implantation-electrospun-vascular-grafts-with-optimized-structure-rat

Implantation of Electrospun Vascular Grafts with Optimized Structure in a Rat Model

Here, we present a protocol to fabricate macroporous PCL vascular graft and describe an evaluation protocol by using a rat model of abdominal aorta ...

implantation-tissue-engineered-vascular-graft-mouse-carotid-artery

Implantation of Tissue-Engineered Vascular Graft in Mouse Carotid Artery <em>via</em> Cuff Technique

The development of small-diameter vascular grafts has been a global endeavor, with numerous research groups contributing to this field. Animal ...

Nankai University

Tiangong University

Tiangong Huikang Medical Technology (Tianjin) Company

The vascular grafts prepared by electrospinning often have relatively small pores, which limit cell infiltration into the grafts and hinder the regeneration and remodeling of the grafts into neoarteries. To overcome this problem, macroporous electrospun polycaprolactone (PCL) scaffolds with thicker fibers (5-6 μm) and larger pores (∼30 μm) were fabricated in the present study. In vitro cell culture indicated that macrophages cultured on thicker-fiber scaffolds tended to polarize into the immunomodulatory and tissue remodeling (M2) phenotype, while those cultured on thinner-fiber scaffolds expressed proinflammatory (M1) phenotype. In vivo implantation by replacing rat abdominal aorta was performed and followed up for 7, 14, 28 and 100 d. The results demonstrated that the macroporous grafts markedly enhanced cell infiltration and extracellular matrix (ECM) secretion. All grafts showed satisfactory patency for up to 100 days. At day 100, the endothelium coverage was complete, and the regenerated smooth muscle layer was correctly organized with abundant ECM similar to those in the native arteries. More importantly, the regenerated arteries demonstrated contractile response to adrenaline and acetylcholine-induced relaxation. Analysis of the cellularization process revealed that the thicker-fiber scaffolds induced a large number of M2 macrophages to infiltrate into the graft wall. These macrophages further promoted cellular infiltration and vascularization. In conclusion, the present study confirmed that the scaffold structure can regulate macrophage phenotype. Our thicker-fiber electrospun PCL vascular grafts could enhance the vascular regeneration and remodeling process by mediating macrophage polarization into M2 phenotype, suggesting that our constructs may be a promising cell-free vascular graft candidate and are worthy for further in vivo evaluation. 

The effect of thick fibers and large pores of electrospun poly(ε-caprolactone) vascular grafts on macrophage polarization and arterial regeneration.

Nitric oxide (NO) is an important signaling molecule in cardiovascular system, and the sustained release of NO by endothelial cells plays a vital role in maintaining patency and homeostasis. In contrast, lack of endogenous NO in artificial blood vessel is believed to be the main cause of thrombus formation. In this study, enzyme prodrug therapy (EPT) technique was employed to construct a functional vascular graft by immobilization of galactosidase on the graft surface. The enzyme-functionalized grafts exhibited excellent catalytic property in decomposition of the exogenously administrated NO prodrug. Localized and on-demand release of NO was demonstrated by in vitro release assay and fluorescent probe tracing in an ex vivo model. The immobilized enzyme retained catalytic property even after subcutaneous implantation of the grafts for one month. The functional vascular grafts were implanted into the rat abdominal aorta with a 1-month monitoring period. Results showed effective inhibition of thrombus formation in vivo and enhancement of vascular tissue regeneration and remodeling on the grafts. Thus, we create an enzyme-functionalized vascular graft that can catalyze prodrug to release NO locally and sustainably, indicating that this approach may be useful to develop new cell-free vascular grafts for treatment of vascular diseases. 

Enzyme-functionalized vascular grafts catalyze in-situ release of nitric oxide from exogenous NO prodrug.

Current in vitro models fail in predicting the degradation rate and mode of magnesium (Mg) stents in vivo. To overcome this, the microenvironment of the stent is simulated here in an ex vivo bioreactor with porcine aorta and circulating medium, and compared with standard static in vitro immersion and with in vivo rat aorta models. In ex vivo and in vivo conditions, pure Mg wires were exposed to the aortic lumen and inserted into the aortic wall to mimic early- and long-term implantation, respectively. Results showed that: 1) Degradation rates of Mg were similar for all the fluid diffusion conditions (in vitro static, aortic wall ex vivo and in vivo); however, Mg degradation under flow condition (i.e. in the lumen) in vivo was slower than ex vivo; 2) The corrosion mode in the samples can be mainly described as localized (in vitro), mixed localized and uniform (ex vivo), and uniform (in vivo); 3) Abundant degradation products (MgO/Mg(OH) and Ca/P) with gas bubbles accumulated around the localized degradation regions ex vivo, but a uniform and thin degradation product layer was found in vivo. It is concluded that the ex vivo vascular bioreactor provides an improved test setting for magnesium degradation between static immersion and animal experiments and highlights its promising role in bridging degradation behavior and biological response for vascular stent research.

