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Biopolymers as biomaterials: mechanical properties of gamma-benzyl-L-glutamate-L-leucine copolymers
Anderson, J. M., A. Hiltner, et al. (1972), J Biomed Mater Res 6(4): 25-35.

Bioreactor cultivation of osteochondral grafts
Vunjak-Novakovic, G., L. Meinel, et al. (2005), Orthod Craniofac Res 8(3): 209-18.
Abstract: The clinical utility of tissue engineering depends upon our ability to direct cells to form tissues with characteristic structural and mechanical properties across different hierarchical scales. Ideally, an engineered graft should be tailored to (re)establish the structure and function of the native tissue being replaced. Engineered grafts of such high fidelity would also foster fundamental research by serving as physiologically relevant models for quantitative in vitro studies. The approach discussed here involves the use of human mesenchymal stem cells (hMSC) cultured on custom-designed scaffolds (providing a structural and logistic template for tissue development) in bioreactors (providing environmental control, biochemical and mechanical cues). Cartilage, bone and ligaments have been engineered by using hMSC, highly porous protein scaffolds (collagen; silk) and bioreactors (perfused cartridges with or without mechanical loading). In each case, the scaffold and bioreactor were designed to recapitulate some aspects of the environment present in native tissues. Medium flow facilitated mass transport to the cells and thereby enhanced the formation of all three tissues. In the case of cartilage, dynamic laminar flow patterns were advantageous as compared to either turbulent steady flow or static (no flow) cultures. In the case of bone, medium flow affected the geometry, distribution and orientation of the forming bone-like trabeculae. In the case of ligament, applied mechanical loading (a combination of dynamic stretch and torsion) markedly enhanced cell differentiation, alignment and functional assembly. Taken together, these studies provide a basis for the ongoing work on engineering osreochondral grafts for a variety of potential applications, including those in the craniofacial complex.

Bioreactor-based engineering of osteochondral grafts: from model systems to tissue manufacturing
Wendt, D., M. Jakob, et al. (2005), J Biosci Bioeng 100(5): 489-94.
Abstract: Osteochondral defects (i.e., those that affect both the articular cartilage and underlying subchondral bone) are often associated with mechanical instability of the joint, and therefore with the risk of inducing osteoarthritic degenerative changes. The in vitro fabrication of osteochondral grafts of predefined size and shape, starting from autologous cells combined with three-dimensional porous biomaterials, is a promising approach for the treatment of osteochondral defects. However, the quality of ex vivo generated cartilage and bone-like tissues is currently restricted by a limited understanding of the regulatory role of physicochemical culture parameters on tissue development. By allowing reproducible and controlled changes in specific biochemical and biomechanical factors, bioreactor systems provide the technological means to reveal fundamental mechanisms of cell function in a three-dimensional environment and the potential to improve the quality of engineered tissues. In addition, by automating and standardizing the manufacturing process in controlled closed systems, bioreactors could reduce production costs and thus facilitate broader clinical impact of engineered osteochondral grafts.

Bioreactors for tissue mass culture: design, characterization, and recent advances
Martin, Y. and P. Vermette (2005), Biomaterials 26(35): 7481-503.
Abstract: This paper reviews reports on three-dimensional mammalian tissue growth in bioreactors and the corresponding mammalian tissue growth requirements. The needs for nutrient and waste removal of several mammalian tissues are reviewed and compared with the environment of many reactors currently in use such as the continuous stirred tank, the hollow fiber, the Couette-Taylor, the airlift, and the rotating-wall reactors developed by NASA. Many studies conclude that oxygen supply appears to be one of the most important factors limiting tissue growth. Various correlations to describe oxygen mass transfer are presented and discussed with the aim to provide some guidance to design, construct, and test reactors for tissue mass culture. To obtain tissue thickness clinically valuable, dimensionless and other types of analysis tend to point out that diffusive transport will have to be matched with an important convection to bring sufficient oxygen molecular flux to the growing cells located within a tissue mass. As learned from solid-state fermentation and hairy root culture, during the growth of large biomass, heterogeneity (i.e., channeling, temperature gradients, non-uniform cell growth, transfer gradients, etc.) can cause some important problems and these should be addressed in tissue engineering as well. Reactors (along with the scaffolds) should be designed to minimize these issues. The role of the uterus, the reactor built by Nature, is examined, and the environment provided to a growing embryo is reported, yielding possible paths for further reactor developments. Finally, the importance of cell seeding methods is also addressed.

