Vascular endothelial growth factor immobilized on mussel-inspired three-dimensional bilayered scaffold for artificial vascular graft application: In vitro and in vivo evaluations

Innovative Substrate Design with Basement Membrane Components for Enhanced Endothelial Cell Function and Endothelization

Enhancing endothelial cell growth on small-diameter vascular grafts produced from decellularized tissues or synthetic substrates is pivotal for preventing thrombosis. While optimized decellularization protocols can preserve the structure and many components of the extracellular matrix (ECM), the process can still lead to the loss of crucial basement membrane proteins, such as laminin, collagen IV, and perlecan, which are pivotal for endothelial cell adherence and functional growth. This loss can result in poor endothelialization and endothelial cell activation causing thrombosis and intimal hyperplasia. To address this, the basement membrane's ECM is emulated on fiber substrates, providing a more physiological environment for endothelial cells. Thus, fibroblasts are cultured on fiber substrates to produce an ECM membrane substrate (EMMS) with basement membrane proteins. The EMMS then underwent antigen removal (AR) treatment to eliminate antigens from the membrane while preserving essential proteins and producing an AR-treated membrane substrate (AMS). Subsequently, human endothelial cells cultured on the AMS exhibited superior proliferation, nitric oxide production, and increased expression of endothelial markers of quiescence/homeostasis, along with autophagy and antithrombotic factors, compared to those on the decellularized aortic tissue. This strategy showed the potential of pre-endowing fiber substrates with a basement membrane to enable better endothelization.

Influence of Substrate Structure and Associated Properties on Endothelial Cell Behavior in the Context of Behaviors Associated with Laminar Flow Conditions

In order to treat most vascular diseases, arterial grafts are commonly employed for replacing small-diameter vessels, yet they often cause thrombosis. The growth of endothelial cells along the interior surfaces of these grafts (substrates) is critical to mitigate thrombosis. Typically, endothelial cells are cultured inside these grafts under laminar flow conditions to emulate the native environment of blood vessels and produce an endothelium. Alternatively, the substrate structure could have a similar influence on endothelial cell behavior as laminar flow conditions. In this study, we investigated whether substrates with aligned fiber structures could induce responses in human umbilical vein endothelial cells (HUVECs) akin to those elicited by laminar flow. Our observations revealed that HUVECs on aligned substrates displayed significant morphological changes, aligning parallel to the fibers, similar to effects reported under laminar flow conditions. Conversely, HUVECs on random substrates maintained their characteristic cobblestone appearance. Notably, cell migration was more significant on aligned substrates. Also, we observed that while vWF expression was similar between both substrates, the HUVECs on aligned substrates showed more expression of platelet/endothelial cell adhesion molecule-1 (PECAM-1/CD31), laminin, and collagen IV. Additionally, these cells exhibited increased gene expression related to critical functions such as proliferation, extracellular matrix production, cytoskeletal reorganization, autophagy, and antithrombotic activity. These findings indicated that aligned substrates enhanced endothelial growth and behavior compared to random substrates. These improvements are similar to the beneficial effects of laminar flow on endothelial cells, which are well-documented compared to static or turbulent flow conditions.

Efforts to promote osteogenesis-angiogenesis coupling for bone tissue engineering

Repair of bone defects exceeding a critical size has been always a big challenge in clinical practice. Tissue engineering has exhibited great potential to effectively repair the defects with less adverse effect than traditional bone grafts, during which how to induce vascularized bone formation has been recognized as a critical issue. Therefore, recently many studies have been launched to attempt to promote osteogenesis-angiogenesis coupling. This review summarized comprehensively and explored in depth current efforts to ameliorate the coupling of osteogenesis and angiogenesis from four aspects, namely the optimization of scaffold components, modification of scaffold structures, loading strategies for bioactive substances, and employment tricks for appropriate cells. Especially, the advantages and the possible reasons for every strategy, as well as the challenges, were elaborated. Furthermore, some promising research directions were proposed based on an in-depth analysis of the current research. This paper will hopefully spark new ideas and approaches for more efficiently boosting new vascularized bone formations.

Incorporation of Controlled Release Systems Improves the Functionality of Biodegradable 3D Printed Cardiovascular Implants

New horizons in cardiovascular research are opened by using 3D printing for biodegradable implants. This additive manufacturing approach allows the design and fabrication of complex structures according to the patient's imaging data in an accurate, reproducible, cost-effective, and quick manner. Acellular cardiovascular implants produced from biodegradable materials have the potential to provide enough support for in situ tissue regeneration while gradually being replaced by neo-autologous tissue. Subsequently, they have the potential to prevent long-term complications. In this Review, we discuss the current status of 3D printing applications in the development of biodegradable cardiovascular implants with a focus on design, biomaterial selection, fabrication methods, and advantages of implantable controlled release systems. Moreover, we delve into the intricate challenges that accompany the clinical translation of these groundbreaking innovations, presenting a glimpse of potential solutions poised to enable the realization of these technologies in the realm of cardiovascular medicine.

