|Articles about Biomaterials|
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| Local treatment of malignant brain tumors using implantable chemotherapeutic polymers
Gallia, G. L., S. Brem, et al. (2005), J Natl Compr Canc Netw 3(5): 721-8.
Abstract: Malignant gliomas are among the most devastating human cancers. The infiltrating nature of these malignancies makes complete surgical resection nearly impossible. Conventional therapy for malignant gliomas consists primarily of surgical debulking followed by radiation therapy and possibly chemotherapy. The major factor limiting intracranial therapeutic levels of systemically administered chemotherapeutics is the physiologic barriers of the brain. This has led to the development of novel methods of drug delivery such as implantable polymers containing chemotherapeutic agents. Several phase III clinical trials show that implantation of carmustine-containing biodegradable polymers prolongs survival in patients with both recurrent and newly diagnosed malignant gliomas. In this article, we summarize these trials and discuss ongoing clinical trials involving implantable chemotherapy-containing polymers in the treatment of patients with malignant gliomas.
| Localized transfection on arrays of magnetic beads coated with PCR products
Isalan, M., M. I. Santori, et al. (2005), Nat Methods 2(2): 113-8.
Abstract: High-throughput gene analysis would benefit from new approaches for delivering DNA or RNA into cells. Here we describe a simple system that allows any molecular biology laboratory to carry out multiple, parallel cell transfections on microscope coverslip arrays. By using magnetically defined positions and PCR product-coated paramagnetic beads, we achieved transfection in a variety of cell lines. Beads may be added to the cells at any time, allowing both spatial and temporal control of transfection. Because the beads may be coated with more than one gene construct, the method can be used to achieve cotransfection within single cells. Furthermore, PCR-generated mutants may be conveniently screened, bypassing cloning and plasmid purification steps. We illustrated the applicability of the method by screening combinatorial peptide libraries, fused to GFP, to identify previously unknown cellular localization motifs. In this way, we identified several localizing peptides, including structured localization signals based around the scaffold of a single C2H2 zinc finger.
| London University Search Instrument: a combinatorial robot for high-throughput methods in ceramic science
Wang, J. and J. R. Evans (2005), J Comb Chem 7(5): 665-72.
Abstract: This paper describes the design, construction, and operation of the London University Search Instrument (LUSI) which was recently commissioned to create and test combinatorial libraries of ceramic compositions. The instrument uses commercially available powders, milled as necessary to create thick-film libraries by ink-jet printing. Multicomponent mixtures are prepared by well plate reformatting of ceramic inks. The library tiles are robotically loaded into a flatbed furnace and, when fired, transferred to a 2-axis high-resolution measurement table fitted with a hot plate where measurements of, for example, optical or electrical properties can be made. Data are transferred to a dedicated high-performance computer. The possibilities for remote interrogation and search steering are discussed.
| Long term culture of epithelia in a continuous fluid gradient for biomaterial testing and tissue engineering
Minuth, W. W., R. Strehl, et al. (2001), J Biomater Sci Polym Ed 12(3): 353-65.
Abstract: Epithelia perform barrier functions being exposed to different fluids on the luminal and basal side. For long-term testing of new biomaterials as artificial basement membrane substitutes, it is important to simulate this fluid gradient. Individually-selected biomaterials can be placed in tissue carriers and in gradient containers, where different media are superfused. Epithelia growing on the tissue carriers form a physiological barrier during the whole culture period. Frequently however, pressure differences between the luminal and basal compartments occur. This is caused by a unilateral accumulation of gas bubbles in the container compartments resulting in tissue damage. Consequently, the occurence of gas bubbles has to be minimized. Air bubbles in the perfusion culture medium preferentially accumulate at sites where different materials come into contact. The first development is new screw caps for media bottles, specifically designed to allow fluid contact with only the tube and not the cap material. The second development is the separation of remaining gas bubbles from the liquid phase in the medium using newly-developed gas expander modules. By the application of these new tools, the yield of embryonic renal collecting duct epithelia with intact barrier function on a fragile natural support material can be significantly increased compared to earlier experiments.
| Long-term delivery of superoxide dismutase and catalase entrapped in poly(lactide-co-glycolide) microspheres: in vitro effects on isolated neonatal porcine pancreatic cell clusters
Giovagnoli, S., G. Luca, et al. (2005), J Control Release 107(1): 65-77.
