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Biomedical subjects

M A Randolph

Publications and source records attributed to M A Randolph.

At least 37 records · Page 2Linked to original sources
PubMed1999

Biomechanical analysis of a chondrocyte-based repair model of articular cartilage.

The objective of this study was to evaluate the biomechanical properties of newly formed cartilaginous tissue synthesized from isolated chondrocytes. Cartilage from articular joints of lambs was either digested in collagenase to isolated chondrocytes or cut into discs that were devitalized by multiple freeze-thaw cycles. Isolated cells were incubated in suspension culture in the presence of devitalized cartilage matrix for 3 weeks. Multiple chondrocyte/matrix constructs were assembled with fibrin glue and implanted subcutaneously in nude mice for up to 6 weeks. Testing methods were devised to quantify integration of cartilage pieces and mechanical properties of constructs. These studies showed monotonic increase with time in tensile strength, fracture strain, fracture energy, and tensile modulus to values 5-10% of normal articular cartilage by 6 weeks in vivo. Histological analysis indicated that chondrocytes grown on dead cartilage matrix produced new matrix that integrated individual cartilage pieces with mechanically functional tissue.

Animals↗
PubMed1999

Transdermal photopolymerized adhesive for seroma prevention.

The purpose of this study was to determine whether or not a synthetic photopolymerized tissue adhesive (polyethylene oxide hydrogel) is useful in seroma prevention using a well established rat mastectomy seroma model. Twenty-three Sprague-Dawley rats received mastectomies. The rats were randomly assigned to either the control group (n = 13) or the experimental group (n = 10). The control animals received 0.2 cc of saline into the wound before closure. The experimental group received either 0.2 cc (n = 5) or 0.4 cc (n = 5) of the polyethylene oxide polymer into their wounds before closure. The experimental animals were placed under an ultraviolet A lamp for 3 minutes to polymerize the adhesive. On postoperative day seven, the resultant seromas were quantified, and wound tissues were harvested for histologic evaluation. The rats in the control group had a mean seroma volume of 3.25 cc (SD = 2.41), whereas the rats treated with polymer had a mean seroma volume of 0.37 cc (SD = 0.51). A Student's t test was performed showing a statistically significant difference between the control and experimental groups (p < 0.005). The volume of polymer used (0.2 cc versus 0.4 cc) did not significantly impact the volume of the resultant seromas. This study demonstrates that photopolymerizable polyethylene oxide hydrogels can be used as a tissue adhesive and that such an adhesive significantly reduces seroma formation in the rat mastectomy model.

Animals↗
PubMed1999

Injectable tissue-engineered cartilage using a fibrin glue polymer.

The purpose of this study was to demonstrate the feasibility of using a fibrin glue polymer to produce injectable tissue-engineered cartilage and to determine the optimal fibrinogen and chondrocyte concentrations required to produce solid, homogeneous cartilage. The most favorable fibrinogen concentration was determined by measuring the rate of degradation of fibrin glue using varying concentrations of purified porcine fibrinogen. The fibrinogen was mixed with thrombin (50 U/cc in 40 mM calcium chloride) to produce fibrin glue. Swine chondrocytes were then suspended in the fibrinogen before the addition of thrombin. The chondrocyte/polymer constructs were injected into the subcutaneous tissue of nude mice using chondrocyte concentrations of 10, 25, and 40 million chondrocytes/cc of polymer (0.4-cc injections). At 6 and 12 weeks, the neocartilage was harvested and analyzed by histology, mass, glycosaminoglycan content, DNA content, and collagen type II content. Control groups consisted of nude mice injected with fibrin glue alone (without chondrocytes) and a separate group injected with chondrocytes suspended in saline only (40 million cells/cc in saline; 0.4-cc injections). The fibrinogen concentration with the most favorable rate of degradation was 80 mg/cc. Histologic analysis of the neocartilage showed solid, homogeneous cartilage when using 40 million chondrocytes/cc, both at 6 and 12 weeks. The 10 and 25 million chondrocytes/cc samples showed areas of cartilage separated by areas of remnant fibrin glue. The mass of the samples ranged from 0.07 to 0.12 g at 6 weeks and decreased only slightly by week 12. The glycosaminoglycan content ranged from 2.3 to 9.4 percent for all samples; normal cartilage controls had a content of 7.0 percent. DNA content ranged from 0.63 to 1.4 percent for all samples, with normal pig cartilage having a mean DNA content of 0.285 percent. The samples of fibrin glue alone produced no cartilage, and the chondrocytes alone produced neocartilage samples with a significantly smaller mass (0.47 g at 6 weeks and 0.46 g at 12 weeks) when compared with all samples produced from chondrocytes suspended in fibrin glue (p < 0.03). Gel electrophoreses demonstrated the presence of type II collagen in all sample groups. This study demonstrates that fibrin glue is a suitable polymer for the formation of injectable tissue-engineered cartilage in the nude mouse model. Forty million chondrocytes per cc yielded the best quality cartilage at 6 and 12 weeks when analyzed by histology and content of DNA, glycosaminoglycan, and type II collagen.