Polydopamine (PDA) coatings with endothelial vascular growth factor (VEGF) immobilization inhibiting neointimal formation post zinc (zn) wire implantation in rat aortas

BACKGROUND

Bioresorbable stents are designed to provide temporary mechanical support to the coronary arteries and then slowly degrade in vivo to avoid chronic inflammation. Zinc (Zn) is a promising material for bioresorbable stents; However, it can cause inflammation and neointimal formation after being implanted into blood vessels.

METHODS

To improve biocompatibility of Zn, we first coated it with polydopamine (PDA), followed by immobilization of endothelial vascular growth factor (VEGF) onto the PDA coatings. Adhesion, proliferation, and phenotype maintenance of endothelial cells (ECs) on the coated Zn were evaluated in vitro. Then, a wire aortic implantation model in rats mimicking endovascular stent implantation in humans was used to assess vascular responses to the coated Zn wires in vivo. Thrombosis in aortas post Zn wire implantation, degradation of Zn wires in vivo, neointimal formation surrounding Zn wires, and macrophage infiltration and extracellular matrix (ECM) remodeling in the neointimas were examined.

RESULTS

In vitro data showed that the PDA-coated Zn encouraged EC adhesion, spreading, proliferation, and phenotype maintenance on its surfaces. VEGF functionalization on PDA coatings further enhanced the biocompatibility of Zn to ECs. Implantation of PDA-coated Zn wires into rat aortas didn't cause thrombosis and showed a faster blood flow than pure Zn or the Zn wires coated with VEGF alone. In addition, the PDA coating didn't affect the degradation of Zn wires in vivo. Besides, the PDA-coated Zn wires reduced neointimal formation, increased EC coverage, decreased macrophage infiltration, and declined aggrecan accumulation in ECM. VEGF immobilization onto PDA coatings didn't cause thrombosis and affect Zn degradation in vivo as well, and further increased the endothelization percentage as compared to PDA coating alone, thus resulting in thinner neointimas.

CONCLUSION

These results indicate that PDA coatings with VEGF immobilization would be a promising approach to functionalize Zn surfaces to increase biocompatibility, reduce inflammation, and inhibit neointimal formation after Zn implantation in vivo.

Investigation of osteogenesis and angiogenesis in perfusion bioreactors using improved multi-layer PCL-nHA-nZnO electrospun scaffolds

PURPOSE

Bone tissue engineering aims to create a three-dimensional, matured, angiogenic scaffold with a suitable thickness that resembles a natural bone matrix. On the other hand, electrospun fibers, which researchers have considered due to their good biomimetic properties, are considered 2D structures. Due to the highly interwoven network and small pore size, achieving the desired thickness for bone lesions has always been challenging. In bone tissue engineering, bioreactors are crucial for achieving initial tissue maturity and introducing certain signals as flow parameters for differentiation.

METHODS

In the present study, Human bone marrow mesenchymal stem cells (hBMSCs) and human umbilical vein endothelial cells (HUVECs) were co-cultured in a perfusion bioreactor on treated (improved pore size by gelatin sacrification and subsequent ultrasonication) 5-layer polycaprolactone-nano hydroxyapatite-nano zinc oxide (T-PHZ) scaffolds to investigate osteogenesis and angiogenesis simultaneously. The flow parameters and stresses on the cells were studied using two patterns of parallel and vertical scaffolds relative to the flow of the culture medium. In dynamic vertical flow (DVF), the culture medium flows perpendicular to the scaffolds, and in dynamic parallel flow (DPF), the culture medium flows parallel to the scaffolds. In all evaluations, static samples (S) served as the control group.

RESULTS

Live/dead, and MTT assays demonstrated the biocompatibility of the 5-layer scaffolds and the suitability of the bioreactor's functional conditions. ALP activity, EDAX analysis, and calcium content measurements exhibited greater osteogenesis for T-PHZ scaffolds in DVF conditions. Calcium content increased by a factor of 2.2, 1.8, and 1.6 during days 7 to 14 of culture under DVF, DPF and S conditions, respectively. After 21 days of co-culturing, an immunohistochemistry (IHC) test was performed to investigate angiogenesis and osteogenesis. Five antibodies were investigated in DVF, CD31, VEGFA, and VEGFR2 for angiogenesis, osteocalcin, and RUNX2 for osteogenesis. Compressive stress applied in DVF mode has increased osteogenic activity compared to DPF.

CONCLUSION

The results indicated the development of ideal systems for osteogenesis and angiogenesis on the treated multilayer electrospun scaffolds in the perfusion bioreactor.