Ex vivo blood vessel bioreactor for analysis of the biodegradation of magnesium stent models with and without vessel wall integration.

Wound healing dressings are increasingly needed clinically due to the large number of skin damage annually. Nitric oxide (NO) plays a key role in promoting wound healing, thus biomaterials with NO-releasing property receive increasing attention as ideal wound dressing. In present study, we prepared a novel functional wound dressing by combining electrospun poly(ε-caprolactone) (PCL) nonwoven mat with chitosan-based NO-releasing biomaterials (CS-NO). As-prepared PCL/CS-NO dressing released NO sustainably under the physiological conditions, which was controlled by the catalysis of β-galactosidase. In vivo wound healing characteristics were further evaluated on full-thickness cutaneous wounds in mice. Results showed that PCL/CS-NO wound dressings remarkably accelerated wound healing process through enhancing re-epithelialization and granulation formation and effectively improved the organization of regenerated tissues including epidermal-dermal junction, which could be ascribed to the pro-angiogenesis, immunomodulation, and enhanced collagen synthesis provided by the sustained release of NO. Therefore, PCL/CS-NO may be a promising candidate for wound dressings, especially for the chronic wound caused by the ischemia.

Functional poly(ε-caprolactone)/chitosan dressings with nitric oxide-releasing property improve wound healing.

Rapid endothelialization is a key factor that determines the success of small-diameter vascular grafts as an artery substitute in the treatment of cardiovascular diseases. Aimed to facilitate vascular regeneration, we developed a vascular scaffold loaded with resveratrol, which is a natural compound extracted from plants and showed multifaceted effects in cardiovascular protection. The tubular poly(ε-caprolactone) (PCL) scaffold was prepared by electrospinning with resveratrol in the PCL solution. In vitro assay demonstrated that resveratrol could be released from the scaffolds in a sustained and controlled manner. Cell culture results indicated that the migration of endothelial cells (ECs), nitric oxide production, and the ability of tube formation increased in the resveratrol-containing PCL scaffold groups compared with the PCL control. Meanwhile, the level of tumor necrosis factor (TNF)-α, the main proinflammatory factor secreted from macrophages, was reduced, and the messenger RNA expressions of the M2 macrophage-related genes were increased in the resveratrol-containing group. Further, in vivo implantation was performed by replacing rat abdominal aorta. We observed fast endothelialization and enhanced vascular regeneration in rats with resveratrol-containing scaffolds. The presence of resveratrol also induced a large number of M2 macrophages to infiltrate into the graft wall. Taken together, the incorporation of resveratrol into the PCL grafts enhanced the vascular regeneration by modulation of ECs and macrophages.

Effect of Resveratrol on Modulation of Endothelial Cells and Macrophages for Rapid Vascular Regeneration from Electrospun Poly(ε-caprolactone) Scaffolds.

Long-term evaluation of vascular grafts is an essential step to facilitate clinical translation. In this study, we investigate the long-term performance of a macro-porous poly(ɛ-caprolactone) (PCL) electrospun vascular graft using the rat abdominal artery replacement model. Long-term patency, endothelialization, and smooth muscle cell regeneration were evaluated, as well as calcification and degradation. The data showed that all the grafts remained open and unobstructed. There was no evidence of aneurysm, stenosis, or calcification one year after implantation. Importantly, neo-vessel was regenerated on the luminal surface of the graft, and was composed of a complete endothelial layer and several layers of smooth muscle cells. The neo-vessel showed vascular physiological function, although not as good as that in native blood vessels, likely due to the remaining scaffold fibers. These data indicated that the PCL macro-porous electrospun vascular graft has potential to be an artery substitute for long-term implantation. Also, this work indicates that continued efforts are needed to develop advanced vascular grafts that exhibit the appropriate balance between the regeneration of the neo-vessel and the complete degradation of the graft materials. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1618-1627, 2018.

The regeneration of macro-porous electrospun poly(ɛ-caprolactone) vascular graft during long-term in situ implantation.

