Vascular Tissue Engineering Applications Research Articles

Surface Modification by Nanobiomaterials for Vascular Tissue Engineering Applications.

Treatment of cardiovascular disease has achieved great success using artificial implants, particularly synthetic-polymer made grafts. However, thrombus formation and restenosis are the current clinical problems need to be conquered. New biomaterials, modifying the surface of synthetic vascular grafts, have been created to improve long-term patency for the better hemocompatibility. The vascular biomaterials can be fabricated from synthetic or natural polymers for vascular tissue engineering. Stem cells can be seeded by different techniques into tissue-engineered vascular grafts in vitro and implanted in vivo to repair the vascular tissues. To overcome the thrombogenesis and promote the endothelialization effect, vascular biomaterials employing nanotopography are more bio-mimic to the native tissue made and have been engineered by various approaches such as prepared as a simple surface coating on the vascular biomaterials. It has now become an important and interesting field to find novel approaches to better endothelization of vascular biomaterials. In this article, we focus to review the techniques with better potential improving endothelization and summarize for vascular biomaterial application. This review article will enable the development of biomaterials with a high degree of originality, innovative research on novel techniques for surface fabrication for vascular biomaterials application.

Preparation and characterization of nanoclay-hydrogel composite support-bath for bioprinting of complex structures

Three-dimensional bioprinting of cell-laden hydrogels in a sacrificial support-bath has recently emerged as a potential solution for fabricating complex biological structures. Physical properties of the support-bath strongly influence the bioprinting process and the outcome of the fabricated constructs. In this study, we reported the application of a composite Pluronic-nanoclay support-bath including calcium ions as the crosslinking agent for bioprinting of cell-laden alginate-based hydrogels. By tuning the rheological properties, a shear-thinning composite support-bath with fast self-recovery behavior was yielded, which allowed continuous printing of complex and large-scale structures. The printed structures were easily and efficiently harvested from the support-bath without disturbing their shape fidelity. Moreover, the results showed that support-bath assisted bioprinting process did not influence the viability of cells encapsulated within hydrogel. This study demonstrates that Pluronic-nanoclay support-bath can be utilized for bioprinting of complex, cell-laden constructs for vascular and other tissue engineering applications.

Design and comprehensive assessment of a biomimetic tri-layer tubular scaffold via biodegradable polymers for vascular tissue engineering applications.

Considering the structural complexity of the native artery wall and the limitations of current treatment strategies, developing a biomimetic tri-layer tissue-engineered vascular graft is a major developmental direction of vascular tissue regeneration. Biodegradable polymers exhibit adequate mechanical characteristics and feasible operability, showing potential prospects in the construction of tissue engineering scaffold. Herein, we present a bio-inspired tri-layer tubular graft using biodegradable polymers to simulate natural vascular architecture. The inner layer made of polycaprolactone (PCL) nanofiber possesses high tensile strength and contributed to endothelial cell adhesion and proliferation. The middle layer consisted of poly(lactic-co-glycolide) (PLGA) with a three-dimensional porous structure is appropriate for vascular smooth muscle cells (SMCs) penetration. The polyurethane (PU) was selected to be the outer layer, aiming to hold the entire tubular structure, suggesting superior mechanical properties and ideal biocompatibility. Adhesion between independent layers is achieved by thermal crosslinking. The compliance, burst pressure and suture retention force of the tubular scaffold were 2.50±1.60%, 2737.73±583.41mmHg and 13.06±1.89N, respectively. The in vivo study of subcutaneous implantation for 8weeks demonstrated the biomimetic tri-layer vascular graft could maintain intimal integrity, cell infiltration, collagen deposition and scaffold biodegradation. Overall, the biomimetic tri-layer vascular graft promises to be a potential candidate for vascular replacement and regeneration.