Bioremediation of contaminated surface water by immobilized Micrococcus roseus
Li, H., P. Li, et al. (2005), Environ Technol 26(8): 931-9.
Abstract: The problems caused by contaminated surface water have gradually become more serious in recent years. Although various remediation technologies were investigated, unfortunately, no efficient method was developed. In this paper, a new bioremediation technology was studied using Micrococcus roseus, which was immobilized in porous spherical beads by an improved polyvinyl alcohol (PVA) - sodium alginate (SA) embedding method. The experimental results indicated that COD removal rate could reach 64.7 % within 72 hours when immobilized M. roseus beads were used, which was ten times as high as that of free cells. The optimum inoculation rate of immobilized M. roseus beads was 10 % (mass percent of the beads in water sample, g g(-1)). Suitable aeration was proved necessary to enhance the bioremediation process. The immobilized cells had an excellent tolerance to pH and temperature changes, and were also more resistant to heavy metal stress compared with free cells. The immobilized M. roseus beads had an excellent regeneration capacity and could be reused after 180-day continuous usage. The Scanning Electronic Microscope (SEM) analysis showed that the bead microstructure was suitable for M. roseus growth, however, some defect structures should still be improved.

Bioresorbable composites prepared by supercritical fluid foaming
Mathieu, L. M., M. O. Montjovent, et al. (2005), J Biomed Mater Res A 75(1): 89-97.
Abstract: Bone is a natural composite construct, with a gradient structure going from a loose interconnected cellular core to an outer dense wall, thus minimizing bone weight while keeping a high mechanical resistance. Due to this unique and complex structure, bone defects are difficult to replace or repair. Tissue engineering aims at providing artificial bone grafts. Several techniques have been proposed to produce porous structures or scaffolds, but, as yet, with no optimal solutions. This article focuses on bioresorbable ceramic-polymer composite foams obtained by supercritical fluid foaming. This flexible technique enables an adequate morphology and suitable properties for bone tissue engineering to be obtained. Composite scaffolds are biocompatible, allowing cell proliferation and differentiation.

Bioresorbable fixation devices for musculoskeletal injuries in adults
Jainandunsing, J. S., M. van der Elst, et al. (2005), Cochrane Database Syst Rev(2): CD004324.
Abstract: BACKGROUND: Bioresorbable implants for musculoskeletal injuries involving bone and ligaments in adults might have significant advantages compared to the conventionally used non-resorbable metal implants because they lead to a gradual transfer of the mechanical load from the implant to the healing bone and do not require a secondary removal operation. Tissue reactions may present a problem and bioresorbable screws are mechanically not as strong as their metal counterparts. OBJECTIVES: To compare bioresorbable implants to non-resorbable implants with respect to functional outcome, wound infections, other complications and reoperation rate,in the fixation of bone fractures or re-attachment of soft tissue to bone. SEARCH STRATEGY: We searched the Cochrane Musculoskeletal Injuries Group Specialised Register (March 2004), the Cochrane Central Register of Controlled Trials (The Cochrane Library Issue 1, 2004), MEDLINE (1966 to February 2004), EMBASE (1988 to February 2004), BL Inside (to February 2004), SIGLE (to February 2004), the metaRegister of Controlled Trials at http//, and reference lists of articles. SELECTION CRITERIA: Randomised controlled trials (RCTs) and quasi-randomised trials, comparing bioresorbable osteosynthesis with metal osteosynthesis (including titanium and stainless steel implants) were included. DATA COLLECTION AND ANALYSIS: Review authors independently assessed trial quality and extracted data. Data were pooled where relevant and possible. Sub-analyses for specific type of fractures and for specific type of tissue reactions were performed. Requests for more information were sent to trialists. MAIN RESULTS: No significant difference between the bioresorbable and other implants could be demonstrated with respect to functional outcome, infections and other complications. Reoperation rates were lower in some of the groups of people treated with bioresorbable implants. AUTHORS' CONCLUSIONS: In a selected group of compliant patients with simple fractures, the use of bioresorbable fixation devices might be advantageous.

Bioresorbable glass fibres facilitate peripheral nerve regeneration
Bunting, S., L. Di Silvio, et al. (2005), J Hand Surg [Br] 30(3): 242-7.
Abstract: This is a proof of principle report showing that fibres of Bioglass 45S5 can form a biocompatible scaffold to guide regrowing peripheral axons in vivo. We demonstrate that cultured rat Schwann cells and fibroblasts grow on Bioglass fibres in vitro using SEM and immunohistochemistry, and provide qualitative and quantitative evidence of axonal regeneration through a Silastic conduit filled with Bioglass fibres in vivo (across a 0.5 cm interstump gap in the sciatic nerves of adult rats). Axonal regrowth at 4 weeks is indistinguishable from that which occurs across an autograft. Bioglass fibres are not only biocompatible and bioresorbable, which are absolute requirements of successful devices, but are also amenable to bioengineering, and therefore have the potential for use in the most challenging clinical cases, where there are long inter-stump gaps to be bridged.

