Appropriate density of PCL nano-fiber sheath promoted muscular remodeling of PGS/PCL grafts in arterial circulation

Engineering Triphasic Nanocomposite Coatings on Pretreated Mg Substrates for Biomedical Applications

Biodegradable polymer-based nanocomposite coatings provide multiple advantages to modulate the corrosion resistance and cytocompatibility of magnesium (Mg) alloys for biomedical applications. Biodegradable poly(glycerol sebacate) (PGS) is a promising candidate used for medical implant applications. In this study, we synthesized a new PGS nanocomposite system consisting of hydroxyapatite (HA) and magnesium oxide (MgO) nanoparticles and developed a spray coating process to produce the PGS nanocomposite layer on pretreated Mg substrates, which improved the coating adhesion at the interface and their cytocompatibility with bone marrow derived mesenchymal stem cells (BMSCs). Prior to the spray coating process of polymer-based nanocomposites, the Mg substrates were pretreated in alkaline solutions to enhance the interfacial adhesion strength of the polymer-based nanocomposite coatings. The addition of HA and MgO nanoparticles (nHA and nMgO) to the PGS matrix, as well as the alkaline pretreatment of the Mg substrates, significantly enhanced the interfacial adhesion strength when compared with the PGS coating on the nontreated Mg control. The average BMSC adhesion densities were higher on the PGS/nHA/nMgO coated Mg than the noncoated Mg controls under direct contact conditions. Moreover, the addition of nHA and nMgO to the PGS matrix and coating the nanocomposite onto Mg substrates increased the average BMSC adhesion density when compared with the PGS/nHA/nMgO coated titanium (Ti) and PGS coated Mg controls under direct contact. Therefore, the spray coating process of PGS/nHA/nMgO nanocomposites on Mg substrates or other biodegradable metal substrates could provide a promising surface treatment strategy for biodegradable implant applications.

Electrospun poly(ε-caprolactone)/poly(glycerol sebacate) aligned fibers fabricated with benign solvents for tendon tissue engineering

The electrospinning technique is a commonly employed approach to fabricate fibers intended for various tissue engineering applications. The aim of this study is to develop a novel strategy for tendon repair through the use of aligned poly(ε-caprolactone) (PCL) and poly(glycerol sebacate) (PGS) fibers fabricated in benign solvents, and further explore the potential application of PGS in tendon tissue engineering (TTE). The fibers were characterized for their morphological and physicochemical properties; amniotic epithelial stem cells (AECs) were used to assess the fibers teno-inductive and immunomodulatory potential due to their ability to teno-differentiate undergoing first a stepwise epithelial to mesenchymal transition, and due to their documented therapeutic role in tendon regeneration. The addition of PGS to PCL improved the spinnability of the polymer solution, as well as the uniformity and directionality of the so-obtained fibers. The mechanical properties were in the range of most TTE applications, specifically in the case of PCL/PGS 4:1 and 2:1 ratios. Compared to PCL alone, the same ratios also allowed a better AECs infiltration and growth over 7 days of culture, and triggered the activation of tendon-related genes (SCX, COL1, TNMD) and the expression of tenomodulin (TNMD) at the protein level. Concerning the immunomodulatory properties, both PCL and PCL/PGS fibers negatively affected the immunomodulatory profile of AECs, up-regulating both anti-inflammatory (IL-10) and pro-inflammatory (IL-12) cytokines over 7 days of culture. Overall, PCL/PGS 2:1 fibers fabricated with benign solvents proved to be the most suitable composition for TTE application based on their topographical cues, mechanical properties, biocompatibility, and teno-inductive properties.

Gelatin/heparin coated bio-inspired polyurethane composite fibers to construct small-caliber artificial blood vessel grafts

Long-term patency and ability for revascularization remain challenges for small-caliber blood vessel grafts to treat cardiovascular diseases clinically. Here, a gelatin/heparin coated bio-inspired polyurethane composite fibers-based artificial blood vessel with continuous release of NO and biopeptides to regulate vascular tissue repair and maintain long-term patency is fabricated. A biodegradable polyurethane elastomer that can catalyze S-nitrosothiols in the blood to release NO is synthesized (NPU). Then, the NPU core-shell structured nanofiber grafts with requisite mechanical properties and biopeptide release for inflammation manipulation are fabricated by electrospinning and lyophilization. Finally, the surface of tubular NPU nanofiber grafts is coated with heparin/gelatin and crosslinked with glutaraldehyde to obtain small-caliber artificial blood vessels (ABVs) with the ability of vascular revascularization. We demonstrate that artificial blood vessel grafts promote the growth of endothelial cells but inhibit the growth of smooth muscle cells by the continuous release of NO; vascular grafts can regulate inflammatory balance for vascular tissue remodel without excessive collagen deposition through the release of biological peptides. Vascular grafts prevent thrombus and vascular stenosis to obtain long-term patency. Hence, our work paves a new way to develop small-caliber artificial blood vessel grafts that can maintain long-term patency in vivo and remodel vascular tissue successfully.

Polyglycerol sebacate-based elastomeric materials for arterial regeneration

Synthetic vascular grafts are commonly used in patients with severe occlusive arterial disease when autologous grafts are not an option. Commercially available synthetic grafts are confronted with challenging outcomes: they have a lower patency rate than autologous grafts and are currently unable to promote arterial regeneration. Polyglycerol sebacate (PGS), a non-toxic polymer with a tunable degradation profile, has shown promising results as a small-diameter vascular graft component that can support the formation of neoarteries. In this review, we first present an overview of the synthesis and modification of PGS followed by an examination of its mechanical properties. We then report on the performance, degradation, regeneration, and remodeling of PGS-based small-diameter vascular grafts, with a focus on efforts to reduce thrombosis, prevent dilation, and promote cellular residency and extracellular matrix regeneration that resembles the native artery in spatial distribution and organization. We also highlight recent advances in the incorporation of novel in situ cell sources for arterial regeneration and their potential application in PGS-based vascular grafts. Finally, we compare vascular grafts fabricated using PGS-based materials with other elastomeric alternatives.

