|Articles about Biomaterials|
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| Novel polyphosphazene-hydroxyapatite composites as biomaterials
Ambrosio, A. M., J. S. Sahota, et al. (2003), IEEE Eng Med Biol Mag 22(5): 18-26.
| Novel powder formulations for controlled delivery of poorly soluble anticancer drug: application and investigation of TPGS and PEG in spray-dried particulate system
Mu, L., M. M. Teo, et al. (2005), J Control Release 103(3): 565-75.
Abstract: Biodegradable poly (lactic-co-glycolic acid) (PLGA), D-alpha-tocopheryl polyethylene glycol 1000 succinate (TPGS) and/or polyethylene glycol (PEG) were combined as pharmaceutical excipient to fabricate microparticles containing sparingly soluble drug paclitaxel by spray-drying technique with successful achievement. The effect of formulation variety on particle morphology, surface composition, thermal property, drug entrapped capability, and drug release profile was investigated. The result indicated that the use of the appropriate mixtures of PLGA, TPGS and/or PEG produced paclitaxel-loaded microparticles characterised by acceptable pharmaceutical properties. Atomic force microcopy (AFM) and scanning electron microscopy (SEM) showed that the produced microparticles were spherical in shape with dimples or pores. The particle size ranged from 0.88 to 2.44 microm with narrow distribution. The combination of TPGS and PEG in the formulation resulted in a narrow particle size distribution in general although the influence of the formulation on the particle size was not significant. Differential scanning calorimetry (DSC) study implied that all those components in consideration were compatible well in the blend formulation systems. The paclitaxel entrapped in the particles existed in an amorphous or disordered-crystalline status in the matrices and was independent of the PLGA/TPGS/PEG ratio. X-ray photoelectron spectroscope (XPS) analysis revealed that after incorporation the particle's surface was dominated with PLGA due to its hydrophobic property. The formulation variety had an important impact on the drug release that was reduced with the presence of large fraction of TPGS resulting from a strong hydrophobic interaction between various matrix materials and the drug inside the particle. A zero order release could be yielded by optimising the ratio of PLGA/TPGS/PEG. The combination of PLGA/TPGS/PEG as safe pharmaceutical excipient to formulate particulate delivery system is beneficial in improving the pharmaceutical properties for further powder dosage application.
| Novel quantitative methods for the determination of biomaterial cytotoxicity
Smith, M. D., J. C. Barbenel, et al. (1992), Int J Artif Organs 15(3): 191-4.
Abstract: Two novel methods for the determination of biomaterial cytotoxicity using cell culture are presented. The methods combine a standardized protocol for producing extracts from medical devices with either the established MTT assay or a new fluorimetric assay. The suitability of both methods for evaluating the toxicity of candidate materials was demonstrated by resolution of the differences in the toxic effects of serial dilutions of a PVC extract on BHK21 and HT1080 cells. The tests yield highly reproducible, quantitative results and can be applied to materials in the usual physical forms applicable to artificial organs.
| Nuclear magnetic resonance spectroscopic studies of lipoteichoic acid adhesion on biomaterials
Cravatt, E. and C. V. Rice (2005), Ethn Dis 15(3 Suppl 4): S4-96-7.
Abstract: Biofilms are responsible for persistent clinical infections and dental cavities. A major component of gram-positive bacterial-biofilms is lipoteichoic acid (LTA). When located at the outer edge of the cell wall, the LTA chain extends away from the surface and is the first cell component to come in contact with surfaces. The prevention of bacterial attachment could include therapies to repel LTA and these efforts will benefit from understanding the molecular-level interactions that promote LTA adsorption. LTA is a long chain of phosphodiesters (anionic) with glucosamine (neutral) and alanine branches (cationic). Charge neutralization is incomplete, allowing LTA to form ionic bonds with water molecules and the substrate. The adsorption mechanism is governed by ionic interactions, but the nature of the surface bonds is unknown. High-resolution magic-angle-spinning nuclear magnetic resonance (HRMAS-NMR) spectroscopy was used to study LTA on silica and hydroxiapatite. NMR data are characteristic of the chemical environment and because each LTA component is chemically unique, we were able to collect sidechain-specific data. The chemical environment is altered by LTA-surface interactions, which are revealed in the NMR data. In this fashion, we are able to follow LTA adsorption on different surfaces.
| Nuclear methods to characterize biomaterials
Irigaray, J. L., H. Oudadesse, et al. (2001), Biomaterials 22(7): 629-40.
