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Update on new biomaterials and their use in reconstructive surgery
Pou, A. M. (2003), Curr Opin Otolaryngol Head Neck Surg 11(4): 240-4.
Abstract: Craniofacial reconstruction may be limited by the paucity of autologous materials available and donor site morbidity. Recent advances in the development of biomaterials have given the reconstructive surgeon new options for restoring form and function. There are now biomaterials (second generation) that can elicit a controlled action and reaction to the surrounding tissue environment (bioactive), and those that can exhibit a controlled chemical breakdown and resorption, with ultimate replacement by regenerating tissue (resorbable). Third-generation biomaterials are being designed to stimulate regeneration of living tissues using tissue engineering and in situ tissue regeneration methods. These techniques will lead to limitless possibilities for tissue regeneration and repair. At present, biomaterials that may find future use in craniofacial reconstruction include newly developed bone and skin substitutes and soft-tissue fillers.

Uptake of silica-coated nanoparticles by HeLa cells
Xing, X., X. He, et al. (2005), J Nanosci Nanotechnol 5(10): 1688-93.
Abstract: Nanoparticles have seen wide applications in cellular research and development. One major issue that is unclear is the uptake of nanoparticles by cells. In this study, we have investigated the uptake of silica-coated nanoparticles by HeLa cells, employing rhoadime 6G isothiocyanate (RITC)-doped nanoparticles as a synchronous fluorescent signal indicator. These nanoparticles were synthesized with reverse microemulsion. A few factors, such as nanoparticle concentration, incubation time and temperature, and serum and inhibitors in culture medium were assessed on the nanoparticle's cellular uptake. The experimental results demonstrated that uptake was maximum after a 6 h incubation and was higher at 37 degrees C than that at 4 degrees C. Nanoparticle uptake depended on the nanoparticle concentration and was inhibited by hyperosmolarity, K+ depletion. In addition, serum in culture medium decreased the cellular uptake of nanoparticles. The results indicated that the uptake of silica-coated nanoparticles by HeLa cells was a concentration-, time-, and energy-dependent endocytic process. Silica-coated nanoparticles could be transported into HeLa cells in part through adsorptive endocytosis and in part through fluid-phase endocytosis.

Urinary tract biomaterials
Beiko, D. T., B. E. Knudsen, et al. (2004), J Urol 171(6 Pt 1): 2438-44.
Abstract: PURPOSE: As a result of endourological advances, biomaterials have become increasingly used within the urinary tract. This review article provides an update on the current status of urinary tract biomaterials, discussing issues of biocompatibility, biomaterials available for use, clinical applications and biomaterial related complications. Perspectives on future materials for use in the urinary tract are also provided. MATERIALS AND METHODS: We performed a comprehensive search of the peer reviewed literature on all aspects of biomaterials in the urinary tract using PubMed and MEDLINE. All pertinent articles were reviewed in detail. RESULTS: Any potential biomaterial must undergo rigorous physical and biocompatibility testing prior to its commercialization and use in humans. There are currently many different bulk materials and coatings available for the manufacturing of biomaterials, although the ideal material has yet to be discovered. For use in the urinary tract, biomaterials may be formed into devices, including ureteral and urethral stents, urethral catheters and percutaneous nephrostomy tubes. Despite significant advances in basic science research involving biocompatibility issues and biofilm formation, infection and encrustation remain associated with the use of biomaterials in the urinary tract and, therefore, limit their long-term indwelling time. CONCLUSIONS: Prosthetic devices formed from biomaterials will continue to be an essential tool in the practicing urologist's armamentarium. Ongoing research is essential to optimize biocompatibility and decrease biomaterial related complications such as infection and encrustation within the urinary tract. Future advances include biodegradables, novel coatings and tissue engineering.

