The evaluation of a small-diameter polysaccharide-based arterial graft in rats

Atomic-layer-deposition application for antibacterial coating of biomedical materials: surgical sutures

Suture-associated surgical site infection (SSI) causes bacterial pathogens to colonize on the suture surface that are highly resistant to antibiotic treatment. Conventional suture materials used in surgical practice are causing complications such as infection and chronic inflammation. Surgical suture materials with antibacterial coatings are widely used in surgical practice. However, all the widely used antibacterial agents are not permanent (limited lasting) due to their instability and release depending on environmental conditions (pH or temperature, for example). Therefore, more long-lasting (low-dose) and effective antibacterial function materials are required. In the present work, we proposed a new material and method of antibacterial coating the surgical sutures based on the atomic layer deposition (ALD) technique to enhance its antibacterial activity for treatment of the SSI. We have proposed applying a vanadium-doped TiO2nanofilm (hybrid nanomaterial, TiVOx) with 27.5 nm thickness to enhance the antibacterial property of surgical sutures using the ALD technique. We have illustrated that a base coating of Al2O3(seed layer) applied to the suture surface, which directly contacts the polypropylene (PP) suture, improves the adhesion of the deposited antibacterial material TiVOx. This provides a long-lasting antibacterial effect on the suture (a prolonged antibacterial effect of the coating material), i.e. increases the stability of the deposition (stable in water, air, in the human body, in different pH mediums, and at temperatures up to 70 °C). The sutures did not deteriorate after several wash cycles with sterilizing solvents. Also, the antibacterial agent (TiVOx) is nontoxic. The concentration of vanadium in the film is below the toxicity limits due to the low diffusivity of vanadium and high adhesion with the base coating material (Al2O3). Sutures coated with V-doped TiO2were characterized using scanning electron microscopy images, and elemental analysis was performed using energy dispersive spectroscopy Spectroscopy. The antibacterial activity of TiVOxcoated sutures against two types of microorganisms,E. coliand Proteus vulgaris (Pr. Vulgaris) was compared to that of noncoated sutures. The quantitative assessment of antibacterial activity of suture materials with and without ALD nanocoating TiVOxagainstE. coliandPr. Vulgarishas been performed. No growth of bacteria around the suture material with antibacterial TiVOxALD nanocoating throughout the entire observation period of 48 and 72 h was observed. However, after 48 h, the concentration of bacteria of theE. Coliaround the suture material without ALD TiVOxnanocoating on nutrient agar was 5.5 ± 0.3 Log CFU cm-3, and after 72 h it was 8.0 ± 0.5 Log CFU cm-3. For Pr. Vilgaris, after 48 h, the concentration of bacteria around the suture material without ALD TiVOxnanocoating on nutrient agar was 2.1 ± 0.1 Log CFU cm-3, while after 72 h it was 4.5 ± 0.2 Log CFU cm-3. ALD-coated TiVOxon the PP sutures inhibited approximately 100% of biofilm formation. Also, the inhibition zones in the disc diffusion assay revealed that all the ALD TiVOxcoating inhibited (100%) the growth ofE. coliandPr. Vulgaris, notably compared to the uncoated suture samples.

Investigating the efficacy of uncrosslinked porcine collagen coated vascular grafts for neointima formation and endothelialization

Introduction

This study evaluates the efficacy of uncrosslinked porcine collagen coated vascular grafts (UPCCVG) in facilitating neointima formation and endothelialization.

Methods

Prior to coating, the uncrosslinked porcine collagen underwent comprehensive characterization employing SDS-PAGE, image analysis, circular dichroism and immunogenicity. The PET substrate of the vascular graft was coated with collagen solution utilizing the dip-coating method. Water permeability, blood leakage resistance, radial compliance, hemolysis, cytotoxicity and cell proliferation of UPCCVG in vitro were studied. Subsequent in vivo evaluation involved the implantation of UPCCVG as a substitute for the porcine abdominal aorta. Digital subtraction angiography (DSA) was employed to evaluate UPCCVG patency post-implantation, while histology, immunohistochemistry, and scanning electron microscopy were utilized to assess neointima formation and endothelialization. The in vivo thrombosis of UPCCVG was analyzed simultaneously to further characterize its blood compatibility.

