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Biomedical subjects

Mark A Randolph

Publications and source records attributed to Mark A Randolph.

30 records · Page 2Linked to original sources
PubMed2004

Heterotopic limb allotransplantation model to study skin rejection in the rat.

Current rodent models for investigation of limb allotransplantation typically utilize orthotopic whole-limb transplantation, a morbid and time-consuming procedure. Our objective was to design a less morbid rat model to explore the immunological obstacles of limb transplantation, and particularly skin. Twenty lower hindlimbs from 10 donors were transplanted into a heterotopic subcutaneous position into 20 animals (10 isogeneic and 10 allogeneic). Each group was further subdivided to include animals with (n = 5) and without (n = 5) a skin paddle for observation of cutaneous signs of rejection. All grafts in the isogeneic group survived for 100 days, i.e., the endpoint of the study. Allogeneic transplants rejected their allografts at a mean of 12.8 days (with skin) and 20.6 days (without). Our heterotopic limb transplantation model takes less time and is less stressful to the animals, while allowing for early observation of graft skin rejection, when compared to orthotopic whole-limb transplantation.

Anastomosis, Surgical↗
PubMed2004

Composite tissue allotransplantation--a new era in plastic surgery?

Composite tissue allotransplantation (CTA) holds great potential for reconstructive surgery. The recent hand transplants have made this a clinical reality. However, concerns about CTA have divided the medical community. The current transplants require life-long immunosuppression, which could place the recipients at risk of serious complications. In addition despite potent immunosuppression, chronic rejection may still negate any early favourable results. This article will outline the clinical experience of CTA, the major problems of the technique and the potential solutions to these problems.

Graft Rejection↗
PubMed2004

Prolongation of skin allograft survival after neonatal injection of donor bone marrow and epidermal cells.

Composite-tissue (e.g., hand allograft) allotransplantation is currently limited by the need for immunosuppression to prevent graft rejection. Inducing a state of tolerance in the recipient could potentially eliminate the need for immunosuppression but requires reprogramming of the immunological repertoire of the recipient. Skin is the most antigenic tissue in the body and is consistently refractory to tolerance induction regimens using bone marrow transplantation alone. It was hypothesized that tolerance to skin allografts could be induced in rats by injecting epidermal cells with bone marrow cells during the first 24 hours of life of the recipients. Brown Norway rats (RT1n) served as donors for the epidermal cells, bone marrow cells, and skin grafts. Epidermal cells were injected intraperitoneally and bone marrow cells were injected intravenously into Lewis (RT1l) newborn recipient rats. In control groups, recipients received saline solution with no cells (group I, n = 12), bone marrow cells only (group II, n = 15), or epidermal cells only (group III, n = 15). In the experimental group (group IV, n = 18), recipients received epidermal and bone marrow cells simultaneously. Skin grafts were transplanted from Brown Norway (RT1n) rats to the Lewis (RT1l) rats 8 weeks after cell injections. Skin grafts survived an average of 8.5 days in group I (10 grafts), 9.2 days in group II (12 grafts), and 12 days in group III (14 grafts). Grafts survived 15.5 days (8 to 26 days) in group IV (15 grafts). The difference was statistically significant (p < 0.05). Hair growth was observed in some accepted grafts in group IV but never in the control groups. This is the first report of prolonged survival of skin allografts in a rat model after epidermal and bone marrow cell injections. Survival prolongation was achieved across a major immunological barrier, without irradiation, myeloablation, or immunosuppression. It is concluded that the presentation of skin-specific antigens generated a temporary state of tolerance to the skin in the recipients that could have delayed the rejection of skin allografts.

Animals↗
PubMed2003

Cell-based bonding of articular cartilage: An extended study.

This study evaluated the biomechanical characteristics of newly formed cartilaginous tissue synthesized from isolated chondrocytes and seeded onto devitalized cartilage in an extended study in vivo. Cartilage from porcine articular joints was cut into regular discs and devitalized by multiple freeze-thaw cycles. Articular chondrocytes were enzymatically isolated and incubated in suspension culture in the presence of devitalized cartilage discs for 21 days. This procedure allowed the isolated chondrocytes to adhere to the devitalized matrix surfaces. Chondrocyte-matrix constructs were assembled with fibrin glue and implanted in dorsal subcutaneous pockets in nude mice for up to 8 months. Histological evaluation and biomechanical testing were performed to quantify the integration of cartilage pieces and the mechanical properties of the constructs over time. Histological analysis indicated that chondrocytes grown on devitalized cartilage discs produced new matrix that bonded and integrated individual cartilage elements with mechanically functional tissue. Biomechanical testing demonstrated a time dependent increase in tensile strength, failure strain, failure energy, and tensile modulus to values 5-30% of normal articular cartilage by 8 months in vivo. The values recorded at 4 months were not statistically different from those collected at the latest time point, indicating that the limits of the biomechanical property values were reached after four months from implantation.