Abstract: To counterbalance the restricted availability of pancreatic islet tissue for transplant in Type 1 Diabetes Mellitus (T1DM), new methods to provide viable and functional islet cells need to be established. We report on our approach to enhance in vitro viability and function of isolated neonatal pancreatic porcine cell clusters (NPCCs) by co-culturing them with PLGA microsphere entrapped, slowly release superoxide dismutase and catalase. These powerful antioxidizing agents were shown to significantly improve morphology, viability and function, as assessed by microscopy, molecular, biochemical and functional studies, of the incubated NPCCs, as compared to control. Preliminarily, in vitro exposure of isolated NPCCs to slow release microsphere-embedded SOD and CAT could permit or contribute to overcome hurdles associated with scarcity in islet tissue procurement for transplant in T1DM.
| Long-term evaluation of five biomaterials for angioplastic enlargement of the pulmonary artery in a young dog model
Planche, C. L., J. M. Fichelle, et al. (1987), J Biomed Mater Res 21(4): 509-23.
Abstract: In 45 young dogs an enlargement angioplasty of the left pulmonary artery was performed using patches made from one of three autologous materials (jugular vein, unmodified pericardium, and glycerolized pericardium) or from two heterologous materials (lyophilized human dura mater and modified bovine carotid artery). Catheterization and angiographic studies performed 5 to 6 months after the operation showed that all patched vessels had remained patent, except in three dogs which had received heterologous implants. The animals were killed 5-24 months after operation (mean weight increase: 84%), and the implants were studied by optical microscopy and morphometry, scanning and transmission electron microscopy, and indirect immunofluorescence with antidog Factor VIII rabbit antiserum. The two heterologous tissues exhibited limited biocompatibility, as estimated from 10 criteria obtained at histologic studies. Conversely, all three autologous biomaterials were characterized by infiltration of noninflammatory cells, near-complete endothelialization, and neosynthesis of structural proteins; infectious foci were very rare or absent. These results suggest that autologous tissues, although deendothelialized at the time of implantation, constitute the most suitable material for patch angioplasty, as far as endothelial triggering, cellularity and resistance to infection are concerned.
| Long-term evaluation of porous poly(epsilon-caprolactone-co-L-lactide) as a bone-filling material
Holmbom, J., A. Sodergard, et al. (2005), J Biomed Mater Res A 75(2): 308-15.
Abstract: Porous poly(epsilon-caprolactone-co-L-lactide) (P(CL-co-LA, wt % ca. 5/95) sponges were prepared, coated biomimetically with CaP/apatite, and implanted with noncoated control sponges into rat femur cortical defects and dorsal subcutaneous space. The implants were inspected histologically at 2, 4, and 33 weeks after the operation. All implants were filled with fibrovascular tissue within 4 weeks. The femur implants were partially ossified with compact bone, which in the CaP-coated sponges was less mature and more fragmented. Approximately equal amounts of bone were observed in both types of implants. The polymer induced a mild inflammatory reaction with foreign body giant cells but no accumulation of fluid. Degradation of the polymer was slow; most of it was found intact at 33 weeks in histological samples. Nondegraded polymer seems to prevent complete ossification. Cultured osteoblasts proliferated well on apatite-coated material, whereas only a few cells were seen on noncoated material. Thus CaP/apatite coating helped the attachment of osteoblasts in cell cultures but did not offer any advantage in bone formation over noncoated material in vivo. We conclude that a shorter degradation time of P(CL-co-LA) is needed to create an optimal implant. Furthermore, in vivo experiments seem to be necessary for the estimation of osteopromotive properties of a biomaterial.
| Long-term expression of erythropoietin from myoblasts immobilized in biocompatible and neovascularized microcapsules
Orive, G., M. De Castro, et al. (2005), Mol Ther 12(2): 283-9.
