In vivo evaluation of an in-body, tissue-engineered, completely autologous valved conduit (biovalve type VI) as an aortic valve in a goat model

Bladder Reconstruction in Cats Using In-Body Tissue Architecture (iBTA)-Induced Biosheet

Urinary tract diseases are common in cats, and often require surgical reconstruction. Here, to explore the possibility of urinary tract reconstruction in cats using in-body tissue architecture (iBTA), biosheets fabricated using iBTA technology were implanted into the feline bladder and the regeneration process was histologically evaluated. The biosheets were prepared by embedding molds into the dorsal subcutaneous pouches of six cats for 2 months. A section of the bladder wall was removed, and the biosheets were sutured to the excision site. After 1 and 3 months of implantation, the biosheets were harvested and evaluated histologically. Implantable biosheets were formed with a success rate of 67%. There were no major complications following implantation, including tissue rejection, severe inflammation, or infection. Urinary incontinence was also not observed. Histological evaluation revealed the bladder lumen was almost entirely covered by urothelium after 1 month, with myofibroblast infiltration into the biosheets. After 3 months, the urothelium became multilayered, and mature myocytes and nerve fibers were observed at the implantation site. In conclusion, this study showed that tissue reconstruction using iBTA can be applied to cats, and that biosheets have the potential to be useful in both the structural and functional regeneration of the feline urinary tract.

Diverse Shape Design and Physical Property Evaluation of In-Body Tissue Architecture-Induced Tissues

Autologous-engineered artificial tissues constitute an ideal alternative for radical surgery in terms of natural anticoagulation, self-repair, tissue regeneration, and the possibility of growth. Previously, we focused on the development and practical application of artificial tissues using "in-body tissue architecture (iBTA)", a technique that uses living bodies as bioreactors. This study aimed to further develop iBTA by fabricating tissues with diverse shapes and evaluating their physical properties. Although the breaking strength increased with tissue thickness, the nominal breaking stress increased with thinner tissues. By carving narrow grooves on the outer periphery of an inner core with narrow grooves, we fabricated approximately 2.2 m long cord-shaped tissues and net-shaped tissues with various designs. By assembling the two inner cores inside the branched stainless-steel pipes, a large graft with branching was successfully fabricated, and its aortic arch replacement was conducted in a donor goat without causing damage. In conclusion, by applying iBTA technology, we have made it possible, for the first time, to create tissues of various shapes and designs that are difficult using existing tissue-engineering techniques. Thicker iBTA-induced tissues exhibited higher rupture strength; however, rupture stress was inversely proportional to thickness. These findings broaden the range of iBTA-induced tissue applications.

Application of Biosheets as Right Ventricular Outflow Tract Repair Materials in a Rat Model

Purposes

We report the experimental use of completely autologous biomaterials (Biosheets) made by “in-body tissue architecture” that could resolve problems in artificial materials and autologous pericardium. Here, Biosheets were implanted into full-thickness right ventricular outflow tract defects in a rat model. Their feasibility as a reparative material for cardiac defects was evaluated.

Methods

As the evaluation of mechanical properties of the biosheets, the elastic moduli of the biosheets and RVOT-free walls of rats were examined using a tensile tester. Biosheets and expanded polytetrafluoroethylene sheet were used to repair transmural defects surgically created in the right ventricular outflow tracts of adult rat hearts (n = 9, each patch group). At 4 and 12 weeks after the operation, the hearts were resected and histologically examined.

Results

The strength and elastic moduli of the biosheets were 421.3 ± 140.7 g and 2919 ± 728.9 kPa, respectively, which were significantly higher than those of the native RVOT-free walls (93.5 ± 26.2 g and 778.6 ± 137.7 kPa, respectively; P < 0.005 and P < 0.001, respectively). All patches were successfully implanted into the right ventricular outflow tract-free wall of rats. Dense fibrous adhesions to the sternum on the epicardial surface were also observed in 7 of 9 rats with ePTFE grafts, whereas 2 of 9 rats with biosheets. Histologically, the vascular-constructing cells were infiltrated into Biosheets. The luminal surfaces were completely endothelialized in all groups at each time point. There was also no accumulation of inflammatory cells.

Conclusions

Biosheets can be formed easily and have sufficient strength and good biocompatibility as a patch for right ventricular outflow tract repair in rats. Therefore, Biosheet may be a suitable material for reconstructive surgery of the right ventricular outflow tract.

