Composite vascular scaffold combining electrospun fibers and physically-crosslinked hydrogel with copper wire-induced grooves structure

Recent Advances in the Fabrication and Performance Optimization of Polyvinyl Alcohol Based Vascular Grafts

Cardiovascular disease is one of the diseases with the highest morbidity and mortality rates worldwide, and coronary artery bypass grafting (CABG) is a fast and effective treatment. More researchers are investigating in artificial blood vessels due to the limitations of autologous blood vessels. Despite the availability of large-diameter vascular grafts (Ø > 6 mm) for clinical use, small-diameter vascular grafts (Ø < 6 mm) have been a challenge for researchers to overcome in recent years. Vascular grafts made of polyvinyl alcohol (PVA) and PVA-based composites have excellent biocompatibility and mechanical characteristics. In order to gain a clearer and more specific understanding of the progress in PVA vascular graft research, particularly regarding the preparation methods, principles, and functionality of PVA vascular graft, this article discusses the mechanical properties, biocompatibility, blood compatibility, and other properties of PVA vascular graft prepared or enhanced with different blends using various techniques that mimic natural blood vessels. The findings reveal the feasibility and promising potential of PVA or PVA-based composite materials as vascular grafts.

Novel Electrospun Polycaprolactone/Calcium Alginate Scaffolds for Skin Tissue Engineering

After decades of research, fully functional skin regeneration is still a challenge. Skin is a multilayered complex organ exhibiting a cascading healing process affected by various mechanisms. Specifically, nutrients, oxygen, and biochemical signals can lead to specific cell behavior, ultimately conducive to the formation of high-quality tissue. This biomolecular exchange can be tuned through scaffold engineering, one of the leading fields in skin substitutes and equivalents. The principal objective of this investigation was the design, fabrication, and evaluation of a new class of three-dimensional fibrous scaffolds consisting of poly(ε-caprolactone) (PCL)/calcium alginate (CA), with the goal to induce keratinocyte differentiation through the action of calcium leaching. Scaffolds fabricated by electrospinning using a PCL/sodium alginate solution were treated by immersion in a calcium chloride solution to replace alginate-linked sodium ions by calcium ions. This treatment not only provided ion replacement, but also induced fiber crosslinking. The scaffold morphology was examined by scanning electron microscopy and systematically assessed by measurements of the pore size and the diameter, alignment, and crosslinking of the fibers. The hydrophilicity of the scaffolds was quantified by contact angle measurements and was correlated to the augmentation of cell attachment in the presence of CA. The in vitro performance of the scaffolds was investigated by seeding and staining fibroblasts and keratinocytes and using differentiation markers to detect the evolution of basal, spinous, and granular keratinocytes. The results of this study illuminate the potential of the PCL/CA scaffolds for tissue engineering and suggest that calcium leaching out from the scaffolds might have contributed to the development of a desirable biological environment for the attachment, proliferation, and differentiation of the main skin cells (i.e., fibroblasts and keratinocytes).

Nanofibrous polytetrafluoroethylene/poly(ε-caprolactone) membrane with hierarchical structures for vascular patch

With the prevalence of cardiovascular diseases, developing cardiovascular supplements is becoming increasingly urgent. The ability of cells to rapidly adhere and proliferate to achieve endothelialization is extremely important for vascular grafts. In this work, we electrospun polytetrafluoroethylene (PTFE) nanofibrous membranes and used induced crystallization to manufacture poly(ε-caprolactone) (PCL) shish-kebab microstructures on PTFE nanofibers to overcome the inertness of PTFE, and promote cell adhesion and proliferation. PCL lamella periodically grew on the surface of PTFE nanofibers yielding a hierarchical structure, which improved the biocompatibility and mechanical properties of the PTFE nanofibrous membrane. The deposition of PCL lamella improved the hydrophilicity of electrospun PTFE nanofibers membrane, leading to good cell proliferation and adhesion. Also, due to the surface inertness of the substrate material PTFE, this PTFE/PCL composite film has good anti-platelet adhesion properties. Furthermore, cell proliferation could be regulated by controlling the integrity of the PCL crystal network. The vascular patch showed similar mechanical properties to natural blood vessels, providing a new strategy for vascular tissue engineering.

