Decellularized Scaffolds with Double-Layer Aligned Microchannels Induce the Oriented Growth of Bladder Smooth Muscle Cells: Toward Urethral and Ureteral Reconstruction

There is a great clinical need for regenerating urinary tissue. Native urethras and ureters have bidirectional aligned smooth muscle cells (SMCs) layers, which plays a pivotal role in micturition and transporting urine and inhibiting reflux. Thus far, urinary scaffolds have not been designed to induce the native-mimicking aligned arrangement of SMCs. In this study, a tubular decellularized extracellular matrix (dECM) with an intact internal layer and bidirectional aligned microchannels in the tubular wall, which is realized by the subcutaneous implantation of a template, followed by the removal of the template, and decellularization, is engineered. The dense and intact internal layer effectively increases the leakage pressure of the tubular dECM scaffolds. Rat-derived dECM scaffolds with three different sizes of microchannels are fabricated by tailoring the fiber diameter of the templates. The rat-derived dECM scaffolds exhibiting microchannels of ≈65 µm show suitable mechanical properties, good ability to induce the bidirectional alignment and growth of human bladder SMCs, and elevated higher functional protein expression in vitro. These data indicate that rat-derived tubular dECM scaffolds manifesting double-layer aligned microchannels may be promising candidates to induce the native-mimicking regeneration of SMCs in urethra and ureter reconstruction.

Transplantation of SDF-1α-loaded liver extracellular matrix repopulated with autologous cells attenuated liver fibrosis in a rat model

Cell-based therapy and tissue engineering are promising substitutes for liver transplantation to cure end-stage liver disorders. However, the limited sources for healthy and functional cells and poor engraftment rate are main challenges to the cell-based therapy approach. On the other hand, feasibility of production and size of bioengineered tissues are primary bottlenecks in tissue engineering. Here, we induce regeneration in a rat fibrotic liver model by transplanting a natural bioengineered scaffold with a native microenvironment repopulated with autologous stem/progenitor cells. In the main experimental group, a 1 mm³ stromal derived factor-1α (SDF-1α; S) loaded scaffold from decellularized liver extracellular matrix (LEM) was transplanted (Tx) into a fibrotic liver and the endogenous stem/progenitor cells were mobilized via granulocyte colony stimulating factor (G-CSF; G) therapy. Four weeks after transplantation, changes in liver fibrosis and necrosis, efficacy of cell engraftment and differentiation, vasculogenesis, and liver function recovery were assessed in this (LEM-TxSG) group and compared to the other groups. We found significant reduction in liver fibrosis stage in the LEM-TxSG, LEM-TxS and LEM-TxG groups compared to the control (fibrotic) group. Liver necrosis grade, and alanine transaminase (ALT) and aspartate transaminase (AST) levels dramatically reduced in all experimental groups compared to the control group. However, the number of engrafted cells into the transplanted scaffold and ratio of albumin (Alb) positive cells per total incorporated cells were considerably higher in the LEM-TxSG group compared to the LEM-Tx, LEM-TxS and LEM-TxG groups. Serum Alb levels increased in the LEM-Tx, LEM-TxS, and LEM-TxG groups, and was highest in the LEM-TxSG group, which was significantly more than the fibrotic group. Small vessel formation in the LEM-TxSG group was significantly higher than the LEM-Tx and LEM-TxS groups. Totally, these findings support application of the in vivo tissue engineering approach as a possible novel therapeutic strategy for liver fibrosis.

Leaflet Tissue Generation from Microfibrous Heart Valve Leaflet Scaffolds with Native Characteristics

Mechanical and bioprosthetic valves that are currently applied for replacing diseased heart valves are not fully efficient. Heart valve tissue engineering may solve the issues faced by the prosthetic valves in heart valve replacement. The leaflets of native heart valves have a trilayered structure with layer-specific orientations; thus, it is imperative to develop functional leaflet tissue constructs with a native trilayered, oriented structure. Its key solution is to develop leaflet scaffolds with a native morphology and structure. In this study, microfibrous leaflet scaffolds with a native trilayered and oriented structure were developed in an electrospinning system. The scaffolds were implanted for 3 months in rats subcutaneously to study the scaffold efficiencies in generating functional tissue-engineered leaflet constructs. These in vivo tissue-engineered leaflet constructs had a trilayered, oriented structure similar to native leaflets. The tensile properties of constructs indicated that they were able to endure the hydrodynamic load of the native heart valve. Collagen, glycosaminoglycans, and elastin─the predominant extracellular matrix components of native leaflets─were found sufficiently in the leaflet tissue constructs. The residing cells in the leaflet tissue constructs showed vimentin and α-smooth muscle actin expression, i.e., the constructs were in a growing state. Thus, the trilayered, oriented fibrous leaflet scaffolds produced in this study could be useful to develop heart valve scaffolds for successful heart valve replacements.

