Rapid fabrication of reinforced and cell-laden vascular grafts structurally inspired by human coronary arteries

Construction of anti-calcification small-diameter vascular grafts using decellularized extracellular matrix/poly (L-lactide-co-ε-caprolactone) and baicalin-cathepsin S inhibitor

The long-term transplantation of small-diameter vascular grafts (SDVGs) is associated with a risk of calcification, which is a key factor limiting the clinical translation of SDVG. Hence, there is an urgency attached to the development of new SDVGs with anti-calcification properties. Here, we used decellularized extracellular matrix (dECM) and poly (L-lactide-co-ε-caprolactone) (PLCL) as base materials and combined these with baicalin, cathepsin S (Cat S) inhibitor to prepare PBC-SDVGs by electrospinning. Baicalin contains carboxyl and hydroxyl groups that can interact with chemical groups in dECM powder, potentially blocking calcium nucleation sites. Cat S inhibitor prevents elastin degradation and further reduces the risk of calcification. PBC-SDVGs were biocompatible and when implanted in rat abdominal aorta, accelerated endothelialization, enhanced vascular tissue regeneration, inhibited elastin degradation, and promoted macrophage polarization M2 phenotype to regulate inflammation. After 3 months of implantation, the results of Doppler ultrasound, MicroCT, and histological staining revealed a significant reduction in calcification. In summary, the developed anti-calcification SDVGs offer a promising strategy for long-term implantation with significant clinical application potential. STATEMENT OF SIGNIFICANCE: The dECM and PLCL were used as base materials, connected with baicalin, and loaded with Cat S inhibitor to prepare PBC-SDVGs. The baicalin and dECM powder formed hydrogen bonds to crosslink together reducing the calcium deposition. In vitro, the vascular graft downregulated the expression level of osteogenic genes and promoted macrophage polarization toward an anti-inflammatory M2 phenotype, thereby reducing calcification. The PBC-SDVGs implanted in rat abdominal aorta can accelerate endothelialization, enhance vascular tissue regeneration, inhibit elastin degradation, reduce inflammation response and calcification.

Semi-automated layer-by-layer biofabrication using rotational internal flow layer engineering technology

The automation of biofabrication processes has the potential to increase both the scale and reproducibility of human tissue production for replacing animal usage in research and ultimately clinical use. The biofabrication technology, Rotational Internal Flow Layer Engineering (RIFLE), produces layered tubular constructs with a resolution commensurate with the microscale strata observed in many human tissue types. The previously published RIFLE process required liquid phase cell-laden hydrogels to be manually applied onto the inner surface of a high-speed rotating mould. Here we describe improvement of the RIFLE system by automating elements of the process, in particular the liquid dispensing element, and present the use of this system for two commonly used biofabrication hydrogels; alginate and collagen. Semi-automatically assembled cell layers matched the viabilities of those produced manually, with automated collagen demonstrating the highest viabilities (>91 %) over the 10 days measured, highlighting its advantages as a material for tissue engineering applications. The encapsulation of labelled cells in predefined collagen layer patterns confirmed that the semi-automated RIFLE system was able to assemble separate cell populations in cell-width layers (≈14 µ m). Semi-automated dosing reduced the manual operations in the RIFLE process, reducing the workload on researchers and minimising the opportunity for human error. Further opportunity exists for higher levels of automation in the overall process, particularly needed in the preparation of cell-hydrogel suspensions, a common manual labour-intensive process in many biofabrication technologies.

Thrombogenicity Assessment of Perfusable Tissue-Engineered Constructs: A Systematic Review

Vascular surgery is facing a critical demand for novel vascular grafts that are biocompatible and thromboresistant. This urgency is particularly applicable to bypass operations involving small caliber vessels. In the realm of tissue engineering, the development of fully vascularized organs is promising as a solution to organ shortage for transplantation. To achieve this, it is essential to (re)construct a biocompatible and nonthrombogenic vascular network within these organs. In this systematic review, we identify, classify, and discuss basic principles and methods used to perform in vitro/ex vivo dynamic thrombogenicity testing of perfusable tissue-engineered organs and tissues. We conducted a preregistered systematic review of studies published in the last 23 years according to PRISMA-P Guidelines. This comprised a systematic data extraction, in-depth analysis, and risk of bias assessment of 116 included studies. We identified shaking (n = 28), flow loop (n = 17), ex vivo (arteriovenous shunt, n = 33), and dynamic in vitro models (n = 38) as the main approaches for thrombogenicity assessment. This comprehensive review reveals a prevalent lack of standardization and provides a valuable guide in the design of standardized experimental setups.

Electronic vascular conduit for in situ identification of hemadostenosis and thrombosis in small animals and nonhuman primates

Patients suffering from coronary artery disease (CAD) or peripheral arterial disease (PAD) can benefit from bypass graft surgery. For this surgery, arterial vascular grafts have become promising alternatives when autologous grafts are inaccessible but suffer from numerous postimplantation challenges, particularly delayed endothelialization, intimal hyperplasia, high risk of thrombogenicity and restenosis, and difficulty in timely detection of these subtle pathological changes. We present an electronic vascular conduit that integrates flexible electronics into bionic vascular grafts for in situ, real-time and long-term monitoring for hemadostenosis and thrombosis concurrent with postoperative vascular repair. Following bypass surgery, the integrated bioelectronic sensor based on the triboelectric effect enables monitoring of the blood flow in the vascular graft and identification of lesions in real time for up to three months. In male nonhuman primate cynomolgus monkeys, the electronic vascular conduit, with an integrated wireless signal transmission module, enables wireless and real-time hemodynamic monitoring and timely identification of thrombi. This electronic vascular conduit demonstrates potential as a treatment-monitoring platform, providing a sensitive and intuitive monitoring technique during the critical period after bypass surgery in patients with CAD and PAD.

Therapeutic functions of medical implants from various material categories with integrated biomacromolecular systems

Medical implants are designed to replace missing parts or improve body functions and must be capable of providing structural support or therapeutic intervention for a medical condition. Advances in materials science have enabled the development of devices made from metals, polymers, bioceramics, and composites, each with its specific advantages and limitations. This review analyzes the incorporation of biopolymers, proteins, and other biomacromolecules into implants, focusing on their role in biological integration and therapeutic functions. It synthesizes advancements in surface modification, discusses biomacromolecules as carriers for controlled drug release, and explores the application of nanoceramics and composites to improve osseointegration and tissue regeneration. Biomacromolecule systems are capable of interacting with device components and therapeutic agents - such as growth factors (GFs), antibiotics, and nanoceramics - allowing control over substance release. Incorporating therapeutic agents into these systems enables localized treatments for tissue regeneration, osseointegration, post-surgery infection control, and disease and pre-existing conditions. The review highlights these materials' therapeutic advantages and customization opportunities, by covering mechanical and biological perspectives. Developing composites and hybrid drug delivery systems align with recent efforts in interdisciplinary personalized medicine and implant innovations. For instance, a trend was observed for integrating inorganic (especially nanoceramics, e.g., hydroxyapatite) and organic phases in composites for better implant interaction with biological tissues and faster recovery. This article supports understanding how integrating these materials can create more personalized, functional, durable, and biocompatible implant devices.

