Autologous granulation tissue tubes for replacement of urethral defects: An experimental study in male rabbits.

INTRODUCTION: Tubularized urethroplasty is commonly performed in clinical practice using genital skin flaps, bladder mucosa, and buccal mucosa. However, the long-term effects are not satisfying, and donor site morbidities remain a problem. Besides, those grafts are unavailable with malignant conditions of the urinary tract, a history of lichen sclerosis, or oral disease. OBJECTIVE: An autologous granulation tissue tube of any required length and diameter can be produced by implanting foreign objects subcutaneously (Summary Fig.). The current study aimed to investigate to what extent of length this fully autologous tissue could be used for tubularized urethroplasty, satisfying urethral patency and tissue regeneration, in male rabbits. STUDY DESIGN: Twenty-seven New Zealand male rabbits were randomly divided into three groups. Silastic tubes were implanted subcutaneously in Group 1 and Group 2. By 2 weeks the granulation tissue encapsulating the tubes was harvested. In Group 1, pendulous urethral segments of 1 cm were excised, and urethroplasty was performed with the granulation tissue tube in an end-to-end fashion. In Group 2, a pendulous urethral segment of 1.5 cm was replaced with the tissue tube. In Group 3, a pendulous urethral defect of 1 cm was repaired by re-anastomosis as control. Serial urethrograms were performed at 1, 2 and 6 months postoperatively. Meanwhile, the neo-urethra were harvested and analyzed grossly and histologically. RESULTS: The urethrograms showed that all animals in Group 1 maintained a wide urethral caliber. In contrast, animals in Group 2 and Group 3 developed progressive strictures. Histologically, an intact urothelium with one to two cell layers lined the graft by 1 month, which was surrounded by increasing organized smooth muscle in Group 1. By 6 months, the grafts were completely integrated into native urethra. Nevertheless, extensive fibrosis occurred in Group 2 and Group 3. DISCUSSION: The tissue successfully maintained patency and guided urethral regeneration across a distance of 1 cm. As an epithelium-free graft, the tissue showed better results than acellular matrix for tubularized urethroplasty compared with previous studies. Nevertheless, several limitations existed: (1) the urethral defect was created in healthy urethra, which could not fully simulate the clinical situation; (2) as a small animal model, rabbit was less informative for clinical problems; (3) the tissue was inadequate for long segmental urethral replacement. Further study is needed before the procedure is used clinically. CONCLUSION: An autologous granulation tissue tube grown subcutaneously could be successfully used to repair urethral defects of 1 cm in male rabbits.

Urethral Reconstruction Using Mesothelial Cell-Seeded Autogenous Granulation Tissue Tube: An Experimental Study in Male Rabbits.

Objective. This study was to evaluate the utility of the compound graft for tubularized urethroplasty by seeding mesothelial cells onto autogenous granulation tissue. Methods. Silastic tubes were implanted subcutaneously in 18 male rabbits, of which nine underwent omentum biopsies simultaneously for in vitro expansion of mesothelial cells. The granulation tissue covering the tubes was harvested 2 weeks after operation. Mesothelial cells were seeded onto and cocultured with the tissue for 7 days. A pendulous urethral segment of 1.5 cm was totally excised. Urethroplasty was performed with mesothelial cell-seeded tissue tubes in an end-to-end fashion in nine rabbits and with unseeded grafts in others as controls. Serial urethrograms were performed at 1, 2, and 6 months postoperatively. Meanwhile, the neourethra was harvested and analyzed grossly and histologically. Results. Urethrograms showed cell-seeded grafts maintained wide at each time point, while strictures formation was found in unseeded grafts. Histologically, layers of urothelium surrounded by increasingly organized smooth muscles were observed in seeded grafts. In contrast, myofibroblasts accumulation and extensive scarring occurred in unseeded grafts. Conclusions. Mesothelial cell-seeded granulation tissue tube can be successfully used for tubularized urethroplasty in male rabbits.

Transplanted abdominal granulation tissue induced bone formation--an in vivo study in sheep.

Many wounds to both soft and hard tissues heal via the formation of a granulation tissue bed. This bed is supportive of neoangiogenesis and releases proangiogenic, migratory, and proliferative growth factors and cytokines. In this study granulation tissue was grown on an intraperitoneal implant (4 mm diameter, 20 mm length) in a sheep. After 2 weeks, this implant was removed and transplanted into a femoral bone defect (4 mm diameter, 20 mm length). The sheep were sacrificed after 3 months, and the implant site examined using micro-CT and histology. A bone plaque formed adjacent to the implant, only in the presence of the peritoneal granulation tissue. This suggests that the formation of granulation tissue is a relatively conserved response at various locations in the body and its transplantation from one location to another can be used to induce tissue healing. This technique may prove useful as a method of improving physiological response to biomaterials.