Animals↗
PubMed1999

A comparative study of nerve healing in adult, neonatal, and fetal rabbits.

This experiment quantitatively compared the human equivalent of a nerve repair following surgical division in the fetal, adult, and early childhood period of development using a rabbit as an experimental animal model. Twelve time-dated pregnant New Zealand White rabbits at 24 days' gestation (term = 31 days) underwent hysterotomy; one hind limb was delivered through the uterine opening. The sciatic nerve was divided and repaired by primary neurorrhaphy using two 11-0 epineural sutures. Sciatic nerve repair was also performed in 10 neonatal and 10 adult New Zealand White rabbits. Following repair, each group was assessed using electromyography examination, measuring distal motor latency and amplitude at 1, 2, 3, and 4 months postrepair. There was no difference in any of the groups in distal motor latency. The amplitude rose incrementally in all groups, and the fetal group had significantly higher amplitudes (p < 0.02) at 1, 2, 3, and 4 months in comparison with the adult group. There was no statistically significant difference between fetal and neonatal nerve repairs at any of the time periods. At the completion of the study, the nerve repair sites were harvested for histologic estimation of mean myelinated fiber density and fiber diameter distribution distal and proximal to the repair site. A greater percentage of myelinated axons crossed the repair site in the fetal group (83 percent) in comparison with the adult group (63 percent) (p < 0.03). Our study also demonstrated significant increases in the number of larger myelinated fibers crossing the repair site in comparison with the neonatal and adult groups (p < 0.04). This study found that fetal nerve healing following surgical repair is superior to that found in adult animals and results in a higher number of larger myelinated fibers crossing the repair site in comparison with adult and neonatal repairs.

Aging↗
PubMed1998

Bonding of cartilage matrices with cultured chondrocytes: an experimental model.

The capacity of isolated chondrocytes to join separate masses of cartilage matrix was investigated with composites implanted in subcutaneous pouches in nude mice. Slices of articular cartilage were harvested from lambs and were devitalized by cyclic freezing and thawing. The slices were then either co-cultured with viable allogeneic lamb chondrocytes (experimental) or cultured without such chondrocytes (control). Composites of three slices were constructed with use of fibrin glue and were implanted in nude mice for periods ranging from 7 to 42 days. Bonding of the experimental matrices with viable chondrocytes was achieved at 28 and 42 days, as assessed by direct examination, histology, thymidine uptake, and fluorescence. No bonding occurred in the control composites without viable chondrocytes. We conclude that devitalized cartilage matrix is a scaffold to which isolated chondrocytes can attach and begin to repopulate.

Animals↗
PubMed1998

Use of swine model in transplantation of vascularized skeletal tissue allografts.

Permanent tolerance to vascularized skeletal tissue allografts can be induced in miniature swine with minor antigen differences using a 12-day course of CsA. Demonstration of skeletal tissue allograft survival in a large animal model without long-term immunosuppression represents an important step toward transplantation of skeletal tissue allografts in humans.