3D-Printed Polymeric Biomaterials for Health Applications

3D printing, also known as additive manufacturing, holds immense potential for rapid prototyping and customized production of functional health-related devices. With advancements in polymer chemistry and biomedical engineering, polymeric biomaterials have become integral to 3D-printed biomedical applications. However, there still exists a bottleneck in the compatibility of polymeric biomaterials with different 3D printing methods, as well as intrinsic challenges such as limited printing resolution and rates. Therefore, this review aims to introduce the current state-of-the-art in 3D-printed functional polymeric health-related devices. It begins with an overview of the landscape of 3D printing techniques, followed by an examination of commonly used polymeric biomaterials. Subsequently, examples of 3D-printed biomedical devices are provided and classified into categories such as biosensors, bioactuators, soft robotics, energy storage systems, self-powered devices, and data science in bioplotting. The emphasis is on exploring the current capabilities of 3D printing in manufacturing polymeric biomaterials into desired geometries that facilitate device functionality and studying the reasons for material choice. Finally, an outlook with challenges and possible improvements in the near future is presented, projecting the contribution of general 3D printing and polymeric biomaterials in the field of healthcare.

Protein and Polysaccharide Fibers via Air Jet Spinning: Emerging Techniques for Biomedical and Sustainable Applications

Polymers play a critical role in the biomedical and sustainable materials fields, serving as key resources for both research and product development. While synthetic and natural polymers are both widely used, synthetic polymers have traditionally dominated due to their ability to meet the specific material requirements of most fiber fabrication methods. However, synthetic polymers are derived from non-renewable resources, and their production raises environmental and health concerns. Natural polymers, on the other hand, are derived from renewable biological sources and include a subset known as biopolymers, such as proteins and polysaccharides, which are produced by living organisms. These biopolymers are naturally abundant and offer benefits such as biodegradability and non-toxicity, making them especially suitable for biomedical and green applications. Recently, air jet spinning has emerged as a promising method for fabricating biopolymer fibers, valued for its simplicity, cost-effectiveness, and safety-advantages that stand out compared to the more conventional electrospinning process. This review examines the methods and mechanisms of air jet spinning, drawing on empirical studies and practical insights to highlight its advantages over traditional fiber production techniques. By assembling natural biopolymers into micro- and nanofibers, this novel fabrication method demonstrates strong potential for targeted applications, including tissue engineering, drug delivery, air filtration, food packaging, and biosensing, utilizing various protein and polysaccharide sources.

Tetramethylpyrazine-derived polyurethane for improved hemocompatibility and rapid endothelialization

Thrombosis and intimal hyperplasia (IH) are the main factors affecting the long-term patency of small-diameter vascular grafts (SDVGs). Fabricating a confluent endothelial cell (EC) layer on surfaces with physiological elasticity to mimic vascular endothelium should be an effective strategy to prevent restenosis that is caused by thrombosis and IH. However, the vascular endothelialization process is time-consuming and always constrained by hemocompatibility of the vascular grafts, since excellent hemocompatibility could guarantee a sufficient time window for the endothelialization process. Tetramethylpyrazine (TMP)-derived polyurethane (PU) with improved hemocompatibility and accelerated endothelialization ability is synthesized by incorporating TMP moieties into PU backbones. Results show that TMP-contained PU films possess improved hemocompatibility by down-regulating platelet adhesion/activation and increasing the clotting time. Furthermore, the in vitro human umbilical vein endothelial cell (HUVEC) test demonstrates that the introduction of TMP can significantly promote HUVEC adhesion and proliferation, and thus accelerate luminal endothelialization of vascular grafts. Moreover, the TMP-containing PU films exhibit excellent biocompatibility especially for HUVECs, and their excellent, adjustable elasticity (1123%) guarantees compliance accommodation of vascular grafts. This newly synthesized TMP-containing material with multiple biological functions is expected to make up for the shortcomings of available SDVGs in clinical practice, and has significant potential in improving the long-term patency of SDVGs.

3D-Printed Hydrogels with Engineered Nanocrystalline Domains as Functional Vascular Constructs

Three-dimensionally printed (3DP) hydrogel-based vascular constructs have been investigated in response to the impaired function of blood vessels or organs by replicating exactly the 3D structural geometry to approach their function. However, they are still challenged by their intrinsic brittleness, which could not sustain the suture piercing and enable the long-term structural and functional stability during the direct contact with blood. Here, we reported the high-fidelity digital light processing (DLP) 3D printing of hydrogel-based vascular constructs from poly(vinyl alcohol)-based inks, followed by mechanical strengthening through engineering the nanocrystalline domains and subsequent surface modification. The as-prepared high-precision hydrogel vascular constructs were imparted with highly desirable mechanical robustness, suture tolerance, swelling resistance, antithrombosis, and long-term patency. Notably, the hydrogel-based bionic vein grafts, with precise valve structures, exhibited excellent control over the unidirectional flow and successfully fulfilled the biological functionalities and patency during a 4-week implantation within the deep veins of beagles, thus corroborating the promising potential for treating chronic venous insufficiency.

The Past, Present, and Future of Tubular Melt Electrowritten Constructs to Mimic Small Diameter Blood Vessels - A Stable Process?

Melt Electrowriting (MEW) is a continuously growing manufacturing platform. Its advantage is the consistent production of micro- to nanometer fibers, that stack intricately, forming complex geometrical shapes. MEW allows tuning of the mechanical properties of constructs via the geometry of deposited fibers. Due to this, MEW can create complex mechanics only seen in multi-material compounds and serve as guiding structures for cellular alignment. The advantage of MEW is also shown in combination with other biotechnological manufacturing methods to create multilayered constructs that increase mechanical approximation to native tissues, biocompatibility, and cellular response. These features make MEW constructs a perfect candidate for small-diameter vascular graft structures. Recently, studies have presented fascinating results in this regard, but is this truly the direction that tubular MEW will follow or are there also other options on the horizon? This perspective will explore the origins and developments of tubular MEW and present its growing importance in the field of artificial small-diameter vascular grafts with mechanical modulation and improved biomimicry and the impact of it in convergence with other manufacturing methods and how future technologies like AI may influence its progress.

