Current Strategies for Engineered Vascular Grafts and Vascularized Tissue Engineering

Evaluation of properties for Carbothane™ 3575A-based electrospun vascular graftsin vitroandin vivo

Bioengineered vascular grafts (VGs) have emerged as a promising alternative to the treatment of damaged or occlusive vessels. It is thought that polyurethane (PU)-based scaffolds possess suitable hemocompatibility and biomechanics comparable to those of normal blood vessels. In this study, we investigated the properties of electrospun scaffolds comprising various blends of biostable polycarbonate-based PU (Carbothane™ 3575A) and gelatin. Scaffolds were characterized by scanning electron microscopy, infra-red spectroscopy, small-angle x-ray scattering, stress-loading tests, and interactions with primary human cells and blood. Data fromin vitroexperiments demonstrated that a scaffold produced from a blend of 5% Carbothane™ 3575A and 10% gelatin has proven to be a suitable material for fabricating a small-diameter VG. A comparativein vivostudy of such VGs and expanded polytetrafluoroethylene (ePTFE) grafts implanted in the abdominal aorta of Wistar rats was performed. The data of intravital study and histological examination indicated that Carbothane-based electrospun grafts outclass ePTFE grafts and represent a promising device for preclinical studies to satisfy vascular surgery needs.

Antithrombogenic polysaccharide coatings to improve hemocompatibility, protein-repellence, and endothelial cell response

Polyester biomaterials play a crucial in vascular surgery, but suffer from unspecific protein adsorption, thrombogenicity, and inadequate endothelial cell response, which limit their success. To address these issues, we investigated the functionalization of polyester biomaterials with antithrombogenic polysaccharide coatings. A two-step and water-based method was used to coat cationized polycaprolactone with different sulfated polysaccharides (SPS), which resulted in long-term stability, tunable morphology, roughness, film thickness, chemical compositions, zeta potential, and water content. The coatings significantly increased the anticoagulant activity and reduced the thrombogenicity of polycaprolactone, particularly with highly sulfated heparin and cellulose sulfate. Less SPS, such as chondroitin sulfate, fucoidan, and carrageenan, despite showing reduced anticoagulant activity, also exhibited lower fibrinogen adsorption. The adhesion and viability of human primary endothelial cells cultured on modified polycaprolactone correlated with the type and sulfate content of the coatings.

Synthesis and characterization of new electrospun medical scaffold-based modified cellulose nanofiber and bioactive natural propolis for potential wound dressing applications

Recently, the design of polymer nanofibers using the electrospinning process has attracted much interest. Particularly the use of natural polymers has promoted many advantages in their biomedical applications. However, the combination of multiple natural polymers remains a great challenge in terms of electrospun production and applied performance. From this perspective, the current investigation highlights the study of the preparation of electrospun nanomaterial scaffolds based on combined natural polymers for improved wound healing performance. First, we have synthesized a crosslinked polymer by reacting microcrystalline cellulose (MC) and chitosan (CS) biopolymer via the intermediate of citric acid as a crosslinking agent. Then a natural propolis biomolecule was incorporated into the polymer network. Different MC/CS blend ratios of 90/10 and 70/30 were then used and various machine parameters were optimized to obtain nanofiber scaffolds with excellent strength and structures. SEM, IR, physicochemical, mechanical, and morpho-logical characterization were then performed. SEM evaluation revealed homogeneous and bead-free nanofibrous structures, with well-defined morphology and a random deposition that could accurately mimic the extracellular matrix of native skin. The calculated average nanofiber diameters for the MC/CS blend ratios at 90/10 and 70/30 were 431.4 and 441.2 nm, respectively. The results showed that when the chitosan amount increased, larger nanofibers with narrow diameter distribution appeared. The prepared nanomaterials had a significant and close water vapor permeability of about 1735.12 and 1698.52 g per m per day for the two blend ratios of 90/10 and 70/30, respectively. The examination of swelling behavior revealed a noteworthy enhancement in hydrophilicity, a necessary attribute for improved healing efficacy. FT-IR analysis confirmed the success and the stability of the chemical crosslinking reaction between the two biopolymers before nanofiber conception. Excellent mechanical properties were acquired, based on the chitosan content. Both developed nanofiber scaffolds exhibited high tensile strength and Young's modulus values. The incorporation of 30% chitosan versus 10% results in an increase in tensile strength of 11% and 14% in Young's modulus. Therefore, we could adjust the different mechanical properties simply by varying the mixing rate of the electrospun polymers. Using epithelial HepG2 cells, viability and kinetic cell adhesion assays were assessed to obtain biological evaluation. No cytotoxicity was observed and good cytocompatibility was confirmed. Functionalized nanofiber biomaterials with different MC/CS ratios substantiated significant bactericidal effectiveness against Gram-positive and Gram-negative bacterial culture strains. The novel functional electrospun wound dressing scaffold demonstrated effective and promising biomedical performance, healing both acute and chronic wounds.

