Eh Blaauw

Poly(DL-lactide-epsilon-caprolactone) nerve guides perform better than autologous nerve grafts.

The aim of this study was to compare the speed and quality of nerve regeneration after reconstruction using a biodegradable nerve guide or an autologous nerve graft. We evaluated nerve regeneration using light microscopy, transmission electron microscopy and morphometric analysis. Nerve regeneration across a short nerve gap, after reconstruction using a biodegradable nerve guide, is faster and qualitatively better, when compared with nerve reconstruction using an autologous nerve graft. Therefore, we conclude that in the case of a short nerve gap (1 cm), reconstruction should be carried out using a biodegradable nerve guide constructed of a copolymer of DL‐lactide and ϵ‐caprolactone.

Electronmicroscopical evaluation of short-term nerve regeneration through a thin-walled biodegradable poly(DLLA-epsilon-CL) nerve guide filled with modified denatured muscle tissue.

The aim of this study was to evaluate short-term peripheral nerve regeneration across a 15-mm gap in the sciatic nerve of the rat, using a thin-walled biodegradable poly(DL-lactide-epsilon-caprolactone) nerve guide filled with modified denatured muscle tissue (MDMT). The evaluation was performed using transmission electron microscopy and morphometric analysis. Evaluation times ranged from 3 to 12 weeks after reconstruction. Already, 3 weeks after reconstruction, myelinated nerve fibers could be observed in the distal nerve stump. Twelve weeks after reconstruction, the number of (non)myelinated nerve fibers had significantly increased in the distal nerve stump. From this study, we can conclude that a thin-walled biodegradable poly(DL-lactide-epsilon-caprolactone) nerve guides filled with MDMT can be successfully applied in the reconstruction of severed nerves in the rat model. Furthermore, we showed fast nerve regeneration across the 15-mm nerve gap and found that the use of MDMT functioned as a mechanical support preventing a collapse of this thin-walled nerve guide.

Modulation of the tissue reaction to biomaterials. II. The function of T cells in the inflammatory reaction to crosslinked collagen implanted in T‐cell–deficient rats

Unwanted tissue reactions are often observed resulting in events such as early resorption of the biomaterial, loosening of the implant, or a chronic (immunologic) response. From immunologic studies it is known that inflammatory reactions can be modulated by use of (anti)-growth factors or anti-inflammatory drugs. Before this can be employed with respect to biomaterials, the role of individual factors (humoral and cellular) has to be studied. In this part of the investigation, the role of T cells was studied by use of T-cell-deficient (nude) rats and control (AO) rats. Hexamethylenediisocyanate-crosslinked dermal sheep collagen (HDSC) was selected as the test material. The results showed that T cells or T cell-related factors played a prominent role in the attraction of macrophages and the formation of giant cells, their antigen presentation, and their phagocytotic capacity. As a consequence, degradation of HDSC was strongly delayed. This study also showed that infiltration of fibroblasts and creation of stromal areas in HDSC was restricted to areas subjected to degradation. However, in time, absence of T cells resulted in increased formation and maturation of autologous rat collagen. Results obtained suggest that the inflammatory reaction to biomaterials might be modulated by controlling T-cell activation.

Morphology and origin of arachnoid cysts scanning and transmission electron microscopy of three cases

SummaryThree surgically removed primary arachnoidal cysts were studied with scanning electron microscopy (SEM) and two of the cases with transmission electron microscopy (TEM). The cells lining the cyst cavity had microvilli at the surface, true cilia were absent. In the cytoplasm multivesicular bodies, many pinocytotic vesicles, some large vacuoles and strands of tonofilaments were prominent features. The cells were interconnected by desmosome-like junctions and were interconnected by desmosome-like junctions and were separated from the surrounding tissue by a distinct but sometimes incomplete basal membrane.Based on these findings it is concluded that arachnoid cysts are derived from the outer arachnoid cells (subdural neurothelium), the formation of the cysts being attributable to secretory capacity of the subdural neurothelium.

(Electron) microscopic observations on tissue integration of collagen-immobilized polyurethane.

The foreign body reactions to collagen-immobilized polyurethane (PU-CI) films during subcutaneous implantation in rats were characterized. The underlying concept is that collagen-immobilization will improve the tissue integration. Since the method of collagen-immobilization involves the covalent coupling of collagen to an acrylic acid (AA) based surface graft, both non-modified PU and PU-AA were used as controls. Bare PU has a flat surface, whereas both PU-AA and PU-CI displayed a slightly roughened surface. Implantation showed that PU-CI induced early after implantation a far more intense foreign body reaction than PU and PU-AA. This reaction consisted of increased presence of fibrin, granulocytes and macrophages. Roughening of the surface as with PU-AA induced only a small increase in fibrin formation and cellular migration. At day 5 the reaction to PU-CI had slowed down; giant cell formation now slowly started but was decreased compared to PU and PU-AA. At day 10 capsules around each type of material looked similar, but in contrast to PU. PU-CI films could no longer be dissected from their capsules. Only at week 3 this also occurred with PU, at which time point again similar capsules with the three materials were observed. At week 6, of the three materials PU-CI showed the thinnest capsule with most immediate adherence of connective tissue. These results show that collagen-immobilization of PU increased the early tissue reaction and therefore the tissue integration. The thin capsule observed at 6 weeks may be beneficial in e.g. infectious circumstances, when easy access for immune reactions is needed. This, and the long-term performance of PU-CI will be a matter of future investigations.