Harnessing the Regenerative Potential of Fetal Mesenchymal Stem Cells and Endothelial Colony-Forming Cells in the Biofabrication of Tissue-Engineered Vascular Grafts (TEVGs)

Tissue engineering is a promising approach for the production of small-diameter vascular grafts; however, there are limited data directly comparing the suitability of applicable cell types for vessel biofabrication. Here, we investigated the potential of adult smooth muscle cells (SMCs), placental mesenchymal stem cells (MSCs), placental endothelial colony-forming cells (ECFCs), and a combination of MSCs and ECFCs on highly porous biocompatible poly(ɛ-caprolactone) (PCL) scaffolds produced via melt electrowriting (MEW) for the biofabrication of tissue-engineered vascular grafts (TEVGs). Cellular attachment, proliferation, and deposition of essential extracellular matrix (ECM) components were analysed in vitro over four weeks. TEVGs cultured with MSCs accumulated the highest levels of collagenous components within a dense ECM, while SMCs and the coculture were more sparsely populated, ascertained via histological and immunofluorescence imaging, and biochemical assessment. Scanning electron microscopy (SEM) enabled visualisation of morphological differences in cell attachment and growth, with MSCs and SMCs infiltrating and covering scaffolds completely within the 28-day culture period. Coverage and matrix deposition by ECFCs was limited. However, ECFCs lined the ECM formed by MSCs in coculture, visualised via immunostaining. Thus, of cells investigated, placental MSCs were identified as the preferred cell source for the fabrication of tissue-engineered constructs, exhibiting extensive population of porous polymer scaffolds and production of ECM components; with the inclusion of ECFCs for luminal endothelialisation, an encouraging outcome warranting further consideration in future studies. In combination, these findings represent a substantial step toward the development of the next generation of small-diameter vascular grafts in the management of cardiovascular disease.

Nonlinear Elasticity of Blood Vessels and Vascular Grafts

The transplantation of vascular grafts has emerged as a prevailing approach to address vascular disorders. However, the development of small-diameter vascular grafts is still in progress, as they serve in a more complicated mechanical environment than their counterparts with larger diameters. The biocompatibility and functional characteristics of small-diameter vascular grafts have been well developed; however, mismatch in mechanical properties between the vascular grafts and native arteries has not been accomplished, which might facilitate the long-term patency of small-diameter vascular grafts. From a point of view in mechanics, mimicking the nonlinear elastic mechanical behavior exhibited by natural blood vessels might be the state-of-the-art in designing vascular grafts. This review centers on elucidating the nonlinear elastic behavior of natural blood vessels and vascular grafts. The biological functionality and limitations associated with as-reported vascular grafts are meticulously reviewed and the future trajectory for fabricating biomimetic small-diameter grafts is discussed. This review might provide a different insight from the traditional design and fabrication of artificial vascular grafts.

Drug eluting protein and polysaccharides-based biofunctionalized fabric textiles- pioneering a new frontier in tissue engineering: An extensive review

In the ever-evolving landscape of tissue engineering, medicated biotextiles have emerged as a game-changer. These remarkable textiles have garnered significant attention for their ability to craft tissue scaffolds that closely mimic the properties of natural tissues. This comprehensive review delves into the realm of medicated protein and polysaccharide-based biotextiles, exploring a diverse array of fabric materials. We unravel the intricate web of fabrication methods, ranging from weft/warp knitting to plain/stain weaving and braiding, each lending its unique touch to the world of biotextiles creation. Fibre production techniques, such as melt spinning, wet/gel spinning, and multicomponent spinning, are demystified to shed light on the magic behind these ground-breaking textiles. The biotextiles thus crafted exhibit exceptional physical and chemical properties that hold immense promise in the field of tissue engineering (TE). Our review underscores the myriad applications of drug-eluting protein and polysaccharide-based textiles, including TE, tissue repair, regeneration, and wound healing. Additionally, we delve into commercially available products that harness the potential of medicated biotextiles, paving the way for a brighter future in healthcare and regenerative medicine. Step into the world of innovation with medicated biotextiles-where science meets the art of healing.

A polyurethane-based hydrophilic elastomer with multi-biological functions for small-diameter vascular grafts

Thrombosis and intimal hyperplasia (IH) are two major problems faced by the small-diameter vascular grafts. Mimicking the native endothelium and physiological elasticity of blood vessels is considered an ideal strategy. Polyurethane (PU) is suitable for vascular grafts in mechanics because of its molecular designability and elasticity; however, it generally lacks the endothelium-like biofunctions and hydrophilicity. To solve this contradiction, a hydrophilic PU elastomer is developed by crosslinking the hydrophobic hard-segment chains containing diselenide with diaminopyrimidine-capped polyethylene glycol (PEG). In this network, the hydrophobic aggregation occurs underwater due to the uninterrupted hard-segment chains, leading to a significant self-enhancement in mechanics, which can be tailored to the elasticity similar to natural vessels by adjusting the crosslinking density. A series of in vitro studies confirm that the hydrophilicity of PEG and biological activities of aminopyrimidine and diselenide give the PU multi-biological functions similar to the native endothelium, including stable catalytic release of nitric oxide (NO) in the physiological level; anti-adhesion and anti-activation of platelets; inhibition of migration, adhesion, and proliferation of smooth muscle cells (SMCs); and antibacterial effect. In vivo studies further prove the good histocompatibility with both significant reduction in immune response and calcium deposition. STATEMENT OF SIGNIFICANCE: Constructing small-diameter vascular grafts similar to the natural vessels is considered an ideal method to solve the restenosis caused by thrombosis and intimal hyperplasia (IH). Because of the long-term stability, bulk modification is more suitable for implanted materials, however, how to achieve the biofunctions, hydrophilicity, and elasticity simultaneously is still a big challenge. In this work, a kind of polyurethane-based elastomer has been designed and prepared by crosslinking the functional long hard-segment chains with PEG soft segments. The underwater elasticity based on hydration-induced stiffening and the multi-biological functions similar to the native endothelium are compatible with natural vessels. Both in vitro and in vivo experiments demonstrate the potential of this PU as small-diameter vascular grafts.

Optimization of Electrospun Bilayer Vascular Grafts through Assessment of the Mechanical Properties of Monolayers

Small-diameter vascular grafts must be obtained with the most appropriate materials and design selection to harmoniously display a variety of features, including adequate tensile strength, compliance, burst strength, biocompatibility, and biodegradability against challenging physiological and hemodynamic conditions. In this study, monolayer vascular grafts with randomly distributed or radially oriented fibers are produced using neat, blended, and copolymer forms of polycaprolactone (PCL) and poly(lactic acid) (PLA) via the electrospinning technique. The blending ratio is varied by increasing 10 in the range of 50-100%. Bilayer graft designs are realized by determining the layers with a random fiber distribution for the inner layer and radial fiber orientation for the outer layer. SEM analysis, wall thickness and fiber diameter measurements, tensile strength, elongation, burst strength, and compliance tests are done for both mono- and bilayer scaffolds. The findings revealed that the scaffolds made of neat PCL show more flexibility than the neat PLA samples, which possess higher tensile strength values than neat PCL scaffolds. Also, in blended samples, the tensile strength values do not show a significant improvement, whereas the elongation values are enhanced in tubular samples, depending on the blending ratio. Also, neat poly(l-lactide-co-caprolactone) (PLCL) samples have both higher elongation and strength values than neat and blended scaffolds, with some exceptions. The blended specimens comprising a combination of PCL and PLA, with blending ratios of 80/20 and 70/30, exhibited the most elevated burst pressures. Conversely, the PLCL scaffolds demonstrated superior compliance levels. These findings suggest that the blending approach and fiber orientation offer enhanced burst strength, while copolymer utilization in PLCL scaffolds without fiber alignment enhances their compliance properties. Thus, it is evident that using a copolymer instead of blending PCL and PLA and combining the PLCL layer with PCL and PLA monolayers in bilayer vascular graft design is promising in terms of mechanical and biological properties.