Fibrous heart valve leaflet substrate with native-mimicked morphology

Tissue-engineered heart valves are a promising alternative solution to prosthetic valves. However, long-term functionalities of tissue-engineered heart valves depend on the ability to mimic the trilayered, oriented structure of native heart valve leaflets. In this study, using electrospinning, we developed trilayered microfibrous leaflet substrates with morphological characteristics similar to native leaflets. The substrates were implanted subcutaneously in rats to study the effect of their trilayered oriented structure on in vivo tissue engineering. The tissue constructs showed a well-defined structure, with a circumferentially oriented layer, a randomly oriented layer and a radially oriented layer. The extracellular matrix, produced during in vivo tissue engineering, consisted of collagen, glycosaminoglycans, and elastin, all major components of native leaflets. Moreover, the anisotropic tensile properties of the constructs were sufficient to bear the valvular physiological load. Finally, the expression of vimentin and α-smooth muscle actin, at the gene and protein level, was detected in the residing cells, revealing their growing state and their transdifferentiation to myofibroblasts. Our data support a critical role for the trilayered structure and anisotropic properties in functional leaflet tissue constructs, and indicate that the leaflet substrates have the potential for the development of valve scaffolds for heart valve replacements.

Application of in-body tissue architecture-induced Biotube vascular grafts for vascular access: Proof of concept in a beagle dog model

INTRODUCTION

The first choice of vascular access for hemodialysis is an autogenous arteriovenous fistula, because prosthetic arteriovenous grafts have a high probability of failure. In this study, Biotubes, in-body tissue architecture-induced autologous collagenous tubes, were evaluated for their potential use as vascular access grafts. Three animal implantation models were developed using beagle dogs, and the in vivo performance of Biotubes was observed after implantation in the acute phase as a pilot study.

METHODS

Biotubes (internal diameter ca. 4.0 mm, length ca. 5.0 cm, and wall thickness ca. 0.7 mm) were prepared through subcutaneous embedding of specially designed molds in beagle dogs for 8 weeks. The Biotubes were then implanted between the common carotid artery and the jugular vein of beagles via three methods, including side-to-side (in) -end-to-end (out) as type 1 (n = 4), side-to-side (both) as type 2 (n = 4), and side-to-end (in) -end-to-side (out) as type 3 (n = 1 using a composite Biotube).

RESULTS

Although two cases in type 1 and 2 resulted in Biotube deformation, all cases were patent for 4 weeks and maintained a continuous turbulent flow. At 4 weeks after implantation, percutaneous puncture could be performed repeatedly without aneurysm formation or hemorrhage.

CONCLUSION

Within a short implantation period, with limited animal numbers, this proof-of-concept study showed that Biotubes may have a high potential for use in vascular access.

Development of xenogeneic decellularized biotubes for off-the-shelf applications

In earlier studies, we developed in vivo tissue-engineered, autologous, small-caliber vascular grafts, called "biotubes," which withstand systemic blood pressure and exhibit excellent performance as small-caliber vascular prostheses in animal models. However, biotube preparation takes 4 weeks; therefore, biotubes cannot be applied in emergency situations. Moreover, for responses to various types of surgery, grafts should ideally be readily available in advance. The aim of this study was to develop novel, off-the-shelf, small-caliber vascular grafts by decellularizing in vivo tissue-engineered xenogeneic tubular materials. Silicone rod molds (diameter: 2 mm, length: 70 mm) placed in subcutaneous pouches of a beagle dog for 4 weeks were harvested with their surrounding connective tissues. Tubular connective tissues were obtained after pulling out the impregnated molds. Subsequently, they were decellularized by perfusion with sodium dodecyl sulfate and Triton X-100. They were stored as off-the-shelf grafts at -20°C for 1 week. The decellularized grafts derived from the beagle dog were xenogeneically transplanted to the abdominal aortas of rats (n = 3). No signs of abnormal inflammation or immunological problems due to the xenogeneic material were observed. Echocardiography confirmed the patency of the grafts at 1 month after implantation. Histological evaluation revealed that the grafts formed neointima on the luminal surface, and that the graft walls had cell infiltration. Little accumulation of CD68-positive macrophages in the graft wall was observed. Xenogeneic decellularized tubular tissues functioned as small-caliber vascular grafts, as well as autologous biotubes. This technology enables the easy fabrication of grafts from xenogeneic animals in advance and their storage for at least a week, satisfying the conditions for off-the-shelf grafts.

