Hyaluronan Biodegradable Scaffold for Small-caliber Artery Grafting: Preliminary Results in an Animal Model

Microfluidic fabrication of X-ray-visible sodium hyaluronate microspheres for embolization

Catheter embolization is a minimally invasive technique that relies on embolic agents and is now widely used to treat various high-prevalence medical diseases. Embolic agents usually need to be combined with exogenous contrasts to visualize the embolotherapy process. However, the exogenous contrasts are quite simply washed away by blood flow, making it impossible to monitor the embolized location. To solve this problem, a series of sodium hyaluronate (SH) loaded with bismuth sulfide (Bi₂S₃) nanorods (NRs) microspheres (Bi₂S₃@SH) were prepared in this study by using 1,4-butaneglycol diglycidyl ether (BDDE) as a crosslinker through single-step microfluidics. Bi₂S₃@SH-1 microspheres showed the best performance among other prepared microspheres. The fabricated microspheres had uniform size and good dispersibility. Furthermore, the introduction of Bi₂S₃ NRs synthesized by a hydrothermal method as Computed Tomography (CT) contrast agents improved the mechanical properties of Bi₂S₃@SH-1 microspheres and endowed the microspheres with excellent X-ray impermeability. The blood compatibility and cytotoxicity test showed that the Bi₂S₃@SH-1 microspheres had good biocompatibility. In particular, the in vitro simulated embolization experiment results indicate that the Bi₂S₃@SH-1 microspheres had excellent embolization effect, especially for the small-sized blood vessels of 500-300 and 300 μm. The results showed the prepared Bi₂S₃@SH-1 microspheres have good biocompatibility and mechanical properties, as well as certain X-ray visibility and excellent embolization effects. We believe that the design and combination of this material has good guiding significance in the field of embolotherapy.

hapln1a+ cells guide coronary growth during heart morphogenesis and regeneration

Although several tissues and chemokines orchestrate coronary formation, the guidance cues for coronary growth remain unclear. Here, we profile the juvenile zebrafish epicardium during coronary vascularization and identify hapln1a+ cells enriched with vascular-regulating genes. hapln1a+ cells not only envelop vessels but also form linear structures ahead of coronary sprouts. Live-imaging demonstrates that coronary growth occurs along these pre-formed structures, with depletion of hapln1a+ cells blocking this growth. hapln1a+ cells also pre-lead coronary sprouts during regeneration and hapln1a+ cell loss inhibits revascularization. Further, we identify serpine1 expression in hapln1a+ cells adjacent to coronary sprouts, and serpine1 inhibition blocks vascularization and revascularization. Moreover, we observe the hapln1a substrate, hyaluronan, forming linear structures along and preceding coronary vessels. Depletion of hapln1a+ cells or serpine1 activity inhibition disrupts hyaluronan structure. Our studies reveal that hapln1a+ cells and serpine1 are required for coronary production by establishing a microenvironment to facilitate guided coronary growth.

Advances in the development of tubular structures using extrusion-based 3D cell-printing technology for vascular tissue regenerative applications

Until recent, there are no ideal small diameter vascular grafts available on the market. Most of the commercialized vascular grafts are used for medium to large-sized blood vessels. As a solution, vascular tissue engineering has been introduced and shown promising outcomes. Despite these optimistic results, there are limitations to commercialization. This review will cover the need for extrusion-based 3D cell-printing technique capable of mimicking the natural structure of the blood vessel. First, we will highlight the physiological structure of the blood vessel as well as the requirements for an ideal vascular graft. Then, the essential factors of 3D cell-printing including bioink, and cell-printing system will be discussed. Afterwards, we will mention their applications in the fabrication of tissue engineered vascular grafts. Finally, conclusions and future perspectives will be discussed.

The sodium hyaluronate microspheres fabricated by solution drying for transcatheter arterial embolization

Transcatheter arterial embolization (TAE) is an effective therapeutic method for several clinical ailments. Interminably, the polymer microsphere is reflected as one of the idyllic embolic materials due to the exceptional...