Results

The uncrosslinked collagen demonstrated high purity, maintaining its triple helix structure and molecular weight akin to the type I bovine collagen standard substrate, indicative of preserved biological activity and low immunogenicity. UPCCVG exhibited water permeability, blood leakage resistance, radial compliance and blood compatibility comparable to commercial grafts. DSA revealed satisfactory patency of UPCCVG without evidence of stenosis or swelling at the 3-week post-implantation mark. Histological analysis illustrated well-developed neointima with appropriate thickness and controlled proliferation. Immunohistochemistry confirmed the presence of endothelial cells (VWF positive) and smooth muscle cells (α-SMA positive) within the neointima, indicating successful endothelialization. Moreover, the morphology of the neointima surface closely resembled that of the natural artery tunica intima, oriented along the direction of blood flow.

Discussion

UPCCVG, composed of uncrosslinked porcine collagen, demonstrates promising potential in fostering neointima formation and endothelialization while mitigating intimal hyperplasia. This biocompatible uncrosslinked porcine collagen merits further investigation for its clinical applications in vascular reconstruction.

Influence of formic acid esterified cellulose nanofibrils on compressive strength, resilience and thermal stability of polyvinyl alcohol-xylan hydrogel

Having competitive compressive strength and resilience as well as biocompatibility simultaneously still remains a challenge for composite hydrogels, which is critical if they are aimed for use as functional biomaterials. In the present work, a facile and green method was designed for producing a composite hydrogel based on polyvinyl alcohol (PVA) and xylan with sodium tri-metaphosphate (STMP) as cross-linker, aiming to specially enhance its compressive properties with the aid of eco-friendly produced formic acid esterified cellulose nanofibrils (CNFs). The CNF addition caused a compressive strength decrease of the hydrogels, although the values (2.34-4.57 MPa at a compressive strain of 70 %) were still at a high level among the reported PVA (or polysaccharide) based hydrogels so far. However, the compressive resilience of the hydrogels was enhanced significantly by the CNF addition, with maximal compressive strength retention of 88.49 % and 99.67 % in height recovery after 1000 compression cycles at a strain of 30 %, which reflects the significant influence of CNFs on the compressive recovery ability of the hydrogel. All materials used in the present work are naturally non-toxic with good biocompatible, which makes the synthesized hydrogels with great potential in biomedical applications, e.g., soft-tissue engineering.

Engineered human liver based on pullulan-dextran hydrogel promotes mice survival after liver failure

Liver tissue engineering approaches aim to support drug testing, assistance devices, or transplantation. However, their suitability for clinical application remains unsatisfactory. Herein, we demonstrate the beneficial and biocompatible use of porous pullulan-dextran hydrogel for the self-assembly of hepatocytes and biliary-like cells into functional 3D microtissues. Using HepaRG cells, we obtained 21 days maintenance of engineered liver polarity, functional detoxification and excretion systems, as well as glycogen storage in hydrogel. Implantation on two liver lobes in mice of hydrogels containing 3800 HepaRG 3D structures of 100 ​μm in diameter, indicated successful engraftment and no signs of liver toxicity after one month. Finally, after acetaminophen-induced liver failure, when mice were transplanted with engineered livers on left lobe and peritoneal cavity, the survival rate at 7 days significantly increased by 31.8% compared with mice without cell therapy. These findings support the clinical potential of pullulan-dextran hydrogel for liver failure management.

Pullulan as promoting endothelialization capacity of electrospun PCL-PU scaffold

OBJECTIVE

This project's primary purpose was to create engineered vascular scaffolds using polyurethane, polycaprolactone, and pullulan polymers, along with suitable mechanical-dynamic conditions. Therefore, electrospun scaffolds with optimized intrinsic physiological properties and the ability to support endothelial cells were prepared in vitro, and cell viability was studied in PCL-PU and PCL-PU scaffolds containing Pullulan.

THE MAIN METHODS

The electrospinning method has been used to prepare PCL-PU and PCL-PU scaffolds containing Pullulan. The scaffold's surface morphology was evaluated using SEM microscopic imaging. The scaffolds' physicochemical properties were prepared using ATR-FTIR, strain stress, and water contact angle tests, and the biocompatibility of PCL-PU and PU-PCL-Pl nanofibers was evaluated using the MTT test.

PRINCIPAL FINDINGS

The test results showed that PCL-PU scaffolds containing Pullulan have more suitable mechanical properties such as stress-strain, water contact angle, swelling rate, biocompatibility, fiber diameter, and pore size compared to PU-PCL. The culture of endothelial cells under static conditions on these scaffolds did not cause cytotoxic effects under static conditions compared to the control group. SEM images confirmed the ability of endothelial cells to attach to the scaffold surface.

