Biomaterials.info - Resources for Engineers

Record 1521 to 1540

Cultured differentiated human urothelial cells in the biomaterials field
Pariente, J. L., L. Bordenave, et al. (2000), Biomaterials 21(8): 835-9.
Abstract: To review the use of normal cultured differentiated human urothelial cells in the biomaterials field, we checked the literature for human urothelial cells in culture (HUC) both for their use in biocompatibility assessment and as bioartificial devices. The in vitro culture of differentiated human urothelium is now a simple and reliable procedure. These techniques provide new tools for biocompatibility assessment of urinary biomaterials, because for the rational design of a testing procedure, it is preferable that the particular cell culture models selected should be closely related to the end-use application. The emerging use of HUC culture should lead to the development of bioartificial tissue for urinary tract reconstruction. Tissue engineering techniques require urothelial cells and cell delivery matrices. The cytocompatibility of novel artificial delivery matrices should be assessed in vitro before implantation using cultured HUC to find the best material available.

Curcumin impregnation improves the mechanical properties and reduces the inflammatory response associated with poly(L-lactic acid) fiber
Su, S. H., K. T. Nguyen, et al. (2005), J Biomater Sci Polym Ed 16(3): 353-70.
Abstract: We investigated poly(L-lactic acid) (PLLA) fibers and coils, simulating stents and the influence of impregnation with curcumin, a non-steroidal anti-inflammatory drug, intended to reduce the pro-inflammatory property of these implants. Fibers obtained by melt extrusion of 137 kDa PLLA resin containing 10% curcumin (C-PLLA) exhibited a stable curcumin release rate for periods up to 36 days. Curcumin increased the fiber tensile strength at break and decreased embrittlement vs. controls in 36 day 37 degrees C saline incubation. A mouse peritoneal phagocyte model was employed to test the anti-inflammatory properties of C-PLLA fibers in vitro. Myeloperoxidase and non-specific esterase activity assays were performed for adherent cells (polymorphonuclear leukocytes (PMN) and macrophages (MPhi), respectively). PMN and MPhi adhesion to C-PLLA fibers were significantly reduced compared to control PLLA fibers (2.6 +/- 0.91) x 10(5) vs. (5.6 +/- 0.67) x 10(5) PMN/cm2 and (3.9 +/- 0.23) x 10(3) vs. (9.1 +/- 0.7) x 10(3) MPhi/cm2 (P < 0.05), respectively. In addition, superoxide release in the phagocyte pool contacting C-PLLA fibers was 97% less than that for PLLA controls. A fresh human whole blood recirculation system was employed to analyze cell adhesion under flow conditions, employing scanning electron microscopy (SEM). Reduced adhesion of cells on C-PLLA fiber coils vs. controls was observed. These in vitro studies demonstrate that bulk curcumin impregnation can reduce the inflammatory response to bioresorbable PLLA fibers, whilst improving mechanical properties, thereby suggesting curcumin loading may benefit PLLA-based implants.

Current biomaterial problems in implants
Skinner, H. B. (1992), Instr Course Lect 41: 137-44.

Current concepts in orthopaedic biomaterials and implant fixation
Bonelli, A. (1994), J Bone Joint Surg Am 76(12): 1897-8.

Current concepts of metal-on-metal hip resurfacing
Clarke, I. C., T. Donaldson, et al. (2005), Orthop Clin North Am 36(2): 143-62, viii.
Abstract: The second-generation, metal-on-metal (MOM) bearing for total hip replacements was launched in the 1980s, and resurfacing followed in the mid-1990s. Remaining challenges include long-term bone remodeling of the femoral resurfacing and consideration of adverse MOM wear conditions. Precise understanding of manufacturing variables such as alloy types, bearing diameters, design tolerances, and surface finish is imperative in obtaining clinical consistency and safety in the patient. This review examines femoral fixation, bone remodeling, and wear studies of MOM implants and provides a brief overview of the latest outcome and retrieval data and how these data integrate with the in vitro wear studies.

Current status of biomaterials in ophthalmology
Refojo, M. F. (1982), Surv Ophthalmol 26(5): 257-65.
Abstract: The artificial materials currently used in ophthalmology are reviewed. Those include poly(methyl methacrylate) in contact lenses, keratoprostheses, and intraocular lenses; cellulose acetate butyrate and the siloxane-containing polymethacrylates in contact lenses; the silicones in contact lenses, scleral buckling materials, and drainage implants in glaucoma; the hydrogels for contact lenses and retinal surgery implants; and the cyanoacrylate adhesives for corneal perforations and ulcers. The properties of the materials and their relationship to ocular tissues, as well as the advantages and disadvantages of their use in the eye are discussed. Probable future advances of biomaterials in ophthalmology are also discussed.

