Acellular Matrix Allograft Research Articles

The constitution of functional model rabbit bladder with acellular matrix

Aim: In this study, for the useable of bladder acelluar matrix in urinary tissue engineering, we compared the urodynamic and histopathological results between normal, partial cystectomy and bladder acellular matrix allograft (BAMA) augmented cystoplasty groups in rabbit model. Methods: There were five groups each consisting three rabbits. Urodynamic investigation was applied to all animals at the beging of the study. Then, in the first control group, the rabbits were sacrified and the bladders were removed for histopathological examination. In the second control group the same procedures were realized at the end of 24th week. In the third group, partial cystectomy was performed to the animals and followed for 24 weeks. Partial cystectomy and BAMA augmented cystoplasty were performed to the animals in the 4th and 5th groups. The animals were sacrified at the end of 12th and 24th weeks, respectively. In the 3th, 4th and 5th groups urodynamic investigations were performed before sacrification. Then bladders were underwent for histopathological examination. Results: There was no significant difference in term of bladder capacity between both control and BAMA augmented groups. Detrusor presures were no statistical different in all groups. However bladder capacity has significantly reduced in partial cystectomy group. In histopathological evaluations there were no differences between control and partial cystectomy groups. In BAMA augmented groups urothelium and vascularization were nearly the same as control groups however muscle layer was less organized and was thinner than control groups. Collagen depositon and innervation in BAMA augmented bladder were more prominent than that of the control group. Conclusion: In our animal study; although the detrusor muscle had less organized with more collagen deposition, the BAMA augmented bladders had near normal capacity and compliance with normal detrusor presures.

VEGF-Loaded Nanoparticle-Modified BAMAs Enhance Angiogenesis and Inhibit Graft Shrinkage in Tissue-Engineered Bladder.

Insufficient angiogenesis is a common problem in bladder tissue engineering and is believed to be a major factor responsible for graft shrinkage. In this study, we investigated the use of bladder acellular matrix allografts (BAMAs) modified with vascular endothelial growth factor (VEGF)-loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) for the long-term sustained release of VEGF to enhance blood supply and inhibit graft shrinkage in a rabbit model of bladder reconstruction. Rabbits underwent partial bladder cystectomy using a 2×3cm BAMA modified with VEGF-loaded PLGA NPs in the experimental group, while no modification was used in the control. Histology and immunohistochemical analyses showed that urothelium, smooth muscle fibers and blood vessels were formed in both groups at 4 and 12weeks postoperatively. The microvessel density in the experiment group was significantly higher than that in control and the contracture rate declined to 27%. In vitro functional experiments indicated that the characteristics of regenerated bladders were similar to native bladders. The VEGF release from BAMA in vivo was almost 83% within 3months. Our data demonstrated the effectiveness of VEGF-loaded PLGA NPs-modified BAMAs to enhance neovascularization and solve the problems of insufficient angiogenesis and graft shrinkage associated with bladder tissue engineering.

A nanomedicine approach to effectively inhibit contracture during bladder acellular matrix allograft-induced bladder regeneration by sustained delivery of vascular endothelial growth factor.

Macroscopic evidence of contracture has been identified as a major issue during the regeneration process. We hypothesize that lack of angiogenesis is the primary cause of contracture and explore a nanomedicine approach to achieve sustained release of vascular endothelial growth factor (VEGF) to stimulate angiogenesis. We evaluate the efficacy of poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) for long-term (3 months) sustained release of VEGF in bladder acellular matrix allografts (BAMA) in a swine model. We anticipate that the sustained release of VEGF could stimulate angiogenesis along the regeneration process and thereby inhibit contracture. Bladder was replaced with BAMA (5×5 cm), modified with PLGA NPs encapsulated with VEGF in a pig model. The time points chosen for sampling were 1, 2, 4, and 12 weeks. The regenerated areas were then measured to obtain the contracture rate, and the extent of revascularization was calculated using histological and morphological features. In the control group of animals, the bladder was replaced with only BAMA. The in vivo release of VEGF was evident for ∼3 months, achieving the goal of long-acting sustained release, and successfully promoted the regeneration of blood vessels and smooth muscle fibers. In addition, less collagen deposition was observed in the experimental group compared with control. Most importantly, the inhibition of contracture was highly significant, and the ultimate contracture rate decreased by ∼57% in the experimental group compared with control. In isolated strips analysis, there were no significant differences between BAMA-regenerated (either VEGF added or not) and autogenous bladder. BAMA modified with VEGF-loaded PLGA-NPs can sustainably release VEGF in vivo (>3 months) to stimulate angiogenesis leading to the inhibition of contracture. This is the first study to report a viable nanomedicine-based strategy to overcome contracture during bladder regeneration induced by BAMA. Furthermore, this study also confirms that insufficient angiogenesis plays a crucial role in the onset of contracture.

