The Tissue-Engineered Vascular Graft-Past, Present, and Future

Cardiovascular disease is the leading cause of death worldwide, with this trend predicted to continue for the foreseeable future. Common disorders are associated with the stenosis or occlusion of blood vessels. The preferred treatment for the long-term revascularization of occluded vessels is surgery utilizing vascular grafts, such as coronary artery bypass grafting and peripheral artery bypass grafting. Currently, autologous vessels such as the saphenous vein and internal thoracic artery represent the gold standard grafts for small-diameter vessels (<6 mm), outperforming synthetic alternatives. However, these vessels are of limited availability, require invasive harvest, and are often unsuitable for use. To address this, the development of a tissue-engineered vascular graft (TEVG) has been rigorously pursued. This article reviews the current state of the art of TEVGs. The various approaches being explored to generate TEVGs are described, including scaffold-based methods (using synthetic and natural polymers), the use of decellularized natural matrices, and tissue self-assembly processes, with the results of various in vivo studies, including clinical trials, highlighted. A discussion of the key areas for further investigation, including graft cell source, mechanical properties, hemodynamics, integration, and assessment in animal models, is then presented

Pre-clinical evaluation of advanced nerve guideconduits using a novel 3D in vitro testing model

Autografts are the current gold standard for large peripheral nerve defects in clinics despite the frequentlyoccurring side effects like donor site morbidity. Hollow nerve guidance conduits (NGC) are proposed alternatives toautografts, but failed to bridge gaps exceeding 3 cm in humans. Internal NGC guidance cues like microfibresare believed to enhance hollow NGCs by giving additional physical support for directed regeneration of Schwann cellsand axons. In this study, we report a new 3D in vitro model that allows the evaluation of different intraluminal fibrescaffolds inside a complete NGC. The performance of electrospun polycaprolactone (PCL) microfibres inside 5 mmlong polyethylene glycol (PEG) conduits were investigated in neuronal cell and dorsal root ganglion (DRG) culturesinvitro. Z-stack confocal microscopy revealed the aligned orientation of neuronal cells along the fibres throughout thewhole NGC length and depth. The number of living cells in the centre of the scaffold was not significantly different tothe tissue culture plastic (TCP) control. For ex vivo analysis, DRGs were placed on top of fibre-filled NGCs to simulatethe proximal nerve stump. In 21 days of culture, Schwann cells and axons infiltrated the conduits along the microfibreswith 2.2 &amp;plusmn; 0.37 mm and 2.1 &amp;plusmn; 0.33 mm, respectively. We conclude that this in vitro model can help define internal NGCscaffolds in the future by comparing different fibre materials, composites and dimensions in one setup prior to animal testing

Morphological response in cancer spheroids for screening photodynamic therapy parameters

Photodynamic therapy (PDT) is a treatment which uses light-activated compounds to produce reactive oxygen species, leading to membrane damage and cell death. Multicellular cancer spheroids are a preferable alternative for PDT evaluation in comparison to monolayer cell cultures due to their ability to better mimic in vivo avascular tumour characteristics such as hypoxia and cell-cell interactions, low cost, and ease of production. However, inconsistent growth kinetics and drug responsiveness causes poor experimental reproducibility and limits their usefulness. Herein, we used image analysis to establish a link between human melanoma C8161 spheroid morphology and drug responsiveness. Spheroids were pre-selected based on sphericity, area, and diameter, reducing variation in experimental groups before treatment. Spheroid morphology after PDT was analyzed using AnaSP and ReViSP, MATLAB-based open-source software, obtaining nine different parameters. Spheroids displayed a linear response between biological assays and morphology, with area (R2 = 0.7219) and volume (R2 = 0.6138) showing the best fit. Sphericity, convexity, and solidity were confirmed as poor standalone indicators of spheroid viability. Our results indicate spheroid morphometric parameters can be used to accurately screen inefficient treatment combinations of novel compounds

Adventures in boron chemistry – the prediction of novel ultra-flexible boron oxide frameworks

We predict a wide range of ultra-flexible low-energy forms of boron oxides in which rigid B–O–B bridges link boron–oxygen heterocycles.</p

Arginine–glycine–aspartic acid functional branched semi-interpenetrating hydrogels

For the first time a series of functional hydrogels based on semi-interpenetrating networks with both branched and crosslinked polymer components have been prepared and we show the successful use of these materials as substrates for cell culture. The materials consist of highly branched poly(N-isopropyl acrylamide)s with peptide functionalised end groups in a continuous phase of crosslinked poly(vinyl pyrrolidone). Functionalisation of the end groups of the branched polymer component with the GRGDS peptide produces a hydrogel that supports cell adhesion and proliferation. The materials provide a new synthetic functional biomaterial that has many of the features of extracellular matrix, and as such can be used to support tissue regeneration and cell culture. This class of high water content hydrogel material has important advantages over other functional hydrogels in its synthesis and does not require postprocessing modifications nor are functional-monomers, which change the polymerisation process, required. Thus, the systems are amenable to large scale and bespoke manufacturing using conventional moulding or additive manufacturing techniques. Processing using additive manufacturing is exemplified by producing tubes using microstereolithography