Glycosaminoglycans: From Vascular Physiology to Tissue Engineering Applications

Cardiovascular diseases represent the number one cause of death globally, with atherosclerosis a major contributor. Despite the clinical need for functional arterial substitutes, success has been limited to arterial replacements of large-caliber vessels (diameter > 6 mm), leaving the bulk of demand unmet. In this respect, one of the most challenging goals in tissue engineering is to design a "bioactive" resorbable scaffold, analogous to the natural extracellular matrix (ECM), able to guide the process of vascular tissue regeneration. Besides adequate mechanical properties to sustain the hemodynamic flow forces, scaffold's properties should include biocompatibility, controlled biodegradability with non-toxic products, low inflammatory/thrombotic potential, porosity, and a specific combination of molecular signals allowing vascular cells to attach, proliferate and synthesize their own ECM. Different fabrication methods, such as phase separation, self-assembly and electrospinning are currently used to obtain nanofibrous scaffolds with a well-organized architecture and mechanical properties suitable for vascular tissue regeneration. However, several studies have shown that naked scaffolds, although fabricated with biocompatible polymers, represent a poor substrate to be populated by vascular cells. In this respect, surface functionalization with bioactive natural molecules, such as collagen, elastin, fibrinogen, silk fibroin, alginate, chitosan, dextran, glycosaminoglycans (GAGs), and growth factors has proven to be effective. GAGs are complex anionic unbranched heteropolysaccharides that represent major structural and functional ECM components of connective tissues. GAGs are very heterogeneous in terms of type of repeating disaccharide unit, relative molecular mass, charge density, degree and pattern of sulfation, degree of epimerization and physicochemical properties. These molecules participate in a number of vascular events such as the regulation of vascular permeability, lipid metabolism, hemostasis, and thrombosis, but also interact with vascular cells, growth factors, and cytokines to modulate cell adhesion, migration, and proliferation. The primary goal of this review is to perform a critical analysis of the last twenty-years of literature in which GAGs have been used as molecular cues, able to guide the processes leading to correct endothelialization and neo-artery formation, as well as to provide readers with an overall picture of their potential as functional molecules for small-diameter vascular regeneration.

Electrospun PCL-Based Vascular Grafts: In Vitro Tests

BACKGROUND

Electrospun fibers have attracted a lot of attention from researchers due to their several characteristics, such as a very thin diameter, three-dimensional topography, large surface area, flexible surface, good mechanical characteristics, suitable for widespread applications. Indeed, electro-spinning offers many benefits, such as great surface-to-volume ratio, adjustable porosity, and the ability of imitating the tissue extra-cellular matrix.

METHODS

we processed Poly ε-caprolactone (PCL) via electrospinning for the production of bilayered tubular scaffolds for vascular tissue engineering application. Endothelial cells and fibroblasts were seeded into the two side of the scaffolds: endothelial cells onto the inner side composed of PCL/Gelatin fibers able to mimic the inner surface of the vessels, and fibroblasts onto the outer side only exposing PCL fibers. Extracellular matrix production and organization has been performed by means of classical immunofluorescence against collagen type I fibers, Scanning Electron-Microscopy (SEM) has been performed in order to evaluated ultrastructural morphology, gene expression by means gene expression has been performed to evaluate the phenotype of endothelial cells and fibroblasts.

RESULTS AND CONCLUSION

results confirmed that both cells population are able to conserve their phenotype colonizing the surface supporting the hypothesis that PCL scaffolds based on electrospun fibers should be a good candidate for vascular surgery.

Carbon nanotubes catalyzed UV-trigger production of hyaluronic acid from Streptococcus equi

Hyaluronic acid (HA) has great importance in biomedical applications. In this work, a novel nanoparticle-based method that stimulates the hyaluronic acid (HA) production by the bacteria Streptococcus equi subsp. Zooepidemicus has been reported. CNTs with diameters of 40-50 nm and lengths of about 20 mm were used at four different concentrations (0, 10, 25, 50, and 100 μg) to the bacteria and determined the mass of the produced HA in dependence on the exposure time under UV-irradiation. The results clearly showed that the exposure for one minute with low power UV light (254 nm) and 100 µg (CNTs) treatments steadily increased HA production from the control (0.062 g/L) to the highest value (0.992) g/L of HA. The incubation of the streptococci with CNTs led to an increase of the HA production by a factor of 4.23 after 300S exposure time under UV light, whereas the HA production was no significant enhancement under visible light. It is explained that the CNTs nanoparticle-stimulated increase of the HA production with the internalization of the nanoparticles by the bacteria since they "serve as co-enzymes" under induced mutation by UV-irradiation. Transformation process was carried out and showed that the major protein band of Streptococcus equi was observed in the Streptococcus DH5α. RAPD analysis indicates that the amplified DNA fragments and the percentage of polymorphism was similar between Streptococcus equi and Streptococcus DH50α. The chemical structure and molecular weight of the photoproduced HA from Streptococcus equi was similar to the chemical structure of the standard sample.

Hyaluronic Acid: Redefining Its Role

The discovery of several unexpected complex biological roles of hyaluronic acid (HA) has promoted new research impetus for biologists and, the clinical interest in several fields of medicine, such as ophthalmology, articular pathologies, cutaneous repair, skin remodeling, vascular prosthesis, adipose tissue engineering, nerve reconstruction and cancer therapy. In addition, the great potential of HA in medicine has stimulated the interest of pharmaceutical companies which, by means of new technologies can produce HA and several new derivatives in order to increase both the residence time in a variety of human tissues and the anti-inflammatory properties. Minor chemical modifications of the molecule, such as the esterification with benzyl alcohol (Hyaff-11® biomaterials), have made possible the production of water-insoluble polymers that have been manufactured in various forms: membranes, gauzes, nonwoven meshes, gels, tubes. All these biomaterials are used as wound-covering, anti-adhesive devices and as scaffolds for tissue engineering, such as epidermis, dermis, micro-vascularized skin, cartilage and bone. In this review, the essential biological functions of HA and the applications of its derivatives for pharmaceutical and tissue regeneration purposes are reviewed.