Bioprinted vascular tissue: Assessing functions from cellular, tissue to organ levels

3D bioprinting technology is widely used to fabricate various tissue structures. However, the absence of vessels hampers the ability of bioprinted tissues to receive oxygen and nutrients as well as to remove wastes, leading to a significant reduction in their survival rate. Despite the advancements in bioinks and bioprinting technologies, bioprinted vascular structures continue to be unsuitable for transplantation compared to natural blood vessels. In addition, a complete assessment index system for evaluating the structure and function of bioprinted vessels in vitro has not yet been established. Therefore, in this review, we firstly highlight the significance of selecting suitable bioinks and bioprinting techniques as they two synergize with each other. Subsequently, focusing on both vascular-associated cells and vascular tissues, we provide a relatively thorough assessment of the functions of bioprinted vascular tissue based on the physiological functions that natural blood vessels possess. We end with a review of the applications of vascular models, such as vessel-on-a-chip, in simulating pathological processes and conducting drug screening at the organ level. We believe that the development of fully functional blood vessels will soon make great contributions to tissue engineering and regenerative medicine.

An advanced biphasic porous and injectable scaffold displays a fine balance between mechanical strength and remodeling capabilities essential for cartilage regeneration

An important challenge in tissue engineering is the regeneration of functional articular cartilage (AC). In the field, biomimetic hydrogels are being extensively studied as scaffolds that recapitulate microenvironmental features or as mechanical supports for transplanted cells. New advanced hydrogel formulations based on salmon methacrylate gelatin (sGelMA), a cold-adapted biomaterial, are presented in this work. The psychrophilic nature of this biomaterial provides rheological advantages allowing the fabrication of scaffolds with high concentrations of the biopolymer and high mechanical strength, suitable for formulating injectable hydrogels with high mechanical strength for cartilage regeneration. However, highly intricate cell-laden scaffolds derived from highly concentrated sGelMA solutions could be deleterious for cells and scaffold remodeling. On this account, the current study proposes the use of sGelMA supplemented with a mesophilic sacrificial porogenic component. The cytocompatibility of different sGelMA-based formulations is tested through the encapsulation of osteoarthritic chondrocytes (OACs) and stimulated to synthesize extracellular matrix (ECM) components in vitro and in vivo. The sGelMA-derived scaffolds reach high levels of stiffness, and the inclusion of porogens impacts positively the scaffold degradability and molecular diffusion, improved fitness of OACs, increased the expression of cartilage-related genes, increased glycosaminoglycan (GAG) synthesis, and improved remodeling toward cartilage-like tissues. Altogether, these data support the use of sGelMA solutions in combination with mammalian solid gelatin beads for highly injectable formulations for cartilage regeneration, strengthening the importance of the balance between mechanical properties and remodeling capabilities.

Advances in Biomedical Applications of Solution Blow Spinning

In recent years, Solution Blow Spinning (SBS) has emerged as a new technology for the production of polymeric, nanocomposite, and ceramic materials in the form of nano and microfibers, with similar features to those achieved by other procedures. The advantages of SBS over other spinning methods are the fast generation of fibers and the simplicity of the experimental setup that opens up the possibility of their on-site production. While producing a large number of nanofibers in a short time is a crucial factor in large-scale manufacturing, in situ generation, for example, in the form of sprayable, multifunctional dressings, capable of releasing embedded active agents on wounded tissue, or their use in operating rooms to prevent hemostasis during surgical interventions, open a wide range of possibilities. The interest in this spinning technology is evident from the growing number of patents issued and articles published over the last few years. Our focus in this review is on the biomedicine-oriented applications of SBS for the production of nanofibers based on the collection of the most relevant scientific papers published to date. Drug delivery, 3D culturing, regenerative medicine, and fabrication of biosensors are some of the areas in which SBS has been explored, most frequently at the proof-of-concept level. The promising results obtained demonstrate the potential of this technology in the biomedical and pharmaceutical fields.

Building Blood Vessel Chips with Enhanced Physiological Relevance

Blood vessel chips are bioengineered microdevices, consisting of biomaterials, human cells, and microstructures, which recapitulate essential vascular structure and physiology and allow a well-controlled microenvironment and spatial-temporal readouts. Blood vessel chips afford promising opportunities to understand molecular and cellular mechanisms underlying a range of vascular diseases. The physiological relevance is key to these blood vessel chips that rely on bioinspired strategies and bioengineering approaches to translate vascular physiology into artificial units. Here, we discuss several critical aspects of vascular physiology, including morphology, material composition, mechanical properties, flow dynamics, and mass transport, which provide essential guidelines and a valuable source of bioinspiration for the rational design of blood vessel chips. We also review state-of-art blood vessel chips that exhibit important physiological features of the vessel and reveal crucial insights into the biological processes and disease pathogenesis, including rare diseases, with notable implications for drug screening and clinical trials. We envision that the advances in biomaterials, biofabrication, and stem cells improve the physiological relevance of blood vessel chips, which, along with the close collaborations between clinicians and bioengineers, enable their widespread utility.

Development and mechanical characterization of decellularized scaffolds for an active aortic graft

Decellularized porcine aortas are proposed as scaffolds for revolutionary active aortic grafts. A change in the static and dynamic mechanical properties, associated with the microstructure of elastin and collagen fibers, corresponds to alteration in the cyclic expansion and perfusion, in addition to possible graft damage. Therefore, the present study thoroughly investigates the mechanical response of the decellularized scaffolds of human and porcine origin to static and dynamic mechanical loads. The responses of the native human and porcine aortas are also compared; this is unavailable in the literature. Because the aorta is subjected to pulsatile blood pressure, dynamical responses to cyclic loads and their associated viscoelastic properties are particularly relevant for advanced graft design. In parallel, this study examines the microstructure of the decellularized aorta. The resulting data are compared to the analogous data obtained for the native human and porcine tissues. The results indicate that by using an optimized decellularization protocol - based on sodium dodecyl sulfate (SDS) and DNase - that minimizes mechanical and structural changes of the tissue, layered scaffolds with static and dynamic properties very similar to natural human aortas are obtained. In particular, a decellularized porcine aorta is non-inferior to a decellularized human aorta. STATEMENT OF SIGNIFICANCE: About 55,000 patients undergo abdominal aortic aneurysm repair annually in the USA. The currently implanted grafts present a large mechanical mismatch with the native tissue. This increases the pulsatile nature of the blood flow with negative consequences to the organ perfusion. For this reason, biomimetic and mechanically compatible grafts for aortic repair are urgently needed and they can be obtained through tissue engineering. In this study, scaffolds from porcine and human aortas are obtained from an optimized decellularization protocol. They are accurately compared to the native tissue and present the ideal static and dynamic mechanical properties for developing innovative aortic grafts.