Urothelial mesh--a new technique of cell culture on biomaterials
Hobbiesiefken, J., M. E. Ehlers, et al. (2003), Eur J Pediatr Surg 13(6): 361-6.
Abstract: INTRODUCTION: Urogenital malformations, trauma or tumours may demand surgical reconstruction in children. Cell culture is an important technology in biomaterial research and tissue engineering. Tissue-engineering of urothelial organs is of interest in children, because the number of complications and re-operations may be reduced. Actually, monolayer cultures of urothelium are used for tissue engineering and biocompatibility testing. A culture system that more closely mimics the physiologic environment of the urothelium would be of interest. The aim of this study was to determine the biological and mechanical characteristics of urothelial mesh cultured in vitro. METHODS: Meshes containing urothelium, lamina propria, and submucosal tissue were generated using a skin mesh graft cutter. Meshes were cultured in 6-well plates, on collagen I/III, polydioxanone/polylactic acid and silicone matrices. Cell morphology was examined by inversion microscopy, histology, and scanning electron microscopy. It was compared to urothelium cultured by methods reported in the literature. To define the basic mechanical properties, meshes were extended longitudinally by a servohydraulic testing machine and strain diagrams generated. RESULTS: Urothelium was reproducibly cultured from meshes. Cell growth could be induced onto fibrillary collagen, polydioxanone-polylactic acid matrices and shaped polyurethane surfaces. Cells formed confluent layers of flat cells, resembling native urothelium. The meshes have unique mechanical properties, allowing for stable fixation, surgical handling and mechanical stimulation. CONCLUSIONS: Meshes can be used for cell culture on biomaterials. They maintain epithelial-stromal integrity and mechanic stability. The small size of tissue bridges allows in vitro culture for long periods with many potential advantages for tissue engineering and biologic research. Applications are possible both in vitro and in vivo.

Use of a sirolimus-eluting stent to treat failure of a nonpolymer release paclitaxel-eluting stent implanted for in-stent restenosis
Porto, I. and A. P. Banning (2005), J Invasive Cardiol 17(5): 270-3.

Use of a tacrolimus-eluting stent to inhibit neointimal hyperplasia in a porcine coronary model
Huang, Y., K. Salu, et al. (2005), J Invasive Cardiol 17(3): 142-8.
Abstract: In-stent restenosis remains an unresolved problem which occurs in 5-20% of patients undergoing coronary stenting within the first 3-6 months. Neointimal formation is the main contributor to in-stent restenosis. Stent-induced arterial injury and peri-strut inflammation are involved in the process of neointimal formation by activating cytokines and growth factors which induce smooth muscle cell dedifferentiation, migration, and proliferation. Histopathological studies found that neointimal hyperplasia is principally composed of smooth muscle cells, inflammatory cells, and extracellular matrix. Stent-based delivery of anti-proliferative and/or anti-inflammatory agents have shown beneficial effects on neointimal hyperplasia in experimental studies and clinical trials. Tacrolimus (FK506) is a water-insoluble macrolide immunosuppressant discovered in 1984. It has been widely used in reducing the incidence and severity of allograft rejection after organ transplantation. It has also been used to treat other inflammatory conditions such as atopic dermatitis. In this study, we evaluated the efficacy of stent-based delivery of tacrolimus on inflammation and neointimal formation in an overstretched coronary stent model.

Use of an artificial dermis (Integra) for the reconstruction of extensive burn scars in children. About 22 grafts
Groos, N., M. Guillot, et al. (2005), Eur J Pediatr Surg 15(3): 187-92.
Abstract: We used an artificial dermis (Integra) for the reconstruction of extensive burn scars in children. Integra was initially developed for the primary coverage of acute burns, but several authors report good experiences with Integra for reconstructive surgery. We present a group of 10 children who underwent Integra grafting at 22 different operational sites. Five children received several grafts with Integra. On average, 260 cm(2) per session were grafted. We compared the surface of Integra on the day of grafting and then again on the evaluation day to measure the secondary retraction of the grafts. Complications (infection of Integra, failure of the epidermal graft) were observed in 5 cases. At the final evaluation, 20 grafts were visible. The surface of the Integra graft represented less than 50% of the initial surface in 7 cases, 51-75% in 5 cases and more than 76% in 8 cases. The disadvantages of Integra in reconstructive surgery are that two operative procedures are necessary and the recurrence of contraction seems to be more significant than with full thickness auto grafts. However, Integra has many advantages: the immediate availability of large quantities, the simplicity and reliability of the technique, the pliability and the cosmetic aspect of the resulting coverage. In light of these preliminary results, Integra appears to offer a new alternative for the reconstruction of extensive burn scars in children.

Use of an osteoinductive biomaterial (rhOP-1) in healing large segmental bone defects
Cook, S. D., S. L. Salkeld, et al. (1998), J Orthop Trauma 12(6): 407-12.
Abstract: OBJECTIVE: To assess the radiographic, histologic, and mechanical characteristics of new bone formation in large segmental bone defects treated with a new osteoconductive material, recombinant human osteogenic protein-1 (rhOP-1). DESIGN: In vivo animal study. INTERVENTION: Sixteen dogs (thirty-two limbs) with an ulna segmental defect (2.5 centimeters) were randomized to three treatment groups: rhOP-1, collagen alone, and no implant. MAIN OUTCOME MEASUREMENTS: Radiographic evidence of defect healing, mechanical testing (torsional strength) as compared with thirty-one control intact dog ulnas, and histologic analysis. RESULTS: At twelve weeks, complete radiographic healing was observed in twenty-five of twenty-eight defects (89 percent) treated with rhOP-1. The mechanical strength of the rhOP-1-treated defects at twelve weeks was 65 percent of that of intact ulnas. Histologic analysis revealed that defects treated with rhOP-1 were bridged with lamellar and woven bone that was in continuity with the host bone. CONCLUSIONS: The results indicate that osteoinductive materials, which have the ability to quickly fill and heal large defects, may have advantages over osteoconductive materials, which are typically used to fill smaller non-load-bearing bone voids.