Abstract: Techniques using X-rays are often used to study biomaterials fields. However, when one is interested by quantitative and very sensitive measurements, it is valuable to develop nuclear instruments and methods, in addition and complement with others. Fast neutron activation is appropriate for non-destructive analysis. Thermal neutron activation can evaluate trace elements as a reference. Proton-induced X-rays emission is applied to cartography of heavy elements. If necessary, proton-induced gamma-rays emission and charged particles scattering are suitable for evaluation and cartography of light elements. Radioactivated nuclei and labelled molecules can tag element transfers and biofunctionality. In our work, these methods are related to biomaterials field.
| Nucleus pulposus replacement: basic science and indications for clinical use
Di Martino, A., A. R. Vaccaro, et al. (2005), Spine 30(16 Suppl): S16-22.
Abstract: STUDY DESIGN: A critical review of available and emerging nucleus pulposus replacement implants. OBJECTIVES: To review the biomechanics, design, and clinical data of currently available and developing nucleus pulposus replacement technologies. SUMMARY OF BACKGROUND DATA: The interest in minimally invasive treatment of degenerative disc disease has grown as the technology for intervertebral motion-sparing devices continues to improve. Replacement of nucleus pulposus without anular obliteration represents a tempting alternative to spinal fusion procedures. The aim in nucleus pulposus replacement is to slow adjacent level degeneration, restore normal loads to the diseased level, and restore segmental spinal biomechanics. METHODS: A literature review of currently available biomaterials, biomechanics, and available preclinical and clinical data on nucleus pulposus replacement implants. RESULTS: New synthetic biomaterials have recently been developed to closely mimic native biomechanics during compressive loading cycles of the intervertebral disc. This, in conjunction with improved understanding of global spine biomechanics, has allowed the development of novel nucleus replacement implants. These implants are currently at different stages of preclinical and clinical investigations. CONCLUSIONS: Although some of the newly designed prosthesis have shown some promising results in preclinical studies, rigorous short- and long-term clinical evaluations will be critical in evaluating their true efficacy.
| Nylon paper: an alternative to cellulose acetate paper for use in conjunctival impression cytology
Meena, M. K., A. Khuteta, et al. (2005), Br J Ophthalmol 89(9): 1223-4.
| Objectivity in the evaluation of biological safety of medical devices and biomaterials
Williams, D. (1991), Med Device Technol 2(1): 44-8.
Abstract: This article attempts to present the current situation with respect to the evaluation of biological safety and biocompatibility where imitations in the methodology and validity are apparent. The introduction of procedures that facilitate the quantitative determination of the parameters of the biological performance of materials, and their objective analysis, should considerably enhance our ability to specify safety and describe biocompatibility.
| Obligate heterodimerization of the archaeal Alba2 protein with Alba1 provides a mechanism for control of DNA packaging
Jelinska, C., M. J. Conroy, et al. (2005), Structure 13(7): 963-71.
Abstract: Organisms growing at elevated temperatures face a particular challenge to maintain the integrity of their genetic material. All thermophilic and hyperthermophilic archaea encode one or more copies of the Alba (Sac10b) gene. Alba is an abundant, dimeric, highly basic protein that binds cooperatively and at high density to DNA. Sulfolobus solfataricus encodes a second copy of the Alba gene, and the Alba2 protein is expressed at approximately 5% of the level of Alba1. We demonstrate by NMR, ITC, and crystallography that Alba2 exists exclusively as a heterodimer with Alba1 at physiological concentrations and that heterodimerization exerts a clear effect upon the DNA packaging, as observed by EM, potentially by changing the interface between adjacent Alba dimers in DNA complexes. A functional role for Alba2 in modulation of higher order chromatin structure and DNA condensation is suggested.
| Ocular biomaterials and implants
Lloyd, A. W., R. G. Faragher, et al. (2001), Biomaterials 22(8): 769-85.
