Biomaterials.info - Resources for Engineers

Record 1581 to 1600

Design and in vitro performance of a novel bileaflet mechanical heart valve prosthesis
Medart, D., C. Schmitz, et al. (2005), Int J Artif Organs 28(3): 256-63.
Abstract: Design and in vitro performance of a novel bileaflet mechanical heart valve prosthesis are presented. The novel heart valve exhibits three main design characteristics: (i) The leaflets form a Venturi passage in open position. Thus, a beneficial pressure distribution is obtained and the leaflets are stabilised in opened position. (ii) The orifice inlet is nozzle-shaped. Flow is convectively accelerated and flow separation at the orifice inlet is avoided. (iii) The hinge design facilitates an additional axial movement of the leaflets and leads to a self cleaning effect and enhances washout of the hinges. The design of the leaflet hinges is of main importance for the functional reliability and durability of mechanical heart valves. After manufacturing first prototypes from titanium and polymeric materials the hydrodynamic performance was evaluated according to ISO 5840 and FDA guidelines. Hydrodynamic performance is comparable with the results of commonly available bileaflet mechanical heart valve prostheses. Initial durability tests showed suitable material couples for further long term studies.

Design and properties of novel self-curing acrylic formulations for application in intervertebral disks restoration
Larraz, E., C. Elvira, et al. (2005), Biomacromolecules 6(4): 2058-66.
Abstract: Novel acrylic formulations incorporating an amphiphilic macromonomer, Triton methacrylate MT, have been prepared to be applied in intervertebral disks (IVD) restoration processes. The solid phase of the formulations is composed of poly (methyl methacrylate), PMMA, incorporating in some cases chondroitin sulfate, CS, as a regenerative bioactive molecule, whereas the liquid phase is constituted by MT and 2-hydroxyethyl methacrylate, HEMA, and in some formulations acrylic acid, AA, was also added. These are prepared similarly to acrylic bone cement formulations. The obtained curing parameters, with maximum temperatures in the range of 41-72 degrees C, make them suitable to be applied as injectable systems. Glass transition temperatures and swelling degree have also been determined. Mechanical properties such as compressive, stress relaxation, and shear tests have been analyzed for all of the prepared IVD formulations exhibiting shape memory characteristics and a pronounced elastic behavior that make them as excellent candidates for the intervertebral application.

Design and synthesis of new biomaterials via macromolecular substitution
Allcock, H. R. (1997), Ann N Y Acad Sci 831: 13-31.

Design and validation of a dynamic flow model simulating encrustation of biomaterials in the urinary tract
Gorman, S. P., C. P. Garvin, et al. (2003), J Pharm Pharmacol 55(4): 461-8.
Abstract: A number of models exist for assessing encrustation on biomaterials employed as devices in the urinary tract. However, static urine models are suitable only for assessment of biomaterials residing in the bladder and the dynamic models available suffer from a number of disadvantages, notably their complexity and limitation to short-term assessment. The dynamic model described herein is a relatively simple design incorporating the ability to assess a large number of biomaterials in replicate fashion and over long periods of time. The biomaterials tested in the dynamic model conform to the urethral catheter and ureteral stent devices that experience urine flow within the urinary tract. The model was initially validated using Percuflex as a test biomaterial. The mass of calcium and magnesium, representing hydroxyapatite and struvite encrustation, respectively, on Percuflex was detected by atomic absorption spectrometry. No significant differences in encrustation levels were detected either between vessels or between biomaterial positions on any mandrel within the vessels, indicating the suitability of the dynamic model for reproducible determination of biomaterial encrustation. The dynamic model was then used to compare the encrustation of biomaterials commonly employed in urinary-tract devices, namely polyurethane, Percuflex and silicone. Calcium and magnesium levels on polyurethane and Percuflex were shown to be statistically similar, whereas silicone exhibited significantly reduced encrustation. When, subsequently, comparisons were made of biomaterial encrustation between the dynamic model and a static model, calcium and magnesium levels arising from the latter model were significantly higher on each of the biomaterials. However, the same rank order of encrustation resistance was observed for the biomaterials in both models, with silicone performing better than polyurethane or Percuflex. The prediction of in-vivo performance based on in-vitro models of encrustation is often difficult, although the model described provides a more accurate method for assessing the potential of novel and existing biomaterials for use in urinary medical devices requiring flow of urine.