Current status of prosthetic bypass grafts: a review
Kannan, R. Y., H. J. Salacinski, et al. (2005), J Biomed Mater Res B Appl Biomater 74(1): 570-81.
Abstract: Polymers such as Dacron and polytetrafluoroethylene (PTFE) have been used in high flow states with relative success but with limited application at lower flow states. Newer polymers with greater compliance, biomimicry, and ability to evolve into hybrid prostheses, suitable as smaller vessels, are now being introduced. In view of the advances in tissue engineering, this makes possible the creation of an ideal off-the-shelf bypass graft. We present a broad overview of the current state of prosthetic bypass grafts.

Current strategies for articular cartilage repair
Meyer, U., A. Buchter, et al. (2005), Eur Cell Mater 9: 39-49.
Abstract: In order to assess how bone substitute materials determine bone formation in vivo it is useful to understand the mechanisms of the material surface/tissue interaction on a cellular level. Artificial materials are used in two applications, as biomaterials alone or as a scaffold for osteoblasts in a tissue engineering approach. Recently, many efforts have been undertaken to improve bone regeneration by the use of structured material surfaces. In vitro studies of bone cell responses to artificial materials are the basic tool to determine these interactions. Surface properties of materials surfaces as well as biophysical constraints at the biomaterial surface are of major importance since these features will direct the cell responses. Studies on osteoblastlike cell reactivity towards materials will have to focus on the different steps of protein and cell reactions towards defined surface properties. The introduction of new techniques allows nowadays the fabrication of materials with ordered surface structures. This paper gives a review of present knowledge on the various stages of osteoblast reactions on material surfaces, focused on basic cell events under in vitro conditions. Special emphasis is given to cellular reactions towards ordered nano-sized topographies.

Current techniques to improve the blood compatibility of biomaterial surfaces
Engbers, G. H. and J. Feijen (1991), Int J Artif Organs 14(4): 199-215.

Current trends in the enhancement of biomaterial osteointegration: biophysical stimulation
Fini, M., G. Giavaresi, et al. (2004), Int J Artif Organs 27(8): 681-90.
Abstract: To enhance bone implant osteointegration, many strategies for improving biomaterial properties have been developed which include optimization of implant material, implant design, surface morphology and osteogenetic coatings. Other methods that have been attempted to enhance endogenous bone healing around biomaterials are different forms of biophysical stimulations such as pulsed electromagnetic fields (PEMFs) and low intensity pulsed ultrasounds (LIPUS), which were initially developed to accelerate fracture healing. To aid in the use of adjuvant biophysical therapies in the management of bone-implant osteointegration, the present authors reviewed experimental and clinical studies published in the literature over the last 20 years on the combined use of biomaterials and PEMFs or LIPUS, and summarized the methodology, and the possible mechanism of action and effectiveness of the different biophysical stimulations for the enhancement of bone healing processes around bone implanted biomaterials.

Custom design of the cardiac microenvironment with biomaterials
Davis, M. E., P. C. Hsieh, et al. (2005), Circ Res 97(1): 8-15.
Abstract: Many strategies for repairing injured myocardium are under active investigation, with some early encouraging results. These strategies include cell therapies, despite little evidence of long-term survival of exogenous cells, and gene or protein therapies, often with incomplete control of locally-delivered dose of the factor. We propose that, ultimately, successful repair and regeneration strategies will require quantitative control of the myocardial microenvironment. This precision control can be engineered through designed biomaterials that provide quantitative adhesion, growth, or migration signals. Quantitative timed release of factors can be regulated by chemical design to direct cellular differentiation pathways such as angiogenesis and vascular maturation. Smart biomaterials respond to the local environment, such as protease activity or mechanical forces, with controlled release or activation. Most of these new biomaterials provide much greater flexibility for regenerating tissues ex vivo, but emerging technologies like self-assembling nanofibers can now establish intramyocardial cellular microenvironments by injection. This may allow percutaneous cardiac regeneration and repair approaches, or injectable-tissue engineering. Finally, materials can be made to multifunction by providing sequential signals with custom design of differential release kinetics for individual factors. Thus, new rationally-designed biomaterials no longer simply coexist with tissues, but can provide precision bioactive control of the microenvironment that may be required for cardiac regeneration and repair.

Cutting directions of bone with biomaterials in situ does influence the outcome of histomorphometrical quantifications
Johansson, C. B. and P. Morberg (1995), Biomaterials 16(13): 1037-9.
Abstract: Ten commercially pure titanium implants were inserted in the tibia of ten mature New Zealand white rabbits for a healing period of 3 months. Cut and ground sections were performed on transversely and longitudinally cut tibia bone with implants in situ. Each implant with surrounding bone was processed by (a) dividing it into two parts by cutting transversely through the tibia and then (b) cutting one of the implant halves longitudinally through the tibia. In both cases 10 microns sections were made. Computerized histomorphometrical calculations of the bone-to-metal contact and the bone area in the threads were performed and comparisons of the differently cut sections were made for the same implant. Larger amounts of bone-to-metal contact and bone area in the threads were observed in the longitudinally cut samples in comparison to transversely cut ones. A strong statistically significant difference was obtained when comparing the transversely with the longitudinally cut samples with respect to bony contacts in the cortical region, demonstrating 25% more bone-to-metal contact lengths in the longitudinal cutting direction of the tibia. Quantitative histomorphometrical comparisons should, therefore, be performed on samples that are cut in the same direction.

