Fabrication of heparinized small diameter TPU/PCL bi-layered artificial blood vessels and in vivo assessment in a rabbit carotid artery replacement model

Fabrication of Vascular Grafts Using Poly(ε-Caprolactone) and Collagen-Encapsuled ADSCs for Interposition Implantation of Abdominal Aorta in Rhesus Monkeys

The production of small-diameter artificial vascular grafts continues to encounter numerous challenges, with concerns regarding the degradation rate and endothelialization being particularly critical. In this study, porous PCL scaffolds were prepared, and PCL vascular grafts were fabricated by 3D bioprinting of collagen materials containing adipose-derived mesenchymal stem cells (ADSCs) on the internal wall of the porous PCL scaffold. The PCL vascular grafts were then implanted in the abdominal aorta of Rhesus monkeys for up to 640 days to analyze the degradation of the scaffolds and regeneration of the aorta. Changes in surface morphology, mechanical properties, crystallization property, and molecular weight of porous PCL revealed a similar degradation process of PCL in PBS at pH 7.4 containing Thermomyces lanuginosus lipase and in situ in the abdominal aorta of rhesus monkeys. The contrast of in vitro and in vivo degradation provided valuable reference data for predicting in vivo degradation based on in vitro enzymatic degradation of PCL for further optimization of PCL vascular graft fabrication. Histological analysis through hematoxylin and eosin (HE) staining and fluorescence immunostaining demonstrated that the PCL vascular grafts successfully induced vascular regeneration in the abdominal aorta over the 640-day period. These findings provided valuable insights into the regeneration processes of the implanted vascular grafts. Overall, this study highlights the significant potential of PCL vascular grafts for the regeneration of small-diameter blood vessels.

Design and preparation of an artificial vascular scaffold with internal surface modification

BACKGROUND

Advances in regeneration methods have brought us improved vascular scaffolds with small diameters (φ < 6 mm) for enhancing biological suitability that solve their propensity for causing intimal hyperplasia post-transplantation.

METHODS

The correlation between the rehydration ratio of the hydrogel and its material concentration is obtained by adjusting the material ratio of the hydrogel solution. The vascular model with helical structure has been established and analyzed to verify the effect of helical microvascular structure on thrombosis formation by the fluid simulation methods. Then, the helical structure vascular has been fabricated by self-developed 3D bioprinter, the vascular scaffolds are freeze-dried and rehydrated in polyethylene glycol (PEG) solution.

RESULTS

The experimental results showed that the hybrid hydrogel had a qualified rehydration ratio when the content of gelatin, sodium alginate, and glycerol was 5, 6, and 3 wt%. The established flow channel model can effectively reduce thrombus deposition and improve long-term patency ratio. After PEG solution modification, the contact angle of the inner wall of the vascular scaffold was less than 30°, showing better hydrophilic characteristics.

CONCLUSION

In study, a small-diameter inner wall vascular scaffold with better long-term patency was successfully designed and prepared by wrinkling and PEG modification of the inner wall of the vascular scaffold. This study not only creates small-diameter vascular scaffolds with helical structure that improves the surface hydrophilicity to reduce the risk of thrombosis but also rekindles confidence in the regeneration of small caliber vascular structures.

Biofabrication of engineered blood vessels for biomedical applications

To successfully engineer large-sized tissues, establishing vascular structures is essential for providing oxygen, nutrients, growth factors and cells to prevent necrosis at the core of the tissue. The diameter scale of the biofabricated vasculatures should range from 100 to 1,000 µm to support the mm-size tissue while being controllably aligned and spaced within the diffusion limit of oxygen. In this review, insights regarding biofabrication considerations and techniques for engineered blood vessels will be presented. Initially, polymers of natural and synthetic origins can be selected, modified, and combined with each other to support maturation of vascular tissue while also being biocompatible. After they are shaped into scaffold structures by different fabrication techniques, surface properties such as physical topography, stiffness, and surface chemistry play a major role in the endothelialization process after transplantation. Furthermore, biological cues such as growth factors (GFs) and endothelial cells (ECs) can be incorporated into the fabricated structures. As variously reported, fabrication techniques, especially 3D printing by extrusion and 3D printing by photopolymerization, allow the construction of vessels at a high resolution with diameters in the desired range. Strategies to fabricate of stable tubular structures with defined channels will also be discussed. This paper provides an overview of the many advances in blood vessel engineering and combinations of different fabrication techniques up to the present time.

Mechanical behaviors of high-strength fabric composite membrane designed for cardiac valve prosthesis replacement

Bovine pericardium has been commonly used as leaflets in cardiac valve prosthesis replacement for decades because of its good short-term hemocompatibility and hemodynamic performance. However, fatigue, abrasion, permanent deformation, calcification, and many other failure modes have been reported as well. The degradation of the performance will have a serious impact on the function of valve prostheses, posing a risk to the patient's health. This study aimed to introduce a flexible fabric composite with better mechanical performance such that it can be employed as a substitute material for bioprosthetic valve leaflets. This composite has a multilayered thin film structure made of ultrahigh molecular weight polyethylene (UHMWPE) fabric and thermoplastic polyurethane (TPU) membranes. The mechanical properties of three specifications with different design parameters were tested. The tensile strength, shear behavior, tear resistance, and bending stiffness of the composites were characterized and compared to those of bovine pericardium. A constitutive model was also established to describe the composites' mechanical behaviors and predict their strength. According to the results of the tests, the composite could maintain a flexible bending stiffness with high in-plane tensile strength and tear strength. Therefore, bioprosthetic valve made of this substitute material can withstand harsher loads in the blood flow environment than those made of bovine pericardium. Moreover, all these test results and constitutive models can be used in future research to evaluate hemodynamic performance and clinical applications of fabric composite valve prostheses.

Design of a Personalized Nasal Device (Matrix-Piston Nasal Device, MPD) for Drug Delivery: a 3D-Printing Application

The purpose of the current study is the development and the in vitro evaluation of a novel device for the nasal delivery of biodegradable polymeric films. The Matrix-Piston nasal Device (MPD) was designed and then printed employing Fused Deposition Modeling. Particularly, the CAD model of MPD was produced considering the human anatomical features of the nasal cavity and aiming to deliver the formulation on the olfactory region. The device consists of two independent parts constructed by different materials. For the 3D-printing process, different materials were tested to decide the most applicable for each part. More precisely, Thermoplastic Polyurethene (TPU) polymer was selected to print the matrix, while Acrylonitrile Butadiene Styrene (ABS) for the piston. Furthermore, two nasal casts were printed to be used for the assessment of the device. Namely, an hydroxypropyl-methyl cellulose-based drug-free film, containing polyethylene glycol 400 as plasticizer and methyl-β-cyclodextrin as permeation enhancer, was formed on the MPD to be tested for its ability to be detached from the device and positioned on the artificial olfactory region of the nasal cast. The deposition of the film on the targeted area of the semi-realistic nasal cast took place successfully.

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.