Current challenges and future trends in manufacturing small diameter artificial vascular grafts in bioreactors

Cardiovascular diseases are a leading cause of death. Vascular surgery is mainly used to solve this problem. However, the generation of a functional and suitable substitute for small diameter (< 6 mm) displacement is challengeable. Moreover, synthetic prostheses, made of polyethylene terephthalate and extended polytetrafluoroethylene show have shown insufficient performance. Therefore, the challenges dominating the use of autografts have prevented their efficient use. Tissue engineering is highlighted in regenerative medicine perhaps in aiming to address the issue of end-stage organ failure. While organs and complex tissues require the vascular supply to support the graft survival and render the bioartificial organ role, vascular tissue engineering has shown to be a hopeful method for cell implantation by the production of tissues in vitro. Bioreactors are a salient point in vascular tissue engineering due to the capability for reproducible and controlled variations showing a new horizon in blood vessel substitution. This review strives to display the overview of current concepts in the development of small-diameter by using bioreactors. In this work, we show a critical look at different factors for developing small-diameter and give suggestions for future studies.

POLYMERIC BIOMATERIALS FOR SCAFFOLD-BASED BONE REGENERATIVE ENGINEERING

Reconstruction of large bone defects resulting from trauma, neoplasm, or infection is a challenging problem in reconstructive surgery. The need for bone grafting has been increasing steadily partly because of our enhanced capability to salvage limbs after major bone loss. Engineered bone graft substitutes can have advantages such as lack of antigenicity, high availability, and varying properties depending on the applications chosen for use. These favorable attributes have contributed to the rise of scaffold-based polymeric tissue regeneration. Critical components in the scaffold-based polymeric regenerative engineering approach often include 1. The existence of biodegradable polymeric porous structures with properties selected to promote tissue regeneration and while providing appropriate mechanical support during tissue regeneration. 2. Cellular populations that can influence and enhance regeneration. 3. The use of growth and morphogenetic factors which can influence cellular migration, differentiation and tissue regeneration in vivo. Biodegradable polymers constitute an attractive class of biomaterials for the development of scaffolds due to their flexibility in chemistry and their ability to produce biocompatible degradation products. This paper presents an overview of polymeric scaffold-based bone tissue regeneration and reviews approaches as well as the particular roles of biodegradable polymers currently in use.

Current development of biodegradable polymeric materials for biomedical applications

In the last half-century, the development of biodegradable polymeric materials for biomedical applications has advanced significantly. Biodegradable polymeric materials are favored in the development of therapeutic devices, including temporary implants and three-dimensional scaffolds for tissue engineering. Further advancements have occurred in the utilization of biodegradable polymeric materials for pharmacological applications such as delivery vehicles for controlled/sustained drug release. These applications require particular physicochemical, biological, and degradation properties of the materials to deliver effective therapy. As a result, a wide range of natural or synthetic polymers able to undergo hydrolytic or enzymatic degradation is being studied for biomedical applications. This review outlines the current development of biodegradable natural and synthetic polymeric materials for various biomedical applications, including tissue engineering, temporary implants, wound healing, and drug delivery.

Dual-acting biofunctionalised scaffolds for applications in regenerative medicine

Off the shelf scaffolds for replacing ultra-small diameter vascular grafts are valuable for reconstruction of diseased or damaged vessels. The limitations for such grafts include optimal handling with ready availability of varied lengths of grafts, graft patency with the ability to replace the function of active cellular mechanisms and adequate mechanical properties to maintain physicochemical function. We used a well-established, solvent casting method for potential tissue replacement scaffold fabrication with incorporated bioactive molecules, which we have previously explored to confer haemocompatibility. These grafts were tested in-vivo within the abdominal aorta of 10 Wistar rats and the patency was clinically and echographically evaluated. Haemocompatibility and endothelialisation were assessed on explants. Biofunctionalised scaffolds were also grafted subcutaneously and intraperitoneally to evaluate integration, inflammation and angiogenesis reactions. The potential wider applications of this dual acting scaffold were evaluated for its interactions with human dermal fibroblasts as well as bronchial epithelial cells. Physicochemical property evaluation of the functionalised grafts has clarified the mechanical strength and permeability. This study confirmed the microsurgical suturability of tubular grafts and graft patency of functionalized scaffolds. The study demonstrated the potential of a dual acting biofunctionalised scaffold's use for a wide range of tissue engineering applications where micro-porous, yet impermeable scaffolds are needed.

