Wall thickness control in biotubes prepared using type-C mold

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.

Involvement of somatic stem cells in encapsulation of foreign-body reaction in canine subcutaneous Biotube tissue formation

Generally, the thickness of tubular tissues formed from silicone rods through encapsulation of the foreign-body reaction is less than approximately 0.2 mm. On the other hand, it is unclear how hollow cylindrical molds can provide thick tubular tissues, known as Biotubes, with a thickness exceeding 1 mm, during in-body tissue architecture (iBTA) using encapsulation. In this study, histological and structural analyses were performed to understand the reason for the formation of thick mold-based Biotubes. Molds were assembled with a gap between a silicone rod and a stainless-steel cylinder and were embedded into the dorsal subcutaneous pouches of beagles for 2 or 4 weeks. Thick Biotubes were obtained from the harvested mold. The histological analysis showed that the lumen side of the thick Biotubes consisted primarily of type I collagen fibers and α-smooth muscle actin-positive cells, similar to the original rod-based thin Biotubes formed only from silicone rods. Interestingly, the outer region of the thick Biotubes was an immature connective tissue consisting of type III collagen, including primitive somatic stem cells expressing CD90 and SSEA4. These stem cells may have contributed to the formation of the thick-walled Biotubes by differentiating into other cell types and through growth factor production. Because of the potential tissue-repair ability of these stem cells, iBTA could be useful for elucidating the regeneration process, remodeling the physiology/pathology of tissue defects/damage, and cell acquisition. This technology can provide autologous stem cells without in vitro cell culture. Moreover, thick-walled Biotubes may be useful as an alternative stem cell-containing material in regenerative medicine.

Modifications of the mechanical properties of in vivo tissue-engineered vascular grafts by chemical treatments for a short duration

In vivo tissue-engineered vascular grafts constructed in the subcutaneous spaces of graft recipients have functioned well clinically. Because the formation of vascular graft tissues depends on several recipient conditions, chemical pretreatments, such as dehydration by ethanol (ET) or crosslinking by glutaraldehyde (GA), have been attempted to improve the initial mechanical durability of the tissues. Here, we compared the effects of short-duration (10 min) chemical treatments on the mechanical properties of tissues. Tubular tissues (internal diameter, 5 mm) constructed in the subcutaneous tissues of beagle dogs (4 weeks, n = 3), were classified into three groups: raw tissue without any treatment (RAW), tissue dehydrated with 70% ET (ET), and tissue crosslinked with 0.6% GA (GA). Five mechanical parameters were measured: burst pressure, suture retention strength, ultimate tensile strength (UTS), ultimate strain (%), and Young’s modulus. The tissues were also autologously re-embedded into the subcutaneous spaces of the same dogs for 4 weeks (n = 2) for the evaluation of histological responses. The burst pressure of the RAW group (1275.9 ± 254.0 mm Hg) was significantly lower than those of ET (2115.1 ± 262.2 mm Hg, p = 0.0298) and GA (2570.5 ± 282.6 mm Hg, p = 0.0017) groups. Suture retention strength, UTS or the ultimate strain did not differ significantly among the groups. Young’s modulus of the ET group was the highest (RAW: 5.41 ± 1.16 MPa, ET: 12.28 ± 2.55 MPa, GA: 7.65 ± 1.18 MPa, p = 0.0185). No significant inflammatory tissue response or evidence of residual chemical toxicity was observed in samples implanted subcutaneously for four weeks. Therefore, short-duration ET and GA treatment might improve surgical handling and the mechanical properties of in vivo tissue-engineered vascular tissues to produce ideal grafts in terms of mechanical properties without interfering with histological responses.

Aortic valve neocuspidization with in-body tissue-engineered autologous membranes: preliminary results in a long-term goat model

OBJECTIVES

Aortic valve neocuspidization has shown satisfactory clinical outcomes; however, autologous pericardium durability is a concern for young patients. This study applied an autologous collagenous membrane (Biosheet®), produced by in-body tissue architecture, to aortic valve neocuspidization and investigated its long-term outcome in a goat model.