Sustained release of VEGF from PLGA nanoparticles embedded thermo-sensitive hydrogel in full-thickness porcine bladder acellular matrix

We fabricated a novel vascular endothelial growth factor (VEGF)-loaded poly(lactic-co-glycolic acid) (PLGA)-nanoparticles (NPs)-embedded thermo-sensitive hydrogel in porcine bladder acellular matrix allograft (BAMA) system, which is designed for achieving a sustained release of VEGF protein, and embedding the protein carrier into the BAMA. We identified and optimized various formulations and process parameters to get the preferred particle size, entrapment, and polydispersibility of the VEGF-NPs, and incorporated the VEGF-NPs into the (poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (Pluronic®) F127 to achieve the preferred VEGF-NPs thermo-sensitive gel system. Then the thermal behavior of the system was proven by in vitro and in vivo study, and the kinetic-sustained release profile of the system embedded in porcine bladder acellular matrix was investigated. Results indicated that the bioactivity of the encapsulated VEGF released from the NPs was reserved, and the VEGF-NPs thermo-sensitive gel system can achieve sol-gel transmission successfully at appropriate temperature. Furthermore, the system can create a satisfactory tissue-compatible environment and an effective VEGF-sustained release approach. In conclusion, a novel VEGF-loaded PLGA NPs-embedded thermo-sensitive hydrogel in porcine BAMA system is successfully prepared, to provide a promising way for deficient bladder reconstruction therapy.

22 week assessment of bladder acellular matrix as a bladder augmentation material in a porcine model

Previous studies on the reconstruction of porcine bladder using bladder acellular matrix allograft (BAMA) have indicated positive preliminary results with respect to graft shrinkage and cellular repopulation. The current study was conducted to investigate the feasibility of using BAMA in a similar model of bladder reconstruction out to longer time frames (22 weeks). At predetermined time points, the macroscopic, histological and mechanical properties of explanted native and BAMA tissues were evaluated and compared. Macroscopically, contracture of the BAMA was observed. The peripheral regions of the grafts experienced extensive cellular repopulation. Towards the centre however, all grafts were consistently devoid of organized smooth muscle bundles and a well-developed urothelium. An alteration in both the amount and organization of collagen was also observed within this region. Significant differences ( p<0.05) in the rupture strain and the elastic modulus of the BAMA compared to native bladder tissue appear to correlate with macroscopic graft contracture as well as the fibroproliferative tissue response of the matrix.

REGENERATION OF FUNCTIONAL BLADDER SUBSTITUTES USING LARGE SEGMENT ACELLULAR MATRIX ALLOGRAFTS IN A PORCINE MODEL

REGENERATION OF FUNCTIONAL BLADDER SUBSTITUTES USING LARGE SEGMENT ACELLULAR MATRIX ALLOGRAFTS IN A PORCINE MODEL

Regeneration of functional bladder substitutes using large segment acellular matrix allografts in a porcine model.