SUMMARY AND CONCLUSION

The results showed that PCL-PU substrate containing pullulan could stimulate endothelial cells' proliferation under static conditions.

Interplay between crosslinking and ice nucleation controls the porous structure of freeze-dried hydrogel scaffolds

Freeze-drying is a process of choice to texture hydrogel scaffolds with pores formed by an ice-templating mechanism. Using state-of-the-art microscopies (cryo-EBSD, μCT, CLSM), this work evidences and quantifies the effect of crosslinking and ice nucleation temperature on the porous structure of thin hydrogel scaffolds freeze-dried at a low cooling rate. We focused on a polysaccharide-based hydrogel and developed specific protocols to monitor or trigger ice nucleation for this study. At a fixed number of intermolecular crosslinks per primary molecule (p = 5), the mean pore size in the dry state decreases linearly from 240 to 170 μm, when ice nucleation temperature decreases from -6 °C to -18 °C. When ice nucleation temperature is fixed at -10 °C, the mean pore size decreases from 250 to 150 μm, as the crosslinking degree increases from p = 3 to p = 7. Scaffold infiltration ability was quantified with synthetic microspheres. The seeding efficiency was assessed with MC3T3-E1 individual cells and HepaRG™ spheroids. These data collapse into a single master curve that exhibits a sharp transition from 100 % to 0 %-efficiency as the entity diameter approaches the mean pore size in the dry state. Altogether, we can thus precisely tune the porosity of these 3D materials of interest for 3D cell culture and cGMP production for tissue engineering.

Tuning Physicochemical Properties of a Macroporous Polysaccharide-Based Scaffold for 3D Neuronal Culture

Central nervous system (CNS) lesions are a leading cause of death and disability worldwide. Three-dimensional neural cultures in biomaterials offer more physiologically relevant models for disease studies, toxicity screenings or in vivo transplantations. Herein, we describe the development and use of pullulan/dextran polysaccharide-based scaffolds for 3D neuronal culture. We first assessed scaffolding properties upon variation of the concentration (1%, 1.5%, 3% w/w) of the cross-linking agent, sodium trimetaphosphate (STMP). The lower STMP concentration (1%) allowed us to generate scaffolds with higher porosity (59.9 ± 4.6%), faster degradation rate (5.11 ± 0.14 mg/min) and lower elastic modulus (384 ± 26 Pa) compared with 3% STMP scaffolds (47 ± 2.1%, 1.39 ± 0.03 mg/min, 916 ± 44 Pa, respectively). Using primary cultures of embryonic neurons from PGKCre, Rosa26tdTomato embryos, we observed that in 3D culture, embryonic neurons remained in aggregates within the scaffolds and did not attach, spread or differentiate. To enhance neuronal adhesion and neurite outgrowth, we then functionalized the 1% STMP scaffolds with laminin. We found that treatment of the scaffold with a 100 μg/mL solution of laminin, combined with a subsequent freeze-drying step, created a laminin mesh network that significantly enhanced embryonic neuron adhesion, neurite outgrowth and survival. Such scaffold therefore constitutes a promising neuron-compatible and biodegradable biomaterial.

Dextran-based scaffolds for in-situ hydrogelation: Use for next generation of bioartificial cardiac tissues

In pursuit of a chemically-defined matrix for in vitro cardiac tissue generation, we present dextran (Dex)-derived hydrogels as matrices suitable for bioartificial cardiac tissues (BCT). The dextran hydrogels were generated in situ by using hydrazone formation as the crosslinking reaction. Material properties were flexibly adjusted, by varying the degrees of derivatization and the molecular weight of dextran used. Furthermore, to modulate dextran's bioactivity, cyclic pentapeptide RGD was coupled to its backbone. BCTs were generated by using a blend of modified dextran and human collagen (hColI) in combination with induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) and fibroblasts. These hColI + Dex blends with or without RGD supported tissue formation and functional maturation of CMs. Contraction forces (hColI + Dex-RGD: 0.27 ± 0.02 mN; hColI + Dex: 0.26 ± 0.01 mN) and frequencies were comparable to published constructs. Thus, we could demonstrate that, independent of the presence of RGD, our covalently linked dextran hydrogels are a promising matrix for building cardiac grafts.