Endothelial progenitor cells for fabrication of engineered vascular units and angiogenesis induction

The promotion of vascularization and angiogenesis in the grafts is a crucial phenomenon in the healing process and tissue engineering. It has been shown that stem cells, especially endothelial progenitor cells (EPCs), can stimulate blood vessel formation inside the engineered hydrogels after being transplanted into the target sites. The incorporation of EPCs into the hydrogel can last the retention time, long-term survival, on-target delivery effects, migration and differentiation into mature endothelial cells. Despite these advantages, further modifications are mandatory to increase the dynamic growth and angiogenesis potential of EPCs in in vitro and in vivo conditions. Chemical modifications of distinct composites with distinct physical properties can yield better regenerative potential and angiogenesis during several pathologies. Here, we aimed to collect recent findings related to the application of EPCs in engineered vascular grafts and/or hydrogels for improving vascularization in the grafts. Data from the present article can help us in the application of EPCs as valid cell sources in the tissue engineering of several ischemic tissues.

A bilayer bioengineered patch with sequential dual-growth factor release to promote vascularization in bladder reconstruction

Bladder tissue engineering holds promise for addressing bladder defects resulting from congenital or acquired bladder diseases. However, inadequate vascularization significantly impacts the survival and function of engineered tissues after transplantation. Herein, a novel bilayer silk fibroin (BSF) scaffold was fabricated with the capability of vascular endothelial growth factor (VEGF) and platelet derived growth factor-BB (PDGF-BB) sequential release. The outer layer of the scaffold was composed of compact SF film with waterproofness to mimic the serosa of the bladder. The inner layer was constructed of porous SF matrix incorporated with SF microspheres (MS) loaded with VEGF and PDGF-BB. We found that the 5% (w/v) MS-incorporated scaffold exhibited a rapid release of VEGF, whereas the 0.2% (w/v) MS-incorporated scaffold demonstrated a slow and sustained release of PDGF-BB. The BSF scaffold exhibited good biocompatibility and promoted endothelial cell migration, tube formation and enhanced endothelial differentiation of adipose derived stem cells (ADSCs) in vitro. The BSF patch was constructed by seeding ADSCs on the BSF scaffold. After in vivo transplantation, not only could the BSF patch facilitate the regeneration of urothelium and smooth muscle, but more importantly, stimulate the regeneration of blood vessels. This study demonstrated that the BSF patch exhibited excellent vascularization capability in bladder reconstruction and offered a viable functional bioengineered patch for future clinical studies.