Membrana amniótica e pericárdio canino como curativos biológicos na preparação do leito receptor para enxertia cutânea autógena / Canine amniotic membrane and pericardium as a biological wound dressing in the preparation of the recipient site to autogenous skin graft

Avaliou-se o tecido de granulação formado com o uso de membrana amniótica e pericárdio canino como curativo biológico oclusivo em feridas cutâneas experimentais. Utilizaram-se 15 cães; em cada animal, foram produzidas três feridas na região torácica dorsal. As feridas craniais e caudais receberam aloenxerto de membrana amniótica e pericárdio canino, respectivamente, e as feridas intermediárias (controle) curativo não aderente. No sétimo dia, sobre todas as feridas, foram feitas auto-enxertias cutâneas. Foram realizadas avaliações clínicas, histológicas, incluindo contagem e diâmetro médio dos vasos sangüíneos do tecido de granulação bem como coleta de secreção das feridas e dos enxertos. Concluiu-se que a aplicação do curativo de membrana amniótica e de pericárdio canino sobre feridas cutâneas durante sete dias não estimula o aparecimento da granulação necessária para a aplicação à enxertia cutânea, podendo, apenas, ser utilizado como curativo biológico oclusivo.

The granulation tissue formed with the use of amniotic membrane (ME) and canine pericardium (PE) as an occlusive biological dressing in experimental cutaneous wounds was evaluated Fifteen dogs, having three wounds on the dorsal thoracic region of each (FA -amniotic, FC -control and FP-pericardium) were used. Clinical and histological evaluations were carried out, including counting and measuring the average diameter of the blood vessels of the granulation tissue, as well as bacteriological exams (swabs) of the wounds and the grafts. The granulation tissue formed after seven days of using the canine amniotic membrane showed a vascular histological aspect, being able to be favorable to the cutaneous grafting. It was concluded that the use of amniotic membrane and canine pericardium dressing on cutaneous wounds during seven days did not stimulate the presence of granulation necessary for the use of cutaneous grafting, however, it can be used as an occlusive biological graft.

Granulation encapsulated stent: a new therapeutic approach for vascular implantation.

OBJECTIVES: To determine if stents could be encapsulated with immunocompatible granulation tissue for the treatment of vascular diseases. METHODS: Bare metal stents were implanted in New Zealand white rabbits so they would be encapsulated with immunocompatible granulation tissue. The granulation encapsulated stents (GES) were then treated with either mitomycin C or saline, and implanted into rabbit iliac arteries for 4 weeks. To test whether the effect of mitomycin C was retained, we co-cultured smooth muscle cells for 3 h with subcutaneous tissue (as control) or with granulation tissue from GES treated with mitomycin C and saline. RESULTS: Vessels with GES treated with mitomycin C (MS) and washed with saline had significantly less neointimal area (NA) after 4 weeks (0.27 (SD 0.03) mm(2) than vessels containing bare metal stents (B) (1.15 (SD 0.10) mm(2), n = 5, p<0.05) or GES treated with saline (S) (4.78 (SD 0.72) mm(2), n = 5, p<0.05). The average vessel injury score was not significantly different among these three groups (S: 1.98 (SD 0.51), MS: 1.46 (SD 0.18) and B: 1.51 (SD 0.32)). GES treated with saline had significantly less NA than the other two groups and also blocked blood flow in the contralateral iliac artery in the abdominal aortic bifurcation immediately after implantation and 4 weeks later. Histology also showed neointimal overgrowth in the vessel wall over the contralateral iliac artery. CONCLUSIONS: GES treated with mitomycin C can significantly inhibit neointimal formation in rabbit arteries due to the formation of granulation tissue. GES treated with saline demonstrated significantly increased NA and resisted normal rabbit artery pressures.

Use of previously burned skin as random cutaneous local flaps in pediatric burn reconstruction.

Reconstruction after post-burn scarring remains a challenge. It is especially true in the severely burned patient, who normally presents with a paucity of donor sites. Healed skin from areas that had been burned and skin from grafted areas (termed as previously burned skin) have been occasionally used as flaps, but their safety is still in debate. We studied all patients undergoing burn reconstruction with normal skin flaps and previously burned skin flaps in the same operative procedure between April 1998 and October 1998 to determine the safety of flaps including burned and healed tissues. Patients served as their own controls. Three hundred and fifty-three local flaps were studied in 74 patients. These included 238 previously burned skin flaps and 115 normal skin flaps. There were no differences in complication rates between groups and only one previously burned skin flap suffered from complete necrosis. The use of local previously burned skin as flaps in burn reconstruction is safe. Reconstruction with flaps should be considered as first choice in burn reconstruction regardless of the quality of the local tissue.