Tethering transforming growth factor β1 to soft hydrogels guides vascular smooth muscle commitment from human mesenchymal stem cells

Mesenchymal stem cells (MSCs) hold great promise for vascular smooth muscle regeneration. However, most studies have mainly relied on extended supplementation of sophisticated biochemical regimen to drive MSC differentiation towards vascular smooth muscle cells (vSMCs). Herein we demonstrate a concomitant method that exploits the advantages of biomimetic matrix stiffness and tethered transforming growth factor β1 (TGF-β1) to guide vSMC commitment from human MSCs. Our designed poly(ethylene glycol) hydrogels, presenting a biomimetic stiffness and tethered TGF-β1, provide an instructive environment to potently upregulate smooth muscle marker expression in vitro and in vivo. Importantly, it significantly enhances the functional contractility of vSMCs derived from MSCs within 3 days. Interestingly, compared to non-tethered one, tethered TGF-β1 enhanced the potency of vSMC commitment on hydrogels. We provide compelling evidence that combining stiffness and tethered TGF-β1 on poly(ethylene glycol) hydrogels can be a promising approach to drastically enhance maturation and function of vSMCs from stem cell differentiation in vitro and in vivo. Statement of SignificanceA fast, reliable and safe regeneration of vascular smooth muscle cells (vSMCs) from stem cell differentiation is promising for vascular tissue engineering and regenerative medicine applications, but remains challenging. Herein, a photo-click hydrogel platform is devised to recapitulate the stiffness of vascular tissue and appropriate presentation of transforming growth factor β1 (TGF-β1) to guide vSMC commitment from mesenchymal stem cells (MSCs). We demonstrate that such concomitant method drastically enhanced regeneration of mature, functional vSMCs from MSCs in vitro and in vivo within only a 3-days span. This work is not only of fundamental scientific importance, revealing how physiochemical factors and the manner of their presentation direct stem cell differentiation, but also attacks the long-standing difficulty in regenerating highly functional vSMCs within a short period.

Bioresorbable silk grafts for small diameter vascular tissue engineering applications: In vitro and in vivo functional analysis

The success of tissue-engineered vascular graft (TEVG) predominantly relies on the selection of a suitable biomaterial and graft design. Natural biopolymer silk has shown great promise for various tissue-engineering applications. This study is the first to investigate Indian endemic non-mulberry silk (Antheraea assama-AA) – which inherits naturally superior mechanical and biological traits (e.g., RGD motifs) compared to Bombyx mori-BM silk, for TEVG applications. We designed bi-layered biomimetic small diameter AA-BM silk TEVGs adopting a new fabrication methodology. The inner layer showed ideally sized (~40 µm) pores with interconnectivity to allow cellular infiltration, and an outer dense electrospun layer that confers mechanical resilience. Biodegradation of silk TEVGs into amino acids as resorbable byproducts corroborates their in vivo remodeling ability. Following our previous reports, we surgically implanted human adipose tissue-derived stromal vascular fraction (SVF) seeded silk TEVGs in Lewis rats as abdominal aortic interposition grafts for 8 weeks. Adequate suture retention strength (0.45 ± 0.1 N) without any blood seepage post-implantation substantiate the grafts’ viability. AA silk-based TEVGs showed superior animal survival and graft patency compared to BM silk TEVGs. Histological analysis revealed neo-tissue formation, host cell infiltration and graft remodeling in terms of extracellular matrix turnover. Altogether, this study demonstrates promising aspects of AA silk TEVGs for vascular tissue engineering applications. Statement of significanceClinical ‘off the shelf’ implementation of tissue-engineered vascular grafts (TEVGs) remains a challenge. Achieving optimal blood vessel regeneration requires the use of bioresorbable materials having suitable degradation rates while producing minimal or no toxic byproducts. Host cell recruitment and preventing acute thrombosis are other pre-requisites for successful graft remodeling. In this study, for the first time we explored the use of naturally derived Indian endemic non-mulberry Antheraea assama silk in combination with Bombyx mori silk for TEVG applications by adopting a new biomimetic approach. Our bi-layered silk TEVGs were optimally porous, mechanically resilient and biodegradable. In vivo implantation in rat aorta showed long-term patency and graft remodeling by host cell infiltration and extracellular matrix deposition corroborating their clinical feasibility.

