Rotating versus perfusion bioreactor for the culture of engineered vascular constructs based on hyaluronic acid

In Vitro Differentiation of Myoblast Cell Lines on Spider Silk Scaffolds in a Rotating Bioreactor for Vascular Tissue Engineering

Functional construction of tissue-engineered vessels as an alternative to autologous vascular grafts has been shown to be feasible, however the proliferation of seeded smooth-muscle cells remains a limiting factor. We employed a rotating bioreactor system to improve myoblast cell differentiation on a spider silk scaffold for tissue-engineered vessel construction. C2C12 myofibroblast cells were seeded on the surface of spider silk scaffold constructs and cultivated in a rotating bioreactor system with a continuous rotation speed (1 rpm). Cell function, cell growth and morphological structure and expression of biomarkers were analyzed using scanning electron microscopy, the LIVE/DEAD^® assay, Western blot and quantitative real-time PCR analyses. A dense myofibroblast cell sheet could be developed which resembled native blood vessel muscular tissue in morphological structure and in function. Bioreactor perfusion positively affected cell morphology, and increased cell viability and cell differentiation. The expression of desmin, MYF5 and MEF2D surged as an indication of myoblast differentiation. Cell-seeded scaffolds showed a tear-down at 18 N when strained at a set speed (20 mm min^-1). Spider silk scaffolds appear to offer a reliable basis for engineered vascular constructs and rotating bioreactor cultivation may be considered an effective alternative to complex bioreactor setups to improve cell viability and biology.

Future Perspectives in Small-Diameter Vascular Graft Engineering

The increased demands of small-diameter vascular grafts (SDVGs) globally has forced the scientific society to explore alternative strategies utilizing the tissue engineering approaches. Cardiovascular disease (CVD) comprises one of the most lethal groups of non-communicable disorders worldwide. It has been estimated that in Europe, the healthcare cost for the administration of CVD is more than 169 billion €. Common manifestations involve the narrowing or occlusion of blood vessels. The replacement of damaged vessels with autologous grafts represents one of the applied therapeutic approaches in CVD. However, significant drawbacks are accompanying the above procedure; therefore, the exploration of alternative vessel sources must be performed. Engineered SDVGs can be produced through the utilization of non-degradable/degradable and naturally derived materials. Decellularized vessels represent also an alternative valuable source for the development of SDVGs. In this review, a great number of SDVG engineering approaches will be highlighted. Importantly, the state-of-the-art methodologies, which are currently employed, will be comprehensively presented. A discussion summarizing the key marks and the future perspectives of SDVG engineering will be included in this review. Taking into consideration the increased number of patients with CVD, SDVG engineering may assist significantly in cardiovascular reconstructive surgery and, therefore, the overall improvement of patients' life.

Shear-resistant hydrogels to control permeability of porous tubular scaffolds in vascular tissue engineering

Aiming to perfuse porous tubular scaffolds for vascular tissue engineering (VTE) with controlled flow rate, prevention of leakage through the scaffold lumen is required. A gel coating made of 8% w/v alginate and 6% w/v gelatin functionalized with fibronectin was produced using a custom-made bioreactor-based method. Different volumetric proportions of alginate and gelatin were tested (50/50, 70/30, and 90/10). Gel swelling and stability, and rheological, and uniaxial tensile tests reveal superior resistance to the aggressive biochemical microenvironment, and their ability to withstand physiological deformations (~10%) and wall shear stresses (5-20 dyne/cm²). These are prerequisites to maintain the physiologic phenotypes of vascular smooth muscle cells and endothelial cells (ECs), mimicking blood vessels microenvironment. Gels can induce ECs proliferation and colonization, especially in the presence of fibronectin and higher percentages of gelatin. The custom-designed bioreactor enables the development of reproducible and homogeneous tubular gel coating. The permeability tests show the effectiveness of tubular scaffolds coated with 70/30 alginate/gelatin gel to occlude wadding pores, and therefore prevent leakages. The synthesized double-layered tubular scaffolds coated with alginate/gelatin gel and fibronectin represent both promising substrate for ECs and effective leakproof scaffolds, when subjected to pulsatile perfusion, for VTE applications.

Aligned Nanofibrous Cell-Derived Extracellular Matrix for Anisotropic Vascular Graft Construction

There is a large demand for tissue engineered vascular grafts for the application of vascular reconstruction surgery or in vitro drug screening tissue model. The extracellular matrix (ECM) composition along with the structural and mechanical anisotropy of native blood vessels is critical to their functional performance. The objective of this study is to develop a biomimetic vascular graft recapitulating the anisotropic features of native blood vessels by employing nanofibrous aligned fibroblast-derived ECM and human mesenchymal stem cells (hMSCs). The nanotopographic cues of aligned ECM direct the initial cell orientation. The subsequent maturation under circumferential stress generated by a rotating wall vessel (RWV) bioreactor further promotes anisotropic structural and mechanical properties in the graft. The circumferential tensile strength is significantly higher than longitudinal strength in bioreactor samples. Expression of smooth muscle cell specific genes, α-smooth muscle actin and calponin, in hMSCs is greatly enhanced in bioreactor samples without any biochemical stimulation. In addition, employment of premade ECM and RWV bioreactor significantly reduces the graft fabrication time to three weeks. Mimicking the ECM composition, cell phenotype, structural and mechanical anisotropy, the vascular graft presented in this study is promising for vascular reconstruction surgery or in vitro tissue model applications.

