Collagen Mesh Research Articles

Grafting of Cultured Uroepithelium and Bladder Mucosa Into De-Epithelialized Segments of Colon in Rabbits

Urinary tract reconstruction using bowel can result in acid-base and electrolyte abnormalities. We tested the feasibility of grafting bladder mucosa and urothelial cells grown on a biodegradable polyglactin 910 scaffold onto de-epithelialized segments of bowel in the rabbit. A segment of de-epithelialized colon was either grafted with cultured urothelium on a collagen mesh scaffold (12 rabbits) or with free bladder mucosa (11 rabbits). In 10 rabbits that served as a control group another segment of bowel was isolated and de-epithelialized. No urothelial or bowel epithelial growth was present 4 weeks later in 10 of the isolated deepithelialized colonic segments grafted with the cultured urothelium. In 2 segments a minute focus of epithelium staining positively for anticytokeratin antibodies AE1 and AE3 was seen but this could not be histologically differentiated as either urothelium or native colonic epithelium. All 7 surviving animals that underwent a bladder mucosal graft had viable urothelium at sacrifice 30 days postoperatively. In 2 of the 7 rabbits microscopic nests of colonic epithelium were also found underneath the urothelial layer. Of the 7 internal controls 6 had no evidence of bowel epithelial regrowth 4 weeks after deepithelialization.This study demonstrated that a confluent layer of urothelial cells could be grown in culture using a scaffold of biodegradable mesh and rat tail collagen. We also showed that bladder mucosal grafts can be grown on de-epithelialized bowel segments. We were unable to graft successfully cultured urothelial cells onto a de-epithelialized bowel segment. Further improvement in understanding the role of the submucosal matrix in cell growth may lead to future success in covering large segments of de-epithelialized bowel with autologous urothelium.

Deposition of cement at reversal lines in rat femoral bone.

Femora from young adult Wistar rats were prepared for both light and electron microscopy. Routinely processed wax sections showed the appearance of cement lines immediately proximal to the resorption surface formed by active osteoclasts and distal to the onset of lamella formation in femoral bone tissue. This early stage of extracellular matrix elaboration at reversal lines was then studied by scanning electron microscopy (SEM) of actively remodeling sites, mainly on trabecular and endosteal surfaces. The resorption surface was shown to comprise a decalcified collagenous mat with individual fibers running either parallel or perpendicular to the surface plane. By examining different, neighboring, areas of resorption lacunae, a temporal sequence of new extracellular matrix production could be established. Before the deposition of new collagen, globular accretions were deposited onto the resorption surface. In areas where individual collagen fibers were oriented perpendicular to the surface plane, this globular matrix was initially deposited on the exposed fiber tips. The globules increased in size and fused laterally to form a continuous cement layer, which not only interdigitated with the collagen mesh of the resorption surface but also provided anchorage for new collagen fibers, which themselves became mineralized. These morphologic results provide a mechanistic explanation of coupling at reversal lines.

Effect of interconnecting collagen fibres on left ventricular function and intramyocardial compression.

The aim was to study the effects of the collagen mesh that interconnects the myocardial fibres on left ventricular mechanics and intramyocardial pressure. An earlier model which integrates a symmetrical left ventricular geometry and transmural muscle fibre structure with muscle fibre mechanics was expanded to include radial stiffness generated by dynamically stretched radial collagen fibres. The calculated end systolic pressure-volume relationship (ESPVR) was compared to left ventricular pressure and volume data from six open chest dogs, obtained over a wide load range. Midwall intramyocardial pressure measurements by flat intramyocardial transducer in six different dogs were also used. Consistent with the experiments, inclusion of radial stiffness yielded an ESPVR that was more curvilinear than the collagen-free model, and modified global left ventricular function in that the end systolic volume increased. A diastolic suction effect, manifested by a negative pressure with a steep diastolic pressure-volume relationship at low end systolic volumes, was predicted. The intramyocardial pressure was higher than the left ventricular pressure at the end of isovolumetric relaxation, when radial stretch is maximal and fibre stresses are relaxed. This is attributed to the radial fibre stress component. Intramyocardial pressure was only weakly dependent on left ventricular cavity pressure under wide load manipulations at constant contractility. The experiments also confirmed model predictions that (1) peak intramyocardial pressure is insensitive to load, (2) intramyocardial pressure is markedly higher than left ventricular pressure at the end of isovolumetric relaxation, and (3) intramyocardial pressure continues to rise during ejection towards a maximum value near end ejection. The transverse radial stiffness due to radial collagen interconnections between myocardial fibrils affects the global systolic left ventricular function, the diastolic suction effect, and the mechanism of systolic coronary compression.