A multiscale computational model of arterial growth and remodeling including Notch signaling

Blood vessels grow and remodel in response to mechanical stimuli. Many computational models capture this process phenomenologically, by assuming stress homeostasis, but this approach cannot unravel the underlying cellular mechanisms. Mechano-sensitive Notch signaling is well-known to be key in vascular development and homeostasis. Here, we present a multiscale framework coupling a constrained mixture model, capturing the mechanics and turnover of arterial constituents, to a cell-cell signaling model, describing Notch signaling dynamics among vascular smooth muscle cells (SMCs) as influenced by mechanical stimuli. Tissue turnover was regulated by both Notch activity, informed by in vitro data, and a phenomenological contribution, accounting for mechanisms other than Notch. This novel framework predicted changes in wall thickness and arterial composition in response to hypertension similar to previous in vivo data. The simulations suggested that Notch contributes to arterial growth in hypertension mainly by promoting SMC proliferation, while other mechanisms are needed to fully capture remodeling. The results also indicated that interventions to Notch, such as external Jagged ligands, can alter both the geometry and composition of hypertensive vessels, especially in the short term. Overall, our model enables a deeper analysis of the role of Notch and Notch interventions in arterial growth and remodeling and could be adopted to investigate therapeutic strategies and optimize vascular regeneration protocols.

An Assessment of Blood Vessel Remodeling of Nanofibrous Poly(ε-Caprolactone) Vascular Grafts in a Rat Animal Model

The development of an ideal vascular prosthesis represents an important challenge in terms of the treatment of cardiovascular diseases with respect to which new materials are being considered that have produced promising results following testing in animal models. This study focuses on nanofibrous polycaprolactone-based grafts assessed by means of histological techniques 10 days and 6 months following suturing as a replacement for the rat aorta. A novel stereological approach for the assessment of cellular distribution within the graft thickness was developed. The cellularization of the thickness of the graft was found to be homogeneous after 10 days and to have changed after 6 months, at which time the majority of cells was discovered in the inner layer where the regeneration of the vessel wall was found to have occurred. Six months following implantation, the endothelialization of the graft lumen was complete, and no vasa vasorum were found to be present. Newly formed tissue resembling native elastic arteries with concentric layers composed of smooth muscle cells, collagen, and elastin was found in the implanted polycaprolactone-based grafts. Moreover, the inner layer of the graft was seen to have developed structural similarities to the regular aortic wall. The grafts appeared to be well tolerated, and no severe adverse reaction was recorded with the exception of one case of cartilaginous metaplasia close to the junctional suture.

Notch signaling regulates strain-mediated phenotypic switching of vascular smooth muscle cells

Mechanical stimuli experienced by vascular smooth muscle cells (VSMCs) and mechanosensitive Notch signaling are important regulators of vascular growth and remodeling. However, the interplay between mechanical cues and Notch signaling, and its contribution to regulate the VSMC phenotype are still unclear. Here, we investigated the role of Notch signaling in regulating strain-mediated changes in VSMC phenotype. Synthetic and contractile VSMCs were cyclically stretched for 48 h to determine the temporal changes in phenotypic features. Different magnitudes of strain were applied to investigate its effect on Notch mechanosensitivity and the phenotypic regulation of VSMCs. In addition, Notch signaling was inhibited via DAPT treatment and activated with immobilized Jagged1 ligands to understand the role of Notch on strain-mediated phenotypic changes of VSMCs. Our data demonstrate that cyclic strain induces a decrease in Notch signaling along with a loss of VSMC contractile features. Accordingly, the activation of Notch signaling during cyclic stretching partially rescued the contractile features of VSMCs. These findings demonstrate that Notch signaling has an important role in regulating strain-mediated phenotypic switching of VSMCs.

Recombinant DTβ4-inspired porous 3D vascular graft enhanced antithrombogenicity and recruited circulating CD93+/CD34+ cells for endothelialization

Matching material degradation with host remodeling, including endothelialization and muscular remodeling, is important to vascular regeneration. We fabricated 3D PGS-PCL vascular grafts, which presented tunable polymer components, porosity, mechanical strength, and degrading rate. Furthermore, highly porous structures enabled 3D patterning of conjugated heparin-binding peptide, dimeric thymosin β4 (DTβ4), which played key roles in antiplatelets, fibrinogenesis inhibition, and recruiting circulating progenitor cells, thereafter contributed to high patency rate, and unprecedentedly acquired carotid arterial regeneration in rabbit model. Through single-cell RNA sequencing analysis and cell tracing studies, a subset of endothelial progenitor cells, myeloid-derived CD93⁺/CD34⁺ cells, was identified as the main contributor to final endothelium regeneration. To conclude, DTβ4-inspired porous 3DVGs present adjustable physical properties, superior anticoagulating, and re-endothelializing potentials, which leads to the regeneration of small-caliber artery, thus offering a promising tool for vessel replacement in clinical applications.