Porous collagen scaffolds enable endothelial lumen formation in vitro under both static and dynamic growth conditions

Despite recent advances in the field of tissue engineering, the development of complex tissue-like structures in vitro is compromised by the lack of integration of a functioning vasculature. In this study, we propose a mesoscale three-dimensional (3D) in vitro vascularized connective tissue model and demonstrate its feasibility to prompt the self-assembly of endothelial cells into vessel-like structures. Moreover, we investigate the effect of perfusion on the organization of the cells. For this purpose, primary endothelial cells (HUVECs) and a cell line of human foreskin fibroblasts are cultivated in ECM-like matrices made up of freeze-dried collagen scaffolds permeated with collagen type I hydrogel. A tailored bioreactor is designed to investigate the effect of perfusion on self-organization of HUVECs. Immunofluorescent staining, two-photon microscopy, second-harmonic generation imaging, and scanning electron microscopy are applied to visualize the spatial arrangement of the cells. The analyses reveal the formation of hollow, vessel-like structures of HUVECs in hydrogel-permeated collagen scaffolds under both static and dynamic conditions. In conclusion, we demonstrate the feasibility of a 3D porous collagen scaffolding system that enables and maintains the self-organization of HUVECs into vessel-like structures independent of a dynamic flow.

Application of a meshed artificial dermal scaffold and negative-pressure wound therapy in the treatment of full-thickness skin defects: a prospective in vivo study

Artificial dermal scaffolds (ADSs) have great value in repairing deep skin defects. However, problems such as unsatisfactory angiogenesis and local dropsy or empyema often occur, resulting in delayed or even failed wound healing. Negative pressure wound therapy (NPWT) is an effective therapy to promote wound healing or shorten wound bed preparation time. Studies on whether it can improve the effects of ADSs have never been interrupted, and no consensus has been reached. In this study, an improved ADS was prepared by mesh technology, physicochemical experiments were conducted, cell adhesion and proliferation were assessed with the meshed ADS, and in vivo experiments were conducted to investigate the effects of meshed ADS or ADS combined with NPWT in repairing full-thickness skin defects. The results showed that the meshed ADS showed through-layer channels arranged in parallel longitudinal and transverse intersections. The cell experiments confirmed the good cytocompatibility. The in vivo experiments showed that there were no differences in the take rate or contraction of grafted skin among all experiment groups. The meshed ADS exhibited good histocompatibility, and there were no differences in tissue inflammation, dermal angiogenesis, or degradation among all groups. In addition, necrosis, dropsy, or empyema of the dermal scaffold were found in all experiment groups except for the meshed ADS + NPWT group, which showed better wound repair results, including fewer scaffold-related complications and satisfactory skin graft survival and wound contraction. In conclusion, this novel meshed ADS, which has a regular through-layer mesh structure and possesses stable physicochemical properties and good biocompatibility, combined with NPWT can ensure adequate subdermal drainage and reduce the risk of scaffold-related complications, thereby improving the quality and efficiency of wound repair, promoting a broader application of biomaterials, and helping physicians and readers implement more effective wound management.

Vascularized versus Free Nerve Grafts: An Experimental Study on Rats

BACKGROUND

Vascularized nerve grafts (VNGs) have been proposed as a superior alternative to free nerve grafts (FNGs) for complex nerve defects. A greater regenerative potential has been suggested by clinical and experimental studies, but conclusive evidence is still lacking.

METHODS

In this experimental study, 10 adult male Wistar rats received a non-vascularized orthotopic sciatic nerve graft on their right side, and a vascularized orthotopic sciatic nerve graft nerve on their left side. Functional outcome following nerve regeneration was evaluated through electrodiagnostic studies, target muscles weight and histomorphology, and data of VNGs and FNGs were compared.

RESULTS

The results of this study showed a significant difference in the motor unit number of Gastrocnemius Medialis (GM) estimated by MUNE in the VNG side compared to the FNG side. No other significant differences in axonal regeneration and muscle reinnervation were evident at either electrodiagnostic, histomorphology studies or muscle weight.

CONCLUSIONS

This experimental model showed slight differences in nerve regeneration between VNGs and FNGs, but cannot support a high clinical advantage for VNGs. The results of this study show that VNGs are not strongly superior to FNGs in the rat model, even in avascular beds. Clinical advantages of VNGs are likely to be limited to extensive and thick nerve defects and can only be assessed on experimental model with bigger animals. Also, we showed that the MUNE technique provided a reliable and reproducible evaluation of functional outcomes in the rat sciatic nerve and defined a reproducible protocol for functional evaluation of muscle reinnervation.