Myocardial mechanics and coronary flow dynamics.

The interaction between cardiac mechanics and coronary flow is highlighted here. Left ventricular (LV) structure and geometry are related to coronary flow dynamics and used in the analysis of experimental coronary flow data. The important role of the collagen mesh in the generation of the intramyocardial pressure (IMP), the pressure in the interstitial fluid, at a wide range of loading conditions is emphasized. The calculated IMP, based on a structural model of the LV myocardium, can explain most of the observed coronary compression characteristics under a variety of loading and contractility conditions. A more general compression function, the extravascular compressive pressure (ECP), is suggested to define coronary compression and is presented here based on the dynamics of the coronary inflow under constant perfusion conditions. Coronary compression is shown to be affected by fluid transport and the bi-directional coupling of coronary hemodynamics and IMP dynamics.

The development of a novel implant: induction of a non-rigid and self-renewing anchorage of artificial implants to bone

Artificial implants currently used in orthopaedic surgery and dentistry are anchored to the surrounding bone by rigid mechanical fixation. Long-term studies indicate that the rate of implant failure due to loosening increases steeply after 10 years of function. The loosening is attributed to the micro-movements occurring at the bone implant interface. Non-rigid, self-renewing ligamentous anchorage is nature's solution to the problem of micro-movements. An excellent example of this type of anchorage is the tooth-bone system, where the tooth is anchored to the bone by a fibrous connective tissue. A novel artificial implant, bearing on its surface a unique biological substrate (BS), was designed to induce a ligamentous anchorage of implant to bone. The implant consists of a metallic core to which the BS is bound. The BS is a composite of plastic material and a collagen mesh which is partly incorporated into the plastic material and partly freely extended from its outer surface as artificial Sharpey's fibers. BS fabrication did not affect the capacity of the collagen to withstand non-specific degradation in vitro. Non-weight-bearing implants implanted into the femoral bone of rats induced and maintained a ligament-like tissue up to 4 months. The collagen fibers of the ligament-like tissue were spliced with the artificial BS Sharpey's fibers and were also anchored as Sharpey's fibers into the surrounding bone. Examination of control plastic implants (without the BS) revealed bone formation in close approximation to the implant surface. It is suggested that the novel biological substrate has the capacity to induce and maintain a ligament-like anchorage of implant to bone.

The effects of selective matrix degradation on the short-term compressive properties of adult human articular cartilage

The effects of proteoglycan and collagen digestion on the transient response of human articular cartilage when tested in unconfined compression were determined. Small cylindrical specimens of cartilage, isolated from the femoral head of the hip joint and from the femoral condyles of the knee joint, were subjected to a suddenly applied compressive load using a test apparatus designed to yield a transient oscillatory response. From this response values of the elastic stiffness and the viscous damping coefficient were determined. Cathepsin D and cathepsin B 1 were used to digest the proteoglycan in some specimens, while in other specimens leukocyte elastase was used to attack the non-helical terminal regions of the Type II tropocollagen molecules and possibly the Type IX collagen molecule and thereby disturb the integrity of the collagen mesh. The results showed that proteoglycan digestion alone reduced the viscous damping coefficient but it did not significantly alter the elastic stiffness as determined from the oscillatory response. In contrast, the action of elastase reduced both the damping coefficient and the elastic stiffness of the cartilage. The results demonstrated the role of proteoglycans in regulating fluid transport in cartilage and hence controlling the time-dependent viscous properties. The elastic stiffness was shown to be dependent on the integrity of the collagen fibre network and not on the proteoglycans.