Anastomosis, Surgical↗
PubMed1998

Tissue engineered neocartilage using plasma derived polymer substrates and chondrocytes.

This study demonstrates that fibrin monomers can be polymerized into moldable gels and used for the encapsulation of isolated chondrocytes. This biologically derived scaffold will maintain three-dimensional spatial support, allowing new tissue development in a subcutaneous space. Chondrocytes isolated from the glenohumeral and humeroradioulnar joints of a calf were combined with cyroprecipitate and polymerized with bovine thrombin to create a fibrin glue gel with a final cell density of 12.5 x 10(6) cells/ml. The polymer-chondrocyte constructs were implanted subcutaneously in 12 nude mice and incubated for 6 and 12 weeks in vivo. Histologic and biochemical analysis including deoxyribonucleic acid (DNA) and glycosaminoglycan quantitation confirmed the presence of actively proliferating chondrocytes with production of a well-formed cartilaginous matrix in the transplanted samples. Control specimens from 12 implantation sites consisting of chondrocytes alone or fibrin glue substrates did not demonstrate any gross or histologic evidence of neocartilage formation. Moldable autogenous fibrin glue polymer systems have a potential to serve as alternatives to current proprietary polymer systems used for tissue engineering cartilage as well as autogenous grafts and alloplastic materials used for facial skeletal and soft-tissue augmentation.

Animals↗
PubMed1998

Monoclonal antibody to intercellular adhesion molecule 1 protects skin flaps against ischemia-reperfusion injury: an experimental study in rats.

The purpose of this study was to evaluate the blockage of polymorphonuclear neutrophil endothelial adhesion by using a monoclonal antibody to the intercellular adhesion molecule 1 (ICAM-1) ligand to prevent ischemia-reperfusion injury in rat skin flaps. A skin and subcutaneous tissue flap (3.0 cm x 4.5 cm) supplied by the superficial epigastric artery and vein including the femoral vessels was isolated unilaterally in 45 male Sprague-Dawley rats and clamped for 9 hours (groups II and III) or 12 hours (groups IV and V) of ischemia. Five animals in group I were sham-operated only with 5 minutes of ischemia. Animals in groups II (n = 10) and IV (n = 10) received 0.05 mg of monoclonal antibody to ICAM-1 (0.20 mg/kg) in 0.5 ml of 0.9% normal saline intravenously 15 minutes before reperfusion; those in groups III (n = 10) and V (n = 10) received 0.5 ml of normal saline. The flaps were assessed histologically, by measuring viable and nonviable areas, and by diffuse reflectance spectroscopy to determine the ratio of oxyhemoglobin to deoxyhemoglobin. Flap measurements revealed that the average area of flap survival was 90.6 +/- 12.8 percent in group II and 18.3 +/- 19.6 percent in the control group (III) (p < 0.002). In the animals subjected to 12 hours of ischemia, those treated with monoclonal antibody to ICAM-1 (group IV) were 57.1 +/- 23.1 percent viable, which was significantly greater than the control animals (group V), in which only 0.3 +/- 1.0 percent of the flap was viable. Analysis of the diffuse reflectance spectra showed a hyperemic response during the first 10 minutes after reperfusion in animals treated with monoclonal antibody to ICAM-1. In group III, however, the spectra demonstrated a decreased amount of oxyhemoglobin, indicating decreased reperfusion of the flap after ischemia when compared with group II. Histopathologically, few inflammatory changes could be observed in groups I, II, and the viable areas of group IV. Marked damage was observed in groups III and V. We concluded that treating ischemic skin flaps with monoclonal antibody to ICAM-1 was effective for alleviating reperfusion injury after 9 or 12 hours of warm ischemia. The reactive hyperemic response determined by diffuse reflectance spectroscopy in groups II and IV correlated with areas of flap survival. Antibodies to particular adhesion molecules, such as ICAM-1, have potential clinical utility in that they could be administered, individually or together, to patients immediately before reestablishing perfusion after free-tissue transfer or replantation to block the adverse effects attributed to reperfusion injury.