Pharmacological manipulation of macrophage autophagy effectively rejuvenates the regenerative potential of biodegrading vascular graft in aging body

Declined regenerative potential and aggravated inflammation upon aging create an inappropriate environment for arterial regeneration. Macrophages are one of vital effector cells in the immune microenvironment, especially during biomaterials mediated repairing process. Here, we revealed that the macrophage autophagy decreased with aging, which led to aggravated inflammation, thereby causing poor vascular remodeling of artificial grafts in aging body. Through loading the autophagy-targeted drugs, rapamycin and 3-MA (3-methyladenine), in PCL (polycaprolactone) sheath of the PGS (poly glycerol sebacate) - PCL vascular graft, the essential role of macrophage autophagy was confirmed in regulating macrophage polarization and biomaterial degradation. Moreover, the utilization of rapamycin promoted anti-inflammatory polarization of macrophage by activating autophagy, which further promoted myogenic differentiation of vascular progenitor cells and accelerated endothelialization. Our study elucidated the contribution of pharmacological manipulation of macrophage autophagy in promoting regeneration of small caliber artery, which may pave a new avenue for clinical translation of vascular grafts in aging body.

In Vivo Evaluation of Gamma-Irradiated and Heparin-Immobilized Small-Diameter Polycaprolactone Vascular Grafts with VEGF in Aged Rats

The effectiveness of small-diameter vascular grafts depends on their antithrombogenic properties and ability to undergo accelerated endothelialization. The extreme hydrophobic nature of poly(ε-caprolactone) (PCL) hinders vascular tissue integration, limiting its use in medical implants. To enhance the antithrombogenicity of PCL as a biomaterial, we grafted 2-aminoethyl methacrylate (AEMA) hydrochloride onto the PCL surface using gamma irradiation; developed a biodegradable heparin-immobilized PCL nanofibrous scaffold using gamma irradiation and N-(3-dimethylaminopropyl)-N′-ethyl carbodiimide hydrochloride/N-hydroxysuccinimide reaction chemistry; and incorporated vascular endothelial growth factor (VEGF) into the scaffold to promote vascular endothelial cell proliferation and prevent thrombosis on the vascular grafts. We assessed the physicochemical properties of PCL, heparin-AEMA-PCL (H-PCL), and VEGF-loaded heparin-AEMA-PCL (VH-PCL) vascular grafts using scanning electron microscopy, attenuated total reflection–Fourier transform infrared spectroscopy, toluidine blue O staining, and fibrinogen adsorption and surface wettability measurement. In addition, we implanted the vascular grafts into 24-month-old Sprague Dawley rats and evaluated them for 3 months. The H-PCL and VH-PCL vascular grafts improved the recovery of blood vessel function by promoting the proliferation of endothelial cells and preventing thrombosis in clinical and histological evaluation, indicating their potential to serve as functional vascular grafts in vascular tissue engineering.

Mechano-regulated cell-cell signaling in the context of cardiovascular tissue engineering

Cardiovascular tissue engineering (CVTE) aims to create living tissues, with the ability to grow and remodel, as replacements for diseased blood vessels and heart valves. Despite promising results, the (long-term) functionality of these engineered tissues still needs improvement to reach broad clinical application. The functionality of native tissues is ensured by their specific mechanical properties directly arising from tissue organization. We therefore hypothesize that establishing a native-like tissue organization is vital to overcome the limitations of current CVTE approaches. To achieve this aim, a better understanding of the growth and remodeling (G&R) mechanisms of cardiovascular tissues is necessary. Cells are the main mediators of tissue G&R, and their behavior is strongly influenced by both mechanical stimuli and cell-cell signaling. An increasing number of signaling pathways has also been identified as mechanosensitive. As such, they may have a key underlying role in regulating the G&R of tissues in response to mechanical stimuli. A more detailed understanding of mechano-regulated cell-cell signaling may thus be crucial to advance CVTE, as it could inspire new methods to control tissue G&R and improve the organization and functionality of engineered tissues, thereby accelerating clinical translation. In this review, we discuss the organization and biomechanics of native cardiovascular tissues; recent CVTE studies emphasizing the obtained engineered tissue organization; and the interplay between mechanical stimuli, cell behavior, and cell-cell signaling. In addition, we review past contributions of computational models in understanding and predicting mechano-regulated tissue G&R and cell-cell signaling to highlight their potential role in future CVTE strategies.

Systematic Review of Tissue-Engineered Vascular Grafts

Pathologies related to the cardiovascular system are the leading causes of death worldwide. One of the main treatments is conventional surgery with autologous transplants. Although donor grafts are often unavailable, tissue-engineered vascular grafts (TEVGs) show promise for clinical treatments. A systematic review of the recent scientific literature was performed using PubMed (Medline) and Web of Science databases to provide an overview of the state-of-the-art in TEVG development. The use of TEVG in human patients remains quite restricted owing to the presence of vascular stenosis, existence of thrombi, and poor graft patency. A total of 92 original articles involving human patients and animal models were analyzed. A meta-analysis of the influence of the vascular graft diameter on the occurrence of thrombosis and graft patency was performed for the different models analyzed. Although there is no ideal animal model for TEVG research, the murine model is the most extensively used. Hybrid grafting, electrospinning, and cell seeding are currently the most promising technologies. The results showed that there is a tendency for thrombosis and non-patency in small-diameter grafts. TEVGs are under constant development, and research is oriented towards the search for safe devices.

A Review: Optimization for Poly(glycerol sebacate) and Fabrication Techniques for Its Centered Scaffolds

Poly(glycerol sebacate) (PGS), an emerging promising thermosetting polymer synthesized from sebacic acid and glycerol, has attracted considerable attention due to its elasticity, biocompatibility, and tunable biodegradation properties. But it also has some drawbacks such as harsh synthesis conditions, rapid degradation rates, and low stiffness. To overcome these challenges and optimize PGS performance, various modification methods and fabrication techniques for PGS-based scaffolds have been developed in recent years. Outlining the current modification approaches of PGS and summarizing the fabrication techniques for PGS-based scaffolds are of great importance to accelerate the development of new materials and enable them to be appropriately used in potential applications. Thus, this review comprehensively overviews PGS derivatives, PGS composites, PGS blends, processing for PGS-based scaffolds, and their related applications. It is envisioned that this review could instruct and inspire the design of the PGS-based materials and facilitate tissue engineering advances into clinical practice.