In the present study, pure zinc stents were implanted into the abdominal aorta of rabbits for 12 months. Multiscale analysis including micro-CT, scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and histological stainings was performed to reveal the fundamental degradation mechanism of the pure zinc stent and its biocompatibility. The pure zinc stent was able to maintain mechanical integrity for 6 months and degraded 41.75 ± 29.72% of stent volume after 12 months implantation. No severe inflammation, platelet aggregation, thrombosis formation or obvious intimal hyperplasia was observed at all time points after implantation. The degradation of the zinc stent played a beneficial role in the artery remodeling and healing process. The evolution of the degradation mechanism of pure zinc stents with time was revealed as follows: Before endothelialization, dynamic blood flow dominated the degradation of pure zinc stent, creating a uniform corrosion mode; After endothelialization, the degradation of pure zinc stent depended on the diffusion of water molecules, hydrophilic solutes and ions which led to localized corrosion. Zinc phosphate generated in blood flow transformed into zinc oxide and small amounts of calcium phosphate during the conversion of degradation microenvironment. The favorable physiological degradation behavior makes zinc a promising candidate for future stent applications.

Evolution of the degradation mechanism of pure zinc stent in the one-year study of rabbit abdominal aorta model.

Long-term results of implants in small animal models can be used to optimize the design of grafts to further promote tissue regeneration. In previous study, we fabricated a poly(ɛ-caprolactone) (PCL) bi-layered vascular graft consisting of an internal layer with circumferentially aligned microfibers and an external layer with random nanofibers. The circumferentially oriented vascular smooth muscle cells (VSMCs) were successfully regenerated after the grafts were implanted in rat abdominal aorta for 3 months. Here we investigated the long-term (18 months) performance of the bi-layered grafts in the same model. All the grafts were patent. No thrombosis, aneurysm, or stenosis occurred. The endothelium maintained complete. However, most of circumferentially oriented VSMCs migrated to luminal surface of the grafts to form a neointima with uniform thickness. Accordingly, extracellular matrix including collagen, elastin, and glycosaminoglycan displayed high density in neointima layer while with low density in the grafts wall because of the incomplete degradation of PCL. A small amounts of calcification occurred in the grafts. The contraction and relaxation function of regenerated neoartery almost disappeared. These data indicated that based on the structure design, many other factors of grafts should be considered to achieve the regenerated neoartery similar to the native vessels after long-term implantation. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2018.

Long-term evaluation of vascular grafts with circumferentially aligned microfibers in a rat abdominal aorta replacement model.

Intracerebral hemorrhage (ICH) is a common and severe brain disease associated with high mortality and morbidity. Accurate measurement of the ICH area is an essential indicator for doctors to determine whether a surgical operation is necessary. However, although currently used clinical detection methods, such as computed tomography (CT) and magnetic resonance imaging (MRI), provide high-quality images, they may have limitations such as high costs, large equipment size, and radiation exposure to the human body in the case of CT. It makes long-term bedside monitoring infeasible. This paper presents a dynamic monitoring method for ICH areas based on magnetic induction. This study investigates the influence of the bleeding area and the position of ICH on the phase difference at the detection point near the area to be measured. The study applies a neural network algorithm to predict the bleeding area using the phase difference data received by the detection coil as the network input and the bleeding area as the network output. The relative error between the predicted and actual values of the neural network is calculated, and the error of each group of data is less than 4%, which confirms the feasibility of this method for detecting and even trend monitoring of the ICH area.

Simulation of dynamic monitoring for intracerebral hemorrhage based on magnetic induction phase shift technology.

The unique ability of piezoelectric materials to generate electricity spontaneously has attracted widespread interest in the medical field. In addition to the ability to convert mechanical stress into electrical energy, piezoelectric materials offer the advantages of high sensitivity, stability, accuracy and low power consumption. Because of these characteristics, they are widely applied in devices such as sensors, controllers and actuators. However, piezoelectric materials also show great potential for the medical manufacturing of artificial organs and for tissue regeneration and repair applications. For example, the use of piezoelectric materials in cochlear implants, cardiac pacemakers and other equipment may help to restore body function. Moreover, recent studies have shown that electrical signals play key roles in promoting tissue regeneration. In this context, the application of electrical signals generated by piezoelectric materials in processes such as bone healing, nerve regeneration and skin repair has become a prospective strategy. By mimicking the natural bioelectrical environment, piezoelectric materials can stimulate cell proliferation, differentiation and connection, thereby accelerating the process of self-repair in the body. However, many challenges remain to be overcome before these concepts can be applied in clinical practice, including material selection, biocompatibility and equipment design. On the basis of the principle of electrical signal regulation, this article reviews the definition, mechanism of action, classification, preparation and current biomedical applications of piezoelectric materials and discusses opportunities and challenges for their future clinical translation.

From electricity to vitality: the emerging use of piezoelectric materials in tissue regeneration.