Estudo micro-mesoscópico das granulações aracnóides humanas

The functional anatomy of the arachnoid granulations of the upper sagittal sinus was studied by means of micromesoscopic techniques in order to contribute to elucidating aspects of drainage pathways of the cerebrospinal fluid through their fibrous components. The arrangement of fibrous elements was analysed at the base of the peduncle, peduncle, middle and apex of granulation. The analysis of serial sections shows collagen bundles at the base of the peduncle with a predominantly circular morphology, longitudinally directed towards the peduncle's longest axis. These bundles arise in the middle of the granulation, them branch off towards its apex and periphery. The elastic bundles present an arrangement similar to that described for collagen bundles, delimiting with such bundles intercommunication channels from the base of the peduncle up to the apex of the granulation. Bundles of reticular fibers arranged in between the collagen meshes were found at the base of the peduncle. The fibrous capsule of granulation is composed of collagen bundles and a small number of elastic fibers.

Degradation of metal-labeled collagen implants: Ultrastructural and X-ray microanalysis

Three different metal salts, silver nitrate, uranyl acetate and lead citrate, are mixed with a collagen gel to produce 3 metal/collagen sponges. These sponges were implanted subcutaneously in the rat and samples harvested after 5 days of implantation. TEM observation shows that sponges are degraded and digested by macrophages, polymorphonuclear cells (PMN) and fibroblasts. We have observed that the location of the precipitates differs according to the metal added to the collagen. Lead precipitates stay longer on the collagen mesh while silver precipitates, after 5 days, are soon digested and are found in phagosomes of macrophages. Uranium precipitates are digested with the collagen and uranium/collagen associated pictures are seen in phagolysosomes. Metal precipitates accumulated in phagolysosomes of macrophagic cells are recognized by X-ray microanalysis. The degradation process of implanted collagen is discussed.

The use of a biodegradable collagen/vicryl composite membrane to repair partial nephrectomy in rabbits.

A composite membrane produced from collagen and vicryl mesh has been used to cover the kidney surface following partial nephrectomy in rabbits. The membrane readily held sutures, gave satisfactory haemostasis, and prevented leakage of urine. The experiments showed that the prosthesis biodegraded in less than twenty weeks. The only observed long-term effect of the material was thickening of the renal capsule. The results indicate that this membrane may be a suitable reparative material for use in traumatised kidneys in humans.

Morphological effects of gas compression on the cortical vitreous.

We used scanning electron microscopy to study vitreous in normal and perfluorocarbon gas-treated eyes of cynomolgus monkeys. The cortical vitreous of the normal (control) eye appeared to be a lamellar structure composed of sheets of collagen mesh. In the gas-treated eye there was shrinking and tearing of the lamellae. At six and 12 weeks after gas injection there was membrane formation at the edges of the torn lamellae.

Influence of cartilage particle size and proteoglycan aggregation on immobilization of proteoglycans.

Mechanisms by which proteoglycan aggregates are retained within cartilage were studied using two approaches: mechanical fragmentation of cartilage and reassociation of proteoglycans within extracted cartilage. The extractability of proteoglycans from fresh bovine nasal cartilage with low ionic strength buffer was found to vary from 13 to 45% depending upon the degree of cartilage fragmentation. Forty per cent of those extracted from finely fragmented cartilage (5-20-mu diameter) were found to be in aggregates which contained "link" proteins. A method was developed to reintroduce proteoglycans, which had been extracted with guanidine hydrochloride, into cartilage from which they had been extracted. Stability of the newly formed associations was assessed by re-extraction with a guanidine hydrochloride gradient. Purified proteoglycans alone or reduced and alkylated proteoglycans formed associations which were disrupted with less than 2 M guanidine hydrochloride. Addition of "link" proteins resulted in associations which required 2-4 M guanidine hydrochloride to be re-extracted. Association of proteoglycans into Sepharose 4B particles gave extraction patterns similar to reassociation into extracted cartilage. These findings are consistent with the hypothesis that proteoglycans are immobilized within cartilage through the formation of aggregates and suggest that retention is dependent upon the integrity of the collagen mesh.

Collagen mesh prosthesis for repair of endopelvic fascial defects

Reconstituted collagen mesh fabric has been used in gynecological surgery as a substitute for endopelvic fascia in colporrhaphy, and for ligamentous support in posthysterectomy vaginal vault prolapse. The 4 cases are detailed. Absence of complications in this small preliminary series is noted. There were good functional and anatomic results seen in follow-up intervals of up to 49 months.