Effects of recipient age, heparin release and allogeneic bone marrow-derived stromal cells on vascular graft remodeling

Improving hemocompatibility in tissue-engineered products employing heparin-loaded nanoplatforms

The enhancement of hemocompatibility through the use of nanoplatforms loaded with heparin represents a highly desirable characteristic in the context of emerging tissue engineering applications. The significance of employing heparin in biological processes is unquestionable, owing to its ability to interact with a diverse range of proteins. It plays a crucial role in numerous biological processes by engaging in interactions with diverse proteins and hydrogels. This review provides a summary of recent endeavors focused on augmenting the hemocompatibility of tissue engineering methods through the utilization of nanoplatforms loaded with heparin. This study also provides a comprehensive review of the various applications of heparin-loaded nanofibers and nanoparticles, as well as the techniques employed for encapsulating heparin within these nanoplatforms. The biological and physical effects resulting from the encapsulation of heparin in nanoplatforms are examined. The potential applications of heparin-based materials in tissue engineering are also discussed, along with future perspectives in this field.

Implantation of Adipose-Derived Mesenchymal Stromal Cells (ADSCs)-Lining Prosthetic Graft Promotes Vascular Regeneration in Monkeys and Pigs

BACKGROUND

Current replacement procedures for stenosis or occluded arteries using prosthetic grafts have serious limitations in clinical applications, particularly, endothelialization of the luminal surface is a long-standing unresolved problem.

METHOD

We produced a cell-based hybrid vascular graft using a bioink engulfing adipose-derived mesenchymal stromal cells (ADSCs) and a 3D bioprinting process lining the ADSCs on the luminal surface of GORE-Tex grafts. The hybrid graft was implanted as an interposition conduit to replace a 3-cm-long segment of the infrarenal abdominal aorta in Rhesus monkeys.

RESULTS

Complete endothelium layer and smooth muscle layer were fully developed within 21 days post-implantation, along with normalized collagen deposition and crosslinking in the regenerated vasculature in all monkeys. The regenerated blood vessels showed normal functionality for the longest observation of more than 1650 days. The same procedure was also conducted in miniature pigs for the interposition replacement of a 10-cm-long right iliac artery and showed the same long-term effective and safe outcome.

CONCLUSION

This cell-based vascular graft is ready to undergo clinical trials for human patients.

Small diameter vascular grafts: progress on electrospinning matrix/stem cell blending approach

The exploration of the next-generation small diameter vascular grafts (SDVGs) will never stop until they possess high biocompatibility and patency comparable to autologous native blood vessels. Integrating biocompatible electrospinning (ES) matrices with highly bioactive stem cells (SCs) provides a rational and promising solution. ES is a simple, fast, flexible and universal technology to prepare extracellular matrix-like fibrous scaffolds in large scale, while SCs are valuable, multifunctional and favorable seed cells with special characteristics for the emerging field of cell therapy and regenerative medicine. Both ES matrices and SCs are advanced resources with medical application prospects, and the combination may share their advantages to drive the overcoming of the long-lasting hurdles in SDVG field. In this review, the advances on SDVGs based on ES matrices and SCs (including pluripotent SCs, multipotent SCs, and unipotent SCs) are sorted out, and current challenges and future prospects are discussed.

Long-term observation of polycaprolactone small-diameter vascular grafts with thickened outer layer and heparinized inner layer in rabbit carotid arteries

In our previous study, the pristine bilayer small-diameterin situtissue engineered vascular grafts (pTEVGs) were electrospun from a heparinized polycaprolactone (PCL45k) as an inner layer and a non-heparinized PCL80k as an outer layer in the thickness of about 131 μm and 202 μm, respectively. However, the hydrophilic enhancement of inner layer stemmed from the heparinization accelerated the degradation of grafts leading to the early formation of arterial aneurysms in a period of 3 months, severely hindering the perennial observation of the neo-tissue regeneration, host cell infiltration and graft remodeling in those implanted pTEVGs. Herein to address this drawback, the thickness of the outer layers was increased with PCL80k to around 268 μm, while the inner layer remained unchangeable. The thickened TEVGs named as tTEVGs were evaluated in six rabbits via a carotid artery interpositional model for a period of 9 months. All the animals kept alive and the grafts remained patent until explantation except for one whose one side of arterial blood vessels was occluded after an aneurysm occurred at 6 months. Although a significant degradation was observed in the implanted grafts at 9 month, the occurrence of aneurysms was obviously delayed compared to pTEVGs. The tissue stainings indicated that the endothelial cell remodeling was substantially completed by 3 months, while the regeneration of elastin and collagen remained smaller and unevenly distributed in comparison to autologous vessels. Additionally, the proliferation of macrophages and smooth muscle cells reached the maximum by 3 months. These tTEVGs possessing a heparinized inner layer and a thickened outer layer exhibited good patency and significantly delayed onset time of aneurysms.

