Bio-Medical Materials and Engineering - Volume 14, issue 4
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Bio-Medical Materials and Engineering is to promote the welfare of humans and to help them keep healthy. This international journal is an interdisciplinary journal that publishes original research papers, review articles and brief notes on materials and engineering for biological and medical systems.
Articles in this peer-reviewed journal cover a wide range of topics, including, but not limited to: Engineering as applied to improving diagnosis, therapy, and prevention of disease and injury, and better substitutes for damaged or disabled human organs; Studies of biomaterial interactions with the human body, bio-compatibility, interfacial and interaction problems; Biomechanical behavior under biological and/or medical conditions; Mechanical and biological properties of membrane biomaterials; Cellular and tissue engineering, physiological, biophysical, biochemical bioengineering aspects; Implant failure fields and degradation of implants. Biomimetics engineering and materials including system analysis as supporter for aged people and as rehabilitation; Bioengineering and materials technology as applied to the decontamination against environmental problems; Biosensors, bioreactors, bioprocess instrumentation and control system; Application to food engineering; Standardization problems on biomaterials and related products; Assessment of reliability and safety of biomedical materials and man-machine systems; and Product liability of biomaterials and related products.
Abstract: Copolymers of 2‐methacryloyloxyethyl phosphorylcholine (MPC) showed good hemocompatibility as hypothesized. The hypothesis was surfaces having phosphorylcholine groups by polymerization of MPC could accumulate phospholipids from blood stream and show good blood compatibility. We designed and prepared a methacylate having a phosphorylcholine group. While it was possible to introduce them by polymer reactions, polymer reaction is not always good method to prepare the desired pure surface. This must be very important point to consider biomaterials, as we have to apply them in our body without any adverse effects. The hypothesis was confirmed by changing copolymer composition. The adsorption amount of…phospholipids on the surfaces increased with increasing the MPC units in the copolymers. On the other hand, increasing MPC units in MPC copolymers decreased adsorption amount of peptides. There is limitation in blood compatibility tests in vitro due to unstable characteristics of blood itself. We evaluated them with series of blood compatibility tests, in vitro, ex vivo and in vivo, on coated PMMA beads, modified hollow fibers for hemodialysis and 2 mm small diameter blood vessels, respectively. These data suggested MPC is a promising methacrylate to develop good blood contacting devises, which may not require systemic anticoagulation. Conventional blood compatible biomaterials were not suitable to make permeable membranes. But MPC is soluble in water and we could prepare permeable membranes to various solutes by the copolymerization. Introduction of MPC copolymers on cellulose and polysulfone hollow fiber membranes gave them nonthrombogenicity but it did not give adverse effect on their permeability. These data suggested that it is possible to apply them to hemodialyzers, oxygenators and percutaneous glucose sensors to keep diabetic patients easier. MPC surfaces are good hydrogel to minimize damage on tissues by lubricating between organs and the coated devices. They do not induce denaturation of peptides, which is beneficial to keep activities of enzymes longer. And poly‐MPC dissolved is applicable to stabilize several bioactive peptides in aqueous phase. So MPC polymers are useful to minimize fouling by inhibiting the adsorption of bioactive proteins. MPC has high potential to develop many varieties of new biomaterials useful in so‐called biotechnology. MPC and their copolymers are commercially available from NOF (Tokyo, Japan) and Biocompatibles (UK, as PC technology).
Abstract: A drug eluting coronary stent was developed for use in preclinical and clinical trial evaluation. The stent was coated with a phosphorylcholine (PC)‐based polymer coating containing the cell migration inhibitor batimastat. A pharmacokinetic study was conducted in a rabbit iliac model using 14 C‐radiolabeled version of the drug; this showed the drug release to be first order with 94% of it being released within 28 days. Unloaded and drug‐loaded stents were implanted in a porcine coronary artery model; a number were explanted at 5 days and scanning electron microscopy was used to show that the presence of the drug did…not affect the rate of stent endothelialisation. The remainder of the stents were removed after 6 months and the stents carefully removed from the arterial tissue. Fourier‐transform infrared (FT‐IR) spectroscopy (both attenuated total reflectance and microscopic imaging) was used to show the presence of the PC coating on control unloaded, drug‐loaded and explanted stents, providing evidence that the coating was still present. This was further confirmed by use of atomic force microscopy (AFM) amplitude‐phase, distance (a‐p,d) curves which generated the characteristic traces of the PC coating. Further AFM depth‐profiling techniques found that the thicknesses of the PC coatings on an control unloaded stent was 252±19 nm, on an control batimastat‐loaded stent 906±224 nm and on an explanted stent 405±224 nm. The increase in thickness after the drug‐loading process was a consequence of drug incorporation in the film, and the return to the unloaded dimensions for the explanted sample indicative of elution of the drug from the coating. The drug delivery PC coating was therefore found to be stable following elution of the drug and after 6 months implantation in vivo.