Fabrication of mechanical skeleton of small-diameter vascular grafts via rolling on water surface

Mimicking the multilayered structure of blood vessels and constructing a porous inner surface are two effective approaches to achieve mechanical matching and rapid endothelialization to reduce occlusion in small-diameter vascular grafts. However, the fabrication processes are complex and time consuming, thus complicating the fabrication of personalized vascular grafts. A simple and versatile strategy is proposed to prepare the skeleton of vascular grafts by rolling self-adhesive polymer films. These polymer films are directly fabricated by dropping a polymer solution on a water surface. For the tubes, the length and wall thickness are controlled by the rolling number and position of each film, whereas the structure and properties are tailored by regulating the solution composition. Double-layer vascular grafts (DLVGs) with microporous inner layers and impermeable outer layers are constructed; a microporous layer is formed by introducing a hydrophilic polymer into a polyurethane (PU) solution. DLVGs exhibit a J-shaped stress-strain deformation profile and compliance comparable to that of coronary arteries, sufficient suture retention strength and burst pressure, suitable hemocompatibility, significant adhesion, and proliferation of human umbilical vein endothelial cells. Freshly prepared PU tubes exhibit good cytocompatibility. Thus, this strategy demonstrates potential for rapid construction of small-diameter vascular grafts for individual customization.

Hydrogel coating based on dopamine-modified hyaluronic acid and gelatin with spatiotemporal drug release capacity for quick endothelialization and long-term anticoagulation

Due to the vital roles of vascular intima in preventing thrombus generation and maintaining vascular patency, methods to promote quick endothelialization on vascular grafts have drawn much attention. In this study, we novelly applied a double-layered hydrogel coating with spatiotemporal drug release capacity on a polycaprolactone (PCL) fibrous scaffold. The composite coating consisted of an inner dopamine-modified hyaluronic acid (HA) hydrogel and an outer gelatin hydrogel, which were generated via different crosslinking methods. Especially, heparin and chondroitin sulfate were introduced to the HA and gelatin hydrogels during the processing, thus endowing the vascular scaffold spatiotemporal drug release behavior. The composite coating developed surface hydrophilicity and mechanical properties of the PCL scaffold meanwhile stimulating the proliferation and angiogenesis behaviors of endothelial cells. Long-term anticoagulation property of the modified scaffold was also demonstrated in vitro. This investigation provides a universal strategy for quick endothelialization and long-term anticoagulation promotion of vascular grafts, which may be potentially used in treating cardiovascular diseases.

Strategies to counteract adverse remodeling of vascular graft: A 3D view of current graft innovations

Vascular grafts are widely used for vascular surgeries, to bypass a diseased artery or function as a vascular access for hemodialysis. Bioengineered or tissue-engineered vascular grafts have long been envisioned to take the place of bioinert synthetic grafts and even vein grafts under certain clinical circumstances. However, host responses to a graft device induce adverse remodeling, to varied degrees depending on the graft property and host's developmental and health conditions. This in turn leads to invention or failure. Herein, we have mapped out the relationship between the design constraints and outcomes for vascular grafts, by analyzing impairment factors involved in the adverse graft remodeling. Strategies to tackle these impairment factors and counteract adverse healing are then summarized by outlining the research landscape of graft innovations in three dimensions-cell technology, scaffold technology and graft translation. Such a comprehensive view of cell and scaffold technological innovations in the translational context may benefit the future advancements in vascular grafts. From this perspective, we conclude the review with recommendations for future design endeavors.

Rapid remodeling observed at mid-term in-vivo study of a smart reinforced acellular vascular graft implanted on a rat model

BACKGROUND

The poor performance of conventional techniques used in cardiovascular disease patients requiring hemodialysis or arterial bypass grafting has prompted tissue engineers to search for clinically appropriate off-the-shelf vascular grafts. Most patients with cardiovascular disease lack suitable autologous tissue because of age or previous surgery. Commercially available vascular grafts with diameters of < 5 mm often fail because of thrombosis and intimal hyperplasia.

RESULT

Here, we tested tubular biodegradable poly-e-caprolactone/polydioxanone (PCL/PDO) electrospun vascular grafts in a rat model of aortic interposition for up to 12 weeks. The grafts demonstrated excellent patency (100%) confirmed by Doppler Ultrasound, resisted aneurysmal dilation and intimal hyperplasia, and yielded neoarteries largely free of foreign materials. At 12 weeks, the grafts resembled native arteries with confluent endothelium, synchronous pulsation, a contractile smooth muscle layer, and co-expression of various extracellular matrix components (elastin, collagen, and glycosaminoglycan).

CONCLUSIONS

The structural and functional properties comparable to native vessels observed in the neoartery indicate their potential application as an alternative for the replacement of damaged small-diameter grafts. This synthetic off-the-shelf device may be suitable for patients without autologous vessels. However, for clinical application of these grafts, long-term studies (> 1.5 years) in large animals with a vasculature similar to humans are needed.

Influence of γ-Radiation on Mechanical Stability to Cyclic Loads Tubular Elastic Matrix of the Aorta

A significant drawback of the rigid synthetic vascular prostheses used in the clinic is the mechanical mismatch between the implant and the prosthetic vessel. When placing prostheses with radial elasticity, in which this deficiency is compensated, the integration of the graft occurs more favorably, so that signs of cell differentiation appear in the prosthesis capsule, which contributes to the restoration of vascular tone and the possibility of vasomotor reactions. Aortic prostheses fabricated by electrospinning from a blend of copolymers of vinylidene fluoride with hexafluoropropylene (VDF/HFP) had a biomechanical behavior comparable to the native aorta. In the present study, to ensure mechanical stability in the conditions of a living organism, the fabricated blood vessel prostheses (BVP) were cross-linked with γ-radiation. An optimal absorbed dose of 0.3 MGy was determined. The obtained samples were implanted into the infrarenal aorta of laboratory animals-Landrace pigs. Histological studies have shown that the connective capsule that forms around the prosthesis has signs of high tissue organization. This is evidenced by the cells of the fibroblast series located in layers oriented along and across the prosthesis, similar to the orientation of cells in a biological arterial vessel.

An Investigation of the Constructional Design Components Affecting the Mechanical Response and Cellular Activity of Electrospun Vascular Grafts

Cardiovascular disease is anticipated to remain the leading cause of death globally. Due to the current problems connected with using autologous arteries for bypass surgery, researchers are developing tissue-engineered vascular grafts (TEVGs). The major goal of vascular tissue engineering is to construct prostheses that closely resemble native blood vessels in terms of morphological, mechanical, and biological features so that these scaffolds can satisfy the functional requirements of the native tissue. In this setting, morphology and cellular investigation are usually prioritized, while mechanical qualities are generally addressed superficially. However, producing grafts with good mechanical properties similar to native vessels is crucial for enhancing the clinical performance of vascular grafts, exposing physiological forces, and preventing graft failure caused by intimal hyperplasia, thrombosis, aneurysm, blood leakage, and occlusion. The scaffold's design and composition play a significant role in determining its mechanical characteristics, including suturability, compliance, tensile strength, burst pressure, and blood permeability. Electrospun prostheses offer various models that can be customized to resemble the extracellular matrix. This review aims to provide a comprehensive and comparative review of recent studies on the mechanical properties of fibrous vascular grafts, emphasizing the influence of structural parameters on mechanical behavior. Additionally, this review provides an overview of permeability and cell growth in electrospun membranes for vascular grafts. This work intends to shed light on the design parameters required to maintain the mechanical stability of vascular grafts placed in the body to produce a temporary backbone and to be biodegraded when necessary, allowing an autologous vessel to take its place.