Abstract: The maintenance of vision is a key determinant of healthy ageing. This has been facilitated over recent decades by the development of a wide range of implants and biomedical devices to correct the functional deficiencies of disease, age and ocular trauma. This brief overview provides an insight into the structure of this unique organ, the major physiological functions of the component tissues and the present state of the art with respect to modern ocular implants. The review focuses primarily on the existing limitations of existing ocular biomaterials used in the fabrication of contact lenses, intraocular lenses, glaucoma filtration implants, keratoprostheses, intracorneal implants, scleral buckles and viscoelastic replacement agents. The challenge of improving ocular compatibility and ensuring the longevity of indwelling ocular devices is addressed along with the need to improve the physicochemical and mechanical properties of existing ocular biomaterials.
| Ocular infections: antibiotics and bacterial adhesion on biomaterials used in ocular surgery
Marone, P., L. Perversi, et al. (1995), Ophthalmologica 209(6): 315-8.
Abstract: The in vitro antibacterial activity of ofloxacin, sagamycin and other antibiotics was evaluated against 85 bacterial isolates [coagulase-negative staphylococci (CNS), n = 37, Staphylococcus aureus, n = 28, and Pseudomonas aeruginosa, n = 20] obtained from patients with ocular infections. The antistaphylococcal activity of ofloxacin was quite elevated with a 90% minimal inhibitory concentration (MIC90) of 1.56 mg/l against CNS and S. aureus. Rokitamycin and erythromycin showed a good activity against methicillin-sensitive staphylococci, but were less active than ofloxacin and sagamycin against methicillin-resistant strains (MIC90 > 100 mg/l). Sagamycin was highly effective against staphylococci (MIC90 0.78 mg/l) and appeared to be the most active compound against P. aeruginosa (MIC90 6.25 mg/l), followed by ofloxacin, tobramycin and gentamicin. In a successive part of the study, the adhesive properties of slime-producing staphylococci were tested on biomaterials used in ocular surgery. Intraocular lenses, Silastic sheetings, circling bands and grooved strips showed a high affinity for slime-producing strains, while round silicone sponges were not covered by bacterial biofilm. In the last part of our study, we demonstrated how subMIC levels of ofloxacin increased the adhesion of slime-producing staphylococci. Our data confirmed the excellent activity of ofloxacin and sagamycin against ocular pathogens and the key role of adhesion in promoting colonization and infections of biomaterials.
| On the dielectric behaviour of collagen-algal sulfated polysaccharide blends: Effect of glutaraldehyde crosslinking
Figueiro, S. D., A. A. Macedo, et al. (2005), Biophys Chem
Abstract: In this paper, impedance measurements in the frequency range from 10(-)(2) to 10(6) Hz are presented for collagen and algal sulfated polysaccharide crosslinked films. We are considering the development of new biomaterials which have potential applications in coating of cardiovascular prostheses, support for cellular growth and in systems for controlled drug delivery. The effect of crosslink sulfated polysaccharide on the physical chemical properties of collagen was studied using FT-infrared spectroscopy, differential scanning calorimetry (DSC), dielectric spectroscopy. The resulting films crosslinked with glutaraldehyde (GA) in concentrations of 0.001% and 0.05% when analysed by DSC, showed that the GA treatment not only left the thermal stability of the collagen unaffected, but it also decreased the thermal transition energy. Dielectric spectroscopy shows that the effect of the crosslink on the blend film was associated to the decrease and stabilization of the dielectric permittivity at low frequencies and decreased its conductivity.
| On the importance of considering porosity when simulating the fatigue of bone cement
Jeffers, J. R., M. Browne, et al. (2005), J Biomech Eng 127(4): 563-70.