CxGELSIX: a novel preparation of type VI collagen with possible use as a biomaterial
Lekskul, M., R. Burrows, et al. (2000), Cornea 19(2): 194-203.
Abstract: PURPOSE: This study was initiated to evaluate tissue acceptance and stability of a novel type VI collagen preparation (CxGelsix) as a biomaterial in the rabbit corneal stroma. We hypothesized that CxGelsix, embedded intrastromally, does not have any adverse affect on surrounding corneal tissues, and remains intact in the presence of an acute inflammatory reaction during corneal wound healing. METHODS: Type VI collagen was extracted and purified from rabbit corneal stroma under nondenaturing conditions. This preparation, Gelsix, was concentrated and cross-linked with polyethylene glycol to produce a transparent film (CxGelsix). Discs of CxGelsix, 4.0-mm diameter, 9- to 35-microm thick were implanted intrastromally and clinically examined periodically for 4 months. In another experiment, implantation of CxGelsix, 2.0-mm-diameter, was followed by corneal wounding adjacent to the implant and examined clinically for 30 weeks. At the end of these periods, the tissues from these experiments were processed for light and transmission electron microscopy. RESULTS: An intralamellar 4.0-mm-diameter disc of CxGelsix does not alter the structure of corneal epithelium above the implant, suggesting normal transport of nutrients through CxGelsix. Moreover, no structural abnormalities were seen in the rest of the cornea, and the cornea remains transparent. Although the cornea accepts the presence of CxGelsix disc as judged by clinical criteria, gradual degradation of the implant is seen ultrastructurally. CxGelsix is remarkably stable despite its exposure to endogenous enzymes during inflammation and wound healing. Partial degradation of the implant occurs only after many months, and it is gradually replaced with bundles of fine collagen fibrils reminiscent of normal cornea. CONCLUSION: The results of this study suggest that CxGelsix is potentially useful as a biomaterial.

Cyanoacrylate tissue glues facilitate the application of Biobrane
Haeney, J. A., O. M. Austin, et al. (2005), Burns 31(3): 396-7.

Cyanogen bromide and tresyl chloride chemistry revisited: the special reactivity of agarose as a chromatographic and biomaterial support for immobilizing novel chemical groups
Jennissen, H. P. (1995), J Mol Recognit 8(1-2): 116-24.
Abstract: The cyanogen bromide and tresyl chloride (2,2,2-trifluoroethanesulfonyl chloride) methods belong to the best-known activation procedures for solid supports in biochemistry. In both cases the originally proposed reaction mechanisms were revised many years later. In this paper important aspects of these two major activation reactions in connection with the singular polysaccharide support, agarose, will be treated with emphasis on the novel reaction mechanism recently proposed for tresyl chloride. In addition, the special role played by sulfur in the new uncharged alkyl-S-S-gels is examined in connection with the phenomenon of base-atom recognition.

Cyclic biaxial strain affects U937 macrophage-like morphology and enzymatic activities
Matheson, L. A., G. N. Maksym, et al. (2006), J Biomed Mater Res A 76(1): 52-62.
Abstract: As monocytes migrate to the site of a foreign body and differentiate into mature monocyte-derived macrophages (MDMs), the cells undergo a morphological transformation that involves mechanical stimulation via membrane stretch. Because the site of many cardiovascular implant devices includes substrates that are also undergoing mechanical change, it is of interest to assess the effect of such dynamic conditions on cellular-biomaterial responses. This study investigated the influence of cyclic (0.25 Hz) biaxial strain (maximum 10% amplitude) on human U937 macrophage-like cells cultured on a flexible siloxane membrane. Cell attachment was unaffected by the strain but total protein levels were significantly higher in stimulated cells. Intracellular esterase and released acid phosphatase activities were elevated by dynamic loading in addition to a strain-induced increase of monocyte-specific esterase protein as demonstrated by immunoblotting analysis. The morphology of static cells changed with cyclic strain from a round cell shape to an irregular, spread phenotype with a progressive reorganization of filamentous actin. The focal adhesion protein vinculin showed distinct reorganization in structure going from a well-defined arrangement in static cells to a diffuse staining pattern in mechano-stimulated cells. This study has demonstrated that U937 cells respond to cyclic deformation with an augmentation of select enzymatic activities that have been identified as being important in polymer biodegradation processes, as well as morphological changes, which may be characteristic of mechanical stress-induced cell activation. (c) 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2006.

