Biomaterials.info - Resources for Engineers

Record 2721 to 2740

Management of thrombectomy for acute thrombosis of aortic composite valve graft in pregnancy
Broscheit, J. A., C. A. Greim, et al. (2005), J Cardiothorac Vasc Anesth 19(2): 222-4.

Mandibular fractures: Historical perspective
Mukerji, R., G. Mukerji, et al. (2005), Br J Oral Maxillofac Surg
Abstract: The principles of the treatment of mandibular fractures have changed recently, although the objective of re-establishing the occlusion and masticatory function remains the same. Splinting of teeth is an old way of immobilising fractures but the advent of modern biomaterials has changed clinical practice towards plating the bone and early restoration of function. We present a brief historical overview of techniques and systems that have been used for stabilisation of mandibular fractures.

Manipulation of cellular interactions with biomaterials toward a therapeutic outcome: a perspective
Pierschbacher, M. D., J. W. Polarek, et al. (1994), J Cell Biochem 56(2): 150-4.
Abstract: Manipulation of the wound healing process and the manner in which tissues interact with inert biomaterials were both made possible with the discovery of arginine-glycine-aspartic (RGD) acid as a major cell recognition signal in the extracellular matrix. Whether promoting cell adhesion or selectively inhibiting cell-cell aggregation mediated by integrin cell surface receptors, RGD-containing peptides can be rationally designed to incorporate both stability and integrin specificity. Synthetic peptides containing this sequence have been linked to biodegradable biopolymers and introduced for the enhancement of dermal and corneal would healing. By accelerating the healing reaction using RGD-containing peptides, the quality of regenerated tissue seems to be improved, the extent of fibrosis restricted, and the risk of microbial infection may be reduced. Controlling the degree of fibrosis that often accompanies the healing of wounds and the reaction of tissue to foreign materials can also be achieved by natural antagonists of fibrogenic activity of TGF-beta animal models of kidney fibrosis. These advances in the biotechnology of wound healing and tissue regeneration eventually will have an overall impact on the quality of health care.

Manufacture of biomaterials by a novel printing process
Limpanuphap, S. and B. Derby (2002), J Mater Sci Mater Med 13(12): 1163-6.
Abstract: Tricalcium phosphate (TCP) scaffolds with controlled internal porosity were fabricated with a suspension of TCP in diacrylate cross-linking monomers using a mold prepared by ink-jet printing. Scaffolds were removed by selective dissolution of the mold. They were heat treated for removal of the acrylic binder followed by sintering. Despite a considerable linear shrinkage, scaffold porosity was retained after sintering. Composite scaffolds were fabricated from TCP in poly(ethylene glycol) diacrylate using an identical gel casting route.

Manufacture of porous polymer nerve conduits through a lyophilizing and wire-heating process
Huang, Y. C., Y. Y. Huang, et al. (2005), J Biomed Mater Res B Appl Biomater 74(1): 659-64.
Abstract: We have developed a method for nerve tissue regeneration using longitudinally oriented channels within biodegradable polymers created by a combined lyophilizing and wire-heating process. This type of cell-adhesive scaffold provides increased area to support and guide extending axons subsequent to nerve injury. Utilizing Ni-Cr wires as mandrels to create channels in scaffold increased safety, effectiveness, and reproducibility. The scaffolds tested were made from different biodegradable polymers, chitosan and poly(D,L-lactide-co-glycolide) (PLGA), because of their availability, ease of processing, low inflammatory response, and approval by the FDA. According to our experimental results, the high permeability and the characteristic porous structure of chitosan proved to be a better material for nerve guidance than PLGA. The scanning electron micrographs revealed that the scaffolds were consistent along the longitudinal axis with channels being distributed evenly throughout the scaffolds. There was no evidence to suggest merging or splitting of individual channels. The diameter of the channels was about 100 mum, similar to the 115 micromameter of the Ni-Cr wire. Regulating the size and quantity of the Ni-Cr wires allow us to control the number and the diameter of the channels. Furthermore, the neutralizing processes significantly influenced the porous structure of chitosan scaffolds. Using weak base (NaHCO(3) 1M) to neutralize chitosan scaffolds made the porous structure more uniform. The innovative method of using Ni-Cr wires as mandrels could be easily tailored to other polymer and solvent systems. The high permeability and the characteristic porous structure of chitosan made it a superior material for nerve tissue engineering. These scaffolds could be useful for guiding regeneration of the peripheral nerve or spinal cord after a transection injury.