Alternating air-medium exposure in rotating bioreactors optimizes cell metabolism in 3D novel tubular scaffold polyurethane foams

Background

In vitro dynamic culture conditions play a pivotal role in developing engineered tissue grafts, where the supply of oxygen and nutrients, and waste removal must be permitted within construct thickness. For tubular scaffolds, mass transfer is enhanced by introducing a convective flow through rotating bioreactors with positive effects on cell proliferation, scaffold colonization and extracellular matrix deposition. We characterized a novel polyurethane-based tubular scaffold and investigated the impact of 3 different culture configurations over cell behavior: dynamic (i) single-phase (medium) rotation and (ii) double-phase exposure (medium-air) rotation; static (iii) single-phase static culture as control.

Methods

A new mixture of polyol was tested to create polyurethane foams (PUFs) as 3D scaffold for tissue engineering. The structure obtained was morphologically and mechanically analyzed tested. Murine fibroblasts were externally seeded on the novel porous PUF scaffold, and cultured under different dynamic conditions. Viability assay, DNA quantification, SEM and histological analyses were performed at different time points.

Results

The PUF scaffold presented interesting mechanical properties and morphology adequate to promote cell adhesion, highlighting its potential for tissue engineering purposes. Results showed that constructs under dynamic conditions contain enhanced viability and cell number, exponentially increased for double-phase rotation; under this last configuration, cells uniformly covered both the external surface and the lumen.

Conclusions

The developed 3D structure combined with the alternated exposure to air and medium provided the optimal in vitro biochemical conditioning with adequate nutrient supply for cells. The results highlight a valuable combination of material and dynamic culture for tissue engineering applications.

Elastic large muscular vessel wall engineered with bone marrow‑derived cells under pulsatile stimulation in a bioreactor

Bone marrow‑derived cells (BMCs) have demonstrated their ability to differentiate into multiple cell lineages and may be a promising cell source for vascular tissue engineering. Although much progress has been made in the engineering of small blood vessels (<6 mm in diameter) with biodegradable materials such as polyglycolic acid (PGA), it remains a challenge to engineer large vessels (>6 mm in diameter) due to unsatisfactory biomechanical properties. The present study was to engineered an elastic large vessel wall (6 mm in diameter) using a PGA unwoven fibre scaffold covered with BMCs from canine humeri. The cell‑PGA sheet was then loaded into a bioreactor designed for the present study, with dynamic pulsatile culture conditions to mimic the physiological vessel environment. After four weeks of the pulsatile stimuli culture, an elastic vessel wall was formed. Histological analyses demonstrated that layers of smooth muscle‑like cells and well‑oriented collagenous fibres were evenly oriented in the dynamic group. By contrast, disorganised cells and randomly collagenous fibres were apparent in the static group. Furthermore, the engineered vessel wall in the dynamic group exhibited significantly improved biomechanical properties compared with those in static culture group. The approach developed in the present study was demonstrated to have promising potential to be used for the engineering of large vessel as well as other smooth muscle cell‑containing tissues, including bladder, urethral and intestinal tissues.

Small diameter electrospun silk fibroin vascular grafts: Mechanical properties, in vitro biodegradability, and in vivo biocompatibility

To overcome the drawbacks of autologous grafts currently used in clinical practice, vascular tissue engineering represents an alternative approach for the replacement of small diameter blood vessels. In the present work, the production and characterization of small diameter tubular matrices (inner diameter (ID)=4.5 and 1.5 mm), obtained by electrospinning (ES) of Bombyx mori silk fibroin (SF), have been considered. ES-SF tubular scaffolds with ID=1.5 mm are original, and can be used as vascular grafts in pediatrics or in hand microsurgery. Axial and circumferential tensile tests on ES-SF tubes showed appropriate properties for the specific application. The burst pressure and the compliance of ES-SF tubes were estimated using the Laplace's law. Specifically, the estimated burst pressure was higher than the physiological pressures and the estimated compliance was similar or higher than that of native rat aorta and Goretex® prosthesis. Enzymatic in vitro degradation tests demonstrated a decrease of order and crystallinity of the SF outer surface as a consequence of the enzyme activity. The in vitro cytocompatibility of the ES-SF tubes was confirmed by the adhesion and growth of primary porcine smooth muscle cells. The in vivo subcutaneous implant into the rat dorsal tissue indicated that ES-SF matrices caused a mild host reaction. Thus, the results of this investigation, in which comprehensive morphological and mechanical aspects, in vitro degradation and in vitro and in vivo biocompatibility were considered, indicate the potential suitability of these ES-SF tubular matrices as scaffolds for the regeneration of small diameter blood vessels.