A new method of primary engineering of esophagus using orthotopic in-body tissue architecture

PURPOSE

Tissue engineering of esophagus is required for management of long-gap esophageal atresia (LGEA). Collagenous connective tissue membranes fabricated by in-body tissue architecture (iBTA), called biosheets, can repair esophageal defects and generate tissues similar to native esophagus. However, iBTA requires second-stage surgery because of heterotopic preparation of biosheets. Our aim was to develop orthotopic iBTA for primary engineering of the esophagus by interposing a tubular mold to the esophageal defect.

METHOD

The cervical esophagus of six rats was transected. An acrylic tube (internal diameter 2.6 mm, length 7.0 mm) was inserted and fixed between the ends of the upper and lower esophagus, and a 3 mm-long esophageal defect was created. Four weeks later, the rats were sacrificed for histological analysis.

RESULTS

Postoperatively the rats could intake liquid food. After four weeks, the esophageal defects were filled with regenerated tissues. Histologically the new esophageal walls stained positive for collagen type I. The inner surfaces were covered with stratified squamous epithelium that expressed pan-cytokeratin. In only one of six rats, regeneration of muscular-like tissue was suggested by positive immunohistochemical staining for desmin.

CONCLUSION

Orthotopic iBTA can regenerate a substitute esophagus with esophageal epithelium and collagenous wall. This technique may be a novel treatment for esophageal atresia with gaps of various lengths including LGEA.

Assessment of the Cardiac Functions Using Full Conventional Echocardiography with Tissue Doppler Imaging before and after Xylazine Sedation in Male Shiba Goats

The present study aimed to provide a complete conventional echocardiographic protocol in adult male Shiba goats by using two-dimensional, M-mode, Pulsed Wave Doppler, and tissue Doppler imaging (TDI) echocardiography, and to study concomitantly xylazine-induced alteration of cardiac functions in a highly sensitive species. For this purpose, 12 male Shiba goats were included and complete conventional echocardiography from the standard right and left parasternal views was carried to report the echocardiographic data in male Shiba goats, and also before and after xylazine (Pre-Xyl and Post-Xyl) administration (0.05 mg/IM/kg). Results revealed that the full echocardiographic protocol was feasible in all goats through different cardiac windows and good Doppler alignment was achieved with non-significant variability for assessment of the left ventricular dimensions, trans-pulmonary, trans-aortic, and trans-mitral blood flow. The TDI, which was not reported previously in goats, was successfully assessed from the standard left apical view and showed distinct systolic and diastolic patterns. Xylazine administration was found to significantly reduce heart rate, fractional shortening, and cardiac output as well as the Doppler hemodynamic parameters of the pulmonary artery, aortic and mitral inflows (p < 0.05). For TDI, the Post-Xyl group revealed a significant decrease in the myocardial velocities of the septal and lateral wall of the left ventricle. The present study provides, for the first time, complete data of conventional echocardiography in male goats using the full protocol, which is routinely used in pet's practice. Further, we illustrate in-depth the adverse effect of short-term sedative, xylazine, as used under field conditions and emphasize a simultaneous reduction in both systolic and diastolic cardiac function in goats based on full echocardiography assessment of the heart.

Effectiveness of a novel, completely biomaterial valved pulmonary arterial conduit: An in vivo study

As a pre-clinical assessment, the present study aimed to investigate the safety and effectiveness of a novel valved pulmonary arterial conduit constructed entirely from biomaterials by transplanting it in the outflow tract of the right ventricle in sheep. Under extracorporeal circulation, the valved pulmonary arterial conduit was used to replace the pulmonary artery of sheep with a beating heart. The performance was assessed at 30, 90 and 180 days post-surgery. Hemodynamic and structural changes were evaluated, and safety was assessed after 180 postoperative days. The hemodynamic effect and biosafety of the implant were further evaluated by observing the changes in various pressure indicators of the heart, echocardiographic results, anatomical and pathological examination results, liver and kidney functions, routine blood tests, a blood coagulation test, and other test results following implantation of the purely biotic valved conduit. The conduit was successfully implanted in 12 sheep and no mortality occurred postoperatively. During the 180-day follow-up, there was no obvious stenosis or regurgitation of the right ventricular outflow tract and pulmonary valve after valved conduit implantation. The findings of autopsy, pathology and laboratory examinations were unremarkable. The implantation of this biosynthetic vascular graft into animals meets the safety and effectiveness requirements for clinical application. This pulmonary arterial conduit has potential clinical application for children with complex congenital heart disease who require pulmonary artery reconstruction to achieve a radical cure.