Animals↗
PubMed2003

Split tolerance to a composite tissue allograft in a swine model.

BACKGROUND: The antigenicity of skin is a major obstacle to expanding human composite tissue transplantation. For example, multiple rejection episodes of the skin have been noted in clinical hand transplant patients. We have previously demonstrated tolerance to vascularized musculoskeletal allografts in major histocompatibility complex (MHC)-matched miniature swine treated with 12 days of cyclosporine. This regimen did not reproducibly lead to tolerance to subsequent frozen donor skin grafts. However, such skin grafts did not have a primary vascular supply. The aim of this study was to determine if tolerance to limb allografts with a vascularized skin component could be achieved with MHC matching and a 12-day course of immunosuppression. METHODS: Hind limb grafts harvested with a 100 cm(2) cutaneous paddle were transplanted heterotopically into six MHC-matched, minor antigen-mismatched miniature swine. All animals received a 12-day course of cyclosporine. One control animal was not immunosuppressed. Grafts were evaluated with biweekly biopsies and tissue viability determined by histologic analysis. To test for sensitization, frozen donor skin grafts were applied to all animals that survived to postoperative day 100. RESULTS: All treated animals (n=6) were tolerant to their musculoskeletal allografts at the time of necropsy (>100 days) regardless of the status of the epidermis. One animal demonstrated tolerance to the skin for more than 180 days. The other five animals demonstrated prolonged survival of the epidermal portion of the graft. The control animal rejected the graft epidermis at 10 days postoperatively. Frozen donor skin grafts demonstrated accelerated rejection (<10 days) in three of the animals and led to simultaneous rejection of both the epidermis of the allograft and the skin graft in the long-term tolerant animal. The rejection of the skin grafts did not break tolerance to the musculoskeletal portion in any of the animals. CONCLUSIONS: All animals exhibited indefinite survival of the musculoskeletal portion of their allografts but only prolonged survival of the epidermis. The loss of the graft skin appears to be the result of an isolated immune reaction to the skin, and, in particular, the epidermis. This observation is further substantiated by the accelerated rejection of secondarily placed frozen donor skin grafts.

Animals↗
PubMed2003

Tissue engineering of cartilage.

The primary goal of engineering cartilage as a therapeutic approach is to restore the physiological conditions of an affected or defective tissue in the body. Cartilage tissue is distributed widely in the human body and possesses an organization related to the specific demand of a particular anatomical region. In selecting the proper material for engineering cartilage, the functional demands of the replacement tissue must be considered. In summary, there is a multitude of scaffolds, naturally occurring and synthetic, that are suitable for engineering cartilage. Investigators have shown that the characteristics of the neocartilage differ significantly depending upon which scaffold is used. There are also large differences when a single scaffold is tested in vitro as opposed to in vivo. Moreover, the addition of other materials internally or externally to the cartilage composite influences the physical and biomechanical properties of the newly formed tissue. The results achieved so far are extremely encouraging and motivate further investigative efforts in the field. The biochemical composition and, more importantly, the biomechanical properties of the native tissue still represent the ideal replacement tissue.

Biocompatible Materials↗
PubMed2002

Recipient bone marrow engraftment in donor tissue after long-term tolerance to a composite tissue allograft.

BACKGROUND: An important component of a composite tissue limb allograft (CTA) is the vascularized bone marrow and bone marrow stroma, which when transplanted could create immediate marrow space and engraftment. We have previously demonstrated that tolerance to musculoskeletal allografts can be achieved with a 12-day course of cyclosporine without the presence of long-term peripheral donor cell chimerism. The objective of this study was to determine the fate of the donor bone marrow after transplantation of a limb allograft in a miniature swine model. METHODS: CTAs from donor swine were heterotopically transplanted into six MHC-matched, minor-antigen-mismatched recipients, and a 12-day course of cyclosporine was given. Previous animals transplanted without cyclosporine rejected their grafts in less than 42 days. A non-MHC-linked marker, pig allelic antigen (PAA), was used to distinguish host and donor cells. Three PAA- animals received PAA+ CTAs, and three PAA+ animals received PAA- CTAs. Bone marrow was harvested from the donor limb grafts and the recipient and analyzed by flow cytometry and histology. Thymus, spleen, and mesenteric lymph nodes were also harvested from the recipient swine and evaluated for the presence of donor cells by flow cytometry. RESULTS: All animals receiving cyclosporine demonstrated permanent tolerance to their allografts. Donor bone marrow cells were present in all grafts at the time of transplantation and during the immediate postoperative period. By 48 weeks, donor cells were no longer detectable within the marrow space of the allograft. In long-term animals host bone marrow cells replaced donor cells in the graft marrow space. No evidence of donor cell engraftment was found in recipient animals. CONCLUSION: This study demonstrates that in long-term tolerant recipients of musculoskeletal allografts there is no evidence of persistent donor bone marrow cells in the hematopoietic tissues of the graft or the host. Rather, the recipient's bone marrow cells and lymphocytes repopulate the donor marrow space of the graft.