Abstract: The present paper investigates the long-term functionality of an ex vivo gene therapy approach based on cell microencapsulation for the continuous delivery of erythropoietin (EPO) without implementation of immunosuppressive protocols. Polymer microcapsules (0.5 ml) loaded with EPO-secreting C(2)C(12) myoblasts and releasing 15,490 +/- 600 IU EPO/24 h were implanted in the peritoneum and subcutaneous tissue of syngeneic and allogeneic mice. High and constant hematocrit levels were maintained for more than 100 days in all implanted mice. Capsules retrieved from the peritoneum were free-floating or forming small capsule clusters, and we detected only a weak fibroblast outgrowth in capsules adhered to organs, whereas capsules explanted from the subcutaneous region appeared altogether as a richly vascularized structure with no signs of major host reaction. Interestingly, the functionality of capsules implanted in the allogeneic mice persisted until day 210 after implantation. These results highlight the feasibility of cell encapsulation technology for the long-term delivery of EPO independent of the method of administration and the mouse strain.
| Long-term histopathological study of new polypeptidic biomaterials
Lescure, F., R. Gurny, et al. (1992), Biomaterials 13(14): 1009-11.
Abstract: The long-term histopathological evaluation of a new class of synthetic polypeptides, the poly(tert-butyloxycarbonylmethyl glutamates), as implantable drug delivery systems is addressed. This evaluation was performed in rat muscles over one year. The histological analysis included the measurement of many parameters, such as the type and thickness of the collagen capsule. The influence of the presence of progesterone, the selected active drug, could also be monitored over time.
| Long-term maintenance of human articular cartilage in culture for biomaterial testing
Strehl, R., T. Tallheden, et al. (2005), Biomaterials 26(22): 4540-9.
Abstract: Cartilage is a tissue that derives its unique mechanical and biological properties from the combination of relatively few cells and a large amount of a complex extracellular matrix. Furthermore, cartilage tissue is comparatively slow to respond to changes or harmful influences. To date, the optimal generation and long-term maintenance of cultured human articular cartilage for in vitro testing of biomaterials, poses an experimental difficulty. Experiments using cultured isolated chondrocytes in combination with scaffolds often fail to yield results comparable to the in-vivo situation. Consequently, our aim was to develop a culture method that allows in vitro maintenance of human hyaline cartilage explants in an optimal quality over an extended period of time. Such a culture could, for example, be used to determine the long-term effect of a new scaffold on intact cartilage, as an in vitro model for repair processes and to investigate biomaterial integration. In this study we compared conventional static cultures with and without serum supplementation to a serum-free perfusion culture for the ability to maintain human articular cartilage explants in a morphologically intact and differentiated state over an extended period of time of up to 56 days. Results were evaluated and compared by morphological, histochemical and immunohistochemical methods. The experiments showed that short-term maintenance of cartilage in a differentiated state for up to 14 days is possible under all culture conditions tested. However, best long-term culture results for up to 56 days were obtained with perfusion culture under serum-free conditions. Such a perfusion culture system can be used to perform biocompatabilty tests in vitro by long-term coculture of biomaterial and intact human articular cartilage.
| Long-term results and survival rate of implants treated with guided bone regeneration: a 5-year case series prospective study
Blanco, J., A. Alonso, et al. (2005), Clin Oral Implants Res 16(3): 294-301.
Abstract: One of the key factors for attaining osseointegration is the presence of an adequate osseous volume. In patients with inadequate osseous width or height, a bone augmentation using the guided bone regeneration (GBR) concept may be applied either with a simultaneous or a staged approach. The aim of this multicenter prospective case series study was to evaluate the efficacy and predictability of the GBR technique (simultaneous approach) in patients with peri-implant osseous defects, both dehiscences and fenestrations. Results 5 years post-treatment (survival rates and marginal bone level) were assessed. A total of 19 consecutive patients with 26 peri-implant osseous defects (20 dehiscences and six fenestrations) were treated during the period from September 1992 to June 1993 with a simultaneous GBR approach using non-resorbable membranes combined with autogenous bone grafts or decalcified freeze-dried bone allograft. The mean osseous augmentation was 94.8%. Marginal bone levels at re-entry and 5 years after surgery were calculated from standardized periapical radiographs. One implant was lost 3 months after loading. Thus, the cumulative survival rate was 96.1% after 5 years. The mean marginal bone level after 5 years was 2.03 mm (SD=+/-0.5), without a difference between mesial and distal sites. This study demonstrates that implants with peri-implant defects that are treated with GBR had similar survival rates and crestal bone levels compared with implants in native bone.
| Long-term stability of autogenous bone grafts following combined application with guided bone regeneration
Donos, N., L. Kostopoulos, et al. (2005), Clin Oral Implants Res 16(2): 133-9.