Abstract: Fatigue cracking in the cement mantle of total hip replacement has been identified as a possible cause of implant loosening. Retrieval studies and in vitro tests have found porosity in the cement may facilitate fatigue cracking of the mantle. The fatigue process has been simulated computationally using a finite element/continuum damage mechanics (FE/CDM) method and used as a preclinical testing tool, but has not considered the effects of porosity. In this study, experimental tensile and four-point bend fatigue tests were performed. The tensile fatigue S-N data were used to drive the computational simulation (FE/CDM) of fatigue in finite element models of the tensile and four-point bend specimens. Porosity was simulated in the finite element models according to the theory of elasticity and using Monte Carlo methods. The computational fatigue simulations generated variability in the fatigue life at any given stress level, due to each model having a unique porosity distribution. The fracture site also varied between specimens. Experimental validation was achieved for four-point bend loading, but only when porosity was included. This demonstrates that the computational simulation of fatigue, driven by uniaxial S-N data can be used to simulate nonuniaxial loadcases. Further simulations of bone cement fatigue should include porosity to better represent the realities of experimental models.
| On the relation between platelet adhesion and the roughness of a synthetic biomaterial
Ward, C. A. and T. W. Forest (1976), Ann Biomed Eng 4(2): 184-207.
| On the study of BSA-loaded calcium-deficient hydroxyapatite nano-carriers for controlled drug delivery
Liu, T. Y., S. Y. Chen, et al. (2005), J Control Release 107(1): 112-21.
Abstract: Calcium-deficient hydroxyapatite (CDHA) nano-crystals incorporated with bovine serum albumin (BSA) to form BSA-loaded nano-carriers were synthesized via both in-situ and ex-situ processes. Amount of BSA uptake by the CDHA nano-crystals and subsequent release behaviors of the BSA-loaded nano-carriers were investigated. The amount of BSA uptake by CDHA decreases with increasing pH but a larger amount was observed in the ex-situ compared to in-situ process above pH=8.0. The release profile showed a bursting behavior for the nano-carrier prepared via the ex-situ process, which is probably due to the desorption of BSA molecules. In contrast, for the sample synthesized via the in-situ process at a higher pH level, a slower release profile without bursting behavior due to the dissolution of the BSA-incorporated CDHA crystal is seen from high solution TEM that indicates different extent of interaction between BSA and CDHA. On the other hand, for the nano-carriers prepared via the same process at lower pH level, a two-stage release profile was detected. An initial bursting release is due to the desorption of BSA from the CDHA surface, followed by a slow release as a result of the dissolution of the BSA-incorporated nano-crystals along its c-axis direction.
| On the tissue compatibility of poly(ether imide) membranes: an in vitro study on their interaction with human dermal fibroblasts and keratinocytes
Altankov, G., W. Albrecht, et al. (2005), J Biomater Sci Polym Ed 16(1): 23-42.
Abstract: Recently we have developed a novel type of membrane based on poly(ether imide) (PEI) which is considered for biomedical application. To improve its physical and biological performance it was modified by blending with poly(benzimidazole) (PBI). In the present study both membranes were characterized in terms of their physicochemical properties and in vitro tissue compatibility using human dermal fibroblasts and keratinocytes. The modified membrane (PEI*) was more hydrophilic, less porous and had an increased surface (zeta) potential. We further found that blending with PBI tends to promote cell contact, at least initially, as indicated by the improved overall cell morphology, adhesion and spreading of fibroblasts, and the development of focal adhesion complexes. The effects of fibronectin (FN) and serum coating were also beneficial when compared to pure PEI and tissue culture polystyrene (TCP), which correlates to a higher adsorption of both FN and vitronectin detected by ELISA. However, a clear tendency for homotypic cellular interaction particularly of keratinocytes was obtained in contact with membranes, which was much stronger pronounced on PEI*. Although the initial adhesion was greater on PEI*, a surprising decrease in cell growth was observed at later stages of incubation, which may be explained with the membrane-promoted cellular aggregation leading to an easier detachment from the substratum. Thus, membranes based on blends of PEI with PBI could provide a tissue compatible scaffold with lowered adhesive properties, which might be a useful tool for the transfer of cells, for example, to in vitro engineered tissue constructs.