Sacrificial Core-Based Electrospinning: a Facile and Versatile Approach to Fabricate Devices for Potential Cell and Tissue Encapsulation Applications

Electrospinning uses an electric field to produce fine fibers of nano and micron scale diameters from polymer solutions. Despite innovation in jet initiation, jet path control and fiber collection, it is common to only fabricate planar and tubular-shaped electrospun products. For applications that encapsulate cells and tissues inside a porous container, it is useful to develop biocompatible hollow core-containing devices. To this end, by introducing a 3D-printed framework containing a sodium chloride pellet (sacrificial core) as the collector and through post-electrospinning dissolution of the sacrificial core, we demonstrate that hollow core containing polyamide 66 (nylon 66) devices can be easily fabricated for use as cell encapsulation systems. ATR-FTIR and TG/DTA studies were used to verify that the bulk properties of the electrospun device were not altered by contact with the salt pellet during fiber collection. Protein diffusion investigations demonstrated that the capsule allowed free diffusion of model biomolecules (insulin, albumin and Ig G). Cell encapsulation studies with model cell types (fibroblasts and lymphocytes) revealed that the capsule supports the viability of encapsulated cells inside the capsule whilst compartmentalizing immune cells outside of the capsule. Taken together, the use of a salt pellet as a sacrificial core within a 3D printed framework to support fiber collection, as well as the ability to easily remove this core using aqueous dissolution, results in a biocompatible device that can be tailored for use in cell and tissue encapsulation applications.

Development of tissue-engineered self-expandable aortic stent grafts (Bio stent grafts) using in-body tissue architecture technology in beagles

In this study, we aimed to describe the development of tissue-engineered self-expandable aortic stent grafts (Bio stent graft) using in-body tissue architecture technology in beagles and to determine its mechanical and histological properties. The preparation mold was assembled by insertion of an acryl rod (outer diameter, 8.6 mm; length, 40 mm) into a self-expanding nitinol stent (internal diameter, 9.0 mm; length, 35 mm). The molds (n = 6) were embedded into the subcutaneous pouches of three beagles for 4 weeks. After harvesting and removing each rod, the excessive fragile tissue connected around the molds was trimmed, and thus tubular autologous connective tissues with the stent were obtained for use as Bio stent grafts (outer diameter, approximately 9.3 mm in all molds). The stent strut was completely surrounded by the dense collagenous membrane (thickness, ∼150 µm). The Bio stent graft luminal surface was extremely flat and smooth. The graft wall of the Bio stent graft possessed an elastic modulus that was almost two times higher than that of the native beagle abdominal aorta. This Bio stent graft is expected to exhibit excellent biocompatibility after being implanted in the aorta, which may reduce the risk of type 1 endoleaks or migration.

Differentiation of human umbilical cord-derived mesenchymal stem cells, WJ-MSCs, into chondrogenic cells in the presence of pulsed electromagnetic fields

During cartilage regeneration, proliferation and differentiation of new chondrocytes are required and towards this goal, in humans electromagnetic stimulation has been used in order to increase the spontaneous regenerative capacity of bone and cartilage tissue. In vivo tissue engineering has pointed out that the absence of an abundant source of cells accelerating the healing process is a limiting factor in the ability to repair articular cartilage. Considering that the umbilical cord is a viable alternative source of mesenchymal stem cells (MSC), our study evaluated the possibility of a combined use of Wharton's jelly - mesenchymal stem cells (WJ-MSCs) and pulsed electromagnetic field (PMEF). The first effect observed was that compared with the untreated cells, when the WJ-MSCs were treated with PMEF, there was an increase in the division of cells and a rapid increase in cell density and the morphological and biochemical data showed that the treatment with PMEF reduced the time to obtain chondrocyte cell differentiation and deposition of extracellular matrix. Taken together these data indicate the capacity of PEMF to induce early differentiation of WJ-MSCs cells towards cartilaginous tissue.