Polydopamine-Coated Polycaprolactone Electrospun Nanofiber Membrane Loaded with Thrombin for Wound Hemostasis

Hemorrhagic shock is the primary cause of death in patients with severe trauma, and the development of rapid and efficient hemostatic methods is of great significance in saving the lives of trauma patients. In this study, a polycaprolactone (PCL) nanofiber membrane was prepared by electrospinning. A PCL-PDA loading system was developed by modifying the surface of polydopamine (PDA), using inspiration from mussel adhesion protein, and the efficient and stable loading of thrombin (TB) was realized to ensure the bioactivity of TB. The new thrombin loading system overcomes the disadvantages of harsh storage conditions, poor strength, and ease of falling off, and it can use thrombin to start a rapid coagulation cascade reaction, which has the characteristics of fast hemostasis, good biocompatibility, high safety, and a wide range of hemostasis. The physicochemical properties and biocompatibility of the PCL-PDA-TB membrane were verified by scanning electron microscopy, the cell proliferation test, the cell adhesion test, and the extract cytotoxicity test. Red blood cell adhesion, platelet adhesion, dynamic coagulation time, and animal models all verified the coagulation effect of the PCL-PDA-TB membrane. Therefore, the PCL-PDA-TB membrane has great potential in wound hemostasis applications, and should be widely used in various traumatic hemostatic scenarios.

Microenvironment Restruction of Emerging 2D Materials and their Roles in Therapeutic and Diagnostic Nano-Bio-Platforms

Engineering advanced therapeutic and diagnostic nano-bio-platforms (NBPFs) have emerged as rapidly-developed pathways against a wide range of challenges in antitumor, antipathogen, tissue regeneration, bioimaging, and biosensing applications. Emerged 2D materials have attracted extensive scientific interest as fundamental building blocks or nanostructures among material scientists, chemists, biologists, and doctors due to their advantageous physicochemical and biological properties. This timely review provides a comprehensive summary of creating advanced NBPFs via emerging 2D materials (2D-NBPFs) with unique insights into the corresponding molecularly restructured microenvironments and biofunctionalities. First, it is focused on an up-to-date overview of the synthetic strategies for designing 2D-NBPFs with a cross-comparison of their advantages and disadvantages. After that, the recent key achievements are summarized in tuning the biofunctionalities of 2D-NBPFs via molecularly programmed microenvironments, including physiological stability, biocompatibility, bio-adhesiveness, specific binding to pathogens, broad-spectrum pathogen inhibitors, stimuli-responsive systems, and enzyme-mimetics. Moreover, the representative therapeutic and diagnostic applications of 2D-NBPFs are also discussed with detailed disclosure of their critical design principles and parameters. Finally, current challenges and future research directions are also discussed. Overall, this review will provide cutting-edge and multidisciplinary guidance for accelerating future developments and therapeutic/diagnostic applications of 2D-NBPFs.

Tissue-engineered small-diameter vascular grafts containing novel copper-doped bioactive glass biomaterials to promote angiogenic activity and endothelial regeneration

Small-diameter vascular grafts frequently fail because of obstruction and infection. Despite the wide range of commercially available vascular grafts, the anatomical uniqueness of defect sites demands patient-specific designs. This study aims to increase the success rate of implantation by fabricating bilayer vascular grafts containing bioactive glasses (BGs) and modifying their composition by removing hemostatic ions to make them blood-compatible and to enhance their antibacterial and angiogenesis properties. The porous vascular graft tubes were 3D printed using polycaprolactone, polyglycerol sebacate, and the modified BGs. The polycaprolactone sheath was then wrapped around the 3D-printed layer using the electrospinning technique to prevent blood leakage. The results demonstrated that the incorporation of modified BGs into the polymeric matrix not only improved the mechanical properties of the vascular graft but also significantly enhanced its antibacterial activity against both gram-negative and gram-positive strains. In addition, no hemolysis or platelet activity was detected after incorporating modified BGs into the vascular grafts. Copper-releasing vascular grafts significantly enhanced endothelial cell proliferation, motility, and VEGF secretion. Additionally, In vivo angiogenesis (CD31 immunofluorescent staining) and gene expression experiments showed that copper-releasing vascular grafts considerably promoted the formation of new blood vessels, low-grade inflammation (decreased expression of IL-1β and TNF-α), and high-level angiogenesis (increased expression of angiogenic growth factors including VEGF, PDGF-BB, and HEBGF). These observations indicate that the use of BGs with suitable compositional modifications in vascular grafts may promote the clinical success of patient-specific vascular prostheses by accelerating tissue regeneration without any coagulation problems.

Bioprinting Technologies and Bioinks for Vascular Model Establishment

Clinically, large diameter artery defects (diameter larger than 6 mm) can be substituted by unbiodegradable polymers, such as polytetrafluoroethylene. There are many problems in the construction of small diameter blood vessels (diameter between 1 and 3 mm) and microvessels (diameter less than 1 mm), especially in the establishment of complex vascular models with multi-scale branched networks. Throughout history, the vascularization strategies have been divided into three major groups, including self-generated capillaries from implantation, pre-constructed vascular channels, and three-dimensional (3D) printed cell-laden hydrogels. The first group is based on the spontaneous angiogenesis behaviour of cells in the host tissues, which also lays the foundation of capillary angiogenesis in tissue engineering scaffolds. The second group is to vascularize the polymeric vessels (or scaffolds) with endothelial cells. It is hoped that the pre-constructed vessels can be connected with the vascular networks of host tissues with rapid blood perfusion. With the development of bioprinting technologies, various fabrication methods have been achieved to build hierarchical vascular networks with high-precision 3D control. In this review, the latest advances in 3D bioprinting of vascularized tissues/organs are discussed, including new printing techniques and researches on bioinks for promoting angiogenesis, especially coaxial printing, freeform reversible embedded in suspended hydrogel printing, and acoustic assisted printing technologies, and freeform reversible embedded in suspended hydrogel (flash) technology.

