthesized via ATRP of NIPPAAm initiated by the self-assembly of α-cyclodextrins (α-CDs) with distal 2-bromopropionyl end-capped poly(caprolactone) (Br–PCL–Br) in water at 25 °C. After that, an azobenzene group was introduced into the polyrotaxane block via the hydroxyl of threaded α-CD to get azo-substituted PRTBP (APRTBP). The structure was characterized in detail by 1H NMR, FTIR and WXRD techniques. Its thermal and light responsive properties were demonstrated by turbidity measurements and UV spectroscopy, respectively. Furthermore, micelles with diameters of around 100 nm were prepared from APRTBP in aqueous solution. Dynamic laser scattering (DLS) measurements demonstrated that the micelles contracted under UV irradiation and successively expanded under visible light, which offers a reversible on–off switch for controlling the drug release behavior of micelles. Consequently, the in vitro drug release curve, which is similar to the pharmacokinetic curve of multiple dosing administrations, was achieved when UV and visible light were applied alternatively to simulate on–off states for drug release. It also showed that the micelle possessed a significantly higher release rate and higher cumulative release amount under UV irradiation than those under visible light. Furthermore, the low critical solution temperature (LCST) of NIPPAAm blocks in APRTBP can be used as another switch to trigger the drug release as implied by in vitro drug release tests using doxorubicin (DOX) as the model drug. Considering its interesting dual stimuli-responsiveness and on–off switch-like behaviors resulting from dual responsiveness, APRTBP shows considerable potential as a candidate for controlled drug delivery systems and other possible biomedical applications.

Nerve regeneration and repair still remain a huge challenge for both central nervous and peripheral nervous system. Although some therapeutic substances, including neuroprotective agents, clinical drugs and stem cells, as well as various growth factors, are found to be effective to promote nerve repair, a carrier system that possesses a sustainable release behavior, in order to ensure high on-site concentration during the whole repair and regeneration process, and high bioavailability is still highly desirable. Hydrogel, as an ideal delivery system, has an excellent loading capacity and sustainable release behavior, as well as tunable physical and chemical properties to adapt to various biomedical scenarios; thus, it is thought to be a suitable carrier system for nerve repair. This paper reviews the structure and classification of hydrogels and summarizes the fabrication and processing methods that can prepare a suitable hydrogel carrier with specific physical and chemical properties. Furthermore, the modulation of the physical and chemical properties of hydrogels is also discussed in detail in order to obtain a better therapeutic effect to promote nerve repair. Finally, the future perspectives of hydrogel microsphere carriers for stroke rehabilitation are highlighted.

The tubular porous poly(ɛ-caprolactone) (PCL) scaffold was fabricated by electrospinning. After then, the scaffold's surface was firstly eroded by hexyldiamine to endow amine group, and heparin was covalently grafted to the surface to get surface heparin modified scaffold (ShPCL scaffold). It was found that ShPCL scaffold can induce smooth muscle cells (SMCs) to penetrate the scaffold surface, while the SMCs cannot penetrate the surface of PCL scaffold. Subsequently, the rabbit SMCs were seeded on the ShPCL scaffold and cultured for 14 days. It was found the expression of α-smooth muscle actin in ShPCL scaffold maintained much higher level than that in culture plate, which implied the SMC differentiation in ShPCL scaffold. Furthermore, the immunefluorescence staining of the cross-sections of ShPCL scaffold exhibited the expression of calponin in ShPCL scaffold can be detected after 7 and 14 days, whereas the expression of smooth muscle myosin heavy chain can also be detected at 14 days. These results proved that penetrated SMCs preferably differentiated in to contractile phenotype. The successful SMC penetration and the contractile phenotype expression implied ShPCL scaffold is a suitable candidate for regenerating smooth muscle layer in vascular tissue engineering. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 2806-2815, 2017.

PCL-heparin conjugates were synthesized by coupling mono-hydroxyl terminated PCL (Mn = 2000-10000 g/mol) with heparin via EDC/NHS chemistry. The conjugates enabled to self-assemble into the core-shell nanoparticles in around 100 nm diameter to load binary anti-cancer drugs. Lipophilic and neutral paclitaxel (PTX) was first encapsulated in the core, and then hydrophilic and positive charged doxorubicin (DOX) was incorporated into the negative charged shell of PTX loaded nanoparticles via the electrostatic interaction. The in vitro release profiles of the binary-drug loaded nanoparticles revealed that both PTX and DOX were sustainably released from the particles but behaved differently. The release of DOX was pH dependent, ensuring more drug to be released in the tumor cells than in the normal ones. Hence these particles were featured by a sequential controlled drug delivery behavior with a significant cytotoxicity to cervical cancer (Hela cell) and breast cancer (MDA-MB-321) cells. The CLSM observations clearly indicated that both loaded PTX and DOX aggregated in the nucleus of tumor cells to exert their anti-tumor pharmacodynamic effect on the cells.