Tripeptide-induced modulation of mesenchymal stem cell biomechanics stimulates proliferation and wound healing.

We demonstrate the ability of two tripeptides to promote proliferation and modulate the mechanical properties of human mesenchymal stem cells (hMSCs). Notably, Young's modulus of peptide-treated hMSCs was found to be ∼2 fold higher compared to the control group. These peptides promoted wound healing in hMSCs, without stimulating osteogenic and adipogenic differentiation, thus showing high potential in vascular tissue engineering applications.

Long Term Evaluation of Nanofibrous, Bioabsorbable Polycarbonate Urethane Grafts for Small Diameter Vessel Replacement in Rodents

Biodegradable materials for in situ vascular tissue engineering could meet the increasing clinical demand for sufficient synthetic small diameter vascular substitutes in aortocoronary bypass and peripheral vascular surgery. The aim of this study was to design a new degradable thermoplastic polycarbonate urethane (dPCU) with improved biocompatibility and optimal biomechanical properties. Electrospun conduits made from dPCU were evaluated in short and long term follow up and compared with expanded polytetrafluoroethylene (ePTFE) controls. Both conduits were investigated prior to implantation to assess their biocompatibility and inflammatory potential via real time polymerase chain reaction using a macrophage culture. dPCU grafts (n=28) and ePTFE controls (n=28) were then implanted into the infrarenal abdominal aorta of Sprague-Dawley rats. After seven days, one, six, and 12 months, grafts were analysed by histology and immunohistochemistry (IHC) and assessed biomechanically. Anti-inflammatory signalling was upregulated in dPCU conduits and increased significantly over time invitro. dPCU and ePTFE grafts offered excellent long and short term patency rates (92.9% in both groups at 12 months) in the rat model without dilatation or aneurysm formation. In comparison to ePTFE, dPCU grafts showed transmural ingrowth of vascular specific cells resulting in a structured neovessel formation around the graft. The graft material was slowly reduced, while the compliance of the neovessel increased over time. The newly designed dPCU grafts have the potential to be safely applied for in situ vascular tissue engineering applications. The degradable substitutes showed good invivo performance and revealed desirable characteristics such as biomechanical stability, non-thrombogenicity, and minimal inflammatory response after long term implantation.

Development and mechanical characterization of bilayer tubular scaffolds for vascular tissue engineering applications

Poly(l-lactide-co-e-caprolactone) (PLCL) is a potential material to fabricate scaffolds for vascular tissue engineering. In this work, scaffolds with a multilayered structure comprising a combination of porous and fibrous structures were developed. PLCL was used to fabricate the inner layer of the tubular scaffolds using the freeze-drying technique. The inner layer was then covered by an outer layer fabricated by the melt-spinning technique. The morphology and physical structure of the scaffolds were evaluated through SEM micrographs. The freeze-drying technique formed a porous structure, while the melt-spinning method formed a fibrous structure for the bilayer scaffolds. Physicochemical properties were also investigated by DSC and FTIR measurements; no new functional groups were found to have formed during the freeze-drying or melt-spinning processes. Mechanical properties and fracture mechanism under a tensile loading condition were carefully analyzed to characterize the deformation and fracture behaviors. It was found that the bilayer scaffolds exhibited better mechanical properties than single-layer scaffolds with higher maximum stress at 675.41 kPa, strain at maximum stress at 69.42%, fracture energy at 412.45 kJ/m3 and burst pressure at 147.93 kPa. Porosity, swelling ratio and in vitro biodegradation were measured to ensure its suitability for vascular tissue applications. The bilayer scaffolds with both porous and fibrous structures meet the requirements for vascular tissue engineering.

Endothelial/Mesenchymal Stem Cell Crosstalk Within Bioprinted Cocultures.