Electrospun hybrid nanofibers: Fabrication, characterization, and biomedical applications

Nanotechnology is one of the most promising technologies available today, holding tremendous potential for biomedical and healthcare applications. In this field, there is an increasing interest in the use of polymeric micro/nanofibers for the construction of biomedical structures. Due to its potential applications in various fields like pharmaceutics and biomedicine, the electrospinning process has gained considerable attention for producing nano-sized fibers. Electrospun nanofiber membranes have been used in drug delivery, controlled drug release, regenerative medicine, tissue engineering, biosensing, stent coating, implants, cosmetics, facial masks, and theranostics. Various natural and synthetic polymers have been successfully electrospun into ultrafine fibers. Although biopolymers demonstrate exciting properties such as good biocompatibility, non-toxicity, and biodegradability, they possess poor mechanical properties. Hybrid nanofibers from bio and synthetic nanofibers combine the characteristics of biopolymers with those of synthetic polymers, such as high mechanical strength and stability. In addition, a variety of functional agents, such as nanoparticles and biomolecules, can be incorporated into nanofibers to create multifunctional hybrid nanofibers. Due to the remarkable properties of hybrid nanofibers, the latest research on the unique properties of hybrid nanofibers is highlighted in this study. Moreover, various established hybrid nanofiber fabrication techniques, especially the electrospinning-based methods, as well as emerging strategies for the characterization of hybrid nanofibers, are summarized. Finally, the development and application of electrospun hybrid nanofibers in biomedical applications are discussed.

Designed and fabrication of triple-layered vascular scaffold with microchannels

Currently, one of the best preparation strategies for the triple-layered vascular scaffold is to imitate the three-layer structure of natural blood vessels to achieve the biofunctional characteristics of vascular transplantation. Here, we developed a combinatorial method to fabricate triple-layered vascular scaffold (TVS) by using electrospinning and coaxial 3 D printing. First, Polycaprolactone-collagen (PCL-Col) was applied to prepared the inner layer of TVS by electrospinning. Second, egg white/sodium alginate (EW/SA) blend hydrogel was extruded to form hollow filaments by coaxial 3 D printing and crosslinking mechanism, which enwound around the surface of the inner layer in a circumferential direction as the intermediate layer of TVS. Finally, electrospun PCL-Col nanofibers were wrapped on the surface of hydrogel layer as the outer layer of TVS. The morphological characterization and mechanical strength of the fabricated TVS were measured. Compared with natural blood vessels, results shown that ultimate tensile stress (UTS), strain to failure (STF), the estimated burst strength and the suture retention strength (SRS) of TVS were superior. Also, the fabricated TVS exhibits good hydrophilicity and excellent flexibility. Moreover, the biocompatibility of TVS was investigated through human umbilical vein endothelial cells (HUVECs), the results demonstrated that cells can successfully attach the surface of graft and maintain high viability. In summary, all of results demonstrated that this method could fabricate a novel triple-layered vascular scaffold, possessing appropriate mechanical properties and good biological properties, which has the potential to be used in tissue engineered vascular grafts applications.

Fabrication of multilayer tubular scaffolds with aligned nanofibers to guide the growth of endothelial cells

Aligned electrospun fibers used for the fabrication of tubular scaffolds possess the ability to regulate cellular alignment and relevant functional expression, with applications in tissue engineering. Despite significant progress in the fabrication of small-diameter vascular grafts (SDVGs) over the past decade, several challenges remain; one of the most problematic of these is the fabrication of aligned nanofibers for multilayer SDVGs. Furthermore, delamination between each layer is difficult to avoid during the fabrication of multilayer structures. This study introduces a new fabrication method for minute delamination four-layer tubular scaffolds (FLTSs) that consist of an interior layer with highly longitudinal aligned nanofibers, two middle layers composed of electrospun sloped and circumferentially aligned fibers, and an exterior layer comprising random fibers. These FLTSs are used to simulate the structures and functions of native blood vessels. Here, thermoplastic polyurethane (TPU)/polycaprolactone (PCL)/polyethylene glycol (PEG) were electrospun to fabricate FLTSs or tubular scaffolds with completely random fibers layer (RLTSs). The surface wettability of the TPU/PCL/PEG tubular scaffold was tested by water contact angle analysis. In particular, compared with RLTSs, FLTSs showed excellent mechanical properties, with higher circumferential and longitudinal tensile properties. Furthermore, the high viability of the human umbilical vein endothelial cells (HUVECs) on the FLTSs indicated the biocompatibility of the tubular scaffolds comparing to RLTSs. The aligned and random composite structure of the FLTSs are conducive to promoting the growth of HUVECs, and the cell adhesion and proliferation on these scaffolds was found to be superior to that on RLTSs. These results demonstrate that the fabricated FLTSs have the potential for application in vascular tissue regeneration and clinical arterial replacements.