Cyclic silicate active site and stereochemical match for apatite nucleation on pseudowollastonite bioceramic-bone interfaces
Sahai, N. and M. Anseau (2005), Biomaterials 26(29): 5763-70.
Abstract: Hydroxyapatite (Ca5(PO4)3(OH)) forms on pseudowollastonite (psW) (alpha-CaSiO3) in vitro in simulated body fluid, human parotid saliva and cell-culture medium, and in vivo in implanted rat tibias. We used crystallographic constraints with ab initio molecular orbital calculations to identify the active site and reaction mechanism for heterogeneous nucleation of the earliest calcium phosphate oligomer/phase. The active site is the planar, cyclic, silicate trimer (Si3O9) on the (001) face of psW. The trimer has three silanol groups (>SiOH) arranged at 60 degrees from each other, providing a stereochemical match for O atoms bonded to Ca2+ on the (001) face of hydroxyapatite. Calcium phosphate nucleation is modeled in steps as hydrolysis of surface Ca-O bonds with leaching of Ca2+ into solution, protonation of the surface Si-O groups to form silanols, calcium sorption as an inner-sphere surface complex and, attachment of HPO4(2-). Our model explains the experimental solution and high resolution transmission electron microscopy data for epitaxial hydroxyapatite growth on psW in vitro and in vivo. We propose that the cyclic silicate trimer is the universal active site for heterogeneous, stereochemically promoted nucleation on silicate-based bioactive ceramics. A critical active site-density and a point of zero charge of the bioceramic less than physiological pH are required for bioactivity.

Cytochrome P450 biosensors-a review
Bistolas, N., U. Wollenberger, et al. (2005), Biosens Bioelectron 20(12): 2408-23.
Abstract: Cytochrome P450 (CYP) is a large family of enzymes containing heme as the active site. Since their discovery and the elucidation of their structure, they have attracted the interest of scientist for many years, particularly due to their catalytic abilities. Since the late 1970s attempts have concentrated on the construction and development of electrochemical sensors. Although sensors based on mediated electron transfer have also been constructed, the direct electron transfer approach has attracted most of the interest. This has enabled the investigation of the electrochemical properties of the various isoforms of CYP. Furthermore, CYP utilized to construct biosensors for the determination of substrates important in environmental monitoring, pharmaceutical industry and clinical practice.

Cytocompatibility of self-assembled beta-hairpin peptide hydrogel surfaces
Kretsinger, J. K., L. A. Haines, et al. (2005), Biomaterials 26(25): 5177-86.
Abstract: MAX1 is a 20 amino acid peptide that undergoes triggered self-assembly to form a rigid hydrogel. When dissolved in aqueous solutions, this peptide exists in an ensemble of random coil conformations rendering it fully soluble. The addition of an exogenous stimulus results in peptide folding into beta-hairpin conformation. This folded structure undergoes rapid assembly into a highly crosslinked hydrogel network. DMEM cell culture media is one stimulus able to initiate folding and consequent self-assembly of MAX1. The cytocompatibility of this gel towards NIH 3T3 murine fibroblasts is demonstrated. Gels were shown to be non-toxic to the fibroblast cells. MAX1 hydrogels also foster the ability of the cells to attach to the hydrogel scaffold in the absence or presence of serum proteins. Additionally MAX1 hydrogels were able to support fibroblast proliferation to confluency with little effect on the rheological properties of the scaffold. MAX1 hydrogels meet the preliminary mechanical and cytocompatibiltiy requirements of a tissue engineering scaffold.

Cytomimetic biomaterials. 3. Preparation and transport studies of an alginate/amphiphilic copolymer/polymerized phospholipid film
Chon, J. H., K. G. Marra, et al. (1999), J Biomater Sci Polym Ed 10(1): 95-107.
Abstract: The significance of molecular design methodologies based upon membrane-mimetic systems lies in the ability to engineer robust materials of varying geometry with a high degree of reproducibility and molecular control over surface order and chemistry. However, non-covalently associated assemblies, in and of themselves, are often insufficiently robust for many applications. We have previously reported the in situ polymerization of a single phospholipid monolayer on a self-assembled film of octadecyltrichrolosilane (OTS) on glass, as well as the polymerization of phospholipids on an amphiphilic, dialkyl-containing terpolymer bound to a gold-coated silicon wafer. We now report the polymerization of a phospholipid monolayer assembly onto an alkylated hydrogel substrate with significant alteration in both surface chemistry and mass transport properties at the hydrogel-water interface. A general platform is thereby created for enhancing the control of either the local delivery of specific macromolecules or the immunoisolation barrier for many cell based therapies.

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