Engineering and repair of diaphragm using biosheet (a collagenous connective tissue membrane) in rabbits

BACKGROUND

Prosthetic patches can be used to repair large congenital diaphragmatic hernia defects but may be associated with infection, recurrence, and thoracic deformity. Biosheets (collagenous connective tissue membranes) have been used in regenerative medicine. We evaluated the efficacy of Biosheets in a rabbit model.

METHODS

Biosheets were prepared by embedding silicone plates in dorsal subcutaneous pouches of rabbits for 4weeks. In group 1 (n=11), Gore-Tex® sheets (1.8×1.8cm) were implanted into a diaphragmatic defect. In group 2 (n=11), Seamdura®, a bioabsorbable artificial dural substitute, was implanted in the same manner. In group 3 (n=14), biosheets were autologously transplanted into the diaphragmatic defects. All rabbits were euthanized 3months after transplantation to evaluate their graft status.

RESULTS

Herniation of liver was observed in 5 rabbits (45%) in group 1, 8 (73%) in group 2, and 3 (21%) in group 3. A significant difference was noted between groups 2 and 3 (P=0.017). Biosheets had equivalent burst strength and modulus of elasticity as native diaphragm. Muscular tissue regeneration in transplanted biosheets in group 3 was confirmed histologically.

CONCLUSION

Biosheets may be applied to diaphragmatic repair and replacement of diaphragmatic muscular tissue.

LEVEL OF EVIDENCE

Level III.

Patch tracheoplasty in body tissue engineering using collagenous connective tissue membranes (biosheets)

BACKGROUND

Collagenous connective tissue membranes (biosheets) are useful for engineering cardiovascular tissue in tissue engineering. The aim was to evaluate the use of biosheets as a potential tracheal substitute material in vivo in a rabbit model.

METHODS

Group 1: Rectangular-shaped Gore-Tex (4×7mm) was implanted into a 3×6mm defect created in the midventral portion of the cervical trachea. Group 2: Rectangular-shaped dermis was implanted into a tracheotomy of similar size. Group 3: Biosheets were prepared by embedding silicone moulds in dorsal subcutaneous pouches in rabbits for 1month. Rectangular-shaped biosheets were implanted into a tracheotomy of similar size in an autologous fashion. All groups (each containing 10 animals) were sacrificed 4weeks after implantation.

MAIN RESULTS

All materials maintained airway structure for up to 4weeks after implantation. Regenerative cartilage in implanted Biosheets in group 3 was confirmed by histological analysis. Tracheal epithelial regeneration occurred in the internal lumen of group 3. There were significant differences in the amounts of collagen type II and glycosaminoglycan between group 3 and group 1 or 2.

CONCLUSION

We confirm that cartilage can self-regenerate onto an airway patch using Biosheets.

Development of an in vivo tissue-engineered valved conduit (type S biovalve) using a slitted mold

In autologous valved conduits (biovalves) using in-body tissue architecture, the limited area available for leaflet formation is a concern. In this study, we designed a novel biovalve mold with slits to enhance in vivo cell migration, regardless of size. As a control, the original mold without slits was used. When both types of molds were embedded into subcutaneous pouches in beagle dogs for 8 weeks, the outer surfaces of all molds were completely covered with connective tissue to form conduit tissue. In the molds without slits, the leaflet size was limited to half of the design. In contrast, in the mold with slits, the complete leaflet area was formed. Upon trimming excess peripheral tissues, removing the mold, and cutting the connective tissue formed at the slits, completely autologous connective tissue biovalves with the designed leaflet area were obtained as type S (diameter, 6-28 mm) biovalves. The slit structure customized to the mold was effective for allowing cells to enter, thereby facilitating cell migration and contributing to the successful preparation of reliable biovalves of various physiological sizes suitable for all clinical uses.

In vitro hydrodynamic evaluation of a biovalve with stent (tubular leaflet type) for transcatheter pulmonary valve implantation