Pullulan in biomedical research and development - A review

Pullulan is an imperative microbial exo-polymer commercially produced by yeast like fungus Aureobasidium pullulans. Its structure contains maltosyl repeating units which comprises two α-(1 → 4) linked glucopyranose rings attached to one glucopyranose ring through α-(1 → 6) glycosidic bond. The co-existence of α-(1 → 6) and α-(1 → 4) glycosidic linkages endows distinctive physico-chemical properties to pullulan. It is highly biocompatible, non-toxic and non-carcinogenic in nature. It is extremely resistant to any mutagenicity or immunogenicity. The unique properties of pullulan make it a potent candidate for biomedical applications viz. drug delivery, gene delivery, tissue engineering, molecular chaperon, plasma expander, vaccination, etc. This review highlights the potential of pullulan in biomedical research and development.

Development of 3D Hepatic Constructs Within Polysaccharide-Based Scaffolds with Tunable Properties

Organoids production is a key tool for in vitro studies of physiopathological conditions, drug-induced toxicity assays, and for a potential use in regenerative medicine. Hence, it prompted studies on hepatic organoids and liver regeneration. Numerous attempts to produce hepatic constructs had often limited success due to a lack of viability or functionality. Moreover, most products could not be translated for clinical studies. The aim of this study was to develop functional and viable hepatic constructs using a 3D porous scaffold with an adjustable structure, devoid of any animal component, that could also be used as an in vivo implantable system. We used a combination of pharmaceutical grade pullulan and dextran with different porogen formulations to form crosslinked scaffolds with macroporosity ranging from 30 µm to several hundreds of microns. Polysaccharide scaffolds were easy to prepare and to handle, and allowed confocal observations thanks to their transparency. A simple seeding method allowed a rapid impregnation of the scaffolds with HepG2 cells and a homogeneous cell distribution within the scaffolds. Cells were viable over seven days and form spheroids of various geometries and sizes. Cells in 3D express hepatic markers albumin, HNF4α and CYP3A4, start to polarize and were sensitive to acetaminophen in a concentration-dependant manner. Therefore, this study depicts a proof of concept for organoid production in 3D scaffolds that could be prepared under GMP conditions for reliable drug-induced toxicity studies and for liver tissue engineering.

Astaxanthin Complexes to Attenuate Muscle Damage after In Vivo Femoral Ischemia-Reperfusion

(1) Background: Reperfusion injury refers to the cell and tissue damage induced, when blood flow is restored after an ischemic period. While reperfusion reestablishes oxygen supply, it generates a high concentration of radicals, resulting in tissue dysfunction and damage. Here, we aimed to challenge and achieve the potential of a delivery system based on astaxanthin, a natural antioxidant, in attenuating the muscle damage in an animal model of femoral hind-limb ischemia and reperfusion. (2) Methods: The antioxidant capacity and non-toxicity of astaxanthin was validated before and after loading into a polysaccharide scaffold. The capacity of astaxanthin to compensate stress damages was also studied after ischemia induced by femoral artery clamping and followed by varied periods of reperfusion. (3) Results: Histological evaluation showed a positive labeling for CD68 and CD163 macrophage markers, indicating a remodeling process. In addition, higher levels of Nrf2 and NQO1 expression in the sham group compared to the antioxidant group could reflect a reduction of the oxidative damage after 15 days of reperfusion. Furthermore, non-significant differences were observed in non-heme iron deposition in both groups, reflecting a cell population susceptible to free radical damage. (4) Conclusions: Our results suggest that the in situ release of an antioxidant molecule could be effective in improving the antioxidant defenses of ischemia/reperfusion (I/R)-damaged muscles.

Biocompatibility and Immunogenicity of Decellularized Allogeneic Aorta in the Orthotopic Rat Model

The generation of a small-caliber arterial graft, utilizing a large vessel of a small animal, such as the aorta of the rat or rabbit, for clinical use in the peripheral arterial tree, can widen the options for arterial prostheses. This in vivo study demonstrated the ability of the decellularization protocol that was used to produce a noncytotoxic acellular small-caliber arterial graft, with sufficient biomechanical and biological integrity to withstand the demanding flow and pressure environment of the rat aorta. This work also demonstrated the superiority of the decellularized homograft over its intact counterpart, in terms of lower immunogenicity.