We previously reported on the short-term (4 weeks) morphometric analysis of a large bladder acellular matrix allograft used as a bladder bioprosthesis (average size 24 cm.2). We demonstrated cellular repopulation through the entire thickness of the graft. We now present the long-term (12 weeks) morphometric results of graft regenerated porcine bladders using segments measuring an average of 40 cm.2. Bladders harvested from pigs were subjected to detergent and enzymatic extractions to render them acellular. Partial cystectomy was performed in 21 pigs and the defect was repaired with a bladder acellular matrix allograft (average size 40.52 cm.2). Of the animals 8 were sacrificed at 1, 2 and 4 weeks and 13 were sacrificed at 8 and 12 weeks. To evaluate cellular repopulation and matrix reorganization the native bladder and graft were analyzed using standard histological and immunofluorescent techniques. To evaluate for calcium deposits in the grafts a radiological evaluation of the graft was performed after explantation. All animals survived the surgical procedure and there were no significant urinary leaks. No stones were noted in any of the bladders. At 1 week there was a diffuse infiltration with acute inflammatory cells. At 2 weeks the luminal surface of the graft was lined with a single layer of urothelium, and there was stromal infiltration with unorganized smooth muscle cells and angiogenesis. At 4 weeks the urothelium was multilayered with organizing groups of smooth muscle cells and angiogenesis. At 8 and 12 weeks there was repopulation throughout the bladder acellular matrix allograft implant with all native cellular components participating. We present evidence that large patch bladder acellular matrix allograft implantation is technically feasible and may prove to be a viable surgical alternative to bladder augmentation with intestinal segments. Its advantages may include the potential for complete and functional regeneration of a bladder substitute.

Acellular bladder matrix allografts in the regeneration of functional bladders: evaluation of large-segment (> 24 cm) substitution in a porcine model.

To evaluate the use of a large-segment (> 24 cm2) bladder substitution with porcine bladder acellular matrix allograft (BAMA) in a large animal model. Materials and methods Bladders were harvested from pigs at the time of necropsy and subjected to detergent and enzymatic extractions to render them acellular. The BAMA produced had the surgical handling and suture-retaining properties of normal bladder tissue. Six pigs had BAMA segments implanted under general anaesthesia, through a low midline abdominal incision and after partial cystectomy. The defect was repaired with a BAMA patch (mean size 43.88 cm2, range 12-72), with no urinary diversion. Two animals each were then killed at 9, 16 and 30 days and the bladders explanted. The native bladder and BAMA patch were analysed morphometrically to evaluate cellular re-population and matrix re-organization. All animals survived surgery; there were no urinary leaks and no stones detected in any of the bladders. At 9 days there was a diffuse infiltration with acute inflammatory cells, but no areas of necrosis. There were isolated areas of smooth muscle cell (SMC) infiltration of the BAMA. At 16 days the luminal surface was lined with a single layer of urothelium, there was stromal infiltration with disorganized SMC and angiogenesis, with mature vessels in the BAMA patch. At 30 days the urothelium was multilayered with organizing groups of SMCs and angiogenesis. The highest cell density was at the periphery of the repopulated BAMA patch, decreasing towards the centre. The implantation of large patches of BAMA is technically feasible and may prove to be a viable surgical alternative to bladder augmentation with intestinal segments. The advantages of BAMA include the potential for complete and functional regeneration of a bladder substitute. This model provides a tool with which to obtain a better understanding of the cellular and molecular aspects of matrix re-population.

Acellular matrix: A biomaterials approach for coronary artery bypass and heart valve replacement

We have developed a multistep detergent-enzymatic extraction process (involving hypotonic and hypertonic solutions, the detergents octyl-phenoxy-polyethoxyethanol and sodium dodecyl sulfate, as well as DNAse and RNAse) which, while inhibiting autolysis, removes all cells from tissues and, with them, cellular antigens together with lipids and more soluble glycosaminoglycans. What remains is acellular matrix with the structural proteins well conserved and normally arranged. Canine arteries extracted to acellular matrix were implanted as coronary artery bypass allografts in a canine model, without the use of cardiopulmonary bypass, and compared with autogenous saphenous veins. Of nine pilot acellular matrix implants, four were patent, as compared with four of seven saphenous vein grafts. All occlusions in both graft types occurred acutely soon after implantation, with almost all patent grafts followed up for 6 months. The acellular matrix allografts showed no inflammation and only minimal cellular repopulation. This model needs further development, but appears promising for preclinical evaluation. Canine aortic and pulmonic valves extracted to acellular matrix using a modification of our extraction process, eliminating the detergent sodium dodecyl sulfate, were implanted heterotopically as allografts in the left main pulmonary artery in dogs, a location chosen to avoid the need for cardiopulmonary bypass. At 1 month, two-dimensional echocardiography of six implants showed leaflet motion and 3- to 5-mm Hg transvalvular gradients. Explant histology of four valves at 1 month showed no inflammation, cellular repopulation at the base of the valve, and partial endothelialization.(ABSTRACT TRUNCATED AT 250 WORDS)