Engineering pre-vascularized 3D tissue and rapid vascular integration with host blood vessels via co-cultured spheroids-laden hydrogel

Recent advances in regenerative medicine and tissue engineering have enabled the biofabrication of three-dimensional (3D) tissue analogues with the potential for use in transplants and disease modeling. However, the practical use of these biomimetic tissues has been hindered by the challenge posed by reconstructing anatomical-scale micro-vasculature tissues. In this study, we suggest that co-cultured spheroids within hydrogels hold promise for regenerating highly vascularized and innervated tissues, bothin vitroandin vivo. Human adipose-derived stem cells (hADSCs) and human umbilical vein cells (HUVECs) were prepared as spheroids, which were encapsulated in gelatin methacryloyl hydrogels to fabricate a 3D pre-vascularized tissue. The vasculogenic responses, extracellular matrix production, and remodeling depending on parameters like co-culture ratio, hydrogel strength, and pre-vascularization time forin vivointegration with native vessels were then delicately characterized. The co-cultured spheroids with 3:1 ratio (hADSCs/HUVECs) within the hydrogel and with a pliable storage modulus showed the greatest vasculogenic potential, and ultimately formedin vitroarteriole-scale vasculature with a longitudinal lumen structure and a complex vascular network after long-term culturing. Importantly, the pre-vascularized tissue also showed anastomotic vascular integration with host blood vessels after transplantation, and successful vascularization that was positive for both CD31 and alpha-smooth muscle actin covering 18.6 ± 3.6μm2of the luminal area. The described co-cultured spheroids-laden hydrogel can therefore serve as effective platform for engineering 3D vascularized complex tissues.

Preparation and performance of random- and oriented-fiber membranes with core-shell structures via coaxial electrospinning

The cells and tissue in the human body are orderly and directionally arranged, and constructing an ideal biomimetic extracellular matrix is still a major problem to be solved in tissue engineering. In the field of the bioresorbable vascular grafts, the long-term functional prognosis requires that cells first migrate and grow along the physiological arrangement direction of the vessel itself. Moreover, the graft is required to promote the formation of neointima and the development of the vessel walls while ensuring that the whole repair process does not form a thrombus. In this study, poly (l-lactide-co-ε-caprolactone) (PLCL) shell layers and polyethylene oxide (PEO) core layers with different microstructures and loaded with sodium tanshinone IIA sulfonate (STS) were prepared by coaxial electrospinning. The mechanical properties proved that the fiber membranes had good mechanical support, higher than that of the human aorta, as well as great suture retention strengths. The hydrophilicity of the oriented-fiber membranes was greatly improved compared with that of the random-fiber membranes. Furthermore, we investigated the biocompatibility and hemocompatibility of different functional fiber membranes, and the results showed that the oriented-fiber membranes containing sodium tanshinone IIA sulfonate had an excellent antiplatelet adhesion effect compared to other fiber membranes. Cytological analysis confirmed that the functional fiber membranes were non-cytotoxic and had significant cell proliferation capacities. The oriented-fiber membranes induced cell growth along the orientation direction. Degradation tests showed that the pH variation range had little change, the material mass was gradually reduced, and the fiber morphology was slowly destroyed. Thus, results indicated the degradation rate of the oriented-fiber graft likely is suitable for the process of new tissue regeneration, while the random-fiber graft with a low degradation rate may cause the material to reside in the tissue for too long, which would impede new tissue reconstitution. In summary, the oriented-functional-fiber membranes possessing core-shell structures with sodium tanshinone IIA sulfonate/polyethylene oxide loading could be used as tissue engineering materials for applications such as vascular grafts with good prospects, and their clinical application potential will be further explored in future research.

Design of 3D polycaprolactone/ε-polylysine-modified chitosan fibrous scaffolds with incorporation of bioactive factors for accelerating wound healing