Mapping Nanostructural Variations in Silk by Secondary Electron Hyperspectral Imaging

Nanostructures underpin the excellent properties of silk. Although the bulk nanocomposition of silks is well studied, direct evidence of the spatial variation of nanocrystalline (ordered) and amorphous (disordered) structures remains elusive. Here, secondary electron hyperspectral imaging can be exploited for direct imaging of hierarchical structures in carbon-based materials, which cannot be revealed by any other standard characterization methods. Through applying this technique to silks from domesticated (Bombyx mori) and wild (Antheraea mylitta) silkworms, a variety of previously unseen features are reported, highlighting the local interplay between ordered and disordered structures. This technique is able to differentiate composition on the nanoscale and enables in-depth studies into the relationship between morphology and performance of these complex biopolymer systems

Modifying pickering polymerized high internal phase emulsion morphology by adjusting particle hydrophilicity

This study investigates the use of submicron polymeric particles with varying crosslinking densities as the sole stabilizer for producing Polymerized High Internal Phase Emulsions (PolyHIPE). We establish a direct correlation between the crosslinking density and the hydrophilicity of the polymer particles. The hydrophilicity of these particles significantly influences the morphology and rheology of HIPEs. These differences manifest as various morphological variations in the resulting PolyHIPE templates. It was discovered that by increasing the crosslinker weight percentage in the particles from 0 % to 100 %, PolyHIPEs with semi-open, open, and closed porous structures can be obtained. Furthermore, non-crosslinked particles were observed to dissolve in the continuous phase, acting as macromolecular surfactants that generate small pores akin to surfactant-stabilized structures in PolyHIPE. These findings offer fresh insights into the relationship between particle localization at the interface, HIPE rheology, and the formation of pore throats in Pickering PolyHIPEs, leading to the creation of either closed or open porous networks. Additionally, interfacial rheological results demonstrate that particles synthesized with varying monomer-to-crosslinker ratios exhibit different interfacial elasticities, which are linked to PolyHIPE morphology

Preparation of interconnected Pickering polymerized high internal phase emulsions by arrested coalescence

Emulsion templating is a method that enables the production of highly porous and interconnected polymer foams called polymerized high internal phase emulsions (PolyHIPEs). Since emulsions are inherently unstable systems, they can be stabilized either by surfactants or by particles (Pickering HIPEs). Surfactant-stabilized HIPEs form materials with an interconnected porous structure, while Pickering HIPEs typically form closed pore materials. In this study, we describe a system that uses submicrometer polymer particles to stabilize the emulsions. Polymers fabricated from these Pickering emulsions exhibit, unlike traditional Pickering emulsions, highly interconnected large pore structures, and we related these structures to arrested coalescence. We describe in detail the morphological properties of this system and their dependence on different production parameters. This production method might provide an interesting alternative to poly-surfactant-stabilized-HIPEs, in particular where the application necessitates large pore structures

A novel bilayer polycaprolactone membrane for guided bone regeneration : combining electrospinning and emulsion templating

Guided bone regeneration is a common dental implant treatment where a barrier membrane (BM) is used between epithelial tissue and bone or bone graft to prevent the invasion of the fast-proliferating epithelial cells into the defect site to be able to preserve a space for infiltration of slower-growing bone cells into the periodontal defect site. In this study, a bilayer polycaprolactone (PCL) BM was developed by combining electrospinning and emulsion templating techniques. First, a 250 µm thick polymerised high internal phase emulsion (polyHIPE) made of photocurable PCL was manufactured and treated with air plasma, which was shown to enhance the cellular infiltration. Then, four solvent compositions were investigated to find the best composition for electrospinning a nanofibrous PCL barrier layer on PCL polyHIPE. The biocompatibility and the barrier properties of the electrospun layer were demonstrated over four weeks in vitro by histological staining. Following in vitro assessment of cell viability and cell migration, cell infiltration and the potential of PCL polyHIPE for supporting blood vessel ingrowth were further investigated using an ex-ovo chick chorioallantoic membrane assay. Our results demonstrated that the nanofibrous PCL electrospun layer was capable of limiting cell infiltration for at least four weeks, while PCL polyHIPE supported cell infiltration, calcium and mineral deposition of bone cells, and blood vessel ingrowth through pores