A percutaneous device as model to study the in vivo performance of implantable amperometric glucose sensors

Glucose kinetics were investigated in subcutaneous tissue of rabbits, in which a percutaneous device was implanted. The device was used for collection of tissue fluid and as carrier of an amperometric glucose sensor. Changes in glycaemia were reflected in subcutaneous tissue fluid. However, a limited number of responses of the implanted sensors were observed. Histologic evaluation showed thin fibrous capsules surrounding the implants. Accumulations of inflammatory cells were observed inside the subcutaneous chamber. The experiments again showed that changes in blood glucose concentration can be measured in subcutaneous tissue fluid collected with a percutaneous device. Nevertheless, implanted glucose sensors could not reliably monitor these changes. Supported by our histological observations and sufficient in vitro performance, we suppose that the cellular reaction to the sensor plays an important role in this poor in vivo performance. In combination with adsorption of tissue fluid proteins, this results in a reversible deactivation of implanted sensors. The exact mechanisms involved in this process are currently unknown and need further investigation.     

In vitro and in vivo microbial adhesion and growth on argon plasma-treated silicone rubber voice prostheses

Patients who undergo a total laryngectomy usually receive a silicone rubber voice prosthesis for voice rehabilitation. Unfortunately, biofilm formation on the esophageal side of voice prostheses limits their lifetime to 3–4 mon on average. The effects of repeated argon plasma treatment of medical grade, hydrophobic silicone rubber on in vitro adhesion and growth of bacteria and yeasts isolated from voice prostheses, as well as in vivo biofilm formation are presented here. In vitro experiments demonstrated that initial microbial adhesion over a 4 h time span to plasma-treated, hydrophilized, silicone rubber was generally less than on original, hydrophobic silicone rubber, both in the absence and presence of a salivary conditioning film on the biomaterial. Growth studies over a time period of 14 d at 37°C in a modified Robbins device, showed that fewer Candida cells adhered on plasma-treated, hydrophilized silicone rubber as compared to on original, hydrophobic silicone rubber. For the in vivo evaluation of biofilm formation on plasma-treated silicone rubber voice prostheses, seven laryngectomized patients received a partly hydrophilized Groningen Button voice prosthesis for a planned evaluation period of 4 wk. After removal of the voice prostheses, the border between the hydrophilized and the original, hydrophobic side of the prostheses was clearly visible. However, biofilm formation was, unexpectedly, less on the original, hydrophobic sides, although the microbial compositions of the biofilms on both sides were not significantly different. Summarizing, this study demonstrates that in vitro microbial adhesion and growth on silicone rubber can be reduced by plasma treatment, but in vivo biofilm formation on silicone rubber voice prostheses is oppositely enhanced by hydrophilizing the silicone rubber surface. Nevertheless, from the results of this study the important conclusion can be drawn that in vivo biofilm formation on voice prostheses is controlled by the hydrophobicity of the biomaterials surface used. © 1998 Chapman & Hall     

Preparation of one-component addition-cure liquid silicone rubber coating with enhanced storage stability and bond strength

Journal of Materials Science: Materials in Electronics - It is of great interest and challenge to simultaneously improve the storage stability and bond strength of one-component addition-cure...     

Facile preparation of graphene nanoribbon filled silicone rubber nanocomposite with improved thermal and mechanical properties

In the present study, graphene nanoribbon was prepared through unzipping the multi walled carbon nanotubes, and its reinforcing effect as a filler to the silicone rubber was further investigated. The results showed that carbon nanotubes could be unzipped to graphene nanoribbon using strong oxidants like potassium permanganate and sulfuric acid. The prepared graphene nanoribbon could homogeneously disperse within silicone rubber matrix using a simple solution mixing approach. It was also found from the thermogravimetric analysis curves that the thermal stability of the graphene nanoribbon filled silicone rubber nanocomposites improved compared to the pristine silicone rubber. Besides, with the incorporation of the nanofiller, the mechanical properties of the resulting nanocomposites were significantly enhanced, in which both the tensile stress and Young’s modulus increased by 67% and 93% respectively when the mass content of the graphene nanoribbon was 2.0 wt%. Thus it could be expected that graphene nanoribbon had large potentials to be applied as the reinforcing filler to fabricate polymers with increased the thermal and mechanical properties.     