METHODS

Moulds were embedded subcutaneously in 6 goats. After 2 months, Biosheets formed in the moulds. We performed aortic valve neocuspidization using a portion of the sheets with a thickness of 0.20-0.35 mm, measured by optical coherence tomography. Animals were subjected to echocardiography and histological evaluation at 6 months (n = 3) and 12 months (n = 3). As a control, the glutaraldehyde-treated autologous pericardium was used in 4 goats that were similarly evaluated at 12 months.

RESULTS

All animals survived the scheduled period. At 6 months, Biosheets maintained valve function and showed a regeneration response: fusion to the annulus, cell infiltration to the leaflets and appearance of elastic fibres at the ventricular side. After 12 months, the regenerative structure had changed little without regression, and there was negligible calcification in the 1/9 leaflets. However, all cases had one leaflet tear, resulting in moderate-to-severe aortic regurgitation. In the pericardium group, three-fourths of the animals experienced moderate-to-severe aortic regurgitation with a high rate of calcification (9/12 leaflets).

CONCLUSIONS

Biosheets may have regeneration potential and anti-calcification properties in contrast to autologous pericardium. However, in order to obtain reliable outcome, further improvements are required to strictly control and optimize its thickness, density and homogeneity.

Spatiotemporal histological changes observed in mouse subcutaneous tissues during the foreign body reaction to silicone

We investigated spatiotemporal changes in host tissues during foreign body reactions. Silicone tube was subcutaneously embedded into ICR mice, and tissue surrounding silicone (TSS) was observed at 2, 7, 14, 21, 28, 43, and 70 days (D) postsurgery. The thin layer (TL) and loose connective tissues (LCTs) (inside and outside the TSS) developed until D21 and densified afterward. Neutrophils infiltrated the TSS until D14 and formed neutrophil extracellular traps (NETs) in the TL during D7-21. In the LCTs, mast cell counts increased until D21, and macrophage numbers peaked at D14. Several macrophages showed LYVE-1 expression, supporting a tissue-remodeling role. Developmental indices of collagen fibers (CFs) and reticular fibers (RFs) increased during D2-21. NETs, but not neutrophils, were detected after D28. Mast cell numbers peaked at D43 and were maintained until D70. Myofibroblasts consistently localized to the TL from D14. During D21-28, the area of connective tissue (CNT), and CFs and RFs decreased and increased, respectively, and both remained constant during D28-70. The CF density remained constant from D21 and increased at D70. Thus, TSS showed two phases: inflammation and CNT development (D2-21), and inflammation convergence and CNT stabilization (D28-70). These results provide insights into foreign body reactions in clinical cases.

Arteriovenous access in hemodialysis: A multidisciplinary perspective for future solutions

In hemodialysis, vascular access is a key issue. The preferred access is an arteriovenous fistula on the non-dominant lower arm. If the natural vessels are insufficient for such access, the insertion of a synthetic vascular graft between artery and vein is an option to construct an arteriovenous shunt for punctures. In emergency situations and especially in elderly with narrow and atherosclerotic vessels, a cuffed double-lumen catheter is placed in a larger vein for chronic use. The latter option constitutes a greater risk for infections while arteriovenous fistula and arteriovenous shunt can fail due to stenosis, thrombosis, or infections. This review will recapitulate the vast and interdisciplinary scenario that characterizes hemodialysis vascular access creation and function, since adequate access management must be based on knowledge of the state of the art and on future perspectives. We also discuss recent developments to improve arteriovenous fistula creation and patency, the blood compatibility of arteriovenous shunt, needs to avoid infections, and potential development of tissue engineering applications in hemodialysis vascular access. The ultimate goal is to spread more knowledge in a critical area of medicine that is importantly affecting medical costs of renal replacement therapies and patients’ quality of life.