Biomimetic tubular scaffold with heparin conjugation for rapid degradation in in situ regeneration of a small diameter neoartery

To address the clinical need for readily available small diameter vascular grafts, biomimetic tubular scaffolds were developed for rapid in situ blood vessel regeneration. The tubular scaffolds were designed to have an inner layer that is porous, interconnected, and with a nanofibrous architecture, which provided an excellent microenvironment for host cell invasion and proliferation. Through the synthesis of poly(spirolactic-co-lactic acid) (PSLA), a highly functional polymer with a norbornene substituting a methyl group in poly(l-lactic acid) (PLLA), we were able to covalently attach biomolecules onto the polymer backbone via thiol-ene click chemistry to impart desirable functionalities to the tubular scaffolds. Specifically, heparin was conjugated on the scaffolds in order to prevent thrombosis when implanted in situ. By controlling the amount of covalently attached heparin we were able to modulate the physical properties of the tubular scaffold, resulting in tunable wettability and degradation rate while retaining the porous and nanofibrous morphology. The scaffolds were successfully tested as rat abdominal aortic replacements. Patency and viability were confirmed through dynamic ultrasound and histological analysis of the regenerated tissue. The harvested tissue showed excellent vascular cellular infiltration, proliferation, and migration with laminar cellular arrangement. Furthermore, we achieved both complete reendothelialization of the vessel lumen and native-like media extracellular matrix. No signs of aneurysm or hyperplasia were observed after 3 months of vessel replacement. Taken together, we have developed an effective vascular graft able to generate small diameter blood vessels that can function in a rat model.

Poly(Glycerol Sebacate) in Biomedical Applications-A Review of the Recent Literature

Poly(glycerol sebacate) (PGS) continues to attract attention for biomedical applications owing to its favorable combination of properties. Conventionally polymerized by a two-step polycondensation of glycerol and sebacic acid, variations of synthesis parameters, reactant concentrations or by specific chemical modifications, PGS materials can be obtained exhibiting a wide range of physicochemical, mechanical, and morphological properties for a variety of applications. PGS has been extensively used in tissue engineering (TE) of cardiovascular, nerve, cartilage, bone and corneal tissues. Applications of PGS based materials in drug delivery systems and wound healing are also well documented. Research and development in the field of PGS continue to progress, involving mainly the synthesis of modified structures using copolymers, hybrid, and composite materials. Moreover, the production of self-healing and electroactive materials has been introduced recently. After almost 20 years of research on PGS, previous publications have outlined its synthesis, modification, properties, and biomedical applications, however, a review paper covering the most recent developments in the field is lacking. The present review thus covers comprehensively literature of the last five years on PGS-based biomaterials and devices focusing on advanced modifications of PGS for applications in medicine and highlighting notable advances of PGS based systems in TE and drug delivery.

Thick PCL Fibers Improving Host Remodeling of PGS-PCL Composite Grafts Implanted in Rat Common Carotid Arteries

Vasculopathy and the consequential ischemia are major medical challenges. Grafting is an effective treatment to vascular occlusion. However, autologous grafting, despite scarcity, is the only choice for small diameter blood vessels. Synthetic grafts can fill the gap if they can work satisfactorily in arterial circulation. Electrospun polycaprolactone (PCL) sheathed porous poly(glycerol sebacate) (PGS) vascular grafts have good performances in arterial circulation in abdominal aortas and carotid arteries in rats. However, a major issue associated with the graft remodeling in vivo is limited neo-tissue formation inside PCL sheaths. Small pores of PCL sheaths inhibit cell infiltration and migration. To increase porosity of PCL sheaths of PGS-PCL composite grafts, diameters of electrospun PCL fibers are increased. The thick PCL fibers encourage cell migration and elicit a higher degree of CD206⁺ cells. In addition, some of the CD206⁺ cells co-express vascular cell markers in the thick-fiber grafts. The thick-fiber grafts also show improved mechanical properties and a higher elastin and collagen content. The data demonstrate the feasibility of improving graft vascular remodeling by increasing PCL fiber diameters and the critical role of CD206⁺ cells during graft vascular remodeling.

Poly(ε-Caprolactone)/Poly(Glycerol Sebacate) Composite Nanofibers Incorporating Hydroxyapatite Nanoparticles and Simvastatin for Bone Tissue Regeneration and Drug Delivery Applications

Herein, we report a drug eluting scaffold composed of a composite nanofibers of poly(ε-caprolactone) (PCL) and poly(glycerol sebacate) (PGS) loaded with Hydroxyapatite nanoparticles (HANPs) and simvastatin (SIM) mimicking the bone extracellular matrix (ECM) to improve bone cell proliferation and regeneration process. Indeed, the addition of PGS results in a slight increase in the average fiber diameter compared to PCL. However, the presence of HANPs in the composite nanofibers induced a greater fiber diameter distribution, without significantly changing the average fiber diameter. The in vitro drug release result revealed that the sustained release of SIM from the composite nanofiber obeying the Korsemeyer–Peppas and Kpocha models revealing a non-Fickian diffusion mechanism and the release mechanism follows diffusion rather than polymer erosion. Biomineralization assessment of the nanofibers was carried out in simulated body fluid (SBF). SEM and EDS analysis confirmed nucleation of the hydroxyapatite layer on the surface of the composite nanofibers mimicking the natural apatite layer. Moreover, in vitro studies revealed that the PCL-PGS-HA displayed better cell proliferation and adhesion compared to the control sample, hence improving the regeneration process. This suggests that the fabricated PCL-PGS-HA could be a promising future scaffold for control drug delivery and bone tissue regeneration application.