| On-demand release of corrosion-inhibiting ions from amorphous Al-Co-Ce alloys
Jakab, M. A. and J. R. Scully (2005), Nat Mater 4(9): 667-70.
Abstract: Controlled release technologies are often used to supply chemicals or drugs at given rates. Release often occurs on contact with solution. However, some applications, such as corrosion protection, require containment of the active species in a reservoir and their slow release when needed. Conductive polymers have been used as reservoirs for corrosion inhibitors whose triggered release occurs by galvanic reduction or ion exchange. This work shows one of the first examples of pH-controlled release of corrosion-inhibiting ions from an amorphous metallic coating where the pH change that triggers release is a consequence of the onset of corrosion. This corrosion-inhibition strategy provides further corrosion protection beyond the traditional roles of barrier and sacrificial cathodic protection using a metal coating. For instance, zinc galvanizing provides sacrificial cathodic protection and acts as a barrier, but does not supply inhibitor ions. In the coating described here, protection of an underlying structural alloy exposed at coating defects is demonstrated by inhibitor ion release in addition to barrier function and sacrificial cathodic protection.
| One or 2 Intacs segments for the correction of keratoconus
Alio, J. L., A. Artola, et al. (2005), J Cataract Refract Surg 31(5): 943-53.
Abstract: PURPOSE: To evaluate the effect of implanting 1 or 2 intracorneal rings (Intacs, KeraVision) as a device to correct, stabilize, and/or improve the best corrected visual acuity in patients with clear cornea keratoconus oriented by the preoperative corneal topography pattern. SETTING: Vissum/Instituto Oftalmologico de Alicante, Miguel Hernandez University, Alicante, Spain. METHODS: In this prospective comparative consecutive study, Intacs segments were implanted in 26 keratoconic eyes with clear central corneas of 19 consecutive patients (9 women and 10 men). Corneas were divided into 2 groups according to the topographic pattern of the cone. Group I included keratoconus not crossing the 180 degrees meridian and Group II included keratoconus crossing the 180 degrees meridian. The Intacs were horizontally placed through a lateral clear corneal incision. According to the corneal topography 1 segment was implanted 0.45 mm inferior in Group I, and 2 segments were implanted, 1 0.25 mm superior and the other 0.45 mm inferior, in Group II. All cases completed a minimum follow-up of 1 year. Differences between preoperative and postoperative uncorrected visual acuity (UCVA), best spectacle-corrected visual acuity (BSCVA), manifest refraction, and keratometry were clinically and statistically evaluated. RESULTS: Spherical equivalent error and refractive astigmatism were significantly reduced. The mean keratometric values were reduced following Intacs insertion in both groups. At the end of the first year of the postoperative follow-up, Group I (1 segment) had an improvement in mean UCVA to 20/50 (0.4 +/- 0.22 decimal value), which was statistically significant when compared to the preoperative UCVA of 20/100 (0.2 +/- 0.13 decimal value) (P=.011). Mean BSCVA was 20/32 (0.62 +/- 0.24 decimal value), which was also statistically significant when compared to the preoperative BSCVA, which was 20/50 (0.4 +/- 0.21 decimal value) (P=.002). In Group II (2 segments), UCVA after 1 year was 20/63 (0.34 +/- 0.17 decimal value), which was statistically significant when compared to the preoperative UCVA of 20/400 (0.06 +/- 0.02 decimal value) (P=.001). Mean BSCVA was 20/32 (0.62 +/- 0.27 decimal value), which was significantly better than the preoperative UCVA of 20/50 (0.38 +/- 0.22 decimal value) (P=.001). In 4 eyes, the inferior segment was removed because of partial extrusion during the postoperative follow-up. CONCLUSIONS: Treatment of keratoconus with 1 or 2 Intacs segments oriented by the preoperative corneal topography used in this study proved to be effective in decreasing the corneal steepening and astigmatism and improving BSCVA. Further follow-up is needed to determine the final effect of Intacs on the progression of the corneal disease.