Surgical treatment of the neglected achilles tendon rupture with Hyalonect

BACKGROUND

The purpose of this study was to report the management and outcomes of ten patients with chronic Achilles tendon rupture treated with a turndown gastrocnemius-soleus fascial flap wrapped with a surgical mesh (Hyalonect).

METHODS

Ten men with neglected Achilles tendon rupture were treated with a centrally based turndown gastrocnemius fascial flap wrapped with Hyalonect. Hyalonect is a knitted mesh composed of HYAFF, a benzyl ester of hyaluronic acid. The Achilles tendon ruptures were diagnosed more than 1 month after injury. The mean patient age was 41 years. All of the patients had weakness of active plantarflexion. The mean preoperative American Orthopaedic Foot and Ankle Society score was 64.8.

RESULTS

The functional outcome was excellent. The mean American Orthopaedic Foot and Ankle Society score was 97.8 at the latest follow-up. There were significant differences between the preoperative and postoperative scores. Ankle range of motion was similar in both ankles. Neither rerupture nor major complication, particularly of wound healing, was observed.

CONCLUSIONS

For patients with chronic Achilles tendon rupture with a rupture gap of at least 5 cm, surgical repair using a single turndown fascial flap covered with Hyalonect achieved excellent outcomes.

Compositional and in Vitro Evaluation of Nonwoven Type I Collagen/Poly-dl-lactic Acid Scaffolds for Bone Regeneration

Poly-dl-lactic acid (PDLLA) was blended with type I collagen to attempt to overcome the instantaneous gelation of electrospun collagen scaffolds in biological environments. Scaffolds based on blends of type I collagen and PDLLA were investigated for material stability in cell culture conditions (37 °C; 5% CO₂) in which post-electrospinning glutaraldehyde crosslinking was also applied. The resulting wet-stable webs were cultured with bone marrow stromal cells (HBMSC) for five weeks. Scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), Fourier transform infra-red spectroscopy (FTIR) and biochemical assays were used to characterise the scaffolds and the consequent cell-scaffold constructs. To investigate any electrospinning-induced denaturation of collagen, identical PDLLA/collagen and PDLLA/gelatine blends were electrospun and their potential to promote osteogenic differentiation investigated. PDLLA/collagen blends with w/w ratios of 40/60, 60/40 and 80/20 resulted in satisfactory wet stabilities in a humid environment, although chemical crosslinking was essential to ensure long term material cell culture. Scaffolds of PDLLA/collagen at a 60:40 weight ratio provided the greatest stability over a five-week culture period. The PDLLA/collagen scaffolds promoted greater cell proliferation and osteogenic differentiation compared to HMBSCs seeded on the corresponding PDLLA/gelatine scaffolds, suggesting that any electrospinning-induced collagen denaturation did not affect material biofunctionality within 5 weeks in vitro.

Vascular replacement using a layered elastin-collagen vascular graft in a porcine model: one week patency versus one month occlusion

A persistent clinical demand exists for a suitable arterial prosthesis. In this study, a vascular conduit mimicking the native 3-layered artery, and constructed from the extracellular matrix proteins type I collagen and elastin, was evaluated for its performance as a blood vessel equivalent. A tubular 3-layered graft (elastin-collagen-collagen) was prepared using highly purified type I collagen fibrils and elastin fibers, resembling the 3-layered native blood vessel architecture. The vascular graft was crosslinked and heparinised (37 ± 4 μg heparin/mg graft), and evaluated as a vascular graft using a porcine bilateral iliac artery model. An intra-animal comparison with clinically-used heparinised ePTFE (Propaten®) was made. Analyses included biochemical characterization, duplex scanning, (immuno)histochemistry and scanning electron microscopy. The tubular graft was easy to handle with adequate suturability. Implantation resulted in pulsating grafts without leakage. One week after implantation, both ePTFE and the natural acellular graft had 100% patencies on duplex scanning. Grafts were partially endothelialised (Von Willebrand-positive endothelium with a laminin-positive basal membrane layer). After one month, layered thrombi were found in the natural (4/4) and ePTFE graft (1/4), resulting in occlusion which in case of the natural graft is likely due to the porosity of the inner elastin layer. In vivo application of a molecularly-defined tubular graft, based on nature's matrix proteins, for vascular surgery is feasible.

Biological reaction to small-diameter vascular grafts made of silk fibroin implanted in the abdominal aortae of rats

BACKGROUND

Bombyx mori silk fibroin (SF) is biocompatible and degradable and has been proposed as a new material for small-diameter vascular grafts. We compared biological reactions to vascular grafts made of SF and polyethylene terephthalate (PET) to reveal the potential ability of SF as a base and/or coating materials for vascular prostheses.

METHODS

SF was combined with PET or gelatin (G) to make 4 types of vascular grafts (SF/SF, SF/G, PET/SF, and PET/G, shown as "base/coating material," respectively), which are 1.5 mm in diameter and 10 mm in length. The 4 types of grafts (n = 6, respectively) were implanted into rat abdominal aortae and explanted 2 weeks or 3 months later.