Electrospun nanofibrous scaffolds show great application potentials for wound healing owing to their effective simulation of extracellular matrix (ECM). Three-dimensional (3D) nanofibrous dressings exhibit relatively high specific surface areas, better mimicry of native ECM, adjustable hydrophilicity and breathability, good histocompatibility, enhanced wound healing, and reduced inflammation. In the present work, we designed the 3D polycaprolactone/ε-polylysine modified chitosan (PCL/PCS) nanofibrous scaffolds by an electrospinning and gas foaming process. Then, gelatin and heparin (Gel/Hep) were assembled onto the surface of PCL/PCS nanofibers by electrostatic adsorption, and vascular endothelial growth factors (VEGFs) were also synchronously incorporated into Gel/Hep layer to form a multifunctional 3D nanofibrous scaffold (PCL/PCS@Gel/Hep+VEGF) for accelerating wound healing. The as-fabricated 3D PCL/PCS@GEL/Hep+VEGF nanofibrous scaffold showed excellent antibacterial ability, hemocompatibility and biocompatibility in vitro and wound healing ability in vivo. Immunological analysis showed that the as-fabricated nanofibrous scaffold inhibited inflammation at the wound sites while promoting angiogenesis during the wound healing process. STATEMENT OF SIGNIFICANCE: The electrospun 3D fibrous scaffolds using polycaprolactone/ε-polylysine modified chitosan (PCL/PCS) have been fabricated as backbone for mimicking the extracellular matrix (ECM). Gelatin and heparin (Gel/Hep) were wrapped onto the surface of PCL/PCS fibers by electrostatic adsorption and vascular endothelial growth factors (VEGFs) were also synchronously incorporated into surface Gel/Hep layer to form multifunctional 3D fibrous scaffolds. The as-fabricated multifunctional 3D fibrous scaffolds with good antibacterial ability and biocompatibility have been used as dressings for accelerating wound healing by inhibiting inflammation at the wound sites while promoting angiogenesis during the wound healing process.

Catching Them Early: Framework Parameters and Progress for Prenatal and Childhood Application of Advanced Therapies

Advanced therapy medicinal products (ATMPs) are medicines for human use based on genes, cells or tissue engineering. After clear successes in adults, the nascent technology now sees increasing pediatric application. For many still untreatable disorders with pre- or perinatal onset, timely intervention is simply indispensable; thus, prenatal and pediatric applications of ATMPs hold great promise for curative treatments. Moreover, for most inherited disorders, early ATMP application may substantially improve efficiency, economy and accessibility compared with application in adults. Vindicating this notion, initial data for cell-based ATMPs show better cell yields, success rates and corrections of disease parameters for younger patients, in addition to reduced overall cell and vector requirements, illustrating that early application may resolve key obstacles to the widespread application of ATMPs for inherited disorders. Here, we provide a selective review of the latest ATMP developments for prenatal, perinatal and pediatric use, with special emphasis on its comparison with ATMPs for adults. Taken together, we provide a perspective on the enormous potential and key framework parameters of clinical prenatal and pediatric ATMP application.

Animal studies for the evaluation of in situ tissue-engineered vascular grafts - a systematic review, evidence map, and meta-analysis

Vascular in situ tissue engineering (TE) is an approach that uses bioresorbable grafts to induce endogenous regeneration of damaged blood vessels. The evaluation of newly developed in situ TE vascular grafts heavily relies on animal experiments. However, no standard for in vivo models or study design has been defined, hampering inter-study comparisons and translational efficiency. To provide input for formulating such standard, the goal of this study was to map all animal experiments for vascular in situ TE using off-the-shelf available, resorbable synthetic vascular grafts. A literature search (PubMed, Embase) yielded 15,896 studies, of which 182 studies met the inclusion criteria (n = 5,101 animals). The reports displayed a wide variety of study designs, animal models, and biomaterials. Meta-analysis on graft patency with subgroup analysis for species, age, sex, implantation site, and follow-up time demonstrated model-specific variations. This study identifies possibilities for improved design and reporting of animal experiments to increase translational value.

Remodeling of Structurally Reinforced (TPU+PCL/PCL)-Hep Electro-spun Small Diameter Bilayer Vascular Grafts Interposed in Rat Ab-dominal Aorta

As the thermoplastic polyurethane (TPU) elastomer possesses good biocompatibility and mechanical properties similar to native vascular tissues as well, it is intended to co-electrospin with poly(ε-caprolactone) (PCL) onto the outer...

Immuno-regenerative biomaterials for in situ cardiovascular tissue engineering - Do patient characteristics warrant precision engineering?

In situ tissue engineering using bioresorbable material implants - or scaffolds - that harness the patient's immune response while guiding neotissue formation at the site of implantation is emerging as a novel therapy to regenerate human tissues. For the cardiovascular system, the use of such implants, like blood vessels and heart valves, is gradually entering the stage of clinical translation. This opens up the question if and to what extent patient characteristics influence tissue outcomes, necessitating the precision engineering of scaffolds to guide patient-specific neo-tissue formation. Because of the current scarcity of human in vivo data, herein we review and evaluate in vitro and preclinical investigations to predict the potential role of patient-specific parameters like sex, age, ethnicity, hemodynamics, and a multifactorial disease profile, with special emphasis on their contribution to the inflammation-driven processes of in situ tissue engineering. We conclude that patient-specific conditions have a strong impact on key aspects of in situ cardiovascular tissue engineering, including inflammation, hemodynamic conditions, scaffold resorption, and tissue remodeling capacity, suggesting that a tailored approach may be required to engineer immuno-regenerative biomaterials for safe and predictive clinical applicability.