The development of viable tissue surrogates requires a vascular network that sustains cell metabolism and tissue development. The coculture of endothelial cells (ECs) and mesenchymal stem cells (MSCs), the two key players involved in blood vessel formation, has been heralded in tissue engineering (TE) as one of the most promising approaches for scaffold vascularization. However, MSCs may exert both proangiogenic and antiangiogenic role. Furthermore, it is unclear which cell type is responsible for the upregulation of angiogenic pathways observed in EC:MSC cocultures. There is disagreement on the proangiogenic action of MSCs, as they have also been shown to negatively affect the formation of capillary networks. To address these issues, we investigated the regulation of key angiogenic pathways in scaffolds hosting different EC:MSC ratios fabricated through extrusion-based bioprinting. Human ECs were cocultured with either rat or human MSCs, and the regulation of fundamental angiogenic and arteriogenic pathways was analyzed through DNA, gene, and protein expression. The use of a hybrid human/rat coculture system facilitated pinpointing each cell type role in the regulation of specific genes and showed that MSCs exert a dose-dependent inhibitory effect on the EC expression of angiogenic factors within the first 24 h. Within a week of coculture, MSCs exert a proangiogenic effect, as corroborated in human/human bioprinted cocultures. Interestingly, juxtacrine signaling promoted secretion of the angiogenic factor vascular endothelial growth factor in direct cocultures (EC and MSC co-encapsulated), while paracrine signaling encouraged secretion of the arteriogenic factor platelet-derived growth factor in indirect cocultures (adjacent bioprinting of EC-laden and MSC-laden scaffolds). Overall, the use of a bioprinted system to elucidate EC:MSC interplay allows rapid leveraging of the data for novel vascular TE applications. Despite the transitory negative effect early in the culture, MSC presence is necessary for the regulation of pathways involved in arteriogenesis. With further validation in vivo, this study provides a possible explanation to the controversial findings present in literature and shows how MSC effect on angiogenic pathway regulation mimics the dynamics of blood vessel formation reported in literature and normally occurring in vivo. Impact Statement The coculturing of endothelial cells (ECs) and mesenchymal stem cells (MSCs) holds great promise in tissue engineering for the development of prevascularized tissue constructs. Yet, different studies report conflicting results on the role of MSCs, which can either support or inhibit vasculature formation. Furthermore, it is unclear how each cell type modulates distinct pathways involved in angiogenesis when cocultured. Using bioprinted hybrid coculture systems, we show that MSCs have both a time- and dose-dependent effect on the gene and protein expression of key angiogenic and arteriogenic factors by ECs. These findings, obtained in translationally relevant setup, can readily inform the design of vascularized scaffolds.

PCL/sulfonated keratin mats for vascular tissue engineering scaffold with potential of catalytic nitric oxide generation.

Heparin-like polymers have a good anticoagulant effect due to some groups similar to heparin. Herein, sulfonated keratin(SK) was prepared by chain transfer radical polymerization of 3-sulfopropyl methacrylate(SPMA) to improve blood coagulation nature of keratin. Poly(ε-caprolactone)(PCL)/SK nanofibrous mats with the ratio of 7 and 3 were then fabricated by electrospinning. In vitro cytotoxicity and blood compatibility tests were performed to assess the biocompatibility. Viability of NIH 3T3 cells on PCL/SK mats was higher than that on the pristine PCL mats, indicating their good cytocompatibility. These sulfonated keratin-containing mats enhanced endothelial cell growth, while inhibited smooth muscle cell proliferation and reduced platelet adhesion in the presence of GSH and GSNO, as a result of NO generation. Furthermore, the biocomposite mats prolonged the activated partial thromboplastin time(APTT) effectively without hemolysis. Taken together, PCL/SK mats are potential for applications in vascular tissue engineering.