A novel diisocyanate, i. e. lysine ethyl ester diisocyanate (LDI), was prepared by the present authors. Poly (epsilon-caprolactone) (PCL) (M(n) = 2000) was used for reacting with LDI to form prepolymer, and then the chain was extended with butanediol (BDO) to form polyurethane (PU). PU was characterized by gel permeation chromatography, FTIR and 1H-NMR. Mechanical properties test revealed that PU possesses excellent tensile strength. Hydrolytic degradation and enzymatic degradation of PU films showed that PU is biodegradable. Finally, vascular scaffold of PU was fabricated by electrospinning. Morphological and biomechanical properties of scaffold were examined. The tensile strength was 8MPa, suture retention strength 12N, porosity 75% and burst pressure strength 150-170 kPa. Cytotoxicity and cell adhesion showed that PU scaffolds are biocompatible. These results demonstrate that PU vascular scaffolds possess excellent physical strength and biocompatibility and can be developed as substitutes for native blood vessels.

To explore the method of preparing the electrospinning of synthesized triblock copolymers of epsilon-caprolactone and L-lactide (PCLA) for the biodegradable vascular tissue engineering scaffold and to investigate its biocompatibility in vitro.The biodegradable vascular tissue engineering scaffold was made by the electrospinning process of PCLA. A series of biocompatibility tests were performed. Cytotoxicity test: the L929 cells were cultured in 96-well flat-bottomed plates with extraction media of PCLA in the experimental group and with the complete DMEM in control group, and MTT method was used to detect absorbance (A) value (570 nm) every day after culture. Acute general toxicity test: the extraction media and saline were injected into the mice's abdominal cavity of experimental and control groups, respectively, and the toxicity effects on the mice were observed within 72 hours. Hemolysis test: anticoagulated blood of rabbit was added into the extracting solution, saline, and distilled water in 3 groups, and MTT method was used to detect A value in 3 groups. Cell attachment test: the L929 cells were seeded on the PCLA material and scanning electron microscope (SEM) observation was performed 4 hours and 3 days after culture. Subcutaneous implantation test: the PCLA material was implanted subcutaneously in rats and the histology observation was performed at 1 and 8 weeks.Scaffolds had the characteristics of white color, uniform texture, good elasticity, and tenacity. The SEM showed that the PCLA ultrafine fibers had a smooth surface and proper porosity; the fiber diameter was 1-5 microm and the pore diameter was in the range of 10-30 microm. MTT detection suggested that there was no significant difference in A value among 3 groups every day after culturing (P0.05). The mice in 2 groups were in good physical condition and had no respiratory depression, paralysis, convulsion, and death. The hemolysis rate was 1.18% and was lower than the normal level (5%). The SEM showed a large number of attached L929 cells were visible on the surface of the PCLA material at 4 hours after implantation and the cells grew well after 3 days. The PCLA material was infiltrated by the inflammatory cells after 1 week. The inflammatory cells reduced significantly and the fiber began abruption after 8 weeks.The biodegradable vascular tissue engineering scaffold material made by the electrospinning process of PCLA has good microstructure without cytotoxicity and has good biocompatibility. It can be used as an ideal scaffold for vascular tissue engineering.

To investigate the effect of surface property of different polyether-ester block copolymers [poly(ethylene glycol-terephthalate)/poly(butylene terephthalate), PEGT/PBT] on the growth of smooth muscle cells (SMCs) and endothelial cells(ECs).Three kinds of copolymers were synthesized, which were 1000-T20 (group A), 1000PEGT70/PBT30 (group B) and 600PEGT70/PBT30 (group C). The water-uptake and contact angle of three polyether-ester membranes were determined. The canine aorta smooth muscle cells and external jugular vein endothelial cells were primarily harvested, subcultured, and then identified. The proliferation of SMCs and ECs on the different polyether-ester membranes were investigated.The water-uptake of three copolymers arranged as the sequence of group Cgroup Agroup B, and contact angle as the sequence of group Cgroup Agroup B, indicating group B being more hydrophilic. However, smooth muscle cells and endothelial cells grew poorly on the membrane of group B after low density seeding, but proliferated well on the membranes of group A and group C.In contrast with more hydrophilic 1000PEGT70/PBT30, moderately hydrophilic 1000-T20 and 600PEGT70/PBT30 has better compatibility with vascular cells. The above results indicate that the vascular cells can grow well on moderately hydrophilic PEGT/PBT and that PEGT/PBT can be used in vascular tissue engineering.