Poly(ε-Caprolactone) Resorbable Auxetic Designed Knitted Scaffolds for Craniofacial Skeletal Muscle Regeneration

Craniofacial microsomia is a congenital deformity caused by asymmetric development of the skull (cranium) and face before birth. Current treatments include corrective surgery and replacement of the deformed structure using autograft tissue, which results in donor site morbidity. An alternative therapy can be achieved by developing a resorbable scaffold for skeletal muscle regeneration which will help restore the symmetry and function of the facial muscles and reduce donor site morbidity. Two resorbable weft knitted scaffolds were fabricated using poly(ε-caprolactone) multifilament yarns with unique auxetic design structures possessing negative Poisson’s ratio (NPR). These scaffolds exhibit their NPR elasticity through an increase in total volume as well as no lateral narrowing when stretched longitudinally, which can provide orientated mechanical supports to the cell growth of skeletal muscle regeneration. These scaffolds were evaluated for the required physical properties, mechanical performance and biocompatibility by culturing them with neonatal human dermal fibroblasts so as to determine their cell metabolic activity, cell attachment and proliferation. This study can facilitate the understanding and engineering of textile-based scaffolds for tissues/organs. The work also paves a pathway to emerge the NPR textiles into tissue engineering, which has an extensive potential for biomedical end-uses.

Dimeric Thymosin β4 Loaded Nanofibrous Interface Enhanced Regeneration of Muscular Artery in Aging Body through Modulating Perivascular Adipose Stem Cell-Macrophage Interaction

Regenerating nonthrombotic and compliant artery, especially in the aging body, remains a major surgical challenge, mainly owing to the inadequate knowledge of the major cell sources contributing to arterial regeneration and insufficient bioactivity of delivered peptides in grafts. Ultrathin nanofibrous sheaths stented with biodegrading elastomer present opening channels and reduced material residue, enabling fast cell recruitment and host remodeling, while incorporating peptides offering developmental cues are challenging. In this study, a recombinant human thymosin β4 dimer (DTβ4) that contains two complete Tβ4 molecules is produced. The adult perivascular adipose is found as the dominant source of vascular progenitors which, when stimulated by the DTβ4-loaded nanofibrous sheath, enables 100% patency rates, near-complete structural as well as adequate functional regeneration of artery, and effectively ameliorates aging-induced defective regeneration. As compared with Tβ4, DTβ4 exhibits durable regenerative activity including recruiting more progenitors for endothelial cells and smooth muscle cells, when incorporated into the ultrathin polycaprolactone sheath. Moreover, the DTβ4-loaded interface promotes smooth muscle cells differentiation, mainly through promoting M2 macrophage polarization and chemokines. Incorporating artificial DTβ4 into ultrathin sheaths of fast degrading vascular grafts creates an effective interface for sufficient muscular remodeling thus offering a robust tool for vessel replacement.

Insights into the angiogenic effects of nanomaterials: mechanisms involved and potential applications

The vascular system, which transports oxygen and nutrients, plays an important role in wound healing, cardiovascular disease treatment and bone tissue engineering. Angiogenesis is a complex and delicate regulatory process. Vascular cells, the extracellular matrix (ECM) and angiogenic factors are indispensable in the promotion of lumen formation and vascular maturation to support blood flow. However, the addition of growth factors or proteins involved in proangiogenic effects is not effective for regulating angiogenesis in different microenvironments. The construction of biomaterial scaffolds to achieve optimal growth conditions and earlier vascularization is undoubtedly one of the most important considerations and major challenges among engineering strategies. Nanomaterials have attracted much attention in biomedical applications due to their structure and unique photoelectric and catalytic properties. Nanomaterials not only serve as carriers that effectively deliver factors such as angiogenesis-related proteins and mRNA but also simulate the nano-topological structure of the primary ECM of blood vessels and stimulate the gene expression of angiogenic effects facilitating angiogenesis. Therefore, the introduction of nanomaterials to promote angiogenesis is a great helpful to the success of tissue regeneration and some ischaemic diseases. This review focuses on the angiogenic effects of nanoscaffolds in different types of tissue regeneration and discusses the influencing factors as well as possible related mechanisms of nanomaterials in endothelial neovascularization. It contributes novel insights into the design and development of novel nanomaterials for vascularization and therapeutic applications.

A riboflavin–ultraviolet light A-crosslinked decellularized heart valve for improved biomechanical properties, stability, and biocompatibility

Riboflavin–ultraviolet light A could effectively crosslink a decellularized heart valve to improve its biomechanical properties, stability and biocompatibility.

Core-Shell Fibers: Design, Roles, and Controllable Release Strategies in Tissue Engineering and Drug Delivery

The key attributes of core-shell fibers are their ability to preserve bioactivity of incorporated-sensitive biomolecules (such as drug, protein, and growth factor) and subsequently control biomolecule release to the targeted microenvironments to achieve therapeutic effects. Such qualities are highly favorable for tissue engineering and drug delivery, and these features are not able to be offered by monolithic fibers. In this review, we begin with an overview on design requirement of core-shell fibers, followed by the summary of recent preparation methods of core-shell fibers, with focus on electrospinning-based techniques and other newly discovered fabrication approaches. We then highlight the importance and roles of core-shell fibers in tissue engineering and drug delivery, accompanied by thorough discussion on controllable release strategies of the incorporated bioactive molecules from the fibers. Ultimately, we touch on core-shell fibers-related challenges and offer perspectives on their future direction towards clinical applications.