Mussel‐Inspired Biomaterials: From Chemistry to Clinic

After several billions of years, nature still makes decisions on its own to identify, develop, and direct the most effective material for phenomena/challenges faced. Likewise, and inspired by the nature, we learned how to take steps in developing new technologies and materials innovations. Wet and strong adhesion by Mytilidae mussels (among which Mytilus edulis—blue mussel and Mytilus californianus—California mussel are the most well‐known species) has been an inspiration in developing advanced adhesives for the moist condition. The wet adhesion phenomenon is significant in designing tissue adhesives and surgical sealants. However, a deep understanding of engaged chemical moieties, microenvironmental conditions of secreted proteins, and other contributing mechanisms for outstanding wet adhesion mussels are essential for the optimal design of wet glues. In this review, all aspects of wet adhesion of Mytilidae mussels, as well as different strategies needed for designing and fabricating wet adhesives are discussed from a chemistry point of view. Developed muscle‐inspired chemistry is a versatile technique when designing not only wet adhesive, but also, in several more applications, especially in the bioengineering area. The applications of muscle‐inspired biomaterials in various medical applications are summarized for future developments in the field.

Clinical Application for Tissue Engineering Focused on Materials

Cardiovascular-related medical conditions remain a significant cause of death worldwide despite the advent of tissue engineering research more than half a century ago. Although autologous tissue is still the preferred treatment, donor tissue is limited, and there remains a need for tissue-engineered vascular grafts (TEVGs). The production of extensive vascular tissue (>1 cm3) in vitro meets the clinical needs of tissue grafts and biological research applications. The use of TEVGs in human patients remains limited due to issues related to thrombogenesis and stenosis. In addition to the advancement of simple manufacturing methods, the shift of attention to the combination of synthetic polymers and bio-derived materials and cell sources has enabled synergistic combinations of vascular tissue development. This review details the selection of biomaterials, cell sources and relevant clinical trials related to large diameter vascular grafts. Finally, we will discuss the remaining challenges in the tissue engineering field resulting from complex requirements by covering both basic and clinical research from the perspective of material design.

Strategies to Promote Vascularization in 3D Printed Tissue Scaffolds: Trends and Challenges

Three-dimensional (3D) printing techniques for scaffold fabrication have shown promising advancements in recent years owing to the ability of the latest high-performance printers to mimic the native tissue down to submicron scales. Nevertheless, host integration and performance of scaffolds in vivo have been severely limited owing to the lack of robust strategies to promote vascularization in 3D printed scaffolds. As a result, researchers over the past decade have been exploring strategies that can promote vascularization in 3D printed scaffolds toward enhancing scaffold functionality and ensuring host integration. Various emerging strategies to enhance vascularization in 3D printed scaffolds are discussed. These approaches include simple strategies such as the enhancement of vascular in-growth from the host upon implantation by scaffold modifications to complex approaches wherein scaffolds are fabricated with their own vasculature that can be directly anastomosed or microsurgically connected to the host vasculature, thereby ensuring optimal integration. The key differences among the techniques, their pros and cons, and the future opportunities for utilizing each technique are highlighted here. The Review concludes with the current limitations and future directions that can help 3D printing emerge as an effective biofabrication technique to realize tissues with physiologically relevant vasculatures to ultimately accelerate clinical translation.

Polydopamine-coated polycaprolactone/carbon nanotubes fibrous scaffolds loaded with brain-derived neurotrophic factor for peripheral nerve regeneration

Carbon nanotubes (CNTs) have attracted increasing attention in the field of peripheral nerve tissue engineering owing to their unique structural and physical characteristics. In this study, a novel type of aligned conductive scaffolds composed of polycaprolactone (PCL) and CNTs were fabricated via electrospinning. Utilizing the mussel-inspired polydopamine (PDA) surface modification, brain-derived neurotrophic factor (BDNF) was loaded onto PCL/CNTs fibrous scaffolds to obtain PCL/CNTs-PDA-BDNF fibrous scaffolds capable of the sustained release of BDNF over 28 days. Schwann cells were cultured on these scaffolds, and the effects of the scaffolds on peripheral nerve regeneration in vitro were assessed by studying cell proliferation, morphology and the expressions of myelination-related genes S100, P0 and myelin basic protein (MBP). Furthermore, the effects of these scaffolds on peripheral nerve regeneration in vivo were investigated using a 10-mm rat sciatic nerve defect model. Both the in vitro and in vivo results indicated that PCL/CNTs-PDA-BDNF fibrous scaffolds could effectively promote sciatic nerve regeneration and functional recovery. Therefore, PCL/CNTs-PDA-BDNF fibrous scaffolds have great potential for peripheral nerve restoration.