MARCO is the major binding receptor for unopsonized particles and bacteria on human alveolar macrophages
Arredouani, M. S., A. Palecanda, et al. (2005), J Immunol 175(9): 6058-64.
Abstract: Alveolar macrophages (AMs) avidly bind and ingest inhaled environmental particles and bacteria. To identify the particle binding receptor(s) on human AMs, we used functional screening of anti-human AM hybridomas and isolated a mAb, PLK-1, which inhibits AM binding of unopsonized particles (e.g., TiO2, latex beads; 63 +/- 5 and 67 +/- 4% inhibition, respectively, measured by flow cytometry; n = 11) and unopsonized bacteria (approximately 84 and 41% inhibition of Escherichia coli and Staphylococcus aureus binding by mAb PLK-1, respectively). The PLK-1 Ag was identified as the human class A scavenger receptor (SR) MARCO (macrophage receptor with collagenous structure) by observing specific immunolabeling of COS cells transfected with human MARCO (but not SR-AI/II) cDNA and by immunoprecipitation by PLK-1 of a protein of appropriate molecular mass (approximately 70 kDa) from both normal human bronchoalveolar lavage cells (>90% AMs) and human MARCO-transfected COS cells. PLK-1 also specifically inhibited particle binding by COS cells, only after transfection with human MARCO cDNA. Immunostaining showed specific labeling of AMs within human lung tissue, bronchoalveolar lavage samples, as well as macrophages in other sites (e.g., lymph node and liver). Using COS transfectants with different truncated forms of MARCO, allowed epitope mapping for the PLK-1 Ab to MARCO domain V between amino acid residues 420 and 431. A panel of Abs to various SRs identified expression on AMs, but failed to inhibit TiO2 or S. aureus binding. The data support a dominant role for MARCO in the human AM defense against inhaled particles and pathogens.

Marginal bone loss pattern around hydroxyapatite-coated versus commercially pure titanium implants after up to 12 years of follow-up
Schwartz-Arad, D., O. Mardinger, et al. (2005), Int J Oral Maxillofac Implants 20(2): 238-44.
Abstract: PURPOSE: The purpose of this study was to compare the marginal bone loss (MBL), complications, and 12-year survival rates of commercially pure titanium (cpTi) and hydroxyapatite (HA)-coated implants placed in the maxilla. MATERIALS AND METHODS: The study group consisted of 120 patients (77 women, 43 men) treated from 1988 to 1997. A total of 388 implants (156 cpTi and 232 HA-coated) were placed in the maxilla. There were 126 immediate (32.5%) and 262 (67.5%) nonimmediate implants. Patients were evaluated annually. Mean follow-up was 60 +/- 32.3 months. MBL was measured on radiographs using the implant threads as the dimensional reference. MBL, complications, and 12-year survival and success rates were correlated with implant coating, time of implantation, implant dimensions, and position in arch. RESULTS: Total mean MBL was 1.07 +/- 2.16 mm. MBL was significantly lower with cpTi implants (0.55 +/- 1.04 mm) compared to HA-coated implants (1.51 +/- 2.71 mm) (P <.001). No statistical difference in regard to MBL was found between immediate and nonimmediate implants (0.86 +/- 1.8 mm vs 1.16 +/- 2.3 mm). The total 12-year survival rate was 91.4%. HA-coated implants had a significantly higher 12-year survival rate than cpTi implants (93.2% vs 89%; P <.03). Nonimmediate implants had a significantly higher failure rate (8.2%) than the immediate implants (1.3%) (P <.009). No correlation was found between type of implant coating and late implant failure. DISCUSSION: Immediate implants can serve as a predictable option, providing higher survival and success rates. HA-coated implants tended to fail less during the surgical phase, but had higher mean MBL compared to cpTi implants. CONCLUSIONS: HA-coated implants had greater MBL than cpTi implants but a higher 12-year survival rate. Immediate implants had a lower failure rate than the nonimmediate implants in this study population.

Market study: biomaterials supply for permanent medical implants
Aronoff, M. S. (1995), J Biomater Appl 9(3): 205-61.
Abstract: The withdrawal of DuPont as a supplier of key raw materials created a major dislocation in the medical device industry. We studied the present and future impact caused by the market removal of polyethylene terephthalate (PET) yarn ("Dacron"), polytetrafluorethylene (PTFE) fiber and resin ("Teflon"), and polyacetal resin ("Delrin"). Findings were: 1) Dollar values of the permanent medical implant markets for PET yarn, PTFE fiber and resin, and polyacetal resin are a minute fraction, of their values for their other commercial markets; 2) The implant market value is clearly not commensurate with the liability risk; and 3) The majority of these materials consumed by this market are used in the production of lifesaving, permanent medical implants [e.g., vital blood vessel replacements made from knitted polyester (PET)]. The remainder is used in life-enhancing, permanent implants [e.g., hernia patches made of polyester (PET) fabric].