Design aspects of compliant, soft layer bearings for an experimental hip prosthesis
Scholes, S. C., A. Unsworth, et al. (2005), Proc Inst Mech Eng [H] 219(2): 79-87.
Abstract: Currently, an artificial hip joint can be expected to last, on average, in excess of 15 years with failure due, in the majority of cases, to late aseptic loosening of the acetabular component. A realistic alternative to the problem of wear in conventional joints is the introduction of bearing surfaces that exhibit low wear and operate in the full fluid-film lubrication regime. Contact analyses and friction tests were performed on compliant layer joints (metal-on-polyurethane) and the design of a prototype ovine arthroplasty model was investigated. When optimized, these components have been shown to achieve full fluid-film lubrication.

Design considerations when using semicrystalline engineering polymers
Poppe, E. A., C. Norrey, et al. (2005), Med Device Technol 16(7): 12-5.
Abstract: Intelligently exploiting the material properties of polymers can lead to multifunctional components that are commercially and functionally superior to previous designs. This article explains how to achieve this.

Design of a UHF applicator for rewarming of cryopreserved biomaterials
Evans, S., M. J. Rachman, et al. (1992), IEEE Trans Biomed Eng 39(3): 217-25.
Abstract: The dielectric properties of cryopreserved biological tissue are discussed in relation to the problems which arise when EM fields are used for rapid rewarming. The UHF band is favored from two aspects: the avoidance of thermal runaway and the uniformity of heating inhomogeneous material. Various resonant cavity applicators are considered for efficient and uniform rewarming. The square-aspect TE 111 cylindrical applicator is favored principally because it allows variation of the E-field orientation as required during the warming profile. An appropriate kidney phantom organ is described. It is used to obtain measured values of the overall efficiency of a TE 111 applicator. The efficiency values are found to fall steadily with increasing temperature from 85% at -40 degrees C to 45% at the phase change, mainly due to the decreasing tan delta value of the phantom material.

Design of functional hollow fiber membranes modified with phospholipid polymers for application in total hemopurification system
Ye, S. H., J. Watanabe, et al. (2005), Biomaterials 26(24): 5032-41.
Abstract: In this study, we prepared cellulose acetate (CA) hollow fiber membranes (HFMs) modified with poly (2-methacryloyloxyethyl phosphorylcholine (MPC)-co-n-butyl methacrylate)(PMB30 and PMB80) by the dry-jet wet spinning process. The physical and chemical structures of the HFMs were controlled in order to design highly functional HFMs that had suitable performance to each targeting HFM device used in a total hemopurification system. The CA HFMs modified with the MPC polymer, such as CA/PMB30, CA/PMB80, and CA/PMB30-80 HFMs, were successfully prepared by controlling the spinning conditions. The modified HFMs showed an improved performance in solute and water permeability, due to the modification by the hydrophilic MPC polymers. The CA/PMB30 and CA/PMB80 showed a high potential in an application for a high performance hemocompatible plasmapheresis and hemofilter device. Furthermore, CA/PMB30-80 HFM, modified asymmetrically with PMB30 and PMB80, showed a potential for application in an advanced total hemopurification system as a highly functional scaffold for a biohybrid renal tubule, or a liver assist bioreactor device, because of their enhanced permeability, hemocompatibility, and cytocompatibility.

Design of functionally graded dental implant in the presence of cancellous bone
Hedia, H. S. (2005), J Biomed Mater Res B Appl Biomater 75(1): 74-80.
Abstract: In a previous work by the author [Hedia HS, Mahmoud NA. Biomed Mater Eng 2004;14(2):133--143], a functionally graded material (FGM) dental implant was designed without cancellous bone in the model. In this investigation, the effect of the presence of cancellous bone as a thin layer around the dental implant was investigated. It is well known that the main inorganic component of natural bone is hydroxyapatite (HAP) and that the main organic component is collagen (Col). HAP implants are not bioabsorbable, and because induction of bone into and around the artificially made HAP is not always satisfactory, loosening or breakage of HAP implants might occur after implantation in the clinical application. The development of a new material that is bioabsorbable and that has osteo-conductive activity is needed. Therefore, the aim of the current investigation was to design an implant, in the presence of cancellous bone as a thin layer around it, from FGM. In this study, a novel biomaterial, Col/HAP, as a FGM, was developed using the finite element and optimization techniques that are available in the ANSYS package. These materials have a self-organized character similar to that of natural bone. The investigations have shown that the maximum stress in the cortical bone and cancellous bone for the Col/HAP functionally graded implant has been reduced by about 40% and 19%, respectively, compared with currently used titanium dental implants.