Fabrication and Comprehensive Characterization of Biomimetic Extracellular Matrix Electrospun Scaffold for Vascular Tissue Engineering Applications

The collagen–hyaluronic acid oligosaccharides (collagen–HA) complex was obtained by covalent attachment using EDC/NHS. The cross-linked product collagen–HA had been confirmed by Fourier transform infrared spectra (FTIR) and the sulfuric acid–carbazole colorimetry, and factors that affect the cross-linking process were investigated. Electrospinning of collagen–HA complex in hexafluoroisopropanol was investigated for the biomimetic nanostructure and biocompatible vascular tissue-engineered inner-layer scaffold. The morphology of the electrospun collagen–HA nanofibers with a series of concentrations was observed by scanning electron microscopy. The thermal behavior and chemical properties of the fabricated scaffolds were characterized using dynamic scanning calorimetry and FTIR after being stabilized by glutaraldehyde vapor. The cell attachment, morphology and proliferation of porcine iliac artery endothelial cells (PIECs) on the electrospun scaffolds were also evaluated. The results indicate that the biomimetic matrix collagen–HA electrospun nanofibrous scaffold could promote PIECs proliferation and may be a better candidate with endothelial potential for the vascular tissue-engineered inner-layer scaffold.

Amnion-Based Scaffold with Enhanced Strength and Biocompatibility for In Vivo Vascular Repair.

This study aimed at developing an amnion-based scaffold suitable for vascular tissue engineering applications and in vivo usage. We successfully produced a multilayered scaffold with improved biomechanical properties and biocompatibility for in vivo vascular implantation. Our approach not only offers an allogeneic "off-the-shelf" solution for clinical use but also it provides the possibility of personalized medicine using a patient's own amnion and stem cells for the production of tissue engineered grafts for reconstructive heart surgery.

Multistructured vascular patches constructed via layer-by-layer self-assembly of heparin and chitosan for vascular tissue engineering applications

With the growing prevalence of cardiovascular diseases, developing applicable vascular patches has become a pressing issue. In this work, we used layer-by-layer (LbL) self-assembly technique to construct vascular patches of polyelectrolyte multilayer (PEM) by alternately depositing heparin and chitosan onto the substrate polyurethane-coated decellularized scaffold (PU/DCS). The biocompatibilities of these PEM vascular patches were evaluated, and the in vivo performance in a porcine model was investigated with B ultrasound, Doppler spectrum and computed tomography angiography (CTA). Compared with the substrate PU/DCS, the PEM vascular patches had improved biocompatibility, including decreased hemolysis rate, prolonged in vitro coagulation time and enhanced resistance to platelet adhesion. They also showed the enhancement in the attachment and proliferation of endothelial progenitor cells. Additionally, CTA indicated that the PEM vascular patches could maintain the long-term patency of the surgical arteries (5 months) while the substrate PU/DCS blocked the surgical arteries even at 2-week implantation. Therefore, the PEM vascular patches showed great potential in vascular tissue engineering applications. This work also provided a feasible strategy to construct multistructured vascular patches and other biomaterials.

Evaluation of an elastic decellularized tendon‐derived scaffold for the vascular tissue engineering application

Due to the limited success rate of currently available vascular replacements, tissue engineering has received tremendous attention in recent years. A main challenge in the field of regenerative medicine is creating a mechanically functional tissue with a well-organized extracellular matrix, particularly of collagen and elastin. In this study, the native collagen scaffold derived from decellularized tendon sections, as a scaffold having the potential to be used for vascular tissue engineering applications, was studied. We showed that the elasticity of the scaffolds was improved when crosslinked with the bovine elastin. The effect of different concentrations of elastin on mechanical properties of the collagen scaffolds was evaluated of which 15% elastin concentration was selected for further analysis based on the results. Addition of 15% elastin to collagen scaffolds significantly decreased Young's modulus and the tensile stress at the maximum load and increased the tensile strain at the maximum load of the constructs as compared to those of the collagen scaffolds or control samples. Moreover, tubular elastin modified collagen scaffolds showed significantly higher burst pressure compared to the control samples. Smooth muscle cells and endothelial cells cultured on the elastin modified collagen scaffolds showed high viability (>80%) after 1, 3, and 7 days. Furthermore, the cells showed a high tendency to align with the collagen fibers within the scaffold and produced their own extracellular matrix over time. In conclusion, the results show that the decellularized tendon sections have a great potential to be used as scaffolds for vascular tissue engineering applications. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1225-1234, 2019.