RESULTS

Two weeks after implantation, there are no significant differences among the 4 kinds of grafts in biological reactions evaluated by histopathologic examination. However, a remarkable difference was observed after 3 months. The area of tissue infiltration into the inside of the graft wall was approximately 2.5 times larger in SF/SF than that in PET/G. The endothelialization was achieved almost 100% in SF/SF, despite only 50% was achieved in PET/G.

CONCLUSIONS

Results show that SF has a higher potential as a base of vascular grafts than the commercially available PET/G graft. The larger tissue infiltration area in PET/SF compared with that in PET/G also indicates the potential of SF as a coating material. In the present study, SF delivered promising results as base and coating materials for small-diameter vascular prostheses.

A cautionary tale for autologous vascular tissue engineering: impact of human demographics on the ability of adipose-derived mesenchymal stem cells to recruit and differentiate into smooth muscle cells

Autologous tissue-engineered blood vessels (TEBVs) generated using adult stem cells have shown promising results, but many preclinical evaluations do not test the efficacy of stem cells from patient populations likely to need therapy (i.e., elderly and diabetic humans). Two critical functions of these cells will be (i) secreting factors that induce the migration of host cells into the graft and (ii) differentiating into functional vascular cells themselves. The purpose of this study was to analyze whether adipose-derived mesenchymal stem cells (AD-MSCs) sourced from diabetic and elderly patients have a reduced ability to promote human smooth muscle cell (SMC) migration and differentiation potential toward SMCs, two important processes in stem cell-based tissue engineering of vascular grafts. SMC monolayers were disrupted in vitro by a scratch wound and were induced to close the wound by exposure to media conditioned by AD-MSCs from healthy, elderly, and diabetic patients. Media conditioned by AD-MSCs from healthy patients promoted the migration of SMCs and did so in a dose-dependent manner; heating the media to 56°C eliminated the media's potency. AD-MSCs from diabetic and elderly patients had a decreased ability to differentiate into SMCs under angiotensin II stimulation; however, only AD-MSCs from elderly donors were unable to promote SMC migration. Gender and body-mass index of the patients showed no effect on either critical function of AD-MSCs. In conclusion, AD-MSCs from elderly patients may not be suitable for autologous TEBVs due to inadequate promotion of SMC migration and differentiation.

Preparation and Properties of 3D Chitosan Microtubes

The preparation of 3D chitosan microtubes from polymer solutions in citric and lactic acids by the wet and dry molding methods is described. The mechanism of formation of the insoluble polymeric layer constructing the walls of these microtubes is characterized. The microtubes obtained from chitosan solutions in citric acid are found to have a fragile porous inner layer. For those obtained from chitosan solutions in lactic acid the morphology, elastic-deformation properties, physicomechanical properties, and biocompatibility were assessed. These samples have smooth outer and inner surfaces with no visible defects and high values of elongation at break. The strength of the microtubes obtained by the dry method is much higher than in the case of the wet one. A high adhesion and high proliferative activity of the epithelial-like MA-104 cellular culture on the surface of our microtubular substrates in model in vitro experiments were revealed. Prospects of using chitosan microtubes as vascular prostheses are suggested.

Bioengineered vascular scaffolds: the state of the art

To date, there is increasing clinical need for vascular substitutes due to accidents, malformations, and ischemic diseases. Over the years, many approaches have been developed to solve this problem, starting from autologous native vessels to artificial vascular grafts; unfortunately, none of these have provided the perfect vascular substitute. All have been burdened by various complications, including infection, thrombogenicity, calcification, foreign body reaction, lack of growth potential, late stenosis and occlusion from intimal hyperplasia, and pseudoaneurysm formation. In the last few years, vascular tissue engineering has emerged as one of the most promising approaches for producing mechanically competent vascular substitutes. Nanotechnologies have contributed their part, allowing extraordinarily biostable and biocompatible materials to be developed. Specifically, the use of electrospinning to manufacture conduits able to guarantee a stable flow of biological fluids and guide the formation of a new vessel has revolutionized the concept of the vascular substitute. The electrospinning technique allows extracellular matrix (ECM) to be mimicked with high fidelity, reproducing its porosity and complexity, and providing an environment suitable for cell growth. In the future, a better knowledge of ECM and the manufacture of new materials will allow us to "create" functional biological vessels - the base required to develop organ substitutes and eventually solve the problem of organ failure.