Biofabrication of small diameter tissue-engineered vascular grafts

Current clinical treatment strategies for the bypassing of small diameter (<6 mm) blood vessels in the management of cardiovascular disease frequently fail due to a lack of suitable autologous grafts, as well as infection, thrombosis, and intimal hyperplasia associated with synthetic grafts. The rapid advancement of 3D printing and regenerative medicine technologies enabling the manufacture of biological, tissue-engineered vascular grafts (TEVGs) with the ability to integrate, remodel, and repair in vivo, promises a paradigm shift in cardiovascular disease management. This review comprehensively covers current state-of-the-art biofabrication technologies for the development of biomimetic TEVGs. Various scaffold based additive manufacturing methods used in vascular tissue engineering, including 3D printing, bioprinting, electrospinning and melt electrowriting, are discussed and assessed against the biomechanical and functional requirements of human vasculature, while the efficacy of decellularization protocols currently applied to engineered and native vessels are evaluated. Further, we provide interdisciplinary insight into the outlook of regenerative medicine for the development of vascular grafts, exploring key considerations and perspectives for the successful clinical integration of evolving technologies. It is expected that continued advancements in microscale additive manufacturing, biofabrication, tissue engineering and decellularization will culminate in the development of clinically viable, off-the-shelf TEVGs for small diameter applications in the near future. STATEMENT OF SIGNIFICANCE: Current clinical strategies for the management of cardiovascular disease using small diameter vessel bypassing procedures are inadequate, with up to 75% of synthetic grafts failing within 3 years of implantation. It is this critically important clinical problem that researchers in the field of vascular tissue engineering and regenerative medicine aim to alleviate using biofabrication methods combining additive manufacturing, biomaterials science and advanced cellular biology. While many approaches facilitate the development of bioengineered constructs which mimic the structure and function of native blood vessels, several challenges must still be overcome for clinical translation of the next generation of tissue-engineered vascular grafts.

A 3D-printed bioactive polycaprolactone scaffold assembled with core/shell microspheres as a sustained BMP2-releasing system for bone repair

Integration of biological factors and hierarchical rigid scaffolds is of great interest in bone tissue engineering for fabrication of biomimetic constructs with high physical and biological performance for enhanced bone repair. Core/shell microspheres (CSMs) delivering bone morphogenetic protein-2 (BMP-2) and a strategy to integrate CSMs with 3D-printed scaffolds were developed herein to form a hybrid 3D system for bone repair. The scaffold was printed with polycaprolactone (PCL) and then coated with polydopamine. Shells of CSMs were electrosprayed with alginate. Cores were heparin-coated polylactic acid (PLA) microparticles fabricated via simple emulsion and heparin coating strategy. Assembly of microspheres and scaffolds was realized via a self-locking method with the assistance of controlled expansion of CSMs. The hybrid system was evaluated in the rat critical-sized bone defect model. CSMs released BMP-2 in a tunable manner and boosted osteogenic performance in vitro. CSMs were then successfully integrated inside the scaffolds. The assembled system effectively promoted osteogenesis in vitro and in vivo. These observations show the importance of how BMP-2 is delivered, and the core/shell microspheres represent effective BMP-2 carriers that could be integrated into scaffolds, together forming a hybrid system as a promising candidate for enhanced bone regeneration.

Endothelialization strategy of implant materials surface: The newest research in recent 5 years

In recent years, more and more metal or non-metal materials have been used in the treatment of cardiovascular diseases, but the vascular complications after transplantation are still the main factors restricting the clinical application of most grafts, such as acute thrombosis and graft restenosis. Implant materials have been extensively designed and surface optimized by researchers, but it is still too difficult to avoid complications. Natural vascular endodermis has excellent function, anti-coagulant and anti-intimal hyperplasia, and it is also the key to maintaining the homeostasis of normal vascular microenvironment. Therefore, how to promote the adhesion of endothelial cells (ECs) on the surface of cardiovascular materials to achieve endothelialization of the surface is the key to overcoming the complications after implant materialization. At present, the surface endothelialization design of materials based on materials surface science, bioactive molecules, and biological function intervention and feedback has attracted much attention. In this review, we summarize the related research on the surface modification of materials by endothelialization in recent years, and analyze the advantages and challenges of current endothelialization design ideas, explain the relationship between materials, cells, and vascular remodeling in order to find a more ideal endothelialization surface modification strategy for future researchers to meet the requirements of clinical biocompatibility of cardiovascular materials.