Structural design and mechanical performance of composite vascular grafts

This study reviews the state of the art in structural design and the corresponding mechanical behaviours of composite vascular grafts. We critically analyse surface and matrix designs composed of layered, embedded, and hybrid structures along the radial and longitudinal directions; materials and manufacturing techniques, such as tissue engineering and the use of textiles or their combinations; and the corresponding mechanical behaviours of composite vascular grafts in terms of their physical–mechanical properties, especially their stress–strain relationships and elastic recovery. The role of computational studies is discussed with respect to optimizing the geometrics designs and the corresponding mechanical behaviours to satisfy specialized applications, such as those for the aorta and its subparts. Natural and synthetic endothelial materials yield improvements in the mechanical and biological compliance of composite graft surfaces with host arteries. Moreover, the diameter, wall thickness, stiffness, compliance, tensile strength, elasticity, and burst strength of the graft matrix are determined depending on the application and the patient. For composite vascular grafts, hybrid architectures are recommended featuring multiple layers, dimensions, and materials to achieve the desired optimal flexibility and function for complying with user-specific requirements. Rapidly emerging artificial intelligence and big data techniques for diagnostics and the three-dimensional (3D) manufacturing of vascular grafts will likely yield highly compliant, subject-specific, long-lasting, and economical vascular grafts in the near-future.

Graphic abstract

Scaffold Engineering with Flavone-Modified Biomimetic Architecture for Vascular Tissue Engineering Applications

BACKGROUND

Vascular intimal hyperplasia (IH) is one of the key challenges in the clinical application of small-diameter vascular grafts. Current tissue engineering strategies focus on vascularization and antithrombotics, yet few approaches have been developed to treat IH. Here, we designed a tissue-engineered vascular scaffold with portulaca flavonoid (PTF) composition and biomimetic architecture.

METHOD

By electrospinning, PTF is integrated with biodegradable poly(ε-caprolactone) (PCL) into a bionic vascular scaffold. The structure and functions of the scaffolds were evaluated based on material characterization and cellular biocompatibility. Human vascular smooth muscle cells (HVSMCs) were cultured on scaffolds for up to 14 days.

RESULTS

The incorporation of PTF and preparation parameters during fabrication influences the morphology of the scaffold, including fibre diameter, structure, and orientation. Compared to the PCL scaffold, the scaffolds integrated with bioactive PTF show better hydrophilicity and degradability. HVSMCs seeded on the scaffold alongside the fibres exhibit fusiform-like shapes, indicating that the scaffold can provide contact guidance for cell morphology alterations. This study demonstrates that the PCL/PTF (9.1%) scaffold inhibits the excessive proliferation of HVSMCs without causing cytotoxicity.

CONCLUSION

The study provides insights into the problem of restenosis caused by IH. This engineered vascular scaffold with complex function and preparation is expected to be applied as a substitute for small-diameter vascular grafts.

Pneumatospinning Biomimetic Scaffolds for Meniscus Tissue Engineering

Nanofibrous scaffolds fabricated via electrospinning have been proposed for meniscus tissue regeneration. However, the electrospinning process is slow, and can only generate scaffolds of limited thickness with densely packed fibers, which limits cell distribution within the scaffold. In this study, we explored whether pneumatospinning could produce thicker collagen type I fibrous scaffolds with higher porosity, that can support cell infiltration and neo-fibrocartilage tissue formation for meniscus tissue engineering. We pneumatospun scaffolds with solutions of collagen type I with thicknesses of approximately 1 mm in 2 h. Scanning electron microscopy revealed a mix of fiber sizes with diameters ranging from 1 to 30 µm. The collagen scaffold porosity was approximately 48% with pores ranging from 7.4 to 100.7 µm. The elastic modulus of glutaraldehyde crosslinked collagen scaffolds was approximately 45 MPa, when dry, which reduced after hydration to 0.1 MPa. Mesenchymal stem cells obtained from the infrapatellar fat pad were seeded in the scaffold with high viability (>70%). Scaffolds seeded with adipose-derived stem cells and cultured for 3 weeks exhibited a fibrocartilage meniscus-like phenotype (expressing COL1A1, COL2A1 and COMP). Ex vivo implantation in healthy bovine and arthritic human meniscal explants resulted in the development of fibrocartilage-like neotissues that integrated with the host tissue with deposition of glycosaminoglycans and collagens type I and II. Our proof-of-concept study indicates that pneumatospinning is a promising approach to produce thicker biomimetic scaffolds more efficiently that electrospinning, and with a porosity that supports cell growth and neo-tissue formation using a clinically relevant cell source.

Role of smooth muscle activation in the static and dynamic mechanical characterization of human aortas

The rupture of aortic aneurysms causes around 10,000 deaths each year in the United States. Prosthetic tubes for aortic repair present a large mismatch of mechanical properties with the natural aorta, which has negative consequences for perfusion. This motivates research into the mechanical characterization of human aortas to develop a new generation of mechanically compatible aortic grafts. Experimental data and a suitable material model for human aortas with vascular smooth muscle (VSM) activation are not available. Hence, the present study provides experimental data that are needed. These data made it possible to develop a precise structure-based model of active aortic tissue. The results show the importance of VSM activation on the static and dynamic mechanical response of human aortas.

Experimental data and a suitable material model for human aortas with smooth muscle activation are not available in the literature despite the need for developing advanced grafts; the present study closes this gap. Mechanical characterization of human descending thoracic aortas was performed with and without vascular smooth muscle (VSM) activation. Specimens were taken from 13 heart-beating donors. The aortic segments were cooled in Belzer UW solution during transport and tested within a few hours after explantation. VSM activation was achieved through the use of potassium depolarization and noradrenaline as vasoactive agents. In addition to isometric activation experiments, the quasistatic passive and active stress–strain curves were obtained for circumferential and longitudinal strips of the aortic material. This characterization made it possible to create an original mechanical model of the active aortic material that accurately fits the experimental data. The dynamic mechanical characterization was executed using cyclic strain at different frequencies of physiological interest. An initial prestretch, which corresponded to the physiological conditions, was applied before cyclic loading. Dynamic tests made it possible to identify the differences in the viscoelastic behavior of the passive and active tissue. This work illustrates the importance of VSM activation for the static and dynamic mechanical response of human aortas. Most importantly, this study provides material data and a material model for the development of a future generation of active aortic grafts that mimic natural behavior and help regulate blood pressure.