Differential regeneration of myocardial infarction depending on the progression of disease and the composition of biomimetic hydrogel

Hydrogel has been used for regenerating myocardial infraction (MI) as a delivery vehicle for cells and growth factors. This study showed that injectable hyaluronic acid (HA)-based hydrogels alone would effectively regenerate the damaged infarcted heart tissue. We found that there are two major factors of regeneration in MI. One is molecular weight of HA and another is the progression of MI; sub-acute and chronic. Rat MI model was prepared by ligating the left anterior descending coronary artery (LAD). Four weeks after injection of hydrogel, functional analysis of the heart and histological analysis was assessed. When different molecular weight HA-based hydrogels with 50 kDa, 130 kDa, and 170 kDa were applied to the infarcted area in the sub-acute model, 50 kDa HA-based hydrogel showed the most significant regeneration of myocardium as well as functional recovery among samples. For the disease progression, 50 kDa HA-based hydrogels were injected to sub-acute and chronic MI models. The regeneration activity was significantly decreased in the chronic models reflecting that injection timing of the therapeutic agents is also major determinants in the regeneration process. These results suggest that injection time and composition of hydrogel are two major points treating MI.

Hyaluronic acid biodegradable material for reconstruction of vascular wall: a preliminary study in rats

The objective of this preliminary study was to develop a reabsorbable vascular patch that did not require in vitro cell or biochemical preconditioning for vascular wall repair. Patches were composed only of hyaluronic acid (HA). Twenty male Wistar rats weighing 250-350 g were used. The abdominal aorta was exposed and isolated. A rectangular breach (1 mm × 5 mm) was made on vessel wall and arterial defect was repaired with HA made patch. Performance was assessed at 1, 2, 4, 8, and 16 weeks after surgery by histology and immunohistochemistry. Extracellular matrix components were evaluated by molecular biological methods. After 16 weeks, the biomaterial was almost completely degraded and replaced by a neoartery wall composed of endothelial cells, smooth muscle cells, collagen, and elastin fibers organized in layers. In conclusion, HA patches provide a provisional three-dimensional support to interact with cells for the control of their function, guiding the spatially and temporally multicellular processes of artery regeneration.

Intra-articular injections for the treatment of osteoarthritis: focus on the clinical use of hyaluronic acid

Osteoarthritis (OA), also called degenerative joint disease, is the most frequently occurring chronic musculoskeletal disease, particularly affecting the aging population. The use of viscosupplementation, i.e. intra-articular (IA) hyaluronic acid (HA) drug therapy, to treat OA, is growing worldwide, due to important results obtained from several clinical trials, which reported IA HA-related improvements in functional activity and pain management. This review is an update of the IA use of this compound in the treatment of OA, with clinical evidence from the last few years being discussed and used to delineate new trends for the future.

Hyaluronan-based scaffold for in vivo regeneration of the rat vena cava: Preliminary results in an animal model

The aim of this study was to develop a prosthetic graft that could perform as a small-diameter vascular conduit for vein regeneration. The difficulty of obtaining significant long-term patency and good wall mechanical strength in vivo has been a significant obstacle in achieving small-diameter vein prostheses. Fifteen Male Wistar rats weighing 250-350 g were used. Tubular structures of hyaluronan (HYAFF-11 tubules, 2 mm diameter, and 1.5 cm length) were implanted in the vena cava of rats as temporary absorbable guides to promote regeneration of veins. Performance was assessed at 30, 60, and 90 days after surgery by histology (hematoxylin-eosin and Weighert solution) and immunohistochemistry (antibodies to von Willebrand factor and to Myosin Light-Chain Kinase). These experiments resulted in two novel findings: (1) sequential regeneration of vascular components led to complete vein wall regeneration 30 days after surgery; (2) the biomaterial used created the ideal environment for the delicate regeneration process during the critical initial phases, yet its biodegradability allowed for complete degradation of the construct 4 months after implantation, at which time, a new vein remained to connect the vein stumps. This work demonstrates the complete vena cava regeneration inside the hyaluronic acid-based prosthesis, opening new perspective of microsurgical applications, like replantation of the upper limb, elongation of vascular pedicle of free flaps, cardiovascular surgery, and pediatric microvascular surgery.

Silk fibroin/hyaluronan scaffolds for human mesenchymal stem cell culture in tissue engineering

The design of new bioactive scaffolds mimicking the physiologic environment present during tissue formation is an important frontier in biomaterials research. Herein, we evaluated scaffolds prepared from blends of two biopolymers: silk fibroin and hyaluronan. Our rationale was that such blends would allow the combination of silk fibroin's superior mechanical properties with the biological characteristics of hyaluronan. We prepared scaffolds with porous microstructures by freeze-drying aqueous solutions of silk fibroin and hyaluronan and subsequent incubation in methanol to induce water insolubility of silk fibroin. Hyaluronan acted as an efficient porogenic excipient for the silk fibroin scaffolding process, allowing the formation of microporous structures within the scaffolds under mild processing conditions. Mesenchymal stem cells were seeded on silk fibroin/hyaluronan scaffolds and cultured for three weeks. Histology of the constructs after cell culture showed enhanced cellular ingrowth into silk fibroin/hyaluronan scaffolds as compared to plain silk fibroin scaffolds. In the presence of tissue-inductive stimuli, in vitro stem cell culture on silk fibroin/hyaluronan scaffolds resulted in more efficient tissue formation when measured by glycosaminoglycan and type-I and type-III collagen gene expression, as compared to plain silk fibroin scaffolds. In conclusion, our data encourages further exploration of silk fibroin/hyaluronan scaffolds as biomimetic platform for mesenchymal stem cells in tissue engineering.