Polycaprolactone usage in additive manufacturing strategies for tissue engineering applications: A review

Polycaprolactone (PCL) has been extensively applied on tissue engineering because of its low-melting temperature, good processability, biodegradability, biocompatibility, mechanical resistance, and relatively low cost. The advance of additive manufacturing (AM) technologies in the past decade have boosted the fabrication of customized PCL products, with shorter processing time and absence of material waste. In this context, this review focuses on the use of AM techniques to produce PCL scaffolds for various tissue engineering applications, including bone, muscle, cartilage, skin, and cardiovascular tissue regeneration. The search for optimized geometry, porosity, interconnectivity, controlled degradation rate, and tailored mechanical properties are explored as a tool for enhancing PCL biocompatibility and bioactivity. In addition, rheological and thermal behavior is discussed in terms of filament and scaffold production. Finally, a roadmap for future research is outlined, including the combination of PCL struts with cell-laden hydrogels and 4D printing.

Facile Preparation of β-Cyclodextrin-grafted Chitosan Electrospun Nanofibrous Scaffolds as a Hydrophobic Drug Delivery Vehicle for Tissue Engineering Applications

Despite advances in the bio-tissue engineering area, the technical basis to directly load hydrophobic drugs on chitosan (CTS) electrospun nanofibers (ENs) has not yet been fully established. In this study, we fabricated CTS ENs by using an electrospinning (ELSP) system, followed by surface modification using succinyl-beta-cyclodextrin (β-CD) under mild conditions. The β-CD-modified CTS (βCTS) ENs had slightly increased hydrophobicity compared to pristine CTS ENs as well as decreased residual amine content on the surface. Through FTIR spectroscopy and thermogravimetric analysis (TGA), we characterized the surface treatment physiochemically. In the drug release test, we demonstrated the stable and sustained release of a hydrophobic drug (e.g., dexamethasone) loaded on β-CD ENs. During in vitro biocompatibility assessments, the grafting of β-CD was shown to not reduce cell viability compared to pristine CTS ENs. Additionally, cells proliferated well on β-CD ENs, and this was confirmed by F-actin fluorescence staining. Overall, the material and strategies developed in this study have the potential to load a wide array of hydrophobic drugs. This could be applied as a drug carrier for a broad range of tissue engineering applications.

Hyaluronic acid-functionalized poly-lactic acid (PLA) microfibers regulate vascular endothelial cell proliferation and phenotypic shape expression

This work was designed to evaluate the efficacy of hyaluronic acid (HA) functionalized tubular poly-lactic acid (PLA) microfibers in directing the luminal pre-endothelialization of vascular endothelial cells (ECs). Tubular HA/PLA microfibers with hierarchical architecture were prepared by electrospinning and chemical cross-linking process. A layer of HA microfibrous film coating was fixed on the inner wall surface of the tubular HA/PLA microfibers, resulting in higher anisotropy wettability and relatively lower surface energy and roughness. We confirmed that HA coating on PLA microfibers surface have reduced hemolytic activity and coagulation degree. Mouse vascular ECs exhibited surface-dependent differences in cell elongation and proliferation (HA/PLA > PLA). Compared with PLA microfibers, the gene expression levels of platelet EC adhesion molecule-1 (PECAM-1/CD31) and vascular endothelial growth factor (VEGF) in ECs of HA/PLA microfibers surface were up-regulated. Immunostaining analysis revealed that the surface of HA/PLA nanofibers supported the expression of mature vascular EC phenotype CD31 protein. In vitro co-culture analysis showed that the luminal pre-endothelialization induced vascular smooth muscle cells (SMCs) to maintain their phenotypic shape and establish natural behavior patterns in the hierarchical tubular scaffold. These studies indicate that the biophysical cues of scaffolds are potent regulators of vascular EC endothelialization.

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.

Collective influence of substrate chemistry with physiological fluid shear stress on human umbilical vein endothelial cells

In the treatment of cardiovascular diseases, vascular scaffold materials play an extremely important role. The appropriate substrate chemistries and 15 dynes/cm² physiological fluid shear stress (FSS) are both required to ensure normal physiological activity of human umbilical vein endothelial cells (HUVECs). The present study reported the collective influence of substrate chemistries and FSS on HUVECs in the sense of its biological functions. The CH₃ , NH₂ , and OH functional groups were adopted to offer a variety of substrate chemistries on glass slides by the technology of self-assembled monolayers, whereas FSS was generated by a parallel-plate fluid flow system. Substrate chemistries on its own by no means had noticeable effects on eNOS, ATP, NO, and PGI₂ expressions, while FSS stimuli enhanced their production. While substrate chemistries, as well as FSS, were both exerted, the releases of ATP, NO, and PGI₂ were dependent on substrate chemistries. Study of F-actin organization and focal adhesions (FAs) formation of HUVECs before FSS exposure proves that F-action organization and FAs formation followed similar chemistry-dependence. Hereby proposed a feasible mechanism, that is, the F-actin organization and FAs formation of HUVECs are controlled by substrate chemistries, further advancing the modulation of FSS-triggered responses of HUVECs.