The effect of surface morphology on endothelial and smooth muscle cells growth on blow-spun fibrous scaffolds

This study aimed to analyze the growth of two types of blood vessel building cells: endothelial cells (ECs) and smooth muscle cells (SMCs) on surfaces with different morphology. Two types of materials, differing in morphology, were produced by the solution blow spinning technique. One-layer materials consisted of one fibrous layer with two fibrous surfaces. Bi-layer materials consisted of one fibrous-solid layer and one fibrous layer, resulting in two different surfaces. Additionally, materials with different average fiber diameters (about 200, 500, and 900 nm) were produced for each group. It has been shown that it is possible to obtain structures with a given morphology by changing the selected process parameters (working distance and polymer solution concentration). Both morphology (solid versus fibrous) and average fiber diameter (submicron fibers versus microfibers) of scaffolds influenced the growth of ECs. However, this effect was only visible after an extended period of culture (6 days). In the case of SMCs, it was proved that the best growth of SMCs is obtained for micron fibers (with an average diameter close to 900 nm) compared to the submicron fibers (with an average diameter below 900 nm).

Collagen fibril assembly: New approaches to unanswered questions

Collagen fibrils are essential for metazoan life. They are the largest, most abundant, and most versatile protein polymers in animals, where they occur in the extracellular matrix to form the structural basis of tissues and organs. Collagen fibrils were first observed at the turn of the 20th century. During the last 40 years, the genes that encode the family of collagens have been identified, the structure of the collagen triple helix has been solved, the many enzymes involved in the post-translational modifications of collagens have been identified, mutations in the genes encoding collagen and collagen-associated proteins have been linked to heritable disorders, and changes in collagen levels have been associated with a wide range of diseases, including cancer. Yet despite extensive research, a full understanding of how cells assemble collagen fibrils remains elusive. Here, we review current models of collagen fibril self-assembly, and how cells might exert control over the self-assembly process to define the number, length and organisation of fibrils in tissues.

Reconstruction of the Swine Pulmonary Artery Using a Graft Engineered With Syngeneic Cardiac Pericytes

The neonatal heart represents an attractive source of regenerative cells. Here, we report the results of a randomized, controlled, investigator-blinded preclinical study, which assessed the safety and effectiveness of a matrix graft cellularized with cardiac pericytes (CPs) in a piglet model of pulmonary artery (PA) reconstruction. Within each of five trios formed by 4-week-old female littermate piglets, one element (the donor) was sacrificed to provide a source of CPs, while the other two elements (the graft recipients) were allowed to reach the age of 10 weeks. During this time interval, culture-expanded donor CPs were seeded onto swine small intestinal submucosa (SIS) grafts, which were then shaped into conduits and conditioned in a flow bioreactor. Control unseeded SIS conduits were subjected to the same procedure. Then, recipient piglets were randomized to surgical reconstruction of the left PA (LPA) with unseeded or CP-seeded SIS conduits. Doppler echocardiography and cardiac magnetic resonance imaging (CMRI) were performed at baseline and 4-months post-implantation. Vascular explants were examined using histology and immunohistochemistry. All animals completed the scheduled follow-up. No group difference was observed in baseline imaging data. The final Doppler assessment showed that the LPA’s blood flow velocity was similar in the treatment groups. CMRI revealed a mismatch in the average growth of the grafted LPA and contralateral branch in both treatment groups. Histology of explanted arteries demonstrated that the CP-seeded grafts had a thicker luminal cell layer, more intraparietal arterioles, and a higher expression of endothelial nitric oxide synthase (eNOS) compared with unseeded grafts. Moreover, the LPA stump adjacent to the seeded graft contained more elastin and less collagen than the unseeded control. Syngeneic CP engineering did not accomplish the primary goal of supporting the graft’s growth but was able to improve secondary outcomes, such as the luminal cellularization and intraparietal vascularization of the graft, and elastic remodeling of the recipient artery. The beneficial properties of neonatal CPs may be considered in future bioengineering applications aiming to reproduce the cellular composition of native arteries.

Hyaluronic Acid/Collagen Nanofiber Tubular Scaffolds Support Endothelial Cell Proliferation, Phenotypic Shape and Endothelialization

In this study, we designed and synthetized artificial vascular scaffolds based on nanofibers of collagen functionalized with hyaluronic acid (HA) in order to direct the phenotypic shape, proliferation, and complete endothelization of mouse primary aortic endothelial cells (PAECs). Layered tubular HA/collagen nanofibers were prepared using electrospinning and crosslinking process. The obtained scaffold is composed of a thin inner layer and a thick outer layer that structurally mimic the layer the intima and media layers of the native blood vessels, respectively. Compared with the pure tubular collagen nanofibers, the surface of HA functionalized collagen nanofibers has higher anisotropic wettability and mechanical flexibility. HA/collagen nanofibers can significantly promote the elongation, proliferation and phenotypic shape expression of PAECs. In vitro co-culture of mouse PAECs and their corresponding smooth muscle cells (SMCs) showed that the luminal endothelialization governs the biophysical integrity of the newly formed extracellular matrix (e.g., collagen and elastin fibers) and structural remodeling of SMCs. Furthermore, in vitro hemocompatibility assays indicated that HA/collagen nanofibers have no detectable degree of hemolysis and coagulation, suggesting their promise as engineered vascular implants.

Cellularized small-caliber tissue-engineered vascular grafts: looking for the ultimate gold standard

Due to the lack of efficacy of synthetic vascular substitutes in the replacement of small-caliber arteries, vascular tissue engineering (VTE) has emerged as a promising solution to produce viable small-caliber tissue-engineered vascular grafts (TEVG). Previous studies have shown the importance of a cellular intimal layer at the luminal surface of TEVG to prevent thrombotic events. However, the cellularization of a TEVG seems to be a critical approach to consider in the development of a TEVG. To date, no standard cellularization method or cell type has been established to create the ideal TEVG by promoting its long-term patency and function. In this review, advances in VTE are described and discussed with a particular focus on the construction approaches of cellularized small-caliber TEVGs, the cell types used, as well as their preclinical and clinical applications.

Cylindrical Polyurethane Scaffold Fabricated Using the Phase Inversion Method: Influence of Process Parameters on Scaffolds' Morphology and Mechanical Properties

This work presents a method of obtaining cylindrical polymer structures with a given diameter (approx. 5 mm) using the phase inversion technique. As part of the work, the influence of process parameters (polymer hardness, polymer solution concentration, the composition of the non-solvent solution, process time) on the scaffolds' morphology was investigated. Additionally, the influence of the addition of porogen on the scaffold's mechanical properties was analyzed. It has been shown that the use of a 20% polymer solution of medium hardness (ChronoFlex C45D) and carrying out the process for 24 h in 0:100 water/ethanol leads to the achievement of repeatable structures with adequate flexibility. Among the three types of porogens tested (NaCl, hexane, polyvinyl alcohol), the most favorable results were obtained for 10% polyvinyl alcohol (PVA). The addition of PVA increases the range of pore diameters and the value of the mean pore diameter (9.6 ± 3.2 vs. 15.2 ± 6.4) while reducing the elasticity of the structure (Young modulus = 3.6 ± 1.5 MPa vs. 9.7 ± 4.3 MPa).