Animals↗
PubMed1998

Cell transplantation from limb allografts.

A murine model of skeletal tissue transplantation was developed to study the allograft rejection process in mice for limb allograft transplantation. Muscle, bone, and skin have been shown to be strong antigenic stimuli in vascularized allograft models, and cells from these sources were used for transplantation. Using enzymatic digestion, keratinocytes, myocytes, and osteocytes were harvested from B10.A mice tissues, dissociated into single cells, and then grown in culture for 14 to 21 days. Each cell type was marked with an intracellular fluorescent marker before transplantation of the cells into pockets in the rectus abdominis muscle of a syngenic host. All cell types remained viable and were detectable 2 weeks following transplantation when examined histologically and observed under a fluorescent microscope. Transplanted osteocytes were found to produce bone 8 weeks following transplantation. These results demonstrate that individual cells transplanted into muscle pockets survive and have the ability to produce extracellular matrix in this mouse model of skeletal tissue transplantation. Use of this model will allow transplantation of the cellular components comprising limb allografts to study the relative antigenicities and the rejection of the separate cells with the advanced immunologic techniques available for mice. A better understanding of immunologic responses to these individual tissue components may enable specific donor tissue or host immune modification to achieve skeletal tissue transplantation without immunosuppression. These findings are particularly valuable to the field of tissue engineering where allogeneic cells may be used in cell/polymer constructs for reconstructive procedures.

Animals↗
PubMed1997

Craniofacial skeletal fixation using biodegradable plates and cyanoacrylate glue.

This study examined the feasibility of fixation of craniofacial bone using Lactosorb biodegradable plates adhered to bone with butyl-2-cyanoacrylate adhesive (Histoacryl) in a pig. The stability and bone-healing characteristics of this rigid fixation method were studied and compared with standard rigid fixation using metal plates and screws on osteotomy sites in the frontal bones and infraorbital rims. Rectangular osteotomies (2.0 x 3.0 cm) were performed on the right and left sides of the frontal bone and wedge-shaped osteotomies (1.5 x 1.7 cm) were made on the left and right infraorbital rims in seven Yorkshire pigs. Metal plates were applied with screws to the osteotomies on one side, and the other side was fixed with a biodegradable plate and butyl-2-cyanoacrylate. The animals were sacrificed at 8 weeks, and both sides were compared biomechanically and histologically. Radiographic, biomechanical, and histologic analyses were performed to evaluate skeletal stability, contour, accurate positioning of bony fragments, bone healing, and maximum torque to failure of the repair sites. Clinical and radiographic observations demonstrated stability of the bone fragments without any evidence of displacement. According to Student's t test for paired data, no statistical difference was found in the maximum torque to failure of fragments fixed with biodegradable plates and glue compared with those fixed with metal plates and screws (p > 0.05), whether or not a gap existed at the osteosynthesis site. Although the sample size was small, no differences were noted between the two types of treatment groups. This study demonstrates that rigid internal fixation of osteotomized cranial bone fragments using biodegradable plates and butyl-2-cyanoacrylate is as effective as metal plate and screw fixation in this animal model.

Animals↗
PubMed1996

Surgical model to assess the effects and optimal timing of craniofacial fixation.

An in utero swine model of craniofacial deformity was developed as a potential alternative to neonatal models currently used for evaluating the optimal timing and long-term effects of rigid fixation techniques on a growing cranium. At 75% gestation, seven fetal piglets were randomly selected to undergo periosteal stripping of frontal and parietal bone segments with and without extensive coronal suture fusion procedures with cyanoacrylate adhesive. Fetal swine were killed postpartum at 4 and 11 weeks after fusion to assess craniofacial deformity. Piglets undergoing coronal fusion had slight deviation of the nose-snout toward the side of fusion and taller cranial vaults. The vertical cranial index of the experimental fusion group was 0.34 in comparison to a vertical index of 0.27 for the controls, suggesting abnormal vertical height expansion. There was no difference in the horizontal cranial index of either control or experimental fusion groups. Neither sows nor piglets were lost to anesthetic complications, uterine sepsis, or preterm labor during the initial laparotomy or subsequent cesarean delivery.