In vivo performance of wax matrix granules prepared by a twin-screw compounding extruder

The in vivo performance of wax matrix granules (WMGs) prepared by a twin-screw compounding extruder was evaluated in fasted beagle dogs. In vitro dissolution behavior of the model drug, diclofenac sodium (DS), from WMGs was strongly influenced by pH in a dissolution medium due to its solubility (DS is soluble in pH 6.8 and insoluble in pH 1.2 and 4.0) and was independent of paddle rotation rate (50, 100, and 200 rpm) of the dissolution apparatus. Pharmacokinetics parameters such as mean residence time (MRT) showed a sustained action of WMGs in beagle dogs; however, the transit time of WMGs in the small intestine is found to control total drug absorption. Furthermore, the values of the area under the curve (AUC) of the plasma concentration-time curve and the maximum concentration Cmax significantly decreased with decreases in hydroxypropylcellulose (HPC) content in WMGs. Good correlation between one in vitro dissolution parameter (mean dissolution time, MDT) and two in vivo parameters (AUC12 and MRT) suggested that it would be possible to design WMGs with a desired in vivo performance by controlling HPC content.     

In vitro and in vivo studies on biocompatibility of carbon fibres

In the present study we focused on the in vitro and in vivo evaluation of two types of carbon fibres (CFs): hydroxyapatite modified carbon fibres and porous carbon fibres. Porous CFs used as scaffold for tissues regeneration could simultaneously serve as a support for drug delivery or biologically active agents which would stimulate the tissue growth; while addition of nanohydroxyapatite to CFs precursor can modify their biological properties (such as bioactivity) without subsequent surface modifications, making the process cost and time effective. Presented results indicated that fibre modification with HAp promoted formation of apatite on the fibre surface during incubation in simulated body fluid. The materials biocompatibility was determined by culturing human osteoblast-like cells of the line MG 63 in contact with both types of CFs. Both tested materials gave good support to adhesion and growth of bone-derived cells. Materials were implanted into the skeletal rat muscle and a comparative analysis of tissue reaction to the presence of the two types of CFs was done. Activities of marker metabolic enzymes: cytochrome c oxidase (CCO) and acid phosphatase were examined to estimate the effect of implants on the metabolic state of surrounding tissues. Presented results evidence the biocompatibility of porous CFs and activity that stimulates the growth of connective tissues. In case of CFs modified with hydroxyapatite the time of inflammatory reaction was shorter than in case of traditional CFs.     

In vivo osseointegration of dental implants with an antimicrobial peptide coating

This study aimed to evaluate the in vivo osseointegration of implants with hydrophobic antimicrobial GL13K-peptide coating in rabbit femoral condyles by micro-CT and histological analysis. Six male Japanese Rabbits (4 months old and weighing 2.5?kg each) were included in this study. Twelve implants (3.75?mm wide, 7?mm long) were randomly distributed in two groups, with six implants in the experimental group coated with GL13K peptide and six implants in the control group without surface coating. Each implant in the test and the control group was randomly implanted in the left or right side of femoral condyles. On one side randomly-selected of the femur, each rabbit received a drill that was left without implant as control for the natural healing of bone. After 3?weeks of healing radiographic evaluation of the implant sites was taken. After 6?weeks of healing, rabbits were sacrificed for evaluation of the short-term osseointegration of the dental implants using digital radiography, micro-CT and histology analysis. To perform evaluation of osseointegration, implant location and group was double blinded for surgeon and histology/radiology researcher. Two rabbits died of wound infection in sites with non-coated implants 2?weeks after surgery. Thus, at least four rabbits per group survived after 6?weeks of healing. The wounds healed without suppuration and inflammation. No implant was loose after 6?weeks of healing. Radiography observations showed good osseointegration after 3 and 6?weeks postoperatively, which proved that the tissues followed a natural healing process. Micro-CT reconstruction and analysis showed that there was no statistically significant difference (P?>?0.05) in volume of bone around the implant between implants coated with GL13K peptide and implants without coating. Histomorphometric analysis also showed that the mineralized bone area was no statistically different (P?>?0.05) between implants coated with GL13K peptide and implants without coating. This study demonstrates that titanium dental implants with an antimicrobial GL13K coating enables in vivo implant osseointegration at similar bone growth rates than gold-standard non-coated dental implants up to 6?weeks of implantation in rabbit femurs.     