Design of modular non-viral gene therapy vectors
De Laporte, L., J. Cruz Rea, et al. (2006), Biomaterials 27(7): 947-54.
Abstract: Gene delivery has numerous potential applications both clinically and for basic science research. Non-viral vectors represent the long-term future of gene therapy and biomaterials are a critical component for the development of efficient delivery systems. Biomaterial development combined with fundamental studies of virus function and cellular processes will enable the molecular level design of modular vectors. Vectors are being developed based on cationic polymers or lipids that contain functional groups to mediate appropriate interactions with the extracellular environment or to interface with specific cellular processes. This review describes recent progress on the development of biomaterials for non-viral vectors and highlights opportunities for future development. Ultimately, efficient vectors will expand the traditional applications of gene therapy within the clinic and may enable numerous other opportunities within diagnostics, biotechnology, and basic science research.

Design of peptides for thin films, coatings and microcapsules for applications in biotechnology
Zheng, B., D. T. Haynie, et al. (2005), J Biomater Sci Polym Ed 16(3): 285-99.
Abstract: A highly-interdisciplinary approach has been developed for minimizing the immunogenicity of films, coatings, microcapsules and other nano-structured materials fabricated from designed polypeptide chains. It is to base the amino-acid sequences on solvent-exposed regions in the folded states of proteins from the same organism. Each such region that meets defined criteria with respect to charge is called a sequence motif. The approach becomes more specifically tailored for intravenous applications by requiring an employed sequence motif to correspond to a known blood protein. An algorithm has been developed to identify sequence motifs in protein-encoding regions of a genome. This work is focused on sequence motifs of charge per unit length >0.5 at neutral pH. It has been found that the number of unique sequence motifs meeting this criterion in available human genome data is maximal for motifs of approx. 7 residues in length. We have designed polypeptides on the basis of computational analysis and shown that they can be used to fabricate nano-structured thin films by electrostatic layer-by-layer assembly (ELBL). The results of this work are discussed with a view to possible applications in biotechnology, notably development of biocompatible coatings and microcapsules.

Design, synthesis, and preliminary characterization of tyrosine-containing polyarylates: new biomaterials for medical applications
Fiordeliso, J., S. Bron, et al. (1994), J Biomater Sci Polym Ed 5(6): 497-510.
Abstract: Five structurally related, aliphatic polyarylates were synthesized from tyrosine-derived diphenols and diacids. The diphenols were a homologous series of three desaminotyrosyl-tyrosine alkyl esters (ethyl, hexyl, octyl) which had previously been used in the synthesis of mechanically strong and tissue-compatible polycarbonates. The diacids (succinic acid, adipic acid, sebacic acid) were selected among compounds that were known to be of low systemic toxicity. By using different diacids as comonomers, the flexibility of the polymer backbone could be varied while the desaminotyrosyl-tyrosine alkyl esters provided pendent chains of various length. Some of the thermal and mechanical properties of the five polymers could be correlated to their chemical structure: the glass transition temperature decreased from 53 to 13 degrees C, and the tensile modulus (measured at room temperature) decreased from 1500 to about 3 MPa when the length of the aliphatic diacid in the polymer backbone and/or the length of the alkyl ester pendent chain was increased. The presence of an arylate bond in the polymer backbone introduced a hydrolytically labile linkage into the polymer structure. Under physiological conditions in vitro all polymers degraded: thin films retained only about 30-40% of their initial molecular weight (Mw) after 26 weeks of storage in phosphate buffer solutions (pH 7.4) at 37 degrees C. Release studies with p-nitroaniline as a model drug indicated that a diffusion controlled release process occurred. The rate of p-nitroaniline release could be correlated with the glass transition temperature of the polymer.