Animals↗
PubMed1996

Injectable cartilage using polyethylene oxide polymer substrates.

This study demonstrates that polyethylene oxide gels, which are biocompatible and biodegradable synthetic polymers, can be utilized for the encapsulation of isolated chondrocytes and maintenance of three-dimensional spatial support for new tissue development. Chondrocytes isolated from the glenohumeral and humeroradioulnar joints of a calf were added to a 20% polyethylene oxide solution in Ham's F-12 medium to generate a final cellular density of 10 x 10(6)/mL. The polymer-chondrocyte constructs were injected through a 22-gauge needle in 500-microliters aliquots subcutaneously in 12 nude mice and incubated for 6 and 12 weeks in vivo. Histologic and biochemical analyses including deoxyribonucleic acid and glycosaminoglycan quantitative analyses confirmed the presence of actively proliferating chondrocytes with production of a well-formed cartilaginous matrix in the transplanted samples. Control specimens from eight implantation sites consisting of chondrocytes alone or polyethylene oxide substrates did not demonstrate any gross or histologic evidence of neocartilage formation. These findings demonstrate the potential use of an injectable and moldable polymer substrate that can support cell proliferation and matrix synthesis after subcutaneous transplantation for neocartilage generation. The use of functional biologic tissue substitutes may serve as an alternative solution to current methods of augmentation or reconstruction of structural craniofacial contour deformities.

Animals↗
PubMed1995

Prolonged survival of vascularized limb tissue allografts by donor irradiation.

The clinical feasibility of transplantation of a vascularized limb tissue allograft depends upon reducing immunosuppression and its associated toxicity for the graft recipient. Donor or allograft irradiation would eradicate allogeneic marrow and provide a possible alternative or beneficial addition to host immunosuppression. The effect of irradiation on survival of limb tissue allograft was investigated in this study. In a rat model, knee allografts consisting of bone, cartilage, and soft tissues were transplanted across a strong histocompatibility barrier by femoral vascular microanastomoses. The grafts were harvested 1 and 2 weeks postoperatively for histologic and immunologic assays. Gamma irradiation of the graft immediately before transplant decreased graft rejection slightly. However, total body irradiation of the donor followed by a "waiting period" of 2 or more days before transplant significantly delayed rejection. After such a 6-day and a 2-day pretreatment protocol, the host cellular immune responses were not observed 1 and 2 weeks after transplantation and eventual progression toward graft rejection coincided with emergence of host antibody production. Rejection of vascularized limb tissue allografts after donor irradiation thus appeared to be mediated primarily through the humoral pathway. We conclude that donor irradiation is a potentially useful adjunct in prolonging survival of vascularized limb tissue allografts.

Animals↗
PubMed1995

Augmented Becker versus modified Kessler tenorrhaphy in monkeys: dynamic mechanical analysis.

The strength and gliding efficiency of an augmented Becker and Kessler tendon repair techniques were compared in fresh cadaver macaque monkey hands. Gliding efficiency was determined by comparing tendon work and load measurements made during tendon excursion to full fist with the same measurements made after tendon repair. Repair strength was then determined by tendon distraction to complete repair rupture. Data were gathered by computer controlled tensiometer and analyzed by factorial and repeated measures ANOVA. The augmented Becker repairs were significantly stronger than Kessler repairs. Repaired tendons required more load and work to bring the fingers into full fist; both repair types resulted in gliding efficiencies of 30% compared to intact controls. The augmented Becker repair is significantly stronger in situ than the modified Kessler and is recommended when early postoperative motion regimens are planned.