Development of salmon collagen vascular graft: mechanical and biological properties and preliminary implantation study

Elastic salmon collagen (SC) vascular grafts were prepared by incubating a mixture of acidic SC solution and a fibrillogenesis-inducing buffer containing a crosslinking agent [water-soluble carbodiimide (WSC)] in a tubular mold at 4 degrees C for 24 h and then at 60 degrees C for 5 min. Subsequently, re-crosslinking in ethanol solution containing WSC was performed. The dimension of the SC grafts was easily controlled by changing the size of the mold used. The compliance (stiffness parameter: beta) and burst strength of the SC grafts (internal diameter, 2 mm; length, 20 mm; and wall thickness, 0.75 mm) that were prepared for implantation were 18.2 and 1434 mmHg, respectively; both these values were comparable with those of native vessels. Upon placement in rat subcutaneous pouches, the SC grafts were gradually biodegraded with little inflammatory reaction. The SC grafts were preliminarily implanted in rat abdominal aortas by using specially designed vascular connecting system. This system was used because the graft exhibited easy tearing and thus inadequate suturability. There was neither aneurysm formation nor graft rupture, but mild thrombus formation was seen within the 4-week observation period. These grafts may be ideal for use in regenerative medicine because we believe that SC would be completely replaced with native vascular tissues after implantation, although further improvement in the mechanical properties of the graft is needed for anastomosis.

Neoarteries grown in vivo using a tissue-engineered hyaluronan-based scaffold

Vascular tissue engineering has emerged as a promising technology for the design of an ideal, responsive, living conduit with properties similar to that of native tissue. The missing link in tissue-engineered blood vessels is elastin biosynthesis. Several biomaterials are currently used but few support elastin biosynthesis in a 3-D array. In previous studies, we demonstrated that a hyaluronan-based scaffold (HYAFF-11) grafted in the infrarenal rat aorta successfully guided the complete regeneration of a well-functioning small-diameter (2 mm) neoartery. The aim of the present study was to test the ability of HYAFF-11 biodegradable grafts to develop into neovessels of larger size (4 mm) in a porcine model, focusing on extracellular matrix (ECM) remodeling and elastin biosynthesis. HYAFF-11 tubes (diameter 4 mm, length 5 cm) were implanted in an end-to-end fashion in the common carotid artery. Grafts were analyzed for patency with a Duplex scan every 15 days. ECM components were evaluated by histological and molecular biological methods. All the animals survived the observation period without complications. Intimal hyperplasia (initiating at the anastomotic site) and graft thrombosis led to 3 cases of partial or complete occlusion, as demonstrated by histological examination. There were no signs of stenoses or aneurysms in the remaining grafts. After 5 months, the biomaterial was almost completely degraded and replaced by a neoartery segment composed of mature smooth muscle cells, collagen, and elastin fibers organized in layers and was completely covered on the luminal surface by endothelial cells (vWF(+)). Whereas in previous small animal studies, patency rates were not optimal, those obtained in the present study using hyaluronan-based grafts of larger size confirmed the ability of these constructs to guide the development of a well-functioning neoartery, with the remarkable additional attribute of facilitating the formation of organized layers of elastin fibers.

Heparin intercalation into reconstituted collagen I fibrils: Impact on growth kinetics and morphology

Collagen type I fibrils, reconstituted in vitro in the presence of heparin, exhibit an unusually thick and straight shape. A detailed structural analysis by scanning force and scanning electron microscopy revealed a non-linear dependence in size distribution, width-to-length ratio, and morphology over a wide range of glycosaminoglycan (GAG) concentrations. By varying molecular weight, degree of sulphation, charge, and concentration of different GAGs we are able to correlate the morphological data with kinetic turbidimetric measurements, and quantitation of fibril-bound GAG. The experiments imply a pronounced impact of the prenucleation phase on the cofibril morphology as a result of the strong electrostatic interaction of heparin with tropocollagen. Heparin is assumed to stabilize the collagen microfibrils and to enhance their parallel accretion during cofibrillogenesis with preservation of the typical asymmetric collagen banding pattern. The heparin quantitation data show heparin to be intercalated as a linker molecule with one specific binding site inside the cofibrils. The reconstituted cofibrils with their unusual morphology and GAG intercalation-a phenomenon not reported in vivo-can be expected to exhibit interesting mechanical and biochemical behaviours as a biomaterial for extracellular matrix scaffolds.