Growth factor loading on aliphatic polyester scaffolds

Cells, scaffolds and growth factors are three elements of tissue engineering. The success of tissue engineering methods relies on precise and dynamic interactions between cells, scaffolds and growth factors. Aliphatic polyester scaffolds are promising tissue engineering scaffolds that possess good mechanical properties, low immunogenicity, non-toxicity, and adjustable degradation rates. How growth factors can be loaded onto/into aliphatic polyester scaffolds and be constantly released with the required bioactivity to regulate cell growth and promote defect tissue repair and regeneration has become the main concern of tissue engineering researchers. In this review, the existing main methods of loading growth factors on aliphatic polyester scaffolds, the release behavior of loaded growth factors and their positive effects on cell, tissue repair and regeneration are introduced. Advantages and shortcomings of each method also are mentioned. It is still a great challenge to control the release of loaded growth factors at a certain time and at a concentration simulating the biological environment of native tissue.

Drug-Eluting Hydrophilic Coating Modification of Intraocular Lens via Facile Dopamine Self-Polymerization for Posterior Capsular Opacification Prevention

Posterior capsular opacification (PCO) is the most important complication in cataract phacoemulsification and intraocular lens (IOL) implantation surgery, mainly stemming from the adhesion, proliferation, and transdifferentiation of the postsurgically residual lens epithelial cells (LECs). Previous investigations mainly focused on the hydrophilic surface modification of the IOLs for PCO prevention, such as heparinization. However, the long-term clinical investigations show that there is no significant difference between pristine and heparinized IOLs. In the present study, a synergetic coating with properties of drug-eluting and hydrophilicity was designed and modified onto the IOL surface via facile dopamine self-polymerization. The antiproliferative drug doxorubicin (DOX) was loaded when a polydopamine (PDA) coating was formed on the IOL surface. The hydrophilic 2-methacryloyloxyethyl phosphorylcholine (MPC) could be subsequently grafted onto the drug-loaded PDA coating surface easily. The hydrophilic outer layer could slow down drug-eluting from underneath the drug-incorporated coating. In vitro and in vivo investigations demonstrated that such multifunctionalized coating-modified IOLs could not only thoroughly and effectively prevent PCO development by induced cell apoptosis but also render safety and biocompatibility to the surrounding tissues.

Freeform 3D printing of vascularized tissues: Challenges and strategies

In recent years, freeform three-dimensional (3D) printing has led to significant advances in the fabrication of artificial tissues with vascularized structures. This technique utilizes a supporting matrix that holds the extruded printing ink and ensures shape maintenance of the printed 3D constructs within the prescribed spatial precision. Since the printing nozzle can be translated omnidirectionally within the supporting matrix, freeform 3D printing is potentially applicable for the fabrication of complex 3D objects, incorporating curved, and irregular shaped vascular networks. To optimize freeform 3D printing quality and performance, the rheological properties of the printing ink and supporting matrix, and the material matching between them are of paramount importance. In this review, we shall compare conventional 3D printing and freeform 3D printing technologies for the fabrication of vascular constructs, and critically discuss their working principles and their advantages and disadvantages. We also provide the detailed material information of emerging printing inks and supporting matrices in recent freeform 3D printing studies. The accompanying challenges are further discussed, aiming to guide freeform 3D printing by the effective design and selection of the most appropriate materials/processes for the development of full-scale functional vascularized artificial tissues.

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.

Biodegradable engineered fiber scaffolds fabricated by electrospinning for periodontal tissue regeneration

Considering the specificity of periodontium and the unique advantages of electrospinning, this technology has been used to fabricate biodegradable tissue engineering materials for functional periodontal regeneration. For better biomedical quality, a continuous technological progress of electrospinning has been performed. Based on property of materials (natural, synthetic or composites) and additive novel methods (drug loading, surface modification, structure adjustment or 3 D technique), various novel membranes and scaffolds that could not only relief inflammation but also influence the biological behaviors of cells have been fabricated to achieve more effective periodontal regeneration. This review provides an overview of the usage of electrospinning materials in treatments of periodontitis, in order to get to know the existing research situation and find treatment breakthroughs of the periodontal diseases.

Combination of electrospinning with other techniques for the fabrication of 3D polymeric and composite nanofibrous scaffolds with improved cellular interactions

The development of three-dimensional (3D) scaffolds with physical and chemical topological cues at the macro-, micro-, and nanometer scale is urgently needed for successful tissue engineering applications. 3D scaffolds can be manufactured by a wide variety of techniques. Electrospinning technology has emerged as a powerful manufacturing technique to produce non-woven nanofibrous scaffolds with very interesting features for tissue engineering products. However, electrospun scaffolds have some inherent limitations that compromise the regeneration of thick and complex tissues. By integrating electrospinning and other fabrication technologies, multifunctional 3D fibrous assemblies with micro/nanotopographical features can be created. The proper combination of techniques leads to materials with nano and macro-structure, allowing an improvement in the biological performance of tissue-engineered constructs. In this review, we focus on the most relevant strategies to produce electrospun polymer/composite scaffolds with 3D architecture. A detailed description of procedures involving physical and chemical agents to create structures with large pores and 3D fiber assemblies is introduced. Finally, characterization and biological assays including in vitro and in vivo studies of structures intended for the regeneration of functional tissues are briefly presented and discussed.