Use of an osteoinductive biomaterial as a bone morphogenetic protein carrier
Yuan, H., J. D. De Bruijn, et al. (2001), J Mater Sci Mater Med 12(9): 761-6.
Abstract: A porous calcium phosphate ceramic, which induced bone formation in soft tissues of dogs, was termed as osteoinductive biomaterial and studied as a carrier of bone morphogenetic protein (rhBMP-2). Cylinder implants (laser spot 4 x 5 mm) impregnated with 0, 1, 10 and 40 microg rhBMP-2 were implanted in dorsal muscles of rabbits for five weeks. Histological observation and histomorphometric analysis were performed on thin un-decalcified sections. No bone formation was detected in the implants without rhBMP-2, while mature lamellar bone was found inside the implants with 1 microg rhBMP-2, both on the outer surface and inside the implants with 10 microg and 40 microg rhBMP-2. Little difference in formed bone was found between 1 microg and 10 microg rhBMP-2, but no difference was found between 10 microg and 40 microg rhBMP-2. A significant difference in bone marrow formation was found among 1, 10 and 40 microg rhBMP-2. The more rhBMP-2, the more bone marrow formed. The present results indicate that osteoinductive biomaterial is a good carrier of BMP and high dose of BMP is not necessary for bone formation in clinic.

Use of analytical microscopy to analyze the speciation of copper and chromium ions onto a low-cost biomaterial
Dupont, L., J. Bouanda, et al. (2004), J Colloid Interface Sci 279(2): 418-24.
Abstract: In this paper, we present our study of the speciation of copper and hexavalent chromium sorbed onto a lignocellulosic substrate, using analytical microscopy. The lignocellulosic substrate constitutes a low-cost biomaterial that can be used in wastewater treatment. Transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDXS) was used to determine the speciation of the two metal ions on the constitutive moieties of the lignocellulosic substrate. The use of a staining agent sensitive to carbon unsaturation allowed us to differentiate between the microstructures rich in lignin entities and those rich in cellulose entities. The EDX analysis showed that metal ions are preferentially sorbed onto microstructures rich in lignin moieties. The energy electron loss spectroscopy (EELS) was used to determine the oxidation states of chromium in association with lignocellulosic moieties. We showed that the sorption process of hexavalent chromium requires the reduction of Cr(VI) into Cr(III) and the probable oxidation of lignin moieties.

Use of biodegradable PLGA microspheres as a slow release delivery system for the Boophilus microplus synthetic vaccine SBm7462
Sales-Junior, P. A., F. Guzman, et al. (2005), Vet Immunol Immunopathol 107(3-4): 281-90.
Abstract: The synthetic anti-Boophilus microplus vaccine SBm7462 derived from the tick intestinal protein, Bm86, induced a protective immune response when emulsified in saponin and used in cattle. Using a mice model, and with the objective of improving the vaccine by continual peptide release, it was encapsulated in PLGA 50:50 microspheres and inoculated in BALB/c mice to assess the immunological response by detection of anti-peptide IgGs. Comparative studies were made with the peptide emulsified in saponin and with another synthetic vaccine, and the microsphere/peptide was characterized for efficiency of encapsulation, in vitro release profile, morphology, size, peptide integrity after encapsulation and stability in different pHs. The findings showed that saponin enhances a better immune response from SBm7462 and that the PLGA 50:50 microspheres are suitable for use with this peptide.

Use of bone graft substitutes and bioactive materials in treatment of distal radius fractures
Hartigan, B. J. and M. S. Cohen (2005), Hand Clin 21(3): 449-54.
Abstract: Although autogenous bone graft has been shown to be useful in the treatment of distal radius fractures, the role of bone graft substitutes and the optimal replacement material remains unclear. Several products are commercially available, each with differing osteoconductive, osteoinductive, and structural properties. Indications and choice of graft substitute should be based on the needs of the individual case with regard to need for structural support, gap filling, or bone healing stimulation. Further comparative research will help clarify the indications and most appropriate material for a given fracture and clinical situation.