Initial 3-year results of first human use of an in-body tissue-engineered autologous “Biotube” vascular graft for hemodialysis

This study presents the initial 3-year results of the first in-human study of internal shunt restoration using completely autologous vascular grafts, “Biotubes,” based on in-body tissue architecture. Biotubes (diameter, 6 mm; length, 7 cm) were prepared as autologous collagenous tubular tissues with approximately 0.5 mm wall thickness by embedding molds (two per patient), assembled with a silicone rod and a stainless steel pipe with many slits, into the patients’ abdominal subcutaneous tissue for 2 months. Two female patients with end-stage renal disease were undergoing hemodialysis with a high probability of failure due to repeated stenosis every few months at the venous outflow regions over 1.5 years. Biotubes formed in both patients and were bypassed over the venous stenosis region of the arteriovenous shunt. After bypass with Biotubes without living cells, palpable thrill and typical turbulent flow pattern were observed by pulsed-wave Doppler. Follow-up angiography showed no signs of dilation or stenosis after implantation, and puncture could be performed easily without graft damage. In both cases, stenosis of Biotubes occurred after 3–4 months. In the first case, percutaneous transluminal angioplasty was not required for over 2 years after implantation even after the development of Biotube stenosis. In the second case, stenosis at the proximal anastomotic site of the Biotube became prominent, and percutaneous transluminal angioplasty was needed 7 months after implantation and then repeated at up to 2 years. This was the first human study successfully supporting the concept of internal shunt restoration for hemodialysis using an autologous Biotube.

Shape memory of in-body tissue-engineered Biotube® vascular grafts and the preliminary evaluation in animal implantation experiments

BACKGROUND

Tissues formed by in-body tissue architecture (iBTA) are soft and flexible. However, strongly bending iBTA-induced vascular grafts, called biotubes, may cause lumen collapse by kinking, subsequently leading to occlusion after implantation. In this study, we developed a method for biotube shape memory and verified its performance in preliminary animal implantation experiments.

METHODS

Straight biotubes were prepared by subcutaneous embedding of straight molds into beagle dogs for two months. Upon overnight immersion of the obtained straight biotubes in a 70% ethanol solution under U-shape framing, the biotubes maintained their U shape even after washing with saline solution. Additionally, spiral-shaped biotubes formed from goats using spiral molds could be stretched straight via the same alcohol treatment.

RESULTS

Within limited acute-phase animal implantation experiments, U-shaped biotubes functioned as AV shunt grafts in the femoral region of the beagle without deformation of vascular shape (N.=11). In addition, the long straight biotubes derived from spiral molds could be interposed between goat carotid arteries while maintaining their straight shape (N.=2). All implants maintained perfect patency at the 1-month follow-up period without any evidence of vascular deformation.

CONCLUSIONS

By retaining iBTA-induced tissues in an alcohol solution in the target shape, the shape of the tissues was imprinted and maintained even after implantation within a limited acute period. Therefore, in order to obtain tissues of various shapes, it is unnecessary to use a mold design to maintain the individual shape.

iBTA-induced bovine Biosheet for repair of abdominal wall defects in a beagle model: proof of concept

INTRODUCTION

We evaluated the usefulness of xeno-Biosheets, an in-body tissue architecture-induced bovine collagenous sheet, as repair materials for abdominal wall defects in a beagle model.

MATERIALS AND METHODS

Biosheets were prepared by embedding cylindrical molds into subcutaneous pouches of three Holstein cows for 2-3 months and stored in 70% ethanol. The Biosheets were 0.5 mm thick, cut into 2 cm × 2 cm, and implanted to replace defects of the same size in the abdominal wall of nine beagles. The abdominal wall and Biosheets were harvested and subjected to histological evaluation at 1, 3, and 5 months after implantation (n = 3 each).

RESULTS

The Biosheet and bovine pericardiac patch (control) were not stressed during the suture operation and did not split, and patches were easily implanted on defective wounds. After implantation, the patch did not fall off and was not perforated, and healing was observed nacroscopically in all cases. During the first month of implantation, accumulation of inflammatory cells was observed along with decomposition around the Biosheet. Decomposition was almost complete after 3 months, and the Biosheet was replaced by autologous collagenous connective tissue without rejection. After 5 months, the abdominal wall muscle elongated from the periphery of the newly formed collagen layer and the peritoneum was formed on the peritoneal cavity surface. Regeneration of almost all layers of the abdominal wall was observed. However, almost all pericardium patches were remained even at 5 months with inflammation.

CONCLUSION

Bovine Biosheets requiring no special post-treatment can be useful as off-the-shelf materials for abdominal wall repair.