Designer self-assembling peptide nanofiber scaffolds for 3D tissue cell cultures
Zhang, S., F. Gelain, et al. (2005), Semin Cancer Biol 15(5): 413-20.
Abstract: Biomedical researchers have become increasingly aware of the limitations of time-honored conventional 2D tissue cell cultures where most tissue cell studies have been carried out. They are now searching for 3D cell culture systems, something between a petri dish and a mouse. It has become apparent that 3D cell culture offers a more realistic micro- and local-environment where the functional properties of cells can be observed and manipulated that is not possible in animals. A newly designer self-assembling peptide scaffolds may provide an ideally alternative system. The important implications of 3D tissue cell cultures for basic cell biology, tumor biology, high-content drug screening, and regenerative medicine and beyond could be profound.

Designing biomaterials to direct biological responses
Healy, K. E., A. Rezania, et al. (1999), Ann N Y Acad Sci 875: 24-35.
Abstract: We have set forth a design strategy for creating biomimetic materials that direct the formation of tissue surrounding implants or regeneration within porous scaffolds. Our studies have established that heterogeneous mimetic peptide surfaces (MPS) containing both the -RGD- (cell-binding) and-FHRRIKA- (putative heparin-binding) peptides, unique to BSP, in the ratio of 75:25 (MPS II) or 50:50 (MPS III) proved to be more biologically relevant and specific for RCO cell function. The initial response of human osteoblast-like cells to these surfaces was mediated by the collagen (alpha 2 beta 1) and vitronectin receptors (alpha v beta 3), whereas the vitronectin receptor alone dominated longer-term events (> 30 min). MPS II and III surfaces enhanced cell spreading and long-term events such as mineralization of the extracellular matrix compared to homogenous peptide surfaces and controls. Furthermore, extensive mineralization of the ECM deposited by RCOs occurred when the peptide was coupled to an interfacial interpenetrating polymer network (IPN) that resisted protein deposition (i.e., non-specific adsorption) and fouling. Work on thermo-reversible P(NIPAAm-co-AAc) hydrogels demonstrated the ability to create materials that can be delivered to the body in a minimally invasive manner and support tissue regeneration. These hydrogels can be modified to incorporate biofunctional components such as the biomimetic peptides, theoretically enhancing their ability to foster tissue regeneration. These results suggest that biomaterials can be engineered to mimic ECM components of bone (e.g., various organs) by grafting peptides in the appropriate ratios of the cell and heparin-binding domains, and ultimately modulate the expression of the osteoblast cell phenotype. Approaches similar to the one presented in this work can be used to design materials for hybrid artificial organs and other tissues.

Designing pattern-recognition surfaces for selective adsorption of copolymer sequences using lattice monte carlo simulation
Jayaraman, A., C. K. Hall, et al. (2005), Phys Rev Lett 94(7): 078103.
Abstract: We describe a simulation method to design surfaces for recognizing specific monomer sequences in copolymers. We fix the monomer sequence statistics of the AB copolymers on a surface containing two types of sites and allow the simulation to iterate towards an optimal surface pattern that can recognize and selectively adsorb the sequence in the copolymer. During the simulation the surface pattern is designed by switching identities of two randomly picked sites. For copolymers with less blocky sequences the designed surfaces recognize the correct sequence well when the segment-surface interactions dominate over the intersegment interactions. For copolymers with more blocky sequences recognition is good when the segment-surface interactions are only slightly stronger than the intersegment interactions.

Detecting surface issues
Bainbridge, S. (2005), Med Device Technol 16(7): 38.
Abstract: Surface analysis can be a significant aid in product development. Recent advances in these techniques allow the fine details of different coatings to be compared and optimised coating processes to be developed.