Thixotropic PVA hydrogel enclosing a hydrophilic PVP core as nucleus pulposus substitute

A thixotropic polyvinyl alcohol (PVA) hydrogel, containing a hydrophilic poly-vinyl pyrrolidone (PVP) core, was obtained in order to develop a preformed 3D network able to maintain injectability. PVA was mixed with PVP in two different molar ratios (1:1 and 1:3) and chemically cross-linked using trisodium trimetaphosphate (STMP), which is able to react only with PVA component. A combination of Time of Flight- Secondary Ion Mass Spectrometry (ToF-SIMS), elemental analysis and UV spectroscopy permitted to determine both the cross-linking arm length and the crosslinking degree. Hydrogels were characterized in terms of swelling pressurization, rheological and mechanical behaviour. In particular, the viscoelastic behaviour of the hydrogel was analysed in shear and compression stress under dynamic conditions and compared with the performance of healthy human nucleus pulposus. In conclusion, the study demonstrated that the scaffold obtained mixing PVA and PVP in a molar ratio 1:1 can be considered a promising material to be utilised in the replacement of nucleus pulposus.

Effect of cross-linking on the physicochemical and in vitro properties of pullulan/dextran microbeads

Hydrogels are very promising for tissue engineering as they provide scaffolds and a suitable microenvironment to control cell behavior and tissue regeneration. We used a patented method to obtain beads of pullulan/dextran cross-linked with sodium trimetaphosphate (STMP), that were already described for in vivo bone repair. The aim of this study was to provide a comparative analysis of microbeads made of polysaccharides prepared using three different STMP feeding ratio of 1.5, 2.25 or 3 % w/w. The morphology, swelling and biodegradability of these structures were assessed. Mesenchymal stem cells were also seeded to evaluate the cell organization onto the beads. We found that the amount of phosphorus resulting from the cross-linking was proportional to the introduced STMP concentration. An increase of cross-linking decreased the in vitro enzymatic degradability, and also decreased the swelling in PBS or water. The microstructures observed by SEM and confocal microscopy indicated that homogeneous spherical microbeads were obtained, except for the lower cross-linking ratio where the shapes were altered. Beads hydrated in PBS exhibited a mean diameter ranging from 400 to 550 µm with the decrease of STMP ratio. Cells adhered to the surface of microbeads even in the absence of protein coating. Cell viability studies revealed an increase in cell numbers over two weeks for the highest cross-linked beads, whereas the two lowest STMP concentrations induced a decrease of cell viability. Overall, this study demonstrated that pullulan/dextran hydrogels can be designed as microbeads with adjustable physicochemical and biological properties to fulfill requirements for tissue engineering approaches.

Design, characterization and in vivo performance of synthetic 2 mm-diameter vessel grafts made of PVA-gelatin blends

Since the development of the first vascular grafts, fabrication of vessel replacements with diameters smaller than 6 mm remains a challenge. The present work aimed to develop PVA (poly (vinyl alcohol))-gelatin hybrids as tubes suitable for replacement of very small vessels and to evaluate their performance using a rat abdominal aorta interposition model. PVA-gelatin hybrid tubes with internal and external diameters of 1.4 mm and 1.8 mm, respectively, composed of 4 different gelatin ratios were prepared using a one-step strategy with both chemical and physical crosslinking. By 3D Time of Flight MRI, Doppler-Ultrasound, Computed Tomography angiography and histology, we demonstrated good patency rates with the 1% gelatin composition until the end of the study at 3 months (50% compared to 0% of PVA control grafts). A reduction of the patency rate during the time of implantation suggested some loss of properties of the hybrid material in vivo, further confirmed by mechanical evaluation until one year. In particular, stiffening and reduction of compliance of the PVA-gelatin grafts was demonstrated, which might explain the observed long-term changes in patency rate. These encouraging results confirm the potential of PVA-gelatin hybrids as ready-to-use vascular grafts for very small vessel replacement.

[Tissue engineering: a multidisciplinary approach]

The prostheses have been around for thousands of years. Initially, it was substitute materials to replace members (leg, foot, hand) or for surgery (suture). The materials used have evolved, but they had never been created for medical applications. Recently, other strategies have emerged to construct or repair tissues. They are based on the use of biological components such as proteins or cells and provide a biological dimension to the term "biomaterial" and they often involve engineering. We illustrate the tissue engineering approaches using the examples of muscle and vessel regeneration strategies in the frame of restorative medicine.