Markets for biomaterials
Halter, P. and R. Yamamoto (1988), J Biomater Appl 2(3): 317-27.

Mast cells and the inflammatory response to different implanted biomaterials
Rezzani, R., L. Rodella, et al. (2004), Arch Histol Cytol 67(3): 211-7.
Abstract: The biocompatibility of dental materials is a topic of increasing importance for dentists. We investigated the effects of alloys for ceramic crowns and removable prostheses on the skin and lymphoid organs of rats. We used three groups of Sprague Dawley rats: group I as the control, with groups II and III implanted with different biomaterials into subcutaneous pockets. After sacrifice, the rat skin around the implant and the lymph nodes was studied. The tissues of implanted rats were morphologically different from the control animals as they showed a number of mast cells that increased 7 days after the implant with both alloys. These cells decreased 14 days after the implant with alloy for ceramic crowns whereas they were still high 28 days after the implant with alloy for removable prostheses. The findings suggest that both alloys induced different and time-dependent inflammatory reactions. Our findings have importance in the future rational design of biocompatible implantable and blood-contact biomaterials.

Mast cells mediate acute inflammatory responses to implanted biomaterials
Tang, L., T. A. Jennings, et al. (1998), Proc Natl Acad Sci U S A 95(15): 8841-6.
Abstract: Implanted biomaterials trigger acute and chronic inflammatory responses. The mechanisms involved in such acute inflammatory responses can be arbitrarily divided into phagocyte transmigration, chemotaxis, and adhesion to implant surfaces. We earlier observed that two chemokines-macrophage inflammatory protein 1alpha/monocyte chemoattractant protein 1-and the phagocyte integrin Mac-1 (CD11b/CD18)/surface fibrinogen interaction are, respectively, required for phagocyte chemotaxis and adherence to biomaterial surfaces. However, it is still not clear how the initial transmigration of phagocytes through the endothelial barrier into the area of the implant is triggered. Because implanted biomaterials elicit histaminic responses in the surrounding tissue, and histamine release is known to promote rapid diapedesis of inflammatory cells, we evaluated the possible role of histamine and mast cells in the recruitment of phagocytes to biomaterial implants. Using i.p. and s. c. implantation of polyethylene terephthalate disks in mice we find: (i) Extensive degranulation of mast cells, accompanied by histamine release, occurs adjacent to short-term i.p. implants. (ii) Simultaneous administration of H1 and H2 histamine receptor antagonists (pyrilamine and famotidine, respectively) greatly diminishes recruitment and adhesion of both neutrophils (<20% of control) and monocytes/macrophages (<30% of control) to implants. (iii) Congenitally mast cell-deficient mice also exhibit markedly reduced accumulation of phagocytes on both i.p. and s.c implants. (iv) Finally, mast cell reconstitution of mast cell-deficient mice restores "normal" inflammatory responses to biomaterial implants. We conclude that mast cells and their granular products, especially histamine, are important in recruitment of inflammatory cells to biomaterial implants. Improved knowledge of such responses may permit purposeful modulation of both acute and chronic inflammation affecting implanted biomaterials.

Material test system for the evaluation of mechanical properties of biomaterials
Hayashi, K. and T. Nakamura (1985), J Biomed Mater Res 19(2): 133-44.
Abstract: A new material test system has been designed to evaluate the mechanical properties of biomaterials which are very often subject to complicated dynamic and repetitive force and deformation inside the body. The test system has high versatility, being incorporated with a miniature servo-hydraulic testing machine which can smoothly apply various modes of load and deformation to materials, and a vidicon displacement analyzer for the accurate, noncontact measurement of specimen length. A minicomputer system is used for the data acquisition and processing. Performance tests of the system and preliminary experiments on elastomeric polymers have indicated that the test system is very useful for the detailed studies of the mechanical properties of various kinds of biomaterials.

Material thrombelastography: an assessment of phosphorylcholine compounds as models for biomaterials
Bird, R. R., B. Hall, et al. (1988), Thromb Res 51(5): 471-83.
Abstract: The use of phosphorylcholine (PC) containing compounds as possible biomaterials has been evaluated by material thrombelastography (MTEG). The detailed analysis of the MTEG technique is discussed. A remarkable reduction of thrombogenicity by compounds containing the PC group is demonstrated. The results observed with a polymerised PC-lipid indicate potential use of such substances as biomaterials with minimal thrombogenicity.

Material witness: body painting
Ball, P. (2005), Nat Mater 4(8): 582.