Use of chemotaxis chambers for studying in vitro bacterial colonization of biomaterials
Leake, E. S., A. G. Gristina, et al. (1982), J Clin Microbiol 15(2): 320-3.
Abstract: Blind-well chemotaxis chambers were used to study the in vitro bacterial adhesion and colonization of biomaterials. Staphylococcus aureus and Pseudomonas aeruginosa were selected for the bacterial inocula. Abundant growth on the surfaces of methyl methacrylate, polyethylene, stainless steel, and Vitallium was detected by using scanning electron microscopy after 24 h of incubation. The culture technique employed proved to be of value for the study of surface bacterial colonization of inert materials.

Use of chitosan as a biomaterial: studies on its safety and hemostatic potential
Rao, S. B. and C. P. Sharma (1997), J Biomed Mater Res 34(1): 21-8.
Abstract: Chitosan, a mucopolysaccharide of marine origin, was studied for its safety and hemostatic potential. Its surface was treated with glutaraldehyde, carbodiimide, and plasma glow discharge to elicit effects of enzyme degradation. Of the seven enzymes used, leucine amino peptidase caused maximum degradation. Autoclaving appeared to be an ideal sterilizing method as it caused least decrease in tensile strength and effected a negligible rate of hemolysis. Sterilizing with glutaraldehyde with a physiologic pH retained the maximum tensile strength of chitosan. In vivo toxicity tests indicated that it is nontoxic, and the sterilized films were free of pyrogen. Coagulation and hemagglutination tests showed that the hemostatic mechanism of chitosan seems to be independent of the classical coagulation cascade and appears to be an interaction between the cell membrane of erythrocytes and chitosan.

Use of diphenylphosphorylazide for cross-linking collagen-based biomaterials
Petite, H., V. Frei, et al. (1994), J Biomed Mater Res 28(2): 159-65.
Abstract: Cross-linking of collagen-based biomaterials increases their strength and persistence in vivo. Recently, we described an efficient cross-linking process via the formation of acyl azide groups on methylated carboxyl groups of collagen using hydrazine and nitrous acid (referred to here as the hydrazine method). In this report, we propose a simpler, faster way to prepare acyl azide groups and to cross-link collagen-based biomaterials, using diphenylphosphorylazide (DPPA) as a reagent. After determining the optimal conditions of cross-linking with DPPA, we compared the efficiency of this protocol with that using hydrazine and with the classical glutaraldehyde treatment. In order to validate and quantitate the extent of reaction, the degree of cross-linking was determined by the measure of the free primary amino group content of the samples. Treatment of native bovine pericardium with 0.5% DPPA for 24 h led to efficient cross-linking, corresponding to a 50% decrease in the free primary amino group content of the sample and raising its thermal stability from 62.8 up to 81.3 degrees C. In comparison, the thermal stabilities of glutaraldehyde or hydrazine-treated pericardium were 85 +/- 0.4 degrees C and 83.4 +/- 0.1 degrees C. Similar decreases in free primary amino group content and increases in thermal stability were obtained for collagen films treated with DPPA, glutaraldehyde, or hydrazine. These results were corroborated by resistance to bacterial collagenase digestion: DPPA-treated pericardium had a resistance to collagenase digestion similar to that of glutaraldehyde- or hydrazine-treated pericardium.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of embryonic stem cell-derived endothelial cells as a cell source to generate vessel structures in vitro
McCloskey, K. E., M. E. Gilroy, et al. (2005), Tissue Eng 11(3-4): 497-505.
Abstract: Embryonic stem (ES) cells could potentially serve as an excellent cell source for various applications in regenerative medicine and tissue engineering. Our laboratory is particularly interested in generating a reproducible endothelial cell source for the development of prevascularized materials for tissue/organ reconstruction. After developing methods to isolate highly purified (>96%) proliferating populations of endothelial cells from mouse embryonic stem cells, we tested their ability to form three-dimensional (3-D) vascular structures in vitro. The ES cell-derived endothelial cells were embedded in 3-D collagen gel constructs with rat tail collagen type I (2 mg/mL) at a concentration of 10(6) cells/mL of gel. The gels were observed daily with a phase-contrast microscope to analyze the time course for endothelial cell assembly. The first vessels were observed between days 3 and 5 after gel construct formation. The number and complexity of structures steadily increased, reaching a maximum before beginning to regress. By 2 weeks, all vessel-like structures had regressed back to single cells. Histology and fluorescent images of the vessel-like structures verified that tube structures were multicellular and could develop patent lumens. We have shown that endothelial cells derived, purified and expanded in vitro from ES cells sustain an important endothelial cell function, the ability to undergo vasculogenesis in collagen gels, indicating that endothelial products derived in vitro from stem cells could be useful in regenerative medicine applications.