Smooth muscle alpha-actin and calponin expression and extracellular matrix production of human coronary artery smooth muscle cells in 3D scaffolds

For a tissue-engineered coronary artery substitute to be a viable clinical option in the treatment of vascular diseases, it is necessary to use tissue-specific human cells. Coronary artery smooth muscle cells are the main resident cells in the tunica media of arteries. In this work, we examined the behavior and differentiation state of human coronary artery smooth muscle cells (HCASMCs) when cultured on 3D polyurethane scaffolds to fabricate hybrid vascular tissues. As the mechanical strength of the scaffold is an important element in engineered hybrid vascular substitutes, porous 3D polyurethane scaffolds fabricated using paraffin spheres and ammonium chloride particles were tested for their mechanical properties both in tension and in compression. The use of ammonium chloride particles as porogen generated scaffolds with superior mechanical properties, which are suitable for vascular tissue engineering. When seeded on uncoated, fibronectin-coated, and Matrigel-coated scaffolds, HCASMCs were well spread and started producing collagen as judged by histochemical analysis but appeared to lack elastin production. Fibronectin coating appeared to promote the infiltration of HCASMCs into the scaffold better than Matrigel coating but did not appear to affect the expression of collagen and elastin. Western blot analyses after successful cell recovery from the scaffolds indicated that HCASMCs, after culturing for 4 and 7 days, expressed similar amounts of smooth muscle alpha-actin and calponin regardless of extracellular matrix coating. Taken together, our data showed that the behavior and differentiation phenotype of HCASMCs can be analyzed after culture in 3D polyurethane scaffolds to establish appropriate conditions that will favor the fabrication of hybrid-engineered vascular substitutes.

Flow dynamics in bioreactors containing tissue engineering scaffolds

Bioreactors are widely used in tissue engineering as a way to distribute nutrients within porous materials and provide physical stimulus required by many tissues. However, the fluid dynamics within the large porous structure are not well understood. In this study, we explored the effect of reactor geometry by using rectangular and circular reactors with three different inlet and outlet patterns. Geometries were simulated with and without the porous structure using the computational fluid dynamics software Comsol Multiphysics 3.4 and/or ANSYS CFX 11 respectively. Residence time distribution analysis using a step change of a tracer within the reactor revealed non-ideal fluid distribution characteristics within the reactors. The Brinkman equation was used to model the permeability characteristics with in the chitosan porous structure. Pore size was varied from 10 to 200 microm and the number of pores per unit area was varied from 15 to 1,500 pores/mm(2). Effect of cellular growth and tissue remodeling on flow distribution was also assessed by changing the pore size (85-10 microm) while keeping the number of pores per unit area constant. These results showed significant increase in pressure with reduction in pore size, which could limit the fluid flow and nutrient transport. However, measured pressure drop was marginally higher than the simulation results. Maximum shear stress was similar in both reactors and ranged approximately 0.2-0.3 dynes/cm(2). The simulations were validated experimentally using both a rectangular and circular bioreactor, constructed in-house. Porous structures for the experiments were formed using 0.5% chitosan solution freeze-dried at -80 degrees C, and the pressure drop across the reactor was monitored.

A double-chamber rotating bioreactor for the development of tissue-engineered hollow organs: from concept to clinical trial

Cell and tissue engineering are now being translated into clinical organ replacement, offering alternatives to fight morbidity, organ shortages and ethico-social problems associated with allotransplantation. Central to the recent first successful use of stem cells to create an organ replacement in man was our development of a bioreactor environment. Critical design features were the abilities to drive the growth of two different cell types, to support 3D maturation, to maintain biomechanical and biological properties and to provide appropriate hydrodynamic stimuli and adequate mass transport. An analytical model was developed and applied to predict oxygen profiles in the bioreactor-cultured organ construct and in the culture media, comparing representative culture configurations and operating conditions. Autologous respiratory epithelial cells and mesenchymal stem cells (BMSCs, then differentiated into chondrocytes) were isolated, characterized and expanded. Both cell types were seeded and cultured onto a decellularized human donor tracheal matrix within the bioreactor. One year post-operatively, graft and patient are healthy, and biopsies confirm angiogenesis, viable epithelial cells and chondrocytes. Our rotating double-chamber bioreactor permits the efficient repopulation of a decellularized human matrix, a concept that can be applied clinically, as demonstrated by the successful tracheal transplantation.