Abstract: The aim of the study was to compare the long-term stability of membranous and endochondral autogenous bone grafts with or without combined application of guided bone regeneration (GBR). Twenty-five, male, 6-month old, albino rats were used in the study. The animals were divided into four groups (A5, A11, B5 and B11). Group A5 (control): The inferior border of the mandible was exposed in both sides. At one side of the jaw, a calvarial bone graft (baseline -3 x 4 x 0.64 mm) was placed at the inferior border of the mandible and was fixed with a standardized screw-type titanium microimplant. At the contralateral side, an ischiac bone graft (baseline -3 x 4 x 0.87) was transplanted. The healing period was 5 months. Group A11 (control): The animals were treated in the same manner as in Group A5 with the difference that the healing period was 11 months. Group B5 (test): The animals were treated in the same manner as in Group A5 with the difference that an e-PTFE membrane was adapted over the bone graft on each side of the jaw. Group B11 (test): The animals were treated in the same manner as in Group B5 with the difference that 5 months following transplantation the animals were subjected to a second operation and the membranes were removed. The healing period was 11 months. The animals were killed at 5 (Groups A5 and B5) or at 11 months (Groups A11 and B11) following mandibular augmentation and the jaws were defleshed. The width, the length and the thickness/height of the bone graft were evaluated by means of a stereomicroscope. At 5 months, both types of the membrane-treated bone grafts presented increase in all dimensions compared with baseline. However at 11 months, both types of the membrane-treated bone grafts exhibited a decrease in their dimensions which were similar to the baseline measurements. In the control groups, both types of bone graft presented significant resorption both at 5 and at 11 months with the ischiac bone grafts presenting more resorption in width and length than the calvarial bone grafts. It can be concluded that the long-term volume stability of autogenous endochondral and membranous onlay bone grafts combined with GBR is superior to that of autogenous endochondral and membranous onlay bone grafts alone.
| Long-term stability of bone tissues induced by an osteoinductive biomaterial, recombinant human bone morphogenetic protein-2 and a biodegradable carrier
Kokubo, S., M. Mochizuki, et al. (2004), Biomaterials 25(10): 1795-803.
Abstract: The long-term stability of bone tissues induced by recombinant human bone morphogenetic protein-2 (rhBMP-2) and poly[L-lactide-co-glycolide] copolymer-coated gelatin sponge (PGS) was examined. In 16 dogs, 2.5 cm unilateral bone defects were created in the left tibial diaphyses. Tibia was fixed with metal plate, and PGS impregnated with (0.4 mg/cm(3)) or without rhBMP-2 was implanted into 15 or one defects, respectively. The metal plates of rhBMP-2-treated limbs were removed 16 weeks after the implantation. The bilateral tibiae of five animals each of the rhBMP-2-treated group were harvested at 32, 52 or 104 weeks, and served for biomechanical testing and histology. Although the defect that received PGS alone resulted in nonunion at 16 weeks, all defects treated with rhBMP-2 achieved radiographic bony union by 8 weeks. Biomechanical properties of the regenerated bones restored to the levels of intact tibiae at 32 weeks, but torsional stiffness was significantly higher. No statistical significances were detected in all parameters between regenerated and intact tibiae at 104 weeks. No radiographic and histological findings suggesting enhanced resorption to the regenerated bones were observed. These results suggest the long-term stability of the bone tissues induced by rhBMP-2, and the usefulness of rhBMP-2-impregnated PGS as a biomaterial for long bone defect filling.
| Long-term success of sinus augmentation using a synthetic alloplast: a 20 patients, 7 years clinical report
Butz, S. J. and L. W. Huys (2005), Implant Dent 14(1): 36-42.