Bioresponsive hydrogel microlenses
Kim, J., S. Nayak, et al. (2005), J Am Chem Soc 127(26): 9588-92.
Abstract: We report investigations of bioresponsive hydrogel microlenses as a new protein detection technology. Stimuli-responsive poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAm-co-AAc) microgels have been synthesized via free-radical precipitation polymerization. These hydrogel microparticles were then functionalized with biotin via EDC coupling. Hydrogel microlenses were prepared from the particles via Coulombic assembly onto a silane-modified glass substrate. Arrays containing both pNIPAm-co-AAc microgels (as an internal control) and biotinylated pNIPAm-co-AAc microgels were then used to detect multivalent binding of both avidin and polyclonal anti-biotin. Protein binding was determined by monitoring the optical properties of the microlenses using a brightfield optical microscopy technique. The microlens method is shown to be very specific for the target protein, with no detectable interference from nonspecific protein binding. Finally, the reversibility of the hydrogel microlens assay has been studied in the case of anti-biotin to determine the potential application of the microlens assay technology in a displacement-type assay. These results suggest that the microlens method may be an appropriate one for label-free detection of proteins or small molecules via displacement of tethered protein--ligand pairs.

Biosensors based on acrylic microgels: a comparative study of immobilized glucose oxidase and tyrosinase
Rubio Retama, J., M. Sanchez-Paniagua Lopez, et al. (2005), Biosens Bioelectron 20(11): 2268-75.
Abstract: Acrylic microgels are proposed as enzyme immobilizing support in amperometric biosensors. Two enzymes, glucose oxidase and tyrosinase, were entrapped in this matrix and their behaviour is compared. The optimum cross-linking of the polymeric matrix required to retain the enzyme, and to allow the diffusion of the substrate is different for each enzyme, 3.2% for glucose oxidase and 4.5% for tyrosinase. The effect of pH and temperature on the biosensor responses has been studied by experimental design methodology and predictions have been compared with independently performed experimental measurements. A quadratic effect of the variables studied (pH and T) on the biosensor response and the small or null interaction between them was confirmed. The pH results obtained with both methods are coincident revealing an reversible effect on the enzyme. However, the temperature optimum value obtained by experimental design was 10 degrees C lower as a result of an activity decay due to irreversible thermal denaturation of both enzymes.

Bio-sorption of acidic gelatine hydro-gels implanted in the back tissues of Fisher's rats
Taira, M., H. Furuuchi, et al. (2005), J Oral Rehabil 32(5): 382-7.
Abstract: Recent advance in tissue engineering therapy requires new scaffold materials. Acidic gelatine powders (10 wt%) were, thus, dissolved in water, were or were not cross-linked, and freeze-dried. After sterilization, prepared small sponges were implanted in 7-week-old Fisher's rats' subcutaneous tissues for up to 2 weeks. Sponges absorbed body fluid and changed into hydro-gels in vivo. Non-cross-linked hydro-gels were absorbed within 3 days, while cross-linked hydro-gels were eliminated after 7 days' implantation. Histological observations revealed that the common captivation process was mild while granulocytes and macrophages were encountered. Because acidic gelatine sponges can accommodate various basic growth factors, it can be speculated that prepared sponges might be used as short-time hydro-gel scaffolds and growth-factor carriers.