Analysis of Variance↗
PubMed1995

Experimental orthotopic transplantation of vascularized skeletal allografts: functional assessment and long-term survival.

Vascularized skeletal tissue allografts would greatly expand the domain of reconstructive surgery. Few studies to date have examined the functional aspects of these allografts or their long-term fate. An orthotopic transplant model of rat distal femur and surrounding muscular cuff was developed to assess graft function in fracture healing and weight bearing. Isografts (RT1l to RT1l, n = 40), weak-barrier allografts (RT1l to RT1lv, n = 40), and strong-barrier allografts (RT1l to RT1n, n = 40) were transplanted. As the histocompatibility barrier increased between the donor and recipient animals, the graft viability and performance deteriorated according to radiographic, histologic, and immunologic analyses. Administration of cyclosporine led to survival of strong-barrier allografts similar to that of isografts. A long-term study of these allografts (RT1l to RT1n) was then performed on various immunosuppressive regimens. After an initial 10-week course of cyclosporine to achieve bony union and remodeling, subsequent cessation (n = 20) or intermittent "pulsing" (n = 20) of the immunosuppressant was insufficient in maintaining graft survival. However, graft viability and function were preserved through 1 year on continuous daily cyclosporine (n = 32). There was no evidence of host renal or hepatic toxicity by serum chemistry or histologic sections. Thus long-term survival of functional skeletal allografts was achieved in this orthotopic model without significant host toxicity from immunosuppression.

Animals↗
PubMed1992

Vascularized growth-plate transplantation: a comparative study in the rat.

The purpose of this study was to evaluate the influence of hormonal milieu on endochondral growth. This was achieved by transplanting hind limbs of juvenile rats to syngeneic adult rats. Because there is no potential for rejection, the limb can be transplanted between animals of different ages, to study the influence of hormonal maturity on stimulation and cessation of physeal growth and maturation. Tibial length and the histologic appearance of the physis were recorded. Whole vascularized hind-limb transplantation in syngeneic Lewis rats was used. Group 1: Thirty-five transplants between animals of the same age (three weeks old) were performed (isochronografts). Group 2: In 35 procedures, the age of the donor was three weeks old and of the recipient, 15 weeks (heterochronografts). In the first two study groups, the transplanted limb was placed on the dorsal flank of the recipient animal without nerve reconstruction. Controls were the contralateral hind limb of the donor animal. Because the limb was transplanted with loss of femoral and sciatic nerve supply to the dorsal flank position, the effects of denervation and lack of weight bearing were also evaluated. Group 3: Thirty-five limbs in three-week-old animals were transposed to the dorsal flank position, after severing the femoral and sciatic nerves. Analysis of variance of tibial length was used to compare study groups. Limbs transplanted to older animals (heterochronografts--Group 2) achieved the greatest length, 91 percent of normal, and significantly more when compared to Groups 1 (84 percent) and 3 (83 percent) (p less than .005). Growth of the limb was adversely affected by limb position and denervation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Relative antigenicity of components of a vascularized limb allograft.

At present, the transplantation of vascularized limb-tissue allografts can be achieved only with generalized host immunosuppression, which results in significant systemic toxicity, thereby precluding their clinical use. A better understanding of the immunogenic mechanisms of these allografts may permit less toxic and thus clinically applicable means of host immunosuppression. In this study, individual vascularized limb tissues (skin, subcutaneous tissue, muscle, bone, and blood vessels) and a whole limb were transplanted microsurgically across a strong histocompatibility barrier in rats. The respective cell-mediated and humoral immune responses generated in the hosts were determined by means of mixed lymphocyte cultures by radioactive 51Cr release assays and compared. No single tissue predominated in the elicited immune response. Rather, the various tissue components interacted with the host immune system in a complex but predictable pattern with differing timing and intensity. Surprisingly, the whole-limb allograft elicited less immune response than did allografts of its individual components. The data presented here also serve as a foundation for further elucidation of the immunogenic mechanisms of vascularized limb-tissue allografts.

Animals↗