We have been developing an autologous heart valve-shaped tissue with a stent (stent-biovalve) for transcatheter pulmonary valve implantation (TPVI) using "in-body tissue architecture" technology. In this study, the hydrodynamic performance of a stent-biovalve with tubular leaflets was evaluated by changing its leaflet height in an in vitro test in order to determine the appropriate stent-biovalve form for the pulmonary valve. A specially designed, self-expandable, stent-mounted, cylindrical acrylic mold was placed in a dorsal subcutaneous pouch of goat, and the implant was extracted 2 months later. Only the cylindrical acrylic mold was removed from the implant, and a tubular hollow structure of membranous connective tissue impregnated with the stent strut was obtained. Half of tubular tissue was completely folded in half inwards, and 3 commissure parts were connected to form 3 leaflets, resulting in the preparation of a stent-biovalve with tubular leaflets (25-mm ID). The stent-biovalve with adjusting leaflet height (13, 14, 15, 17, 20, and 25 mm) was fixed to a specially designed pulsatile mock circulation circuit under pulmonary valve conditions using 37 °C saline. The mean pressure difference and effective orifice area were better than those of the biological valve. The lowest and highest leaflet heights had a high regurgitation rate due to lack of coaptation or prevention of leaflet movement, respectively. The lowest regurgitation (ca. 11%) was observed at a height of 15 mm. The leaflet height was found to significantly affect the hydrodynamics of stent-biovalves, and the existence of an appropriate leaflet height became clear.

Sutureless aortic valve replacement using a novel autologous tissue heart valve with stent (stent biovalve): proof of concept

We developed an autologous, trileaflet tissue valve ("biovalve") using in-body tissue architecture technology to overcome the disadvantages of current bioprosthetic valves. We designed a novel biovalve with a balloon-expandable stent: the stent biovalve (SBV). This study evaluated the technical feasibility of sutureless aortic valve replacement using the SBV in an orthotopic position, as well as the functionality of the SBV under systemic circulation, in an acute experimental goat model. Three adult goats (54.5-56.1 kg) underwent sutureless AVR under cardiopulmonary bypass (CPB). The technical feasibility and functionality of the SBVs were assessed using angiography, pressure catheterization, and two-dimensional echocardiography. The sutureless AVR was successful in all goats, and all animals could be weaned off CPB. The mean aortic cross-clamp time was 45 min. Angiogram, after weaning the animals off CPB, showed less than mild paravalvular leakage and central leakage was not detected in any of the goats. The mean peak-to-peak pressure gradient was 6.3 ± 5.0 mmHg. Epicardial two-dimensional echocardiograms showed smooth leaflet movement, including adequate closed positions with good coaptation; the open position demonstrated a large orifice area (average aortic valve area 2.4 ± 0.1 cm2). Sutureless AVR, using SBVs, was feasible in a goat model. The early valvular functionalities of the SBV were sufficient; future long-term experiments are needed to evaluate its durability and histological regeneration potential.

Implantation study of a tissue-engineered self-expanding aortic stent graft (bio stent graft) in a beagle model

The use of stent grafts for endovascular aortic repair has become an important treatment option for aortic aneurysms requiring surgery. This treatment has achieved excellent outcomes; however, problems like type 1 endoleaks and stent graft migration remain. Bio stent grafts (BSGs), which are self-expanding stents covered with connective tissue, were previously developed using "in-body tissue architecture" technology. We assessed their early adaptation to the aorta after transcatheter implantation in a beagle model. BSGs were prepared by subcutaneous embedding of acryl rods mounted with self-expanding nitinol stents in three beagles for 4 weeks (n = 3/dog). The BSGs were implanted as allografts into infrarenal abdominal aortas via the femoral artery of three other beagles. After 1 month of implantation, aortography revealed no stenosis or aneurysmal changes. The luminal surface of the BSGs was completely covered with neointimal tissue, including endothelialization, without any thrombus formation. The cover tissue could fuse the luminal surface of the native aorta with tight conjunctions even at both ends of the stents, resulting in complete impregnation of the strut into the reconstructed vascular wall, which is expected to prevent endoleaks and migration in clinical 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.

Right ventricular failure and pathobiology in patients with congenital heart disease - implications for long-term follow-up

Right ventricular dysfunction represents a common problem in patients with congenital heart defects, such as Tetralogy of Fallot or pulmonary arterial hypertension. Patients with congenital heart defects may present with a pressure or volume overloaded right ventricle (RV) in a bi-ventricular heart or in a single ventricular circulation in which the RV serves as systemic ventricle. Both subsets of patients are at risk of developing right ventricular failure. Obtaining functional and morphological imaging data of the right heart is technically more difficult than imaging of the left ventricle. In contrast to findings on mechanisms of left ventricular dysfunction, very little is known about the pathophysiologic alterations of the right heart. The two main causes of right ventricular dysfunction are pressure and/or volume overload of the RV. Until now, there are no appropriate models available analyzing the effects of pressure and/or volume overload on the RV. This review intends to summarize clinical aspects mainly focusing on the current research in this field. In future, there will be increasing attention to individual care of patients with right heart diseases. Hence, further investigations are essential for understanding the right ventricular pathobiology.