3D Bioprinting Strategies for the Regeneration of Functional Tubular Tissues and Organs

It is difficult to fabricate tubular-shaped tissues and organs (e.g., trachea, blood vessel, and esophagus tissue) with traditional biofabrication techniques (e.g., electrospinning, cell-sheet engineering, and mold-casting) because these have complicated multiple processes. In addition, the tubular-shaped tissues and organs have their own design with target-specific mechanical and biological properties. Therefore, the customized geometrical and physiological environment is required as one of the most critical factors for functional tissue regeneration. 3D bioprinting technology has been receiving attention for the fabrication of patient-tailored and complex-shaped free-form architecture with high reproducibility and versatility. Printable biocomposite inks that can facilitate to build tissue constructs with polymeric frameworks and biochemical microenvironmental cues are also being actively developed for the reconstruction of functional tissue. In this review, we delineated the state-of-the-art of 3D bioprinting techniques specifically for tubular tissue and organ regeneration. In addition, this review described biocomposite inks, such as natural and synthetic polymers. Several described engineering approaches using 3D bioprinting techniques and biocomposite inks may offer beneficial characteristics for the physiological mimicry of human tubular tissues and organs.

Fabrication and preliminary study of a biomimetic tri-layer tubular graft based on fibers and fiber yarns for vascular tissue engineering

Designing a biomimetic and functional tissue-engineered vascular graft has been urgently needed for repairing and regenerating defected vascular tissues. Utilizing a multi-layered vascular scaffold is commonly considered an effective way, because multi-layered scaffolds can easily simulate the structure and function of natural blood vessels. Herein, we developed a novel tri-layer tubular graft consisted of Poly(L-lactide-co-caprolactone)/collagen (PLCL/COL) fibers and Poly(lactide-co-glycolide)/silk fibroin (PLGA/SF) yarns via a three-step electrospinning method. The tri-layer vascular graft consisted of PLCL/COL aligned fibers in inner layer, PLGA/SF yarns in middle layer, and PLCL/COL random fibers in outer layer. Each layer possessed tensile mechanical strength and elongation, and the entire tubular structure provided tensile and compressive supports. Furthermore, the human umbilical vein endothelial cells (HUVECs) and smooth muscle cells (SMCs) proliferated well on the materials. Fluorescence staining images demonstrated that the axially aligned PLCL/COL fibers prearranged endothelium morphology in lumen and the circumferential oriented PLGA/SF yarns regulated SMCs organization along the single yarns. The outside PLCL/COL random fibers performed as the fixed layer to hold the entire tubular structure. The in vivo results showed that the tri-layer vascular graft supported cell infiltration, scaffold biodegradation and abundant collagen production after subcutaneous implantation for 10weeks, revealing the optimal biocompatibility and tissue regenerative capability of the tri-layer graft. Therefore, the specially designed tri-layer vascular graft will be beneficial to vascular reconstruction.

A novel method for fabricating engineered structures with branched micro-channel using hollow hydrogel fibers

Vascularization plays a crucial role in the regeneration of different damaged or diseased tissues and organs. Vascularized networks bring sufficient nutrients and oxygen to implants and receptors. However, the fabrication of engineered structures with branched micro-channels (ESBM) is still the main technological barrier. To address this problem, this paper introduced a novel method for fabricating ESBM; the manufacturability and feasibility of this method was investigated. A triaxial nozzle with automatic cleaning function was mounted on a homemade 3D bioprinter to coaxially extrude sodium alginate (NaAlg) and calcium chloride (CaCl₂) to form the hollow hydrogel fibers. With the incompleteness of cross-linking and proper trimming, ESBM could be produced rapidly. Different concentrations of NaAlg and CaCl₂ were used to produce ESBM, and mechanical property tests were conducted to confirm the optimal material concentration for making the branched structures. Cell media could be injected into the branched channel, which showed a good perfusion. Fibroblasts were able to maintain high viability after being cultured for a few days, which verified the non-cytotoxicity of the gelation and fabrication process. Thus, hollow hydrogel fibers were proved to be a potential method for fabricating micro-channels for vascularization.