Keywords: Phosphorylcholine, coronary stent, drug delivery, in vivo stability
Abstract: In order to prepare ecologically and biologically safety physical cross‐linked hydrogel of a‐PVA/NaCl/H2 O system, we prepared blend hydrogel of natural polymeric binders like gelatin and starch in above system, and effect of these binder additives were evaluated on terbutaline release kinetics. Terbutaline (1%) hydrogels of a‐PVA(7%)/NaCl(11%)/H2 O and a‐PVA(7%)/H2 O system (Cyclic FT process) were prepared along with various concentrations of gelatin and soluble starch by feed‐mixture dissolving method. In case of a‐PVA/NaCl/H2 O system only one cycle gelation was done at −20°C for 24 h. On the other hand 3 cycles were done by freezing at −30°C for…16 h followed by thawing at room temperature for 8 h. Drug release was done by paddle method (USP type II) with a rotation of 50 rpm at 37°C in distilled water. Swelling of the gel was done at 37°C for 45 h and melting temperatures of the gel were also studied using the upside‐down test tube method. Comparatively lower values of release rate, diffusion coefficient and kinetic constant were found from the blend hydrogel of a‐PVA/starch/NaCl/H2 O system. When % cumulative release was plotted vs. square root of time it showed straight lines, which indicated Higuchi Matrix Dissolution Model. Inclusion of starch binder increased the degree of swelling compared with that of gelatin. 15 h was found as equilibrium swelling time. A Fickian swelling of this blend hydrogel system indicated the swelling controlled Fickian diffusion type of drug release. Melting temperatures of the blend hydrogels were characteristically higher (94–95°C) than that of cyclic FT (72–76°C), resulting a thermostable hydrogel for biological system. SEM morphological studies of gel surface indicated the well‐developed interpenetrating macromolecular network structure like fish net in starch blend gel prevails over other hydrogel studied here. Gelatin has got characteristic tunnel (200 μm in diameter) inside the macromolecular network that contributes this system higher release kinetics than that of starch.
Abstract: Delivery of drugs to the front‐side of the eye is routinely done through eye drops. It is known that approximately 80% of each eye‐drop is lost, as a result of rapid clearance of the tear fluid via the naso‐lacrymal canal. Consequently, repeated administration through several droplets is usually necessary to achieve a desired effect, e.g., mydriasis (widening of the pupil) prior to corneal surgery. Studies with a new ocular drug delivery device are reported. The new device is believed to provide a basis for more convenient and efficient method for ocular drug delivery. The device is a metallic coil with…a hydrophilic, drug‐containing polymeric coating. The coil is placed in the conjunctival fornix (under the lower eye‐lid), and the drug is released slowly, by diffusion into the tear fluid. The capacity of the device could be increased by using the lumen of the coils as a depot for the drug to be released. Preliminary experiments with the new device are reported. These experiments were performed largely in vitro, but partly also in vivo. The latter experiments comprised release of the fluorescent dye, and delivery of atropine (a potent mydriatic agent), in the eyes of several healthy volunteers. The first results obtained with the new device indicate its potential utility. It is discussed that much more research and development work is required, e.g., to define the optimal design of the coil in order to minimise the risk for irritation. Furthermore, the parameters that define the kinetics of the intraocular drug release must be defined and optimised with respect to the exact application.
Keywords: Drug delivery, hydrophilic coatings, antibiotics release, mydriasis
Abstract: Postoperative endophthalmitis following intraocular lens (IOL) implantation is still one of the most feared complications of cataract surgery. Bacterial adhesion to IOLs during their insertion is a prominent etiological factor. Polypropylene was the first biomaterial that allowed this relation of cause and effect to be proven. Following adhesion, bacteria replicate, congregate and form multiple layers of microcolonies which actually represent the basic structural unit of the biofilm. The bacteria are embedded in a slime layer. Personal photographs illustrate the different steps of biofilm formation. This slime matrix is not only an adhesive medium; it also affects virulence. Adhesion to IOLs…has been studied by several in vitro studies and discrepancies can be found between them which are due to variations of experimental conditions. The strains, the incubation times and the methods all varied. Adhesion is affected by the nature of the IOLs, the isolates and the surrounding medium. Since this medium is very difficult to model because of its complexity, in vivo studies seemed essential. We have recently determined in vivo evolution of the amount of attached bacteria to five types of IOLs. Crystalline lenses from 90 domestic pigs were removed aseptically and replaced with previously infected IOLs. There have been few epidemiological studies published to determine the relationship between endophthalmitis and the IOL type. However, the perfect biomaterial that could prevent postoperative endophthalmitis does not yet exist. Globally, hydrophilic materials and hydrophobic acrylic seem to be less sticky than silicone or PMMA, but this remains to be proven clinically.