Macrophages are primary immune cells that play a crucial role in tissue regeneration during the early stages of biomaterial implantation. They create a microenvironment that facilitates cell infiltration, angiogenesis, and tissue remodeling. In the field of vascular tissue engineering, numerous studies have been conducted to modulate the macrophage phenotype by designing various biomaterials, which in turn enhances the regenerative capacity and long-term patency of vascular grafts. However, the mechanism underlying the different phenotypes of macrophages involved in the tissue regeneration of vascular grafts remains unclear. In this study, vascular grafts loaded with various macrophage phenotypes were developed, and their effects were evaluated both in vivo and in vitro. The RAW 264.7 macrophages (M0) were initially treated with LPS or IL-4/IL-10 and polarized into M1 and M2 phenotypes. Subsequently, M0, M1, and M2 macrophages were seeded onto electrospun PCL scaffolds to obtain macrophage-loaded vascular grafts (PCL-M0, PCL-M1, and PCL-M2). As prepared vascular grafts were implanted into the mouse carotid artery for up to one month. The results indicate that the loading of M2 macrophages effectively enhances the patency rate and neotissue formation of vascular grafts. This is achieved through the development of a well-defined endothelium and smooth muscle layer. RNA sequencing was used to investigate the mechanisms of action of different macrophages on tissue regeneration. The study found that M1 macrophages inhibited tissue regeneration by mediating angiogenesis and chronic inflammation through upregulation of VEGFa, IL-1β, and IL-6 expression. In contrast, M2 macrophages regulate the immune microenvironment by upregulating the expression of IL-4 and TGF-β, thereby promoting tissue regeneration. In conclusion, our study demonstrates how different macrophage phenotypes contribute to the initial inflammatory microenvironment surrounding vascular grafts, thereby modulating the biological process of vascular remodeling. STATEMENT OF SIGNIFICANCE: Regulating the biophysical and biochemical characteristics of biomaterials can induce macrophage polarization and enhance vascular remodeling. In previous work, we fabricated a vascular graft with a macroporous structure that promoted macrophage infiltration and polarization into a pro-regenerative phenotype. To illustrate the mechanism, we established a new mouse model and evaluated the effects of different macrophages on vascular regeneration. The study revealed that tuning macrophage phenotype can impact the initial inflammatory microenvironment by secreting cytokines, which can increase the patency rate and regenerative capacity of vascular grafts. These findings provide essential theoretical support for the development of immunoregulatory scaffolds for vascular and other tissue regeneration.

Article Total : 2	Year
Publication title	2018
Publication title	2025

Article	Year
The effect of thick fibers and large pores of electrospun poly(ε-caprolactone) vascular grafts on macrophage polarization and arterial regeneration. Biomaterials\| PubMed ID: 24746961	2014
Enzyme-functionalized vascular grafts catalyze in-situ release of nitric oxide from exogenous NO prodrug. Journal of controlled release : official journal of the Controlled Release Society\| PubMed ID: 26004323	2015
Ex vivo blood vessel bioreactor for analysis of the biodegradation of magnesium stent models with and without vessel wall integration. Acta biomaterialia\| PubMed ID: 28013101	2017
Functional poly(ε-caprolactone)/chitosan dressings with nitric oxide-releasing property improve wound healing. Acta biomaterialia\| PubMed ID: 28285076	2017
Effect of Resveratrol on Modulation of Endothelial Cells and Macrophages for Rapid Vascular Regeneration from Electrospun Poly(ε-caprolactone) Scaffolds. ACS applied materials & interfaces\| PubMed ID: 28539044	2017
The regeneration of macro-porous electrospun poly(ɛ-caprolactone) vascular graft during long-term in situ implantation. Journal of biomedical materials research. Part B, Applied biomaterials\| PubMed ID: 28834076	2018
Evolution of the degradation mechanism of pure zinc stent in the one-year study of rabbit abdominal aorta model. Biomaterials\| PubMed ID: 28858721	2017
Long-term evaluation of vascular grafts with circumferentially aligned microfibers in a rat abdominal aorta replacement model. Journal of biomedical materials research. Part B, Applied biomaterials\| PubMed ID: 29412507	2018
Simulation of dynamic monitoring for intracerebral hemorrhage based on magnetic induction phase shift technology. The Review of scientific instruments\| PubMed ID: 37862492	2023
From electricity to vitality: the emerging use of piezoelectric materials in tissue regeneration. Burns & trauma\| PubMed ID: 38957661	2024
Tuning macrophage phenotype for enhancing patency rate and tissue regeneration of vascular grafts. Acta biomaterialia\| PubMed ID: 40158766	2025

Yifan Wu

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