Blood-compatible Polyaniline Coated Electrospun Polyurethane Fiber Scaffolds for Enhanced Adhesion and Proliferation of Human Umbilical Vein Endothelial Cells

The endothelialization and anti-thrombotic abilities of tissue engineered vascular scaffolds are considered to be effective properties for improving the performance small-caliber vascular scaffolds. For this purpose, we designed and developed electrically conductive fibrous scaffolds based on polyaniline coated polyurethane (PANI-PU) electrospun fibers for vascular tissue engineering applications. The porosity of PANI-PU fibers was 75.27±2.04 %. The obtained PANI-PU fibers were characterized by SEM observations, XPS analysis, water contact angle (WCA) measurement and mechanical property. The PANI functionalization aimed to improve the performance of anticoagulation and endothelialization. The WCA of PAIN-PU decreased to 35° from 135° of PU fibers. Blood compatibility and cytocompatibility were compared before and after PANI coating. The adhered platelet cells on PANI-PU was 6.87×105/cm2 and plasma recalcification time was 123 s. Platelet adhesion and plasma recalcification time test showed that the PANI-PU scaffolds had a certain anticoagulant effect. The hemolysis rate of PANI-PU fibers was 0.14 %, which showed that the PANI-PU scaffolds could be used as blood contact materials. The observation of endothelial cell proliferation and morphology in human umbilical vein endothelial cells showed that PANI-PU fibers were more beneficial to cell adhesion, proliferation and extension than that of PU fibers. The results demonstrates the PANI coated electrospun PU fibers have great potential in application as small-diameter vascular grafts and this work shows new insights into conductive scaffolds for vascular tissue engineering.

Determination of critical shear stress for maturation of human pluripotent stem cell‐derived endothelial cells towards an arterial subtype

Human pluripotent stem cell-derived endothelial cells (hPSC-ECs) present an attractive alternative to primary EC sources for vascular grafting. However, there is a need to mature them towards either an arterial or venous subtype. A vital environmental factor involved in the arteriovenous specification of ECs during early embryonic development is fluid shear stress; therefore, there have been attempts to employ adult arterial shear stress conditions to mature hPSC-ECs. However, hPSC-ECs are naïve to fluid shear stress, and their shear responses are still not well understood. Here, we used a multiplex microfluidic platform to systematically investigate the dose-time shear responses on hPSC-EC morphology and arterial-venous phenotypes over a range of magnitudes coincidental with physiological levels of embryonic and adult vasculatures. The device comprised of six parallel cell culture chambers that were individually linked to flow-setting resistance channels, allowing us to simultaneously apply shear stress ranging from 0.4 to 15 dyne/cm 2 . We found that hPSC-ECs required up to 40 hr of shear exposure to elicit a stable phenotypic change. Cell alignment was visible at shear stress <1 dyne/cm 2 , which was independent of shear stress magnitude and duration of exposure. We discovered that the arterial markers NOTCH1 and EphrinB2 exhibited a dose-dependent increase in a similar manner beyond a threshold level of 3.8 dyne/cm 2 , whereas the venous markers COUP-TFII and EphB4 expression remained relatively constant across different magnitudes. These findings indicated that hPSC-ECs were sensitive to relatively low magnitudes of shear stress, and a critical level of ~4 dyne/cm 2 was sufficient to preferentially enhance their maturation into an arterial phenotype for future vascular tissue engineering applications.

Poly(trimethylene carbonate-co-L-lactide) electrospun scaffolds for use as vascular grafts.