Hybrid electrospun rapamycin-loaded small-diameter decellularized vascular grafts effectively inhibit intimal hyperplasia

For the surgical treatment of coronary artery disease, renal artery stenosis and other peripheral vascular diseases, there is significant demand for small diameter (inner diameter <6 mm) vascular grafts. However, autologous grafts are not always available when the substitute vascular grafts are severely diseased. In our previous work, hybrid small-diameter vascular grafts were successfully fabricated by combining electrospun polycaprolactone (PCL) and decellularized rat aorta (DRA). However, histological assessments of these grafts revealed the development of intimal hyperplasia, indicating potential negative impacts on the long-term patency of these grafts. To address this challenge, PCL nanofibers blended with rapamycin (RM) were electrospun outside the decellularized vascular graft to fabricate a RM-loaded hybrid tissue-engineered vascular graft (RM-HTEV), endowing the graft with a drug delivery function to prevent intimal hyperplasia. RM-HTEV possessed superior mechanical properties compared to DRA and exhibited a sustained drug release profile. To evaluate the applicability of RM-HTEV in vivo, abdominal aorta transplantation was performed on rats. Doppler sonography showed that the grafts were functional for up to 8 weeks in vivo. Moreover, histological analysis of explanted grafts 12 weeks postimplantation demonstrated that RM-HTEV significantly decreased neo-intimal hyperplasia compared with HTEV, without impairing reendothelialization and M2 macrophage polarization. Overall, RM-HTEV represents a promising strategy for developing small-diameter vascular grafts with great clinical translational potential. STATEMENT OF SIGNIFICANCE: In this study, a new type of rapamycin-loaded hybrid tissue-engineered vascular graft (RM-HTEV) was fabricated using electrospinning technology. The unique hybrid bi-layer structure endowed the RM-HTEV with multi-functionality: the exterior rapamycin-loaded electrospun PCL nanofibrous layer enhanced the mechanical properties of the graft and possessed drug releasing property; the interior decellularized aorta layer with porous structure could facilitate cell proliferation and migration. In in vivo implantation experiment, RM-HTEV exhibited satisfying long-term patency rate and significantly inhibited intimal hyperplasia without impairing re-endothelialization and M2 macrophage polarization. This strategy is expected to be a promising strategy for developing bioactive small-diameter vascular grafts with great clinical translational potential.

Optimized Synthesis of Biodegradable Elastomer PEGylated Poly(glycerol sebacate) and Their Biomedical Application

Poly(glycerol sebacate) (PGS), a biodegradable elastomer, has been extensively explored in biomedical applications for its favorable mechanical properties and biocompatibility. Efforts have been made to fabricate multifunctional PGS copolymer in recent years, in particular PGS-co-PEG (poly(glycerol sebacate)-co-polyethylene glycol) polymers. However, rare research has been systematically conducted on the effect of reactant ratios on physicochemical properties and biocompatibility of PGS copolymer till now. In this study, a serial of PEGylated PGS (PEGS) with PEG content from 20% to 40% and carboxyl to hydroxyl from 0.67 to 2 were synthesized by thermal curing process. The effects of various PEGS on the mechanical strength and biological activity were further compared and optimized. The results showed that the PEGS elastomers around 20PEGS-1.0C/H and 40PEGS-1.5C/H exhibited the desirable hydrophilicity, degradation behaviors, mechanical properties and cell viability. Subsequently, the potential applications of the 20PEGS-1.0C/H and 40PEGS-1.5C/H in bone repair scaffold and vascular reconstruction were investigated and the results showed that 20PEGS-1.0C/H and 40PEGS-1.5C/H could significantly improve the mechanical strength for the calcium phosphate scaffolds and exhibited preferable molding capability for fabrication of the vascular substitute. These results confirmed that the optimized PEGS elastomers should be promising multifunctional substrates in biomedical applications.

Microporous elastomeric membranes fabricated with polyglycerol sebacate improved guided bone regeneration in a rabbit model

Purpose

We aimed to fabricate guided bone regeneration (GBR) membrane using polyglycerol sebacate (PGS) and investigate the impact of scaffold pore size on osteogenesis.

Materials and methods

PGS microporous membrane was fabricated by salt-leaching technique with various pore sizes. Twenty-eight male New Zealand rabbits were randomly divided into four groups: 25 µm PGS membrane, 53 µm PGS membrane, collagen membrane, and blank control group. Subsequently, standardized and critical-sized tibia defects were made in rabbits and the defective regions were covered with the specifically prepared membranes. After 4 and 12 weeks of in vivo incubation, bone samples were harvested from tibia. Micro-computed tomography scanning was performed on all bone samples. A three-dimensional visible representation of the constructs was obtained and used to compare the ratios of the ossifying volume to total construct volume (bone volume to tissue volume [BV/TV]) of each sample in different groups; then, bone samples were stained with H&E and Masson's trichrome stain for general histology.

Results

At 4 weeks, the BV/TV in the 25 µm PGS group was found higher than that in the 53 µm PGS and collagen groups. At 12 weeks, the bone defect site guided by the 25 µm PGS membrane was almost completely covered by the new bone. However, the site guided by the 53 µm PGS membrane or collagen membrane was covered only most of the defects and the left part of the defect was unoccupied. Histological observation further verified these findings.

Conclusion

We thus concluded that the 25 µm PGS membrane played an advantageous role during 4-12 weeks as compared with those earlier degraded counterparts.