Biostability and macrophage-mediated foreign body reaction of silicone-modified polyurethanes
Christenson, E. M., M. Dadsetan, et al. (2005), J Biomed Mater Res A 74(2): 141-55.
Abstract: In this study, the effect of soft segment chemistry on the phase morphology and in vivo response of commercial-grade poly(ether urethane) (PEU), silicone-modified PEU (PEU-S), poly(carbonate urethane) (PCU), and silicone-modified PCU (PCU-S) elastomers were examined. Silicone-modified polyurethanes were developed to combine the biostability of silicone with the mechanical properties of PEUs. Results from the infrared spectroscopy confirmed the presence of silicone at the surface of the PEU-S and PCU-S films. Atomic force microscopy phase imaging indicated that the overall two-phase morphology of PEUs, necessary for its thermoplastic elastomeric properties, was not disrupted by the silicone modification. After material characterization, the in vivo foreign body response and biostability of the polyurethanes were studied using a subcutaneous cage implant protocol. The results from the cage implant study indicated that monocytes adhere, differentiate to macrophages which fuse to form foreign body giant cells on all of the polyurethanes. However, the silicone-modified surfaces promoted apoptosis of adherent macrophages at 4 days and high levels of macrophage fusion after 21 days. These results confirm that the surface of a biomaterial may influence the induction of apoptosis of adherent macrophages in vivo and are consistent with previous cell culture studies of these materials. This study validates the use of our standard cell culture protocol to predict in vivo behavior and further supports the hypothesis that interleukin-4 is the primary mediator of macrophage fusion and foreign body giant cell formation in vivo. The impact of these findings on the biostability of polyurethanes is the subject of current investigations. Attenuated total reflectance-Fourier transform infrared analysis of explanted specimens provided evidence of chain scission and crosslinking at the surface of all of the polyurethanes. The silicone modification did not fully inhibit the oxidative biodegradation of the polyether or polycarbonate soft segments; however, the rate of chain scission of PEU-S and PCU-S seemed to be slower than the control polyurethanes. To verify this finding and to quantify the rate of chain scission in order to predict long-term biostability, an in vitro environment that simulated the microenvironment at the adherent cell-material interface was used to accelerate the biodegradation of the polyurethanes. Polyurethane films were treated in vitro for up to 36 days in 20% hydrogen peroxide/0.1M cobalt chloride solution at 37 degrees Celsius. Characterization with attenuated total reflectance-Fourier transform infrared and scanning electron microscopy showed soft segment and hard segment degradation consistent with the chemical changes observed after long-term in vivo treatment. The biostability ranking of these four materials based on rate of chain scission and surface pitting was as follows: PEU < PEU-S PCU < PCU-S. The silicone modification increased the biostability of the PEU and PCU elastomers while maintaining the thermoplastic elastomeric properties.

Biostability of polyether-urethane scaffolds: a comparison of two novel processing methods and the effect of higher gamma-irradiation dose
Haugen, H., L. C. Gerhardt, et al. (2005), J Biomed Mater Res B Appl Biomater 73(2): 229-37.
Abstract: This article deals with enzyme-induced biodegradation behavior of thermoplastic polyether-urethane (TPU). Porous scaffolds were processed by a new foaming method applied in hot pressing and injection molding. The scaffolds were subsequently gamma sterilized. The samples were incubated with cholesterol esterase (CE) for 28 days to simulate an enzymatic degradation order to assess polymer biostability. The main focus of degradation products was the most toxic one: methylene dianiline (MDA). LC/MS was used to separate the breakdown products and to identify possible MDA amounts. The results showed that (a) the hot-pressed sample released an MDA amount almost twice as large (0.26 ng +/- 0.008) as that of the injection-molded samples (0.15 ng +/- 0.003) after incubation with enzyme activity in the physiological range, and (b) a tenfold increase in CE activity revealed considerably higher MDA amounts (7540.0 ng +/- 0.004). This enzyme concentration is physiologically unlikely, however, but may occur for extreme high inflammation behavior. Even for extremely high levels of CE enzyme, the scaffold will not discharge MDA above toxic levels. The injection-molded samples sterilized at 25 kGy seem to represent the most promising processing method. Therefore, the new injection-molding foaming process of polyether-urethane can be considered appropriate for use as a biomaterial.

Biotechnology applications in biomaterials
Hellman, K. B., G. L. Picciolo, et al. (1994), J Cell Biochem 56(2): 143-4.

Biotechnology meets biomaterials
Bell, E. (1994), J Cell Biochem 56(2): 147-9.

Biotinylated GHK peptide incorporated collagenous matrix: A novel biomaterial for dermal wound healing in rats
Arul, V., D. Gopinath, et al. (2005), J Biomed Mater Res B Appl Biomater 73(2): 383-91.
Abstract: Matrikines are small peptide fragments of extracellular matrix proteins that display potent tissue repair activities. Difficulties in achieving sustained delivery of bioactive concentration of matrikines in the affected area limits their therapeutic use. The present study evaluates the effects biotinylated matrikine peptide (bio-glycyl-histidyl-lysine) incorporated collagen membrane for dermal wound healing processes in rats. Biotinylated peptide incorporated collagen matrix (PIC) showed better healing when compared to wounds treated with collagen matrix [CF (collagen film)] and without collagen [CR (control)]. Binding studies indicate that biotinylated GHK (Bio-GHK) binds effectively to the collagen matrix and red blood cell (RBC) membrane when compared with t-butyloxycarbonyl substituted GHK (Boc-GHK). Wound contraction, increased cell proliferation, and high expression of antioxidant enzymes in PIC treated group indicate enhanced wound healing activity when compared to CF and CR groups. Interestingly Bio-GHK incorporated collagen increases the copper concentration by ninefold at the wound site indicating the wound healing property of Bio-GHK can also be linked with both copper localization and matrikine activities. These results demonstrate the possibility of using Bio-GHK incorporated collagen film as a therapeutic agent in the wound healing process.