Abstract: An adverse architecture of the maxillary sinus is no longer a contraindication for implant placement. Grafting the sinus has become an accepted treatment modality. Techniques for lifting the sinuses are well documented and numerous articles have been published. The main difference between the multitude of articles seems to be the graft material used. After having used different grafts, with varying success, this article reflects the authors' impressions on one particular grafting material, a composite synthetic bone substitute. The objective of this clinical study was to evaluate the effectiveness, reliability and predictability of that synthetic graft material (Bioplant HTR). After treating 20 patients (22 sites, 56 implants), and after a follow-up period as long as 7 years, it was clinically and radiographically observed that achieved results are enhanced if this synthetic graft material is used and that its use enhances sinus augmentation outcome and predictability. It provides the patient with the benefits of implant-supported restorations in a simple, quick, cost-effective, predictable, and secure manner.
| Long-term urethral catheterization and the urine-biomaterial interface
Elves, A. W. and R. C. Feneley (1997), Br J Urol 80(1): 1-5.
| Lovastatin suppresses invasiveness of anaplastic thyroid cancer cells by inhibiting Rho geranylgeranylation and RhoA/ROCK signaling
Zhong, W. B., Y. C. Liang, et al. (2005), Endocr Relat Cancer 12(3): 615-29.
Abstract: Lovastatin, a competitive inhibitor of 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase, inhibits the conversion of mevalonate from HMG-CoA. Previously, we have reported that lovastatin treatment induced the occurrence of apoptosis and differentiation in ARO anaplastic thyroid cancer cells. Here, we demonstrated that lovastatin inhibited the ARO cell invasiveness and delineated the underlying molecular mechanism. Lovastatin significantly suppressed the EGF-induced cell adhesion, actin filament reorganization and transmigration. Lovastatin also reduced EGF-induced increases in the levels of phosphorylated p125(FAK) and paxillin. These inhibitory effects mediated by lovastatin can be prevented by pretreatment of the cells with mevalonate or geranylgeraniol (GGOH), but not farnesol (FOH). Accordingly, the consuming and depletion of geranylgeranyl pyrophosphate and consequent suppression of the protein geranylgeranylation, which is essential for activation of Rho GTPases, might account for the lovastatin-induced inhibition of cell motility and invasion. Western blot analysis showed that lovastatin inhibited membrane translocation of Rho (e.g. RhoA and Rac1) through decreasing post-translational geranylgeranyl modification of Rho. In addition, treatment of the cells with specific inhibitors against Rho (Clostridium botulinum C3 transferase) or ROCK (Y-27632) abolished the GGOH-mediated prevention of, and restored the lovastatin-induced decrease of cell invasion. Taken together, our results suggested that lovastatin suppressed EGF-induced ARO cell invasiveness through the reduction of Rho geranylgeranylation, which in turn suppressed the membrane translocation, and subsequent suppression of Rho/ROCK and FAK/paxillin signaling.
| Low viscosity hydrogel of guar gum: preparation and physicochemical characterization
Cunha, P. L., R. R. Castro, et al. (2005), Int J Biol Macromol 37(1-2): 99-104.
Abstract: Guar gum was cross-linked with glutaraldehyde and characterized by GPC, rheology, WADX, SEM and TGA. This guar gum is a galactomannan polysaccharide, that contains small amount of arabinose, glucose and uronic acid, besides galactose and mannose. The polymer has high molar mass, with Mw, Mn and Mv values of 2.0x10(6), 1.2x10(6) and 1.9x10(6)g/mol, respectively. The reticulation follows a slow process and lead to a viscosity increase of 40 times compared with the original gum solution. The final viscosity was similar to that of Hylan G-F 20, a hyaluronate derivative, commercially used in viscosupplementation treatment. The gel contains 95.6% of water and the amount of residual glutaraldehyde is much lower than the LD-50. Porous structure was detected by SEM and thermal stability was improved by the cross-linking. The low viscosity, the small amount of remained glutaraldehyde, and the thermal stability indicates that the guar hydrogel has potential to be applied as biomaterial with specific rheological requirements.
| LPS increases biomaterial degradation by human monocytes in vitro
Benahmed, M., D. Heymann, et al. (1997), J Biomed Mater Res 34(1): 115-9.