Optimization of Electrospun Poly(caprolactone) Fiber Diameter for Vascular Scaffolds to Maximize Smooth Muscle Cell Infiltration and Phenotype Modulation

Due to the morphological resemblance between the electrospun nanofibers and extracellular matrix (ECM), electrospun fibers have been widely used to fabricate scaffolds for tissue regeneration. Relationships between scaffold morphologies and cells are cell type dependent. In this study, we sought to determine an optimum electrospun fiber diameter for human vascular smooth muscle cell (VSMC) regeneration in vascular scaffolds. Scaffolds were produced using poly(caprolactone) (PCL) electrospun fiber diameters of 0.5, 0.7, 1, 2, 2.5, 5, 7 or 10 μm, and VSMC survivals, proliferations, infiltrations, and phenotypes were recorded after culturing cells on these scaffolds for one, four, seven, or 10 days. VSMC phenotypes and macrophage infiltrations into scaffolds were evaluated by implanting scaffolds subcutaneously in a mouse for seven, 14, or 28 days. We found that human VSMC survival was not dependent on the electrospun fiber diameter. In summary, increasing fiber diameter reduced VSMC proliferation, increased VSMC infiltration and increased macrophage infiltration and activation. Our results indicate that electrospun PCL fiber diameters of 7 or 10 µm are optimum in terms of VSMC infiltration and macrophage infiltration and activation, albeit at the expense of VSMC proliferation.

Biodegrading highly porous elastomeric graft regenerates muscular and innervated carotid artery-Comparative study with vein graft

This study aims to investigate the superiorities of fast degrading elastomeric poly(glycerol sebacate) (PGS)/polycaprolactone (PCL) grafts over autologous vein grafts in the reconstruction of carotid artery, thus providing more suitable vascular grafts for carotid artery replacement. We fabricated small arterial grafts from microporous tubes of PGS reinforced with PCL nanofibers on the outer surface. As control, autologous jugular veins were harvested as vein grafts. Both types of grafts were interpositioned in rat carotid arteries and evaluated at 1 year postoperatively. PGS/PCL grafts remodelled into "neoarteries" (regenerated arteries) with smooth and even vessel wall approximate to native carotid arteries. In contrast, dilated vessel cavity and thickening vessel wall presented in neoarteries remoulded from vein. Histologically, neoarteries from both groups mimic arterial tissue architecture with a confluent endothelium and media and adventita-like layers, whereas PGS/PCL neoarteries presented well-organized muscular component and elastic fibres, which contributed more flexibility and elasticity. Different from vein grafts, PGS/PCL neoarteries acquired reinnervation and displayed apparent vascular function of contraction and relaxation, as was confirmed with responsiveness to various vasoactivators, which suggests that vascular cells within neoarteries express functional phenotypes and potential of autonomic reactivity that carotid arteries owned. To conclude, according to the requirement of strong flexibility, innervation from sympathetic and parasympathetic nerves which can response the carbon dioxide and blood pressure, the muscular remodelling and innervation possessed promising possibility of clinical application.

Electrospun vascular grafts fabricated from poly(L-lactide-co-ε-caprolactone) used as a bypass for the rabbit carotid artery

The study involved the electrospinning of the copolymer poly(L-lactide-co-ε-caprolactone) (PLCL) into tubular grafts. The subsequent material characterization, including micro-computed tomography analysis, revealed a level of porosity of around 70%, with pore sizes of 9.34 ± 0.19 μm and fiber diameters of 5.58 ± 0.10 μm. Unlike fibrous polycaprolactone, the electrospun PLCL copolymer promoted fibroblast and endothelial cell adhesion and proliferation in vitro. Moreover, the regeneration of the vessel wall was detected following implantation and, after six months, the endothelialization of the lumen and the infiltration of arranged smooth muscle cells producing collagen was observed. However, the degradation rate was found to be accelerated in the rabbit animal model. The study was conducted under conditions that reflected the clinical requirements-the prostheses were sutured in the end-to-side fashion and the long-term end point of prosthesis healing was assessed. The regeneration of the vessel wall in terms of endothelialization, smooth cell infiltration and the presence of collagen fibers was observed after six months in vivo. A part of the grafts failed due to the rapid degradation rate of the PLCL copolymer.

Synergistic Effects of Electrical Stimulation and Aligned Nanofibrous Microenvironment on Growth Behavior of Mesenchymal Stem Cells

Incontrollable cellular growth behavior is a significant issue, which severely affects the functional tissue formation and cellular protein expression. Development of natural extracellular matrix (ECM) like biomaterials to present microenvironment cues for regulation of cell responses can effectively overcome this problem. The external simulation and topological characteristics as typical guiding cues are capable of providing diverse influences on cellular growth. Herein, we fabricated two-dimensional aligned conductive nanofibers (2D-ACNFs) by an electrospinning process and surface polymerization, and the obtained 2D-ACNFs provided the effects of both alignment and electrical stimulation (ES) on cellular response of human mesenchymal cells (hMSCs). The results of cellular responses implied that the obtained 2D-ACNFs could offer a synergistic effect of both ES and aligned nanopattern on hMSC growth behavior. The effects could not only promote hMSCs to contact each other and maintain cellular activity but also provide positive promotion to regulate cellular proliferation. Thus, we believe that the obtained 2D-ACNFs will have a broad application in the biomedical field, such as cell culture with ES, directional induction for cell growth, and damaged tissue repair, etc.