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.

Dexamethasone loaded bilayered 3D tubular scaffold reduces restenosis at the anastomotic site of tracheal replacement: in vitro and in vivo assessments

Despite recent developments in the tracheal tissue engineering field, the creation of a patient specific substitute possessing both appropriate mechanical and biointerfacial properties remains challenging. Most tracheal replacement therapies fail due to restenosis at the anastomosis site. In this study, we designed a robust, biodegradable, 3D tubular scaffold by combining electrospinning (ELSP) and 3D (three-dimensional) printing techniques for use in transplantation therapy. After that, we loaded dexamethasone (DEX) onto the 3D tubular scaffold using mild surface modification reactions by using polydopamine (PDA), polyethyleneimine (PEI), and carboxymethyl-β-cyclodextrin (βCD). As a result, the fabricated 3D tubular scaffold had robust mechanical properties and the chemical modifications were confirmed to have proceeded successfully by physico-chemical analysis. The surface treatments allowed for a larger amount of DEX to be loaded onto the βCD modified scaffold as compared to the bare group. In vitro and in vivo studies demonstrated that the DEX loaded 3D tubular scaffold exhibited significantly enhanced anti-inflammation activity, enhanced tracheal mucosal regeneration, and formation of a patent airway. From our results, we believe that our system may represent an innovative paradigm in tracheal tissue engineering by providing proper mechanical properties and successful formation of tracheal tissue as a means of remodeling and healing tracheal defects for use in transplantation therapy.

Electrospun PET/PCL small diameter nanofibrous conduit for biomedical application

In recent years, the mortality rate caused by cardiovascular diseases has increased dramatically around the world. Tissue engineering is considered as a novel and efficient approach to offer a substituent of engineered tissues for defective body tissues. For this purpose, fabrication of the scaffold that resembles the physical and mechanical properties of natural body vessels, and culturing appropriate cells seems to be a promising approach. Due to the fibrous structure of the vascular wall, the nanofibrous scaffold produced by electrospinning could be a proper choice for vascular tissue engineering. One of the main properties of artificial vessels is its mechanical properties consistency with the native one in order to mimic its natural characteristics. To do so, in present study two biocompatible polymers, polyethylene terephthalate (PET) and polycaprolactone (PCL) with different blend ratio were electrospun into a tubular nanofibrous structure with 6 mm internal diameter and the mechanical properties such as tensile strength, modulus, compliance, bursting pressure, elastic recovery, and suture retention were investigated. The results revealed that PET/PCL (1:3) had better similar properties with the reported natural one as its longitudinal and transverse tensile strength was about 9.47 and 6.38 MPa, respectively. The longitudinal strain at break, compliance, bursting pressure, and suture retention were 205.88 ± 51.12%, 4.19 ± 0.78%/100 mmHg, 6378.76 ± 2159.20 mmHg, and 287.73 ± 13.10 gmf, respectively. The elasticity of this studied sample was 60.21 ± 12.49% as it was relieved, and this may be a good candidate for the artificial vessel in this size, as the MTT test confirmed its appropriate substrate for cell culture.

Nanobiomaterials: from 0D to 3D for tumor therapy and tissue regeneration

Nanobiomaterials have attracted tremendous attention in the biomedical field. Especially in the past few years, a large number of low dimensional nanobiomaterials, including 0D nanostructures, 1D nanotubes and 2D nanosheets, were employed for tumor therapy due to their optically triggered tumor therapy effects and drug loading capacities. However, these low dimensional nanobiomaterials cannot support cell adhesion and possess poor tissue regeneration ability, thus they are not suitable for application in regenerative medicine. Three dimensional (3D) nanofiber scaffolds have attracted extensive attention in tissue regeneration, including bone, skin, nerve and cardiac tissues, due to their similar extracellular matrix structures. Additionally, many 3D scaffolds displayed bone and cartilage regeneration abilities. Therefore, to obtain materials with both tumor therapy and tissue regeneration abilities, it is meaningful and necessary to develop 3D nanobiomaterials with multifunctions. In this review, we systematically review the research progress of nanobiomaterials with varied dimensional structures including 0D, 1D, 2D and 3D, as well as evolutional functions from single tumor therapy to simultaneous tumor therapy and tissue regeneration. This review may pave the way for developing an interdisciplinary research of nanobiomaterials in combination of tumor therapy and regenerative medicine.

Acellular Small-Diameter Tissue-Engineered Vascular Grafts

Tissue-engineered vascular grafts (TEVGs) are considered one of the most effective means of fabricating vascular grafts. However, for small-diameter TEVGs, there are ongoing issues regarding long-term patency and limitations related to long-term in vitro culture and immune reactions. The use of acellular TEVG is a more convincing method, which can achieve in situ blood vessel regeneration and better meet clinical needs. This review focuses on the current state of acellular TEVGs based on scaffolds and gives a summary of the methodologies and in vitro/in vivo test results related to acellular TEVGs obtained in recent years. Various strategies for improving the properties of acellular TEVGs are also discussed.