Surface microstructure and cell biocompatibility of silicon-substituted hydroxyapatite coating on titanium substrate prepared by a biomimetic process

Silicon-substituted hydroxyapatite (Si-HA) coatings with 0.14 to 1.14 at.% Si on pure titanium were prepared by a biomimetic process. The microstructure characterization and the cell compatibility of the Si-HA coatings were studied in comparison with that of hydroxyapatite (HA) coating prepared in the same way. The prepared Si-HA coatings and HA coating were only partially crystallized or in nano-scaled crystals. The introduction of Si element in HA significantly reduced P and Ca content, but densified the coating. The atom ratio of Ca to (P + Si) in the Si-HA coatings was in a range of 1.61–1.73, increasing slightly with an increase in the Si content. FTIR results displayed that Si entered HA in a form of SiO₄ unit by substituting for PO₄ unit. The cell attachment test showed that the HA and Si-HA coatings exhibited better cell response than the uncoated titanium, but no difference was observed in the cell response between the HA coating and the Si-HA coatings. Both the HA coating and the Si-HA coatings demonstrated a significantly higher cell growth rate than the uncoated pure titanium (p < 0.05) in all incubation periods while the Si-HA coating exhibited a significantly higher cell growth rate than the HA coating (p < 0.05). Si-HA with 0.42 at.% Si presented the best cell biocompatibility in all of the incubation periods. It was suggested that the synthesis mode of HA and Si-HA coatings in a simulated body environment in the biomimetic process contribute significantly to good cell biocompatibility.     

In vitro and in vivo biocompatibility of apatite-coated magnetite nanoparticles for cancer therapy

The aim of this study was to determine the biocompatibility and potential toxicity of apatite-coated magnetite nanoparticles. The in vitro biocompatibility with human red blood cells was evaluated, not hemolytic effects were found at concentrations lower than 3 mg/ml. For the in vivo study, Balb/c mice were used. The animals were injected intravenously or intraperitoneally, the doses ranged from 100 to 2,500 mg/Kg. All the injected animals showed normal kidney and liver function. No significant changes were found in the body weight, the organs weight and the iron levels in liver due to the administration. In conclusion, apatite-coated magnetite nanoparticles did not induce any abnormal clinical signs in the laboratory animals. The results demonstrated that apatite-coated magnetite nanoparticles of 8 ± 2 nm in size did not have hemolytic effect in human erythrocytes and did not cause apparent toxicity in Balb/c mice under the experimental conditions of this study.     

In vivo biocompatibility of radiation induced acrylamide and acrylamide/maleic acid hydrogels

In vitro swelling and in vivo biocompatibility of radiation induced acrylamide (AAm) and acrylamide/maleic acid (AAm/MA) hydrogels were investigated. The swelling kinetics of AAm and AAm/MA hydrogels of are investigated in distilled water, human serum and some simulated physiological fluids such as phosphate buffer at pH 7.4, glycine-HCl buffer at pH 1.1, physiological saline solution and, some swelling and diffusion parameters have been calculated. AAm and AAm/MA hydrogels were subcutaneously implanted in rats for up to 10 weeks and the tissue response to these implants was studied. Histological analysis indicated that tissue reaction at the implant site progressed from an initial acute inflammatory response characterized. No necrosis, tumorigenesis or infection was observed at the implant site up to 10 week. In vivo studies indicated that the radiation induced acrylamide and acrylamide/maleic acid hydrogels were found to be well-tolerated, non-toxic and highly biocompatible.     