Jejunal Flap as an In Vivo Vascular Carrier for Transplanted Adipose Tissue

Few manuscripts describe the construction of an adipose tissue composite flap able to create an in vivo microenvironment and a neovasculature that can grow with and service implanted adipose tissue. Creation of an in vivo vascular carrier and tissue chamber for volume-stable transplanted adipose tissue was attempted using jejunum segments with intact circulation in 18 male Wistar rats. Intestinal segments were filled with autologous adipose tissue. Histologic (hematoxylin-eosin), immunohistochemical (antibodies to leptin and to vascular endothelial growth factor) and ultrastructural analyses were used to evaluate the results at 6, 18, and 60 days after surgery. Macroscopic observation confirmed the feasibility of this prefabricated adipose tissue flap: no loss of weight or volume occurred at any time point. Histologic analysis showed normal morphologic features of transplanted adipose tissue. Immunohistochemical studies confirmed the vitality of adipose tissue and the presence of a microvascular network within the flap. Small intestinal segments denuded of the mucosal layer can support in vivo transplanted adipose tissue.

Analysis of the Cellular Infiltration of Benzyl-Esterified Hyaluronan Sponges Implanted in Rats

Unseeded sponges of benzyl-esterified hyaluronan (HYAFF11) and HYAFF11 coated with unmodified hyaluronan were implanted subcutaneously and intramuscularly in adult rats for 1, 2, 4, 8, 12, and 26 weeks. Explanted samples were stained tincturally using Van Geison, von Kossa, and hematoxylin and eosin, enzyme histochemically by chloroacetate esterase, and by immunohistochemistry for the specific identification of cell types and subpopulations, targeting immature (ED1) and mature macrophages (ED2), MHC-I subset, MHC-II subset, CD54, T-cell alpha-beta receptor, T-cell gamma-delta receptor, CD2, CD4, CD8, natural killer cells, B-cells, vimentin, and TGFbeta. Little or no fibrous tissue formation was observed in any sample in either sponge type at any implantation site. Little degradation was observed in either location until 26 weeks. Little neovascularization occurred at early time periods but was in evidence at 26 weeks. Complete cellular infiltration was observed after 4 weeks, with some mature adipocytes observed within the center of the subcutaneous implants, but these cells were mainly observed around the periphery of the sponges. At 26 weeks, cells were mostly macrophages, with small numbers of T-lymphocytes present. No natural killer cells, B-cells, helper/inducer, or cytotoxic/suppressor T-cells were observed in any sample. Most infiltrating cells were MHC-II positive, and discrete pockets of TGFbeta protein were observed within the sponges. While a sustained inflammatory response was observed within both sponge types at 26 weeks, it was relatively benign and nonspecific immunologically, and inflammatory markers such as MHC-II were declining after 12 weeks. No fibrous capsule was observed, and sponge degradation was only observed at 26 weeks, an event essential for induction of neovasculargenesis. At 26 weeks, there was significant staining for vimentin and ED2 on macrophages. Taken with the pattern of other macrophage activation markers, angiogenic environment and absence of inhibitory matrix proteins, the conditions were consistent with the onset of neoadipogenesis, although this would need to be confirmed by longer term studies. For the generation of neoadipose tissue for clinical therapy, we hypothesize that macrophages require an inflammatory stimulus for infiltration, then a reduction in proinflammatory cytokine secretion simultaneous with angiogenic conditions allowing macrophage differentiation into adipocytes.

The magic glue hyaluronan and its eraser hyaluronidase: a biological overview

Hyaluronan (HA) is a multifunctional high molecular weight polysaccharide found throughout the animal kingdom, especially in the extracellular matrix (ECM) of soft connective tissues. HA is thought to participate in many biological processes, and its level is markedly elevated during embryogenesis, cell migration, wound healing, malignant transformation, and tissue turnover. The enzymes that degrade HA, hyaluronidases (HAases) are expressed both in prokaryotes and eukaryotes. These enzymes are known to be involved in physiological and pathological processes ranging from fertilization to aging. Hyaluronidase-mediated degradation of HA increases the permeability of connective tissues and decreases the viscosity of body fluids and is also involved in bacterial pathogenesis, the spread of toxins and venoms, acrosomal reaction/ovum fertilization, and cancer progression. Furthermore, these enzymes may promote direct contact between pathogens and the host cell surfaces. Depolymerization of HA also adversely affects the role of ECM and impairs its activity as a reservoir of growth factors, cytokines and various enzymes involved in signal transduction. Inhibition of HA degradation therefore may be crucial in reducing disease progression and spread of venom/toxins and bacterial pathogens. Hyaluronidase inhibitors are potent, ubiquitous regulating agents that are involved in maintaining the balance between the anabolism and catabolism of HA. Hyaluronidase inhibitors could also serve as contraceptives and anti-tumor agents and possibly have antibacterial and anti-venom/toxin activities. Additionally, these molecules can be used as pharmacological tools to study the physiological and pathophysiological role of HA and hyaluronidases.