Abstract: Different cell lines are involved during an immunological reaction, principally lymphocytes and monocytes. Monocyte/macrophage cells, which are among the first to appear in wound-healing and infection sites, are largely implicated in phagocytosis and could be involved in calcium-phosphate degradation. Their role in these processes may relate to cytokine secretions and/or their sensitivity to certain cytokines. We tested the behavior of human monocytes placed on the surface of biphasic calcium-phosphate (BCP) tablets in the presence of two lipopolysaccharide (LPS) concentrations. After short-term culture (48 h), cytokine release (IL-1beta, IL-6) was measured by ELISA, and morphological cell events and biomaterial degradation were observed in scanning electron microscopy. BCP surface pits were noted near cells stimulated by 0.5 microg/mL LPS but were not apparent with 10 microg/mL LPS. The number of lacunae on BCP was increased after LPS treatment of human monocytes. An upmodulation of IL-1beta and IL-6 (in culture medium) released by LPS-activated human monocytes was observed, indicating good cell stimulation. This study demonstrates that LPS-activated human monocytes can degrade the surface of calcium-phosphate ceramic and confirms the role of human monocytes in biomaterial degradation.
| Lymphocytes and the foreign body response: lymphocyte enhancement of macrophage adhesion and fusion
Brodbeck, W. G., M. Macewan, et al. (2005), J Biomed Mater Res A 74(2): 222-9.
Abstract: The host foreign body response ensues immediately following implantation of medical devices and prostheses. We have previously identified the role of macrophages in adhering to biomaterial surfaces and guiding the foreign body response while fusing into foreign body giant cells (FBGCs) and concentrating degradative and phagocytic activities. Despite their early and transient presence around implanted biomaterials, few studies have focused on the role of lymphocytes in the foreign body response and biocompatibility. To address this, an in vitro human lymphocyte/macrophage coculture system has been developed. Using this system, it has been shown that when lymphocytes are present during the initial adhesion of monocytes, the rate of monocyte adhesion and fusion is significantly increased (1,500 cells/mm2 and 60%, respectively) when compared to either no lymphocytes present (500 cells/mm2 adhesion and 0% fusion). Although lymphocytes adhered to the tissue culture polystyrene surface, 90% of the lymphocytes were associated with adherent macrophages. However, these cell-cell direct interactions were not necessary to influence macrophage adhesion or fusion as separating the two cell types by a Transwell insert still resulted in significantly increased levels of macrophage adhesion (p < 0.05 when compared to macrophage only cultures). Conversely, the presence of macrophages in Transwell experiments increased lymphocyte proliferation rates at all time points tested. These studies begin to detail the interactions between lymphocytes and macrophages in the absence of known antigen that appropriately relates to the scenarios experienced upon implantation of biomedical devices and the initiation of the foreign body response.
| Lysine-enhanced glutaraldehyde crosslinking of collagenous biomaterials
Simionescu, A., D. Simionescu, et al. (1991), J Biomed Mater Res 25(12): 1495-505.
Abstract: Crosslinking of collagenous biomaterials currently employs the use of glutaraldehyde. The putative enhancement of glutaraldehyde crosslinking by lysine was investigated in three model systems: bovine pericardium, collagen membranes, and bovine serum albumin. Repetitive sequential treatment of bovine pericardium with glutaraldehyde and lysine and finally with formaldehyde produced a matrix which, by the two criteria used (shrinkage temperature and urea/SDS soluble collagen), was shown to be more highly crosslinked than pericardium fixed in glutaraldehyde alone. Essentially the same results were obtained when membranes prepared from pepsin-soluble pericardial collagen were subjected to sequential glutaraldehyde and lysine treatments, reaching shrinkage temperatures of more than 90 degrees C. Heart valves prepared from lysine-enhanced glutaraldehyde crosslinked bovine pericardium were tested in vitro in an accelerated fatigue tester and have been shown to behave satisfactorily after 300 million cycles. These additional crosslinks proved to be stable in saline at 37 degrees C. Studies on bovine serum albumin attempted to get an insight into the mechanisms of lysine enhancement of glutaraldehyde crosslinking by treating sequentially albumin with glutaraldehyde and lysine and analysis of the products by gel filtration and SDS-PAGE. These studies suggest that free amino groups exposed by proteins are initially reacted with glutaraldehyde and then bridged by the diamino compound (lysine) producing more extensive intermolecular crosslinking than glutaraldehyde alone.
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