Materials analysis using x-ray linear attenuation coefficient measurements at four photon energies
Midgley, S. M. (2005), Phys Med Biol 50(17): 4139-57.
Abstract: The analytical properties of an accurate parameterization scheme for the x-ray linear attenuation coefficient are examined. The parameterization utilizes an additive combination of N compositional- and energy-dependent coefficients. The former were derived from a parameterization of elemental cross-sections using a polynomial in atomic number. The compositional-dependent coefficients are referred to as the mixture parameters, representing the electron density and higher order statistical moments describing elemental distribution. Additivity is an important property of the parameterization, allowing measured x-ray linear attenuation coefficients to be written as linear simultaneous equations, and then solved for the unknown coefficients. The energy-dependent coefficients can be determined by calibration from measurements with materials of known composition. The inverse problem may be utilized for materials analysis, whereby the simultaneous equations represent multi-energy linear attenuation coefficient measurements, and are solved for the mixture parameters. For in vivo studies, the choice of measurement energies is restricted to the diagnostic region (approximately 20 keV to 150 keV), where the parameterization requires N >or= 4 energies. We identify a mathematical pathology that must be overcome in order to solve the inverse problem in this energy regime. An iterative inversion strategy is presented for materials analysis using four or more measurements, and then tested against real data obtained at energies 32 keV to 66 keV. The results demonstrate that it is possible to recover the electron density to within +/-4% and fourth mixture parameter. It is also a key finding that the second and third mixture parameters cannot be recovered, as they are of minor importance in the parameterization at diagnostic x-ray energies.

Materials and biomaterials for interventional radiology
Laurent, A. (1998), Biomed Pharmacother 52(2): 76-88.
Abstract: Devices used in interventional radiology have significantly developed in the past few years. In order to understand the trends of this development, we analyzed how new interventional devices are progressively incorporating materials having original physical properties, and how developers are today progressively turning towards biomaterials, with respect to the new regulatory environment, and the requirements of biocompatibility.

Materials characterization of explanted mechanical heart valves and comparison to patients' clinical data
Fare, S., M. F. Brunella, et al. (2005), Int J Artif Organs 28(7): 701-10.
Abstract: In the present study, twelve explanted mechanical heart valves (MHVs)with pyrolitic carbon tilting disc and 14 bileaflet MHVs were analyzed to investigate the effects of material properties on valve performance and patients' general health conditions. Optical and scanning electron microscopy was used to investigate material imperfections, wear patterns or damages to housing and occluder components. All analyzed tilting disc valves exhibited wear effects, particularly due to abrasion and impact to both disc and housing. Wear of pyrolitic carbon disc and housing did not influence their in vivo performance. In the bileaflet MHVs, breakaway of the pyrolitic carbon coating sometimes caused malfunctioning and required surgical retrieval of the valve. In all cases, occurrence of clinical symptoms was more likely when wear effects were located in critical areas. The study supports a correlation between the properties of the MHVs material and patients' symptoms.

Materials for urinary catheters: a review of their history and development in the UK
Lawrence, E. L. and I. G. Turner (2005), Med Eng Phys 27(6): 443-53.
Abstract: The Foley catheter, introduced in the mid-1930s and originally manufactured from latex, is still the most commonly used device for the management of urinary incontinence (UI). Despite the passage of time, there are still problems associated with the use of these devices. It is currently estimated that the management and treatment of UI costs the UK National Health Service (NHS) in the order of 500 million pound per annum. Faced with the known demographic changes in the adult population these costs will continue to rise for the foreseeable future. This review examines the range of materials currently used to manufacture Foley catheters from both latex and silicone. It outlines the common problems associated with their clinical use-infection, encrustation and blockage. The main changes that have been made to the materials employed in response to these problems are analysed. In the first instance the use of controlled release glass and slow release polymers to introduce disinfectants and antibacterial agents is considered. Attempts to alter surface properties by using coatings based on silver, polytetrafluoroethylene (PTFE), hydrogels and silicone are then described. It can be seen that despite these approaches, problems remain with the design and materials currently used to manufacture catheters. The review concludes that changes to the materials currently used for the manufacture of commercially available catheters could potentially alleviate many of the existing problems. However, standards need to be developed in order to enable direct comparison of the mechanical and physical properties of existing and potential catheter designs to ensure their effective function in-service.

Materials or biomaterials?
Bruck, S. D. (1990), Int J Artif Organs 13(8): 469-71.

Materials science. Smart biomaterials
Anderson, D. G., J. A. Burdick, et al. (2004), Science 305(5692): 1923-4.

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