| One year clinical follow up of paclitaxel eluting stents for acute myocardial infarction compared with sirolimus eluting stents
Hofma, S. H., A. T. Ong, et al. (2005), Heart 91(9): 1176-80.
Abstract: OBJECTIVE: To compare clinical outcome of paclitaxel eluting stents (PES) versus sirolimus eluting stents (SES) for the treatment of acute ST elevation myocardial infarction. DESIGN AND PATIENTS: The first 136 consecutive patients treated exclusively with PES in the setting of primary percutaneous coronary intervention for acute myocardial infarction in this single centre registry were prospectively clinically assessed at 30 days and one year. They were compared with 186 consecutive patients treated exclusively with SES in the preceding period. SETTING: Academic tertiary referral centre. RESULTS: At 30 days, the rate of all cause mortality and reinfarction was similar between groups (6.5% v 6.6% for SES and PES, respectively, p = 1.0). A significant difference in target vessel revascularisation (TVR) was seen in favour of SES (1.1% v 5.1% for PES, p = 0.04). This was driven by stent thrombosis (n = 4), especially in the bifurcation stenting (n = 2). At one year, no significant differences were seen between groups, with no late thrombosis and 1.5% in-stent restenosis (needing TVR) in PES versus no reinterventions in SES (p = 0.2). One year survival free of major adverse cardiac events (MACE) was 90.2% for SES and 85% for PES (p = 0.16). CONCLUSIONS: No significant differences were seen in MACE-free survival at one year between SES and PES for the treatment of acute myocardial infarction with very low rates of reintervention for restenosis. Bifurcation stenting in acute myocardial infarction should, if possible, be avoided because of the increased risk of stent thrombosis.
| One-year clinical outcome after coronary stenting of very small vessels using 2.25 mm sirolimus- and paclitaxel-eluting stents: a comparison between the RESEARCH and T-SEARCH registries
Rodriguez-Granillo, G. A., M. Valgimigli, et al. (2005), J Invasive Cardiol 17(8): 409-12.
Abstract: BACKGROUND: The efficacy of sirolimus-eluting stents (SES) compared to paclitaxel-eluting stents (PES) remains unknown. We evaluated the clinical outcomes after implantation of 2.25 mm diameter SES and PES. METHODS AND RESULTS: PES have been used as the stent of choice for all percutaneous coronary interventions as part of the prospective Taxus-Stent Evaluated At Rotterdam Cardiology Hospital (T-SEARCH) Registry. Ninety consecutive patients received at least one 2.25 mm PES (PES group), and were compared with 107 patients who received at least one 2.25 mm SES as part of the RESEARCH registry. The overall population presented high-risk characteristics commonly excluded from most studies. Populations were well-matched. There were 2 (2.2%) incidents of subacute stent thrombosis in the PES group (in a 2.25 mm stent), and none in the SES group. At one year, the cumulative incidence of major adverse cardiac events was 5.6% in the SES group, and 17.8% in the PES group (p = 0.007). After adjustments for other significant univariate variables, presentation with acute coronary syndrome (ACS) (adjusted OR 5.2 [95% CI 1.8-15.0], p = 0.002) and PES utilization (adjusted OR 3.7 [95% CI 1.3-10.5], p = 0.013) were found to be significant independent predictors of major adverse cardiac events (MACE). CONCLUSIONS: In an unselected population treated for very small vessel disease, SES were associated with better 12-month clinical outcomes and the use of PES was identified as an independent predictor of adverse events.
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