An in vitro Perfused Macroencapsulation Device to Study Hemocompatibility and Survival of Islet-Like Cell Clusters

Transplantation of hydrogel-encapsulated pancreatic islets is a promising long-term treatment for type 1 diabetes that restores blood glucose regulation while providing graft immunoprotection. Most human-scale islet encapsulation devices that rely solely on diffusion fail to provide sufficient surface area to meet islet oxygen demands. Perfused macroencapsulation devices use blood flow to mitigate oxygen limitations but increase the complexity of blood-device interactions. Here we describe a human-scale in vitro perfusion system to study hemocompatibility and performance of islet-like cell clusters (ILCs) in alginate hydrogel. A cylindrical perfusion device was designed for multi-day culture without leakage, contamination, or flow occlusion. Rat blood perfusion was assessed for prothrombin time and international normalized ratio and demonstrated no significant change in clotting time. Ex vivo perfusion performed with rats showed patency of the device for over 100 min using Doppler ultrasound imaging. PET-CT imaging of the device successfully visualized metabolically active mouse insulinoma 6 ILCs. ILCs cultured for 7 days under static conditions exhibited abnormal morphology and increased activated caspase-3 staining when compared with the perfused device. These findings reinforce the need for convective transport in macroencapsulation strategies and offer a robust and versatile in vitro system to better inform preclinical design.

3D Composite Bioprinting for Fabrication of Artificial Biological Tissues

Three-dimensional (3D) bioprinting is an important technology for fabricating artificial tissue. To effectively reconstruct the multiscale structure and multi-material gradient of natural tissues and organs, 3D bioprinting has been increasingly developed into multi-process composite mode. The current 3D composite bioprinting is a combination of two or more printing processes, and oftentimes, physical field regulation that can regulate filaments or cells during or after printing may be involved. Correspondingly, both path planning strategy and process control all become more complex. Hence, the computer-aided design and computer-aided manufacturing (CAD/CAM) system that is traditionally used in 3D printing system is now facing challenges. Thus, the scale information that cannot be modeled in the CAD process should be considered in the design of CAM by adding a process management module in the traditional CAD/CAM system and add more information reflecting component gradient in the path planning strategy.

Surface Engineering of Cardiovascular Devices for Improved Hemocompatibility and Rapid Endothelialization

Cardiovascular devices have been widely applied in the clinical treatment of cardiovascular diseases. However, poor hemocompatibility and slow endothelialization on their surface still exist. Numerous surface engineering strategies have mainly sought to modify the device surface through physical, chemical, and biological approaches to improve surface hemocompatibility and endothelialization. The alteration of physical characteristics and pattern topographies brings some hopeful outcomes and plays a notable role in this respect. The chemical and biological approaches can provide potential signs of success in the endothelialization of vascular device surfaces. They usually involve therapeutic drugs, specific peptides, adhesive proteins, antibodies, growth factors and nitric oxide (NO) donors. The gene engineering can enhance the proliferation, growth, and migration of vascular cells, thus boosting the endothelialization. In this review, the surface engineering strategies are highlighted and summarized to improve hemocompatibility and rapid endothelialization on the cardiovascular devices. The potential outlook is also briefly discussed to help guide endothelialization strategies and inspire further innovations. It is hoped that this review can assist with the surface engineering of cardiovascular devices and promote future advancements in this emerging research field.

Construction of vascular graft with circumferentially oriented microchannels for improving artery regeneration

Design and fabrication of scaffolds with three-dimensional (3D) topological cues inducing regeneration of the neo-tissue comparable to native one remains a major challenge in both scientific and clinical fields. Here, we developed a well-designed vascular graft with 3D highly interconnected and circumferentially oriented microchannels by using the sacrificial sugar microfiber leaching method. The microchannels structure was capable of promoting the migration, oriented arrangement, elongation, and the contractile phenotype expression of vascular smooth muscle cells (VSMCs) in vitro. After implantation into the rat aorta defect model, the microchannels in vascular grafts simultaneously improved the infiltration and aligned arrangement of VSMCs and the oriented deposition of extracellular matrix (ECM), as well as the recruitment and polarization of macrophages. These positive results also provided protection and support for ECs growth, and ultimately accelerated the endothelialization. Our research provides a new strategy for the fabrication of grafts with the capability of inducing arterial regeneration, which could be further extended to apply in preparing other kinds of oriented scaffolds aiming to guide oriented tissue in situ regeneration.

Promotion of Endothelial Cell Adhesion and Antithrombogenicity of Polytetrafluoroethylene by Chemical Grafting of Chondroitin Sulfate

Polytetrafluoroethylene (PTFE) is one of the polymers extensively applied in biomedicine. However, the application of PTFE as a small-diameter vascular graft results in thrombosis and intimal hyperplasia because of the immune response. Therefore, improving the biocompatibility and anticoagulant properties of PTFE is a key to solving this problem. In this study, a hydroxyl group-rich surface was obtained by oxidizing a benzoin-reduced PTFE membrane. Then, chondroitin sulfate (CS), an anticoagulant, was grafted on the surface of the hydroxylated PTFE membrane using 3-aminopropyltriethoxysilane. The successful modification of the membrane in each step was demonstrated by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Hydroxylation and the grafting of CS greatly increased the hydrophilicity and roughness of membrane samples. Moreover, the hydroxylated PTFE membrane enhanced the adhesion ability of endothelial cells, and the grafting of CS also promoted the proliferation of endothelial cells and decreased platelet adhesion. The results indicate that the PTFE membranes grafted with CS are able to facilitate rapid endothelialization and inhibit thrombus formation, which makes the proposed method outstanding for artificial blood vessel applications.

Honeycomb-like pH-responsive γ-cyclodextrin electrospun particles for highly efficient tumor therapy

We report here the tumor-implantable microparticles with a honeycomb-like porous structure. These microparticles were prepared by electrospinning using γ-cyclodextrin (γ-CD) conjugated with 3-(diethylamino)propylamine (DEAP, as a pH-responsive moiety), named γ-CD-DEAP. The resulting microparticles had pore channels (constructed using γ-CD-DEAP) extending into the deep compartment of the microparticles and allowing efficient paclitaxel (PTX, as a chemotherapeutic model drug) entrapment by a simple hole-filling encapsulation process. Importantly, the hydrophobic DEAP (at pH 7.4) in the γ-CD-DEAP microparticles changed to hydrophilic DEAP (at pH 6.8) because of its acidic pH-induced protonation. This phenomenon resulted in an acidic pH-activated particle destruction by a charge-charge repulsion between the protonated DEAP moieties and allowed a pH-triggered release of the encapsulated PTX from the collapsed microparticles. Consequently, γ-CD-DEAP microparticles implanted at the tumor site caused a significant enhancement of the in vitro/in vivo tumor cell ablation, suggesting their significant potential as a chemotherapeutic implant for tumor therapy.