Electrochemical performance, biocompatibility, and adhesion of new polymer matrices for solid-state ion sensors.

Ammonium and potassium ion-selective membranes formulated with PVC/hydroxylated PVC, polyurethane/hydroxylated PVC, and moisture-curable silicone rubber matrices are studied in an effort to extend the lifetime of solid-state ion sensors through improved membrane adhesion. The PVC/membranes exhibit electrochemical performance equivalent to that of conventional PVC membranes in terms of slope, detection limit, and selectivity. The polyurethane- and silicone-rubber-based membranes have better adhesion to silicon nitride than do PVC or hydroxylated PVC matrices. Incorporating a silanizing reagent (silicon tetrachloride) significantly improves the adhesion of the polyurethane matrix. The use of silicon tetrachloride in membrane matrices also enhances the electrochemical stability of the interfacial potential between ion-selective polymer-matrix membranes and silver epoxy inner reference electrodes of solid-state sensors. The biocompatibility of the polymer matrices is examined via radiotracer protein adsorption studies and whole blood clotting time measurements. The polyurethane- and silicone-rubber-based membranes exhibit less overall nonspecific protein adsorption than the PVC or hydroxylated PVC matrices.     

Improving the electromechanical performance of dielectric elastomers using silicone rubber and dopamine coated barium titanate

In this work, a new soft dielectric elastomer (DE) was fabricated from dopamine coated barium titanate particles and silicone rubber (SR). The results showed that the barium titanate (BaTiO₃, BT) was coated by dopamine and the coated particles were highly compatible with SR. In order to achieve a maximum voltage-induced deformation, the minimum secant moduli of DEs were obtained in experimentation at a stretch ratio of approximately 1.6 by applying equi-biaxial tensile strain using the bubble inflation method. Additionally, it was found that the addition of DP-BT into SR led to an increased dielectric constant and decreased dielectric loss tangent for the matrix by comparison with SR/BT composites. Furthermore, the electromechanical properties of the SR/DP-BT composites were greatly improved in terms of voltage-induced deformation (s_a), electromechanical energy density (e) and coupling efficiency (K²). A maximum actuated area strain of approximately 78%, which was 30% larger than that of the SR/BT composites, was achieved for the sample having a DP-BT content of 20 wt.%. This strain corresponded to a low dielectric strength of around 53 V/μm, the composite exhibited a maximum energy density of 0.07 MJ/m³ and coupling efficiency of 0.68.     

In vitro metal ion release and biocompatibility of amorphous Mg67Zn28Ca5 alloy with/without gelatin coating

Amorphous zinc-rich Mg–Zn–Ca alloys have exhibited good tissue compatibility and low hydrogen evolution in vivo. However, suboptimal cell–surface interaction on magnesium alloy surface observed in vitro could lead to reduced integration with host tissue for regenerative purpose. This study aims to improve cell–surface interaction of amorphous Mg₆₇Zn₂₈Ca₅ alloy by coating a gelatin layer by electrospinning. Coated/uncoated alloys were immersed and extracted for 3 days under different CO₂. The immersion results showed that pH and metal ion release in the alloy extracts were affected by gelatin coating and CO₂, suggesting their roles in alloy biocorrosion and a mechanism has been proposed for the alloy–CO₂ system with/without coating. Cytotoxicity results are evident that gelatin-coated alloy with 2-day crosslinking not only exhibited no indirect cytotoxicity, but also supported attachment of L929 and MG63 cell lines around/on the alloy with high viability. Therefore, amorphous Mg₆₇Zn₂₈Ca₅ alloy coated with gelatin by electrospinning technique provides