Currently, there is great clinical need for suitable synthetic grafts that can be used in vascular diseases. Synthetic grafts have been successfully used in medium and large arteries, however, their use in small diameter vessels is limited and presents a high failure rate. In this context, the aim of this study was to develop tissue engineering scaffolds, using poly(trimethylene carbonate-co-L-lactide) (PTMCLLA), for application as small diameter vascular grafts. For this, copolymers with varying trimethylene carbonate/lactide ratios – 20/80, 30/70, and 40/60 – were submitted to electrospinning and the resulting scaffolds were evaluated in terms of their physicochemical and biological properties. The scaffolds produced with PTMCLLA 20/80, 30/70, and 40/60 showed smooth fibers with an average diameter of 771±273, 606±242, and 697±232 nm, respectively. When the degradation ratio was evaluated, the three scaffold groups had a similar molecular weight (M w) on the final day of analysis. PTMCLLA 30/70 and 40/60 scaffolds exhibited greater flexibility than the PTMCLLA 20/80. However, the PTMCLLA 40/60 scaffolds showed a large wrinkling and their biological properties were not evaluated. The PTMCLLA 30/70 scaffolds supported the adhesion and growth of mesenchymal stem cells (MSCs), endothelial progenitor cells, and smooth muscle cells (SMCs). In addition, they provided a spreading of MSCs and SMCs. Given the results, the electrospun scaffolds produced with PTMCLLA 30/70 copolymer can be considered promising candidates for future applications in vascular tissue engineering.

Modified Bi-Layered Polycaprolactone Nanofiber Scaffolds for Vascular Tissue Engineering Applications

Modified Bi-Layered Polycaprolactone Nanofiber Scaffolds for Vascular Tissue Engineering Applications

Facile preparation of a controlled-release tubular scaffold for blood vessel implantation

Salvianic acid-loaded mesoporous silica nanoparticles into gelatin/polyurethane bilayered small-diameter tubular scaffold were prepared by thermally induced phase separation (TIPS) and electrospinning. Mesoporous silica nanoparticles (MSNs) were selected as carriers to load salvianic acid (SAL). The SAL-loaded MSNs (SAL@MSNs) with an optimized SAL loading efficiency of 10% was initially dispersed in gelatin solution and under a vacuum freeze-drying process as an inner layer of vascular scaffolds. Then, poly(ester-urethane)urea (C-PEEUU) nanofibers were electrospun outside the SAL@MSNs/Gelatin vascular scaffold to strengthen the spongy matrix. The loaded SAL within the MSNs/Gelatin/C-PEEUU bilayered small-diameter tubular scaffold showed a sustained release profile and good mechanical properties. In addition, the drug-loaded composite scaffold showed no unfavorable effects on the adhesion and proliferation of endothelial cells. Moreover, no intimal hyperplasia and acute thrombosis was observed in the short-term implantation in rabbit's carotid artery. We believe the SAL@MSNs/Gelatin/C-PEEUU bilayered vascular scaffolds have promise for vascular tissue engineering applications.

Substrate topography interacts with substrate stiffness and culture time to regulate mechanical properties and smooth muscle differentiation of mesenchymal stem cells.

Substrate stiffness and topography are two powerful means by which mesenchymal stem cells (MSCs) activities can be modulated. The effects of substrate stiffness on the MSCs mechanical properties were investigated previously, however, the role of substrate topography in this regard is not yet well understood. Moreover, in vessel wall, these two physical cues act simultaneously to regulate cellular function, hence it is important to investigate their cooperative effects on cellular activity. Herein, we investigated the combined effects of substrate stiffness, substrate topography and culture time on the mechanical behavior of MSCs. The MSCs were cultured on the stiff and soft substrates with or without micro-grooved topography for 10 days and their viscoelastic properties and smooth muscle (SM) gene expression were investigated on days 2, 6 and 10. In general, substrate topography significantly interacted with substrate stiffness as well as culture time in the modulation of cell viscoelastic behavior and SM gene expression. The micro-grooved, stiff substrates resulted in the maximum cell stiffness and gene expression of α-actin and h1-calponin, and these values were detected to be minimum in the smooth, soft substrates. The findings can be helpful in the mechano-regulation of MSCs for vascular tissue engineering applications.