Use of isothermal heat-conduction microcalorimetry (IHCMC) for the evaluation of synthetic biomaterials
Lewis, G. and A. U. Daniels (2003), J Biomed Mater Res B Appl Biomater 66(2): 487-501.
Abstract: Isothermal heat-conduction microcalorimetry (IHCMC) allows measurement of extremely small rates of heat flow-on the order of 0.1 microwatt. This provides, for example, the ability to directly observe-and quantitate in a few days-rates of degradation as low as 1% per year at body temperature, in solid material samples of a few grams. Also, one method of IHCMC data analysis allows direct determination of the reaction-rate constant at the temperature of interest, thereby avoiding possible errors due to rate mechanism changes with temperature, an issue that needs to be considered when the Arrhenius method is used. IHCMC can also be used to measure transient phenomena, such as heat of adsorption, and initial metabolic responses of cellular entities to biomaterials. The purposes of this review article are to (a) explain the basic principles, attractive features, limitations, and methods of IHCMC; (b) describe biomaterials applications to date--including studies of the stability of ultra-high-molecular-weight polyethylene and implant-grade calcium sulfate, setting reactions of dental adhesives, and macrophage response to biomaterial particles; (c) provide a discussion of issues and concerns that should be addressed in order to maximize the utility of IHCMC in biomaterials studies; and (d) suggest a number of possible future biomaterials applications for this technique.

Use of microelectrodes as electrochemical sensors of metal ions released from biomaterials
Sousa, J. P., S. B. Morais, et al. (1994), Biomaterials 15(10): 821-6.
Abstract: In vitro studies to determine Fe3+ levels in mice liver samples were performed using platinum microelectrodes and atomic absorption spectrophotometry. Microelectrodes have been shown to be useful for quantitative analysis of metal ions released during the biodegradation process that occurs on implanted metallic biomaterials.

Use of p-nitrophenyl chloroformate chemistry to immobilize protein on orthopedic biomaterials
Mikulec, L. J. and D. A. Puleo (1996), J Biomed Mater Res 32(2): 203-8.
Abstract: Biochemical surface modification involves covalently immobilizing biomolecules onto biomaterial surfaces to induce specific biological responses. This approach may be useful for enhancing the fixation of orthopedic implants. p-Nitrophenyl chloroformate (p-NPC) was used to immobilize protein on bulk samples of Co-Cr-Mo and Ti-6Al-4V. Activation of both materials was dependent on the concentration of p-NPC, with a maximum of approximately 1.5 active groups/nm2 of nominal surface area. Trypsin was used as a model protein because much is known about its structure and mode of action. Derivatization with 0.65 mg p-NPC/cm2 resulted in significantly greater enzymatic activity (7.4 BAEE [N-(alpha)-benzoyl-L-arginine ethyl ester hydrochloride] units) on the Co-Cr-Mo samples compared with higher concentrations of p-NPC (5 BAEE units) and with simple adsorption of trypsin (1.5 BAEE units). An activity of 10.5 BAEE units was measured on both adsorbed and p-NPC-activated Ti-6Al-4V, with the exception of samples derivatized with 1.95 mg p-NPC/cm2, on which activity was significantly lower (4 BAEE units). In probing the linkages between trypsin and biomaterial by treatment with chaotropic agents, guanidine hydrochloride (GuHCl) was observed to eliminate more enzymatic activity than was urea. On Co-Cr-Mo samples, GuHCl removed nearly all the trypsin activity, while urea significantly decreased the activity only at a concentration of 0.65 mg p-NPC/cm2. Treatment of Ti-6Al-4V samples with GuHCl caused a trend of decreasing activity with increasing concentration of p-NPC, whereas urea had no effect on immobilized trypsin activity.

Use of rigid spherical inclusions in Young's moduli determination: application to DNA-crosslinked gels
Lin, D. C., B. Yurke, et al. (2005), J Biomech Eng 127(4): 571-9.
Abstract: Current techniques for measuring the bulk shear or elastic (E) modulus of small samples of soft materials are usually limited by materials handling issues. This paper describes a nondestructive testing method based on embedded spherical inclusions. The technique simplifies materials preparation and handling requirements and is capable of continuously monitoring changes in stiffness. Exact closed form derivations of E as functions of the inclusion force-displacement relationship are presented. Analytical and numerical analyses showed that size effects are significant for medium dimensions up to several times those of the inclusion. Application of the method to DNA-crosslinked gels showed good agreement with direct compression tests.

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Last Modified: 8 February 2006