A Tubular Biomaterial Construct Exhibiting a Negative Poisson's Ratio

Developing functional small-diameter vascular grafts is an important objective in tissue engineering research. In this study, we address the problem of compliance mismatch by designing and developing a 3D tubular construct that has a negative Poisson's ratio νxy (NPR). NPR constructs have the unique ability to expand transversely when pulled axially, thereby resulting in a highly-compliant tubular construct. In this work, we used projection stereolithography to 3D-print a planar NPR sheet composed of photosensitive poly(ethylene) glycol diacrylate biomaterial. We used a step-lithography exposure and a stitch process to scale up the projection printing process, and used the cut-missing rib unit design to develop a centimeter-scale NPR sheet, which was rolled up to form a tubular construct. The constructs had Poisson's ratios of -0.6 ≤ νxy ≤ -0.1. The NPR construct also supports higher cellular adhesion than does the construct that has positive νxy. Our NPR design offers a significant advance in the development of highly-compliant vascular grafts.

Composite Scaffolds of Interfacial Polyelectrolyte Fibers for Temporally Controlled Release of Biomolecules

Various scaffolds used in tissue engineering require a controlled biochemical environment to mimic the physiological cell niche. Interfacial polyelectrolyte complexation (IPC) fibers can be used for controlled delivery of various biological agents such as small molecule drugs, cells, proteins and growth factors. The simplicity of the methodology in making IPC fibers gives flexibility in its application for controlled biomolecule delivery. Here, we describe a method of incorporating IPC fibers into two different polymeric scaffolds, hydrophilic polysaccharide and hydrophobic polycaprolactone, to create a multi-component composite scaffold. We showed that IPC fibers can be easily embedded into these polymeric structures, enhancing the capability for sustained release and improved preservation of biomolecules. We also created a composite polymeric scaffold with topographical cues and sustained biochemical release that can have synergistic effects on cell behavior. Composite polymeric scaffolds with IPC fibers represent a novel and simple method of recreating the cellular niche.

Composite pullulan-dextran polysaccharide scaffold with interfacial polyelectrolyte complexation fibers: a platform with enhanced cell interaction and spatial distribution

Hydrogels are highly preferred in soft tissue engineering because they recapitulate the hydrated extracellular matrix. Naturally derived polysaccharides, like pullulan and dextran, are attractive materials with which to form hydrophilic polymeric networks due to their non-immunogenic and non-antigenic properties. However, their inherent hydrophilicity prevents adherent cell growth. In this study, we modified pullulan-dextran scaffolds with interfacial polyelectrolyte complexation (IPC) fibers to improve their ability to support adherent cell growth. We showed that the pullulan-dextran-IPC fiber composite scaffold laden with extracellular matrix protein has improved cell adhesion and proliferation compared to the plain polysaccharide scaffold. We also demonstrated the zero-order release kinetics of the biologics bovine serum albumin and vascular endothelial growth factor (VEGF) incorporated in the composite scaffold. Lastly, we showed that the VEGF released from the composite scaffold retained its capacity to stimulate endothelial cell growth. The incorporation of IPC fibers in the pullulan-dextran hydrogel scaffold improved its functionality and biological activity, thus enhancing its potential in tissue engineering applications.

Polysaccharide-based strategies for heart tissue engineering

Polysaccharides are abundant biomolecules in nature presenting important roles in a wide variety of living systems processes. Considering the structural and biological functions of polysaccharides, their properties have raised interest for tissue engineering. Herein, we described the latest advances in cardiac tissue engineering mediated by polysaccharides. We reviewed the data already obtained in vitro and in vivo in this field with several types of polysaccharides. Cardiac injection, intramyocardial in situ polymerization strategies, and scaffold-based approaches involving polysaccharides for heart tissue engineering are thus discussed.

Polysaccharide electrospun fibers with sulfated poly(fucose) promote endothelial cell migration and VEGF-mediated angiogenesis

This study demonstrates the potential of fucoidan-incorporated pullulan–dextran fibers as tunable reservoirs for VEGF delivery to promote angiogenesis.

Design of Biomimetic Vascular Grafts with Magnetic Endothelial Patterning

The development of small diameter vascular grafts with a controlled pluricellular organization is still needed for effective vascular tissue engineering. Here, we describe a technological approach combining a tubular scaffold and magnetically labeled cells to create a pluricellular and organized vascular graft, the endothelialization of which could be monitored by MRI prior to transplantation. A novel type of scaffold was developed with a tubular geometry and a porous bulk structure enabling the seeding of cells in the scaffold pores. A homogeneous distribution of human mesenchymal stem cells in the macroporous structure was obtained by seeding the freeze-dried scaffold with the cell suspension. The efficient covering of the luminal surface of the tube was then made possible thanks to the implementation of a magnetic-based patterning technique. Human endothelial cells or endothelial progenitors were magnetically labeled with iron oxide nanoparticles and successfully attracted to the 2-mm lumen where they attached and formed a continuous endothelium. The combination of imaging modalities [fluorescence imaging, histology, and 3D magnetic resonance imaging (MRI)] evidenced the integrity of the vascular construct. In particular, the observation of different cell organizations in a vascular scaffold within the range of resolution of single cells by 4.7 T MRI is reported.