Modulation of the tissue reaction to biomaterials

Although in the last few years in general the biocompatibility of biomaterials has significantly improved, unwanted tissue reactions are often observed resulting in early resorption of the biomaterial, loosening of the implant or in a chronic (immunologic) response. From immunologic studies it is known that inflammatory reactions can be modulated by use of (anti) growth factors or anti-inflammatory drugs. Before this can be employed the role of individual factors (humoral and cellular) involved in the inflammatory reaction against biomaterials has to be studied. In this part of the study the role of macrophages is studied with and without depletion by use of the liposomes-mediated macrophage suicide technique. Crosslinked dermal sheep collagens were used as biodegradable test materials. The results showed that macrophage depletion increases vascularization, and decreases the infiltration of granulocytes into the collagens. The foreign body reaction, i.e. the infiltration of macrophages and giant cells was significantly inhibited, resulting in a strongly delayed degradation time of the biomaterials. However, macrophage depletion did not inhibit attraction of fibroblasts and even resulted in increased formation of autologous rat-collagen, which improved the biocompatibility and the function of the biomaterials as a tempory scaffold.

THE EFFECT OF DOXYCYCLINE ON POLYVINYLPYRROLIDONE-INDUCED GRANULOMA-FORMATION IN THE RAT-LIVER

SummaryThe tetracyclines specifically inhibit mitochondrial protein synthesis when present at the same low concentrations as used for their antibacterial action. Inhibition of mitochondrial protein synthesis leads to decrease in the oxidative energy-generating capacity of cells. Therefore, the presence of tetracyclines may result in proliferation arrest.In the present study we show that continuous intravenous administration of polyvinylpyrrolidone (PVP) induces the formation of granulomas in the normal rat liver; the rats usually die within 2 weeks of continuous PVP treatment. Athymic (nude) rats appear to be more résistent to the deleterious effects of PVP as they survivce the treatment for at least 5 weeks. Although the livers of the PVP-treated nude rats are heavily infiltrated with phagocytic cells, they seldom show granulomas. Reconstitution of nude rats with syngenic thymocytes leads, on the other hand, to extensive granuloma formation. Normal rats treated continuously with PVP plus doxycycline, however, all survive, their livers showing only a few very small granulomas and the normal low number of phagocytic cells.We conclude that the formation of granulomas induced by PVP is a process which is mediated by T-lymphocytes. Because doxycycline prevents this kind of granuloma formation it seems likely that doxycycline not only impairs the proliferation and differentiation of T-lymphocytes but also of monocytes and macrophages.

INCIDENCE OF INFECTION IN IMPLANTED POLYURETHANE TUBING SEGMENTS SERIALLY INJECTED WITH STAPHYLOCOCCI

One of the major clinical complications in the biomedical application of synthetic materials is the incidence of implant-associated infections. Such infections are very often induced by Staphylococcus aureus. To obtain information on tissue reactions and minimal bacterial challenge needed to create an infection related to untreated implant surfaces, we injected polyurethane tubing segments with a series of Staphylococcus aureus. The segments were subcutaneously implanted in rats. Implantation periods varied from 2, 5 and 10 days to 3 weeks. Specimen were evaluated using light and transmission electron microscopy. At least 0.25×104 of Staphylococci aureus were needed to clearly recognize that bacteria had been injected in the polyurethane tubing segments. The evidence was indirect, showing high infiltration and activation of neutrophils and macrophages, but not bacteria. Furthermore, 0.25×106S. aureus were needed to induce a persistent specific inflammatory reaction with high concentrations of lymphocytes, i.e. mainly plasma-cells, at 3 weeks. The results indicate that this model functioned well to obtain the wanted information. Results are discussed with respect to (a-) specific inflammatory reactions occurring with (bacterial-challenged) biomaterials. Ultimately, our goal is to develop infection-resistant materials, for which the in vivo model developed may be used to qualify the processed materials

Tissue reactions to bacteria-challenged implantable leads with enhanced infection resistance

Tissue reactions to implantable pacemaker leads were investigated in an early infection model in rabbits. Both standard leads and surface-modified leads were used. The surface modification technique was applied to achieve controlled release of the antibiotic gentamicin. The insulating polyurethane tubing material of the leads was provided with an acrylic acid/acrylamide copolymer surface graft and then loaded with gentamicin. Implantation periods varied from day 4, to week 3 1/2, to week 10. We investigated tissue reactions in the absence of an infectious challenge and also the efficacy of surface-modified leads in preventing infection after challenge with Staphylococcus aureus was evaluated. It was demonstrated that the applied surface modification did not induce adverse effects although during early postimplantation an increase in infiltration of granulocytes and macrophages and wound fluid and fibrin deposition were observed. After bacterial challenge, standard leads were heavily infected at each explantation period, denoted by abscesses, cellular debris, and bacterial colonies. In contrast, little or no infection was observed, either macroscopically or by bacterial cultures, with the surface-modified leads. Microscopy showed little evidence of the bacterial challenge, and that primarily at day 4. It was concluded that the applied surface modification demonstrated enhanced infection resistance and thus represents a sound approach to the battle against infectious complications with biomaterials.