Animals↗
PubMed2002

Histomorphometric analysis of a cell-based model of cartilage repair.

This study examined the morphology of chondrocytes in an established model of articular cartilage repair. Articular cartilage was harvested from young sheep and seeded onto pieces of devitalized sheep cartilage. The seeded pieces were stacked in pairs and wrapped in fibrin glue, and then implanted subcutaneously in the dorsum of athymic mice. Samples were harvested after 6 weeks and examined by transmission electron microscopy (TEM) or by light microscopy. TEM revealed that the cells in direct apposition to the devitalized cartilage were elongated, with an enlarged cytoplasm, and a ruffled border. TEM of cells far from the interface with scaffold tissue revealed rounded cells with large nuclei that appeared similar to normal chondrocytes. Quantitative morphometry of histologic specimens revealed that cell area, relative amount of cytoplasm, cell aspect ratio, and relative nuclear displacement were all higher in cells near the interface with the scaffold tissue, and decreased with distance from the interface. These indices of cell morphology are all consistent with an active remodeling of the scaffold at the cell-scaffold interface.

Animals↗
PubMedDate not supplied

Controlled degradation and mechanical behavior of photopolymerized hyaluronic acid networks.

Hyaluronic acid is a natural polysaccharide found abundantly throughout the body with many desirable properties for application as a biomaterial, including scaffolding for tissue engineering. In this work, hyaluronic acid with molecular weights ranging from 50 to 1100 kDa was modified with methacrylic anhydride and photopolymerized into networks with a wide range of physical properties. With macromer concentrations from 2 to 20 wt %, networks exhibited volumetric swelling ratios ranging from approximately 42 to 8, compressive moduli ranging from approximately 2 to over 100 kPa, and degradation times ranging from less than 1 day up to almost 38 days in the presence of 100 U/mL of hyaluronidase. When 3T3-fibroblasts were photoencapsulated in the hydrogels, cells remained viable with low macromer concentrations but decreased sequentially as the macromer concentration increased. Finally, auricular swine chondrocytes produced neocartilage when photoencapsulated in the hyaluronic acid networks. This work presents a next step toward the development of advanced in vivo curable biomaterials.

3T3 Cells↗
PubMedDate not supplied

Integrative repair of cartilage with articular and nonarticular chondrocytes.

Articular chondrocytes can synthesize new cartilaginous matrix in vivo that forms functional bonds with native cartilage. Other sources of chondrocytes may have a similar ability to form new cartilage with healing capacity. This study evaluates the ability of various chondrocyte sources to produce new cartilaginous matrix in vivo and to form functional bonds with native cartilage. Disks of articular cartilage and articular, auricular, and costal chondrocytes were harvested from swine. Articular, auricular, or costal chondrocytes suspended in fibrin glue (experimental), or fibrin glue alone (control), were placed between disks of articular cartilage, forming trilayer constructs, and implanted subcutaneously into nude mice for 6 and 12 weeks. Specimens were evaluated for neocartilage production and integration into native cartilage with histological and biomechanical analysis. New matrix was formed in all experimental samples, consisting mostly of neocartilage integrating with the cartilage disks. Control samples developed fibrous tissue without evidence of neocartilage. Ultimate tensile strength values for experimental samples were significantly increased (p < 0.05) from 6 to 12 weeks, and at 12 weeks they were significantly greater (p < 0.05) than those of controls. We conclude that articular, auricular, and costal chondrocytes have a similar ability to produce new cartilaginous matrix in vivo that forms mechanically functional bonds with native cartilage.

Animals↗
PubMedDate not supplied

Cell-based therapy for meniscal repair: a large animal study.

BACKGROUND: The avascular portion of the meniscus cartilage in the knee does not have the ability to repair spontaneously. HYPOTHESIS: Cell-based therapy is able to repair a lesion in the swine meniscus. STUDY DESIGN: Controlled laboratory study. METHODS: Sixteen Yorkshire pigs were divided into four groups. A longitudinal tear was produced in the avascular portion of the left medial meniscus of 4 pigs. Autologous chondrocytes were seeded onto devitalized allogenic meniscal slices and were secured inside the lesion with two sutures. Identical incisions were created in 12 other pigs, which were used as three separate control groups: 4 animals treated with an unseeded scaffold, 4 were simply sutured, and 4 were left untreated. Meniscal samples were collected after 9 weeks, and the samples were analyzed grossly, histologically, and histomorphometrically. RESULTS: Gross results showed bonding of the lesion margins in the specimens of the experimental group, whereas no repair was noted in any of the control group specimens. Histological and histomorphometrical analysis showed multiple areas of healing in the specimens of the experimental group. CONCLUSIONS: This study demonstrated the ability of seeded chondrocytes to heal a meniscal tear. CLINICAL RELEVANCE: Cell-based therapy could be a potential tool for avascular meniscus repair.

Animals↗