Animal models for vascular tissue-engineering

Because of rise in cardiovascular disease throughout the world, there is increasing demand for small diameter blood vessels as replacement grafts. The present review focuses on the animal models that have been used to test small-diameter TEVs with emphasis on the attributes of each model. Small animal models are used to test short-term patency and address mechanistic hypotheses; and large, preclinical animal models are employed to test long-term patency, remodeling and function in an environment mimicking human physiology. We also discuss recent clinical trials that employed laboratory fabricated TEVs and showed very promising results. Ultimately, animal models provide a testing platform for optimizing vascular grafts before clinical use in patients without suitable autologous vessels.

Tissue engineered vascular grafts--preclinical aspects

Tissue engineering enables the development of fully biological vascular substitutes that restore, maintain and improve tissue function in a manner identical to natural host tissue. However the development of the appropriate preclinical evaluation techniques for the generation of fully functional tissue-engineered vascular graft (TEVG) is required to establish their safety for use in clinical trials and to test clinical effectiveness. This review gives an insight on the various preclinical studies performed in the area of tissue engineered vascular grafts highlighting the different strategies used with respect to cells and scaffolds, typical animal models used and the major in vivo evaluation studies that have been carried out. The review emphasizes the combined effort of engineers, biologists and clinicians which can take this clinical research to new heights of regenerative therapy.

Pharmaceutical applications of dynamic mechanical thermal analysis

The successful development of polymeric drug delivery and biomedical devices requires a comprehensive understanding of the viscoleastic properties of polymers as these have been shown to directly affect clinical efficacy. Dynamic mechanical thermal analysis (DMTA) is an accessible and versatile analytical technique in which an oscillating stress or strain is applied to a sample as a function of oscillatory frequency and temperature. Through cyclic application of a non-destructive stress or strain, a comprehensive understanding of the viscoelastic properties of polymers may be obtained. In this review, we provide a concise overview of the theory of DMTA and the basic instrumental/operating principles. Moreover, the application of DMTA for the characterization of solid pharmaceutical and biomedical systems has been discussed in detail. In particular we have described the potential of DMTA to measure and understand relaxation transitions and miscibility in binary and higher-order systems and describe the more recent applications of the technique for this purpose.

Mesenchymal stem cell delivery into rat infarcted myocardium using a porous polysaccharide-based scaffold: a quantitative comparison with endocardial injection

The use of mesenchymal stem cells (MSCs) for tissue regeneration is often hampered by modest engraftment in host tissue. This study was designed to quantitatively compare MSCs engraftment rates after delivery using a polysaccharide-based porous scaffold or endocardial (EC) injection in a rat myocardial infarction model. Cellular engraftment was measured by quantitative reverse transcription-polymerase chain reaction using MSCs previously transduced with a lentiviral vector that expresses green fluorescent protein (GFP). The use of a scaffold promoted local cellular engraftment and survival. The number of residual GFP(+) cells was greater with the scaffold than after EC injection (9.7% vs. 5.1% at 1 month and 16.3% vs. 6.1% at 2 months, respectively [n=5]). This concurred with a significant increase in mRNA vascular endothelial growth factor level in the scaffold group (p<0.05). Clusters of GFP+ cells were detected in the peri-infarct area, mainly phenotypically consistent with immature MSCs. Functional assessment by echocardiography at 2 months postinfarct also showed a trend toward a lower left ventricular dilatation and a reduced fibrosis in the scaffold group in comparison to direct injection group (n=10). These findings demonstrate that using a porous biodegradable scaffold is a promising method to improve cell delivery and engraftment into damaged myocardium.

Tissue Engineering of Blood Vessels: Functional Requirements, Progress, and Future Challenges

Vascular disease results in the decreased utility and decreased availability of autologus vascular tissue for small diameter (< 6 mm) vessel replacements. While synthetic polymer alternatives to date have failed to meet the performance of autogenous conduits, tissue-engineered replacement vessels represent an ideal solution to this clinical problem. Ongoing progress requires combined approaches from biomaterials science, cell biology, and translational medicine to develop feasible solutions with the requisite mechanical support, a non-fouling surface for blood flow, and tissue regeneration. Over the past two decades interest in blood vessel tissue engineering has soared on a global scale, resulting in the first clinical implants of multiple technologies, steady progress with several other systems, and critical lessons-learned. This review will highlight the current inadequacies of autologus and synthetic grafts, the engineering requirements for implantation of tissue-engineered grafts, and the current status of tissue-engineered blood vessel research.