Keywords: Bacterial adhesion, biofilm, Staphylococcus epidermidis, intraocular lenses, endophthalmitis, in vitro & in vivo studies
Abstract: The full quaternisation of DEAE‐dextran was successfully attempted and an application of the quaternised product was suggested. Commercial DEAE‐dextran was reacted with iodomethane at 60°C in the presence of NaOH. The raw product was purified by dialysis, during which the iodide ion was replaced by chloride. N‐methylation and O‐methylation resulted from the reaction. A second methylation step produced no further changes in the molecule. Alkalimetry indicated the absence of amino groups in the methylated polymer molecule, thus testifying to a complete quaternisation. N‐acetylcysteine (AcCy) was neutralised with the polymer in the hydroxide form, thus obtaining the methyl DEAE‐dextran salt of…AcCy (Me‐DEAE‐dextran/AcCy), whereby an ophthalmic formulation for the treatment of the dry eye syndrome was prepared. For comparison, the neutral AcCy salt of commercial DEAE‐dextran (DEAE‐dextran/AcCy) was prepared. The AcCy content in Me‐DEAE‐dextran/AcCy was higher than in DEAE‐dextran/AcCy (23 vs 13%), while the viscosity of a solution containing the salt concentration corresponding to the therapeutic AcCy concentration (4%w/v) was lower with the former compared to the latter salt (20.5 vs 23.9 mPa s). Both solutions were ipotonic (245 mOsm/kg), whereas the commercial Tirocular® is strongly hypertonic (900 mOsm/kg) and irritant.
Abstract: Reoperation of aldehyde tanned bioprotheses due to calcific degeneration remains their major drawback. Based on experiments studying mechanisms and factors that influence the time phase, extent and progression of calcification and evaluating the efficiency of anticalcification treatments and the effects of surface seeding with vital cells a new concept to avoid calcification emerged: masking aldehyde‐residues with a covalently bound polymer that supports surface cell seeding. Different covalently bound polymers were tested for their suitability to grow cells. Dense cell growth was achieved on some polymers but without correlation to physico‐chemical properties. Ultrathin coating of biological materials appears a promising…approach to achieve lining with vital cells.
Abstract: We have reported that poly(2‐methoxyethyl acrylate) (PMEA) shows excellent blood compatibility with respect to the coagulation, complement, leukocyte and platelet systems in vitro and ex vivo when compared with other polymer surfaces. In this study, to clarify the reasons for this good compatibility, the structure of water in the hydrated PMEA were investigated and compared to water structure of poly(2‐hydroxyethyl methacrylate) (PHEMA) and polyacrylate analogs as references. The hydrated water in PMEA could be classified into three types; free water, freezing‐bound water, and non‐freezing water. Cold crystallization of water in the heating process was clearly observed at −42°C. This cold…crystallization is interpreted as the phase transition from the amorphous ice to the crystal ice that belongs to the freezing‐bound water in PMEA. On the other hand, the cold crystallization peak (freezing bound water; which prevents the biocomponents from contacting the polymer surface or non‐freezing water on the polymer surface) was not observed for hydrated PHEMA and PMEA analogous polymers. We hypothesized that the freezing‐bound water layer between free water and non‐freezing water was an important factor for the excellent blood compatibility of PMEA.
Abstract: Application of porous polymer materials to novel bio‐interfaces for tissue engineering scaffold and artificial organs including blood filters, dialyzer, and oxygenator membranes have been in progress. The present study describes the fabrication and characterization of self‐organized highly regular porous polymer films with uniform pore sizes are prepared by simple casting technique. Various fabrication parameters affecting the pore size such as polymer concentration, boiling point of solvent, cast volume and substrate are studied. The pore size can be controlled in the range from 1 to 50 μm by changing the evaporation rate of the polymer solutions. The porous film with uniform…pore size is used for tissue engineering scaffold and cell separation membrane. To simulate the leukocyte eliminating from human blood, the porous film was attached to a module. The films with 5–9 μm pores provided the complete selectivity of separation for the leukocyte from the whole blood. The leukocyte elimination ratio depends on pore structures (size and depth) as well as recovery of platelet and erythrocyte.