Detection of biofilm formation in Staphylococcus epidermidis from implant infections. Comparison of a PCR-method that recognizes the presence of ica genes with two classic phenotypic methods
Arciola, C. R., D. Campoccia, et al. (2006), J Biomed Mater Res A 76(2): 425-30.
Abstract: Biofilm-forming ability is increasingly being recognized as an important virulence factor in Staphylococcus epidermidis. This study compares three different techniques for the detection of biofilm-positive strains. The presence of icaA and icaD genes responsible for biofilm synthesis was investigated by a PCR method in a collection of 80 S. epidermidis strains isolated from orthopedic implant infections. The results from molecular analysis were compared with those obtained by two classic phenotypic methods, the Congo red agar (CRA) plate test and the microtiter plate test (MtP). Fifty-seven percent of all the examined strains were found icaA/icaD-positive, of which only three were not positive for CRA test. Differently, by the MtP method, 66% of the strains were found to be biofilm-producers but only a limited agreement with the PCR-method was noticeable because of the observation of (icaA/icaD+)/MtP- strains (8%) and of a surprising ambiguous result of (icaA/icaD-)/MtP+ strains (16%). The category of the weak biofilm-producers provided the highest contribution to these mismatching results (10%). The better agreement between the CRA plate test with the molecular detection of ica genes indicates the former as a reliable test for the phenotypic characterization of virulence of clinical isolates. However, MtP method remains a precious tool for the in vitro screening of different biomaterials for the adhesive properties using a reference strain. (c) 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2006.

Detection of biomaterial-associated infections in orthopaedic joint implants
Neut, D., J. R. van Horn, et al. (2003), Clin Orthop Relat Res(413): 261-8.
Abstract: Biomaterial-associated infection of orthopaedic joint replacements is the second most common cause of implant failure. Yet, the microbiologic detection rate of infection is relatively low, probably because routine hospital cultures are made only of swabs or small pieces of excised tissue and not of the surfaces of potentially infected implants. Joint replacements from patients in whom infection was suspected, after clinical, radiologic, and biochemical examinations, were used in this study. The aim of the current study was to compare the detection rate of infection in total joint replacements based on cultures of the excised tissue and scrapings from the biomaterial surface. Joint prostheses were retrieved from 22 patients requiring orthopaedic revision surgery because of suspected infection of their prostheses. Routine hospital culturing of tissue only showed bacterial growth in nine patients (41%). However, after prolonged culturing, bacterial growth was observed in 14 patients (64%), whereas extensive culturing of scrapings from the biomaterial surface indicated bacterial growth in 19 of the 22 patients (86%). In addition, confocal laser scanning microscopy enabled observation of biofilm bacteria on the surfaces of the explanted prostheses. Diagnosis in orthopaedic revision surgery should consider using a microbial or microscopic analysis of the surface of an explanted prosthesis, where the biofilm mode of growth firmly anchors and protects the infecting organisms. Improved detection of infection by analysis of the implant surface is expected to yield ameliorated therapy and a reduced need for revision surgery.

Determination of the degree of deacetylation of chitin and chitosan by X-ray powder diffraction
Zhang, Y., C. Xue, et al. (2005), Carbohydr Res 340(11): 1914-7.
Abstract: A new method to determine the degree of deacetylation (DD) of alpha-chitin and chitosan in the range of 17-94% DD using X-ray powder diffraction (XRD) is proposed. The results were calibrated using (1)H NMR spectroscopy for chitosan and FTIR for chitin, in comparison with the potentiometric titration method. The results showed a good linear correlation between the CrI020 from XRD and the calibrated DD value. This method is found to be simple, rapid and nondestructive to the sample.

Developing correlations between fibrinogen adsorption and surface properties using multivariate statistics. Student Research Award in the Doctoral Degree Candidate Category, 20th annual meeting of the Society for Biomaterials, Boston, MA, April 5-9, 1994
Perez-Luna, V. H., T. A. Horbett, et al. (1994), J Biomed Mater Res 28(10): 1111-26.
Abstract: A multivariate model based on the partial least squares algorithm (PLS) was constructed in order to establish a correlation between the surface properties of common polymeric materials and the amount and retention of fibrinogen absorbed from a complex mixture. Surface characterization was performed by means of static secondary ion mass spectroscopy (SIMS), electron spectroscopy for chemical analysis (ESCA), and by contact angle measurements of several liquids on those materials. 125I-fibrinogen was adsorbed from a 1% plasma solution in buffer and the amount adsorbed after 2 h was determined. After 5 days of residence time in buffer, the adsorbed fibrinogen was eluted with a 1% solution of the surfactant sodium dodecyl sulfate (SDS). The percent of fibrinogen that remained on the surfaces after elution is referred to as fibrinogen retention. Correlations between surface properties and the amounts of fibrinogen adsorbed or fibrinogen retention were established. These models also show the most important variables that are related to the protein behavior on these surfaces.

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