Stress Analysis-Driven Design of Bilayered Scaffolds for Tissue-Engineered Vascular Grafts

Continuing advances in the fabrication of scaffolds for tissue-engineered vascular grafts (TEVGs) are greatly expanding the scope of potential designs. Increasing recognition of the importance of local biomechanical cues for cell-mediated neotissue formation, neovessel growth, and subsequent remodeling is similarly influencing the design process. This study examines directly the potential effects of different combinations of key geometric and material properties of polymeric scaffolds on the initial mechanical state of an implanted graft into which cells are seeded or migrate. Toward this end, we developed a bilayered computational model that accounts for layer-specific thickness and stiffness as well as the potential to be residually stressed during fabrication or to swell during implantation. We found that, for realistic ranges of parameter values, the circumferential stress that would be presented to seeded or infiltrating cells is typically much lower than ideal, often by an order of magnitude. Indeed, accounting for layer-specific intrinsic swelling resulting from hydrophilicity or residual stresses not relieved via annealing revealed potentially large compressive stresses, which could lead to unintended cell phenotypes and associated maladaptive growth or, in extreme cases, graft failure. Metrics of global hemodynamics were also found to be inversely related to markers of a favorable local mechanobiological environment, suggesting a tradeoff in designs that seek mechanical homeostasis at a single scale. These findings highlight the importance of the initial mechanical state in tissue engineering scaffold design and the utility of computational modeling in reducing the experimental search space for future graft development and testing.

Self-assembled Collagen-Fibrin Hydrogel Reinforces Tissue Engineered Adventitia Vessels Seeded with Human Fibroblasts

Efforts for tissue engineering vascular grafts focuses on the tunica media and intima, although the tunica adventitia serves as the primary structural support for blood vessels. In surgery, during endarterectomies, surgeons can strip the vessel, leaving the adventitia as the main strength layer to close the vessel. Here, we adapted our recently developed technique of forming vascular tissue rings then stacking the rings into a tubular structure, to accommodate human fibroblasts to create adventitia vessels in 8 days. Collagen production and fibril cross-linking was augmented with TGF-β and ascorbic acid, significantly increasing tensile strength to 57.8 ± 3.07 kPa (p = 0.008). Collagen type I gel was added to the base fibrin hydrogel to further increase strength. Groups were: Fibrin only; 0.7 mg/ml COL; 1.7 mg/ml COL; and 2.2 mg/ml COL. The 0.7 mg/ml collagen rings resulted in the highest tensile strength at 77.0 ± 18.1 kPa (p = 0.015). Culture periods of 1–2 weeks resulted in an increase in extracellular matrix deposition and significantly higher failure strength but not ultimate tensile strength. Histological analysis showed the 0.7 mg/ml COL group had significantly more, mature collagen. Thus, a hydrogel of 0.7 mg/ml collagen in fibrin was ideal for creating and strengthening engineered adventitia vessels.

Biomaterial-driven in situ cardiovascular tissue engineering-a multi-disciplinary perspective

There is a persistent and growing clinical need for readily-available substitutes for heart valves and small-diameter blood vessels. In situ tissue engineering is emerging as a disruptive new technology, providing ready-to-use biodegradable, cell-free constructs which are designed to induce regeneration upon implantation, directly in the functional site. The induced regenerative process hinges around the host response to the implanted biomaterial and the interplay between immune cells, stem/progenitor cell and tissue cells in the microenvironment provided by the scaffold in the hemodynamic environment. Recapitulating the complex tissue microstructure and function of cardiovascular tissues is a highly challenging target. Therein the scaffold plays an instructive role, providing the microenvironment that attracts and harbors host cells, modulating the inflammatory response, and acting as a temporal roadmap for new tissue to be formed. Moreover, the biomechanical loads imposed by the hemodynamic environment play a pivotal role. Here, we provide a multidisciplinary view on in situ cardiovascular tissue engineering using synthetic scaffolds; starting from the state-of-the art, the principles of the biomaterial-driven host response and wound healing and the cellular players involved, toward the impact of the biomechanical, physical, and biochemical microenvironmental cues that are given by the scaffold design. To conclude, we pinpoint and further address the main current challenges for in situ cardiovascular regeneration, namely the achievement of tissue homeostasis, the development of predictive models for long-term performances of the implanted grafts, and the necessity for stratification for successful clinical translation.

Melt electrospinning of daunorubicin hydrochloride-loaded poly (ε-caprolactone) fibrous membrane for tumor therapy

Daunorubicin hydrochloride is a cell-cycle non-specific antitumor drug with a high therapeutic effect. The present study outlines the fabrication of daunorubicin hydrochloride-loaded poly (ε-caprolactone) (PCL) fibrous membranes by melt electrospinning for potential application in localized tumor therapy. The diameters of the drug-loaded fibers prepared with varying concentrations of daunorubicin hydrochloride (1, 5, and 10 wt%) were 2.48 ± 1.25, 2.51 ± 0.78, and 2.49 ± 1.58 μm, respectively. Fluorescence images indicated that the hydrophobic drug was dispersed in the hydrophilic PCL fibers in their aggregated state. The drug release profiles of the drug-loaded PCL melt electrospun fibrous membranes were approximately linear, with slow release rates and long-term release periods, and no observed burst release. The MTT assay was used to examine the cytotoxic effect of the released daunorubicin hydrochloride on HeLa and glioma cells (U87) in vitro. The inhibition ratios of HeLa and glioma cells following treatment with membranes prepared with 1, 5, and 10 wt% daunorubicin hydrochloride were 62.69%, 76.12%, and 85.07% and 62.50%, 77.27%, and 84.66%, respectively. Therefore, PCL melt electrospun fibrous membranes loaded with daunorubicin hydrochloride may be used in the local administration of oncotherapy.

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Daunorubicin hydrochloride-loaded PCL fibrous membranes were prepared by melt electrospinning.

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Hydrophilic drug was dispersed in the PCL melt electrospun fiber in the form of aggregation.

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Daunorubicin hydrochloride-loaded PCL fibrous membranes showed low drug release rate and long-term release periods.

Effect of the electrical conductivity of core solutions on the morphology and structure of core–shell CA-PCL/CS nanofibers

CA-PCL/CS nanofibers with controllable core to shell ratios were prepared by altering the electrical conductivities of core solutions.