Biphasic calcium phosphate/hydrosoluble polymer composites: a new concept for bone and dental substitution biomaterials
Daculsi, G., P. Weiss, et al. (1999), Bone 25(2 Suppl): 59S-61S.
Abstract: Calcium phosphate materials have been increasingly employed in orthopedic and dental applications in recent years and are now being developed for use in noninvasive surgery or as carriers for drug delivery systems. We developed an injectable bone substitute (IBS) constituted of biphasic calcium phosphate and a hydrosoluble polymer as a carrier. In vivo biocompatibility and biofunctionality of IBS were tested in rabbits using implants in osseous and nonosseous areas. The results obtained demonstrated that the concept of IBS, a filler without initial mechanical properties but able to be rapidly resorbed and replaced by newly formed bone, can be applied to new surgical applications in orthopedic surgery, maxillofacial surgery, and dentistry for pulp capping and root filling.

Bisphenol A and its biomaterial monomer derivatives alteration of in vitro cytochrome P450 metabolism in rat, minipig, and human
Cannon, J. M., E. Kostoryz, et al. (2000), Biomacromolecules 1(4): 656-64.
Abstract: Bisphenol A (BPA) is a common structural component in a wide variety of biomaterial monomers. The effects of BPA and the following derivatives: bisphenol A glycidyl methacrylate (BisGMA), bisphenol A glycidyl diacrylate (BAGDA), bisphenol A ethoxylate dimethacrylate (BAEDM), bisphenol A dimethacrylate (BADM), and bisphenol A diglycidyl ether (BADGE) on mixed function oxidases (MFOs) are reported in this study. The rate of formation of metabolites from isoform-specific substrates for the MFOs (or cytochromes) CYP 1A, 2A, 2C, 2E, 3A, and 4A in the absence (control) and presence of BPA and derivatives was used to assess inhibition or stimulation of human, rat (male and female) liver, and minipig liver microsomal MFO activity. For human preparations the strongest inhibition by BPA was observed for CYP 2C. The inhibition was most prominent when a lower dose of BPA was used on the complete post-mitochondrial fraction. BPA inhibited rat microsomal CYP 1A isoform-specific metabolite production to 29 +/- 3% of control levels (100%). Biomaterial monomers exhibited mixed effects. For example, BPA stimulated CYP 4A in pooled human S9 to 129 +/- 1% of control. Also, BADM and BAGDA stimulated CYP 4A to 141% and 142% of control values, respectively.

Bisphosphonate inhibition of bone resorption induced by particulate biomaterial-associated macrophages
Pandey, R., J. M. Quinn, et al. (1996), Acta Orthop Scand 67(3): 221-8.
Abstract: Aseptic loosening of total joint replacements is associated with bone resorption. A heavy infiltrate of foreign body macrophages in response to biomaterial wear particles is commonly found in the fibrous membrane surrounding loose components. It has recently been shown that foreign body macrophages can differentiate into osteoclastic cells. To determine whether pharmacological inhibitors of bone resorption have a role to play in controlling the osteolysis of aseptic loosening, we analyzed the effect of a bisphosphonate, disodium ethane-1, 1-diphosphonate (EHDP) on this process. Murine monocytes and foreign body macrophages (derived from granulomas formed by subcutaneous implantation of particles of prosthetic biomaterials) were co-cultured with UMR106 osteoblast-like cells in the presence of 1,25 dihydroxyvitamin D3 for 14 days on glass coverslips and bone slices. EHDP significantly inhibited bone resorption in these co-cultures. There was little or no expression of the osteoclast-associated enzyme, tartrate-resistant acid phosphatase (TRAP) in EHDP-treated co-cultures. Addition of EHDP to monocyte-UMR106 co-cultures after the appearance of TRAP-positive cells did not abolish bone resorption, indicating that EHDP, in addition to its known inhibitory effect on osteoclast function, suppresses differentiation of osteoclast precursors. EHDP inhibition of the osteolysis induced by particulate biomaterial-associated macrophages shows that pharmacological inhibition of bone resorption might be used to control the osteolysis of aseptic loosening.

Blood compatibility of biomaterials: evaluation of a simple screening test
Mason, R. G. (1973), Biomater Med Devices Artif Organs 1(1): 131-9.

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Last Modified: 8 February 2006