Fabrication of porous polysaccharide-based scaffolds using a combined freeze-drying/cross-linking process

Biocompatible three-dimensional (3-D) porous scaffolds are of great interest for tissue engineering applications. We here present a novel combined freeze-drying/cross-linking process to prepare porous polysaccharide-based scaffolds. This process does not require an organic solvent or porogen agent. We unexpectedly found that cross-linking of biomacromolecules such as pullulan and dextran with sodium trimetaphosphate could be performed during freeze-drying. We have demonstrated that the freeze-drying pressure modulates the degree of porosity. High freeze-drying pressure scaffolds presented pores with a mean diameter of 55 +/- 4 microm and a porosity of 33 +/- 12%, whereas low freeze-drying pressure scaffolds contained larger pores with a mean diameter of 243 +/- 14 microm and a porosity of 68 +/- 3%. Porous scaffolds of the desired shape could be easily obtained and were stable in culture medium for weeks. In vitro viable mesenchymal stem cells were found associated with porous scaffolds in higher proportions than with non-porous scaffolds. Moreover, cells penetrated deeper into scaffolds with larger pores. This novel combined freeze-drying/cross-linking processing of polysaccharides enabled the fabrication of biocompatible scaffolds with controlled porosity and architectures suitable for 3-D in vitro culture and biomedical applications.

Films of dextran-graft-polybutylmethacrylate to enhance endothelialization of materials

We have synthesized new structures obtained from amphiphilic copolymers of dextran and polybutylmethacrylate with the aim of endothelialization of biomaterials. Grafting of butylmethacrylate onto dextran has been carried out using ceric ammonium nitrate as initiator. Three copolymers were obtained (11, 30 and 37 wt.% dextran) and homogeneous thin films were successfully prepared. In contrast to dextran, the resulting films were stable in water, and copolymers characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry and dynamic mechanical analysis showed evidence of hybrid properties between the parent homopolymers. Surfaces of films were smooth when analyzed by atomic force microscopy (roughness 2+/-1 nm) but greatly differed in their hydrophilicity by increasing the dextran content (water contact angle from 99 degrees to 57 degrees). In contrast to polybutylmethacrylate, where the proliferation of vascular smooth muscle cells (VSMCs) was excellent but that of endothelial cells was very low, the copolymer containing 11% of dextran was excellent for endothelial cells but very limited for VSMCs. An in vitro wound assay demonstrated that copolymer with 11% dextran is even more favorable for endothelial cell migration than tissue-culture polystyrene. Increasing the dextran content in the copolymers decreased the proliferation for both vascular cell types. Altogether, these results show that transparent and water-insoluble films made from copolymers of dextran and butylmethacrylate copolymers with an appropriate composition could enhance endothelial cell proliferation and migration. Therefore, a potential benefit of this approach is the availability of surfaces with tunable properties for the endothelialization of materials.

Magnetic micro-manipulations to probe the local physical properties of porous scaffolds and to confine stem cells

The in vitro generation of engineered tissue constructs involves the seeding of cells into porous scaffolds. Ongoing challenges are to design scaffolds to meet biochemical and mechanical requirements and to optimize cell seeding in the constructs. In this context, we have developed a simple method based on a magnetic tweezer set-up to manipulate, probe, and position magnetic objects inside a porous scaffold. The magnetic force acting on magnetic objects of various sizes serves as a control parameter to retrieve the local viscosity of the scaffolds internal channels as well as the stiffness of the scaffolds pores. Labeling of human stem cells with iron oxide magnetic nanoparticles makes it possible to perform the same type of measurement with cells as probes and evaluate their own microenvironment. For 18 microm diameter magnetic beads or magnetically labeled stem cells of similar diameter, the viscosity was equivalently equal to 20 mPa s in average. This apparent viscosity was then found to increase with the magnetic probes sizes. The stiffness probed with 100 microm magnetic beads was found in the 50 Pa range, and was lowered by a factor 5 when probed with cells aggregates. The magnetic forces were also successfully applied to the stem cells to enhance the cell seeding process and impose a well defined spatial organization into the scaffold.