Granulation tissue flap technique in extensive wounds for covering exposed bone after tumor excision.

BACKGROUND: Second intention partial wound healing followed by skin grafting is a well-established method in dermatosurgery. In wide tumor excision, where periosteum is removed, growth of granulation tissue in the central areas of bare bone can be prolonged. OBJECTIVE: We describe a new technique for a faster, reliable closure of large defects utilizing granulation tissue flaps. METHODS: Postoperative wounds were treated with wet dressings until granulation tissue had developed on the wound edges. The central defects were then covered with lateral granulation tissue flaps. Subsequently split skin grafting was performed. RESULTS: Thirty-eight patients (37-99 years old) were treated between 1991 and 1999. Skin defects were located primarily on the scalp and forehead, and ranged from 3 to 13 cm in diameter. Wound bed preparation for skin grafting was achieved in all patients. Only minor complications, such as partial granulation flap necrosis in 5 of 38 patients or delayed skin graft healing in 4 of 38 patients, were seen. CONCLUSIONS: This technique for the closure of extensive skin defects is safe and effective.

Role of macrophages in the stimulation and regeneration of sensory nerves by transposed granulation tissue and temporal aspects of the response.

Application of granulation tissue, which is rich in macrophages, to a peripheral nerve induces a conditioning effect, in that it enhances the regeneration capability of peripheral nerves after a test crush lesion. The temporal aspects of this response and the role of macrophages and interleukin-1 beta (IL-1 beta) were studied in the sciatic nerves of 71 rats. Granulation tissue was implanted close to the sciatic nerve and test crush lesions were applied after various periods of time (0-21 days). Regeneration was evaluated after an additional two, three, four, or six days. Regeneration distances were longer in granulation-treated nerves than in nerves treated with subcutaneous tissue. Furthermore, in animals in which the test crush lesion was made at the same time as the granulation tissue was implanted (n = 6), regeneration distances were longer, 8.1 (0.8) mm compared with 7.2 (0.6), than those in which the crush was made after conditioning intervals of 3 (n = 6, 7.6 (0.4) compared with 6.9 (0.4), p = 0.03); 7 (n = 6, 7.4 (0.4) compared with 6.6 (0.1), p = 0.03); and 21 days [(n = 8, 7.2 (0.6) compared with 6.4 (0.5)]. Inactivation of the granulation tissue by freezing suppressed the conditioning effect. There were numerous ED1 and ED2 positive macrophages as well as positive staining for IL-1 beta in the granulation tissue on day 0. Positive staining for IL-1 beta was also seen in nerve fibres as well as in non-neuronal cells after a conditioning interval. The results suggest that regeneration is stimulated by factors released from the cells of the granulation tissue, and that the amount of factors released or the responsiveness of the regenerating nerve change during the conditioning interval.

Implants of hypertrophic scars and keloids into the nude (athymic) mouse: viability and morphology.

Pieces of hypertrophic scars and keloids were implanted into subcutaneous pockets of nude (athymic) mice and carried for varying times up to 246 days. No rejection phenomena were observed. Microvascular anastomosis occurred between host and implant within the first several days. Remodeling of the edges of the implant occurred very early. Multiple regression analysis of volume measurements suggests there was a size reduction of the implants with time. Yet virtually all implants retained their original histotypic character regardless of the length of implantation. The nodular character typical of all hypertrophic scars and keloids was retained in every case. Histologic analysis, confirmed by transmission electron microscopy, demonstrated a sustained cellular character. The degree and magnitude of microvascular occlusion was also sustained. Use of the nude mouse for implants of hypertrophic scar or keloid sustains true viability and morphology of the lesions. This procedure shows clear potential as an experimental model for the study of these lesions.

Graft adherence to de-epithelialized surfaces: a comparative study.

Graft adherence may be divided into two distinct phases: Phase I, which is fibrin dependent and Phase II, which begins after 72 hours with fibro-vascular ingrowth or vascular anastomosis with the graft material. Adherence values for autograft, homograft, heterograft, silicone membrane and a modified collagen membrane were evaluated during the fibrin-dependent Phase I period at 5 and 72 hours on dermal, fascial and granulating surfaces on rats. Modified collagen membrane demonstrated a superior adherence at both times tested on dermal and fascial surfaces, while autograft and homograft were significantly more adherent on granulating surfaces at 72 hours. The inert silicone membrane was consistently the least adherent. Granulating surfaces produced the highest adherence values at 5 hours and fascial surfaces at 72 hours. The higher values found with collagen indicate that future research directed toward the production of a synthetic wound dressing or skin should be directed toward biologically derived materials, rather than inert materials. The data supports the concept of the role of fibrin as the bonding factor in Phase I adherence and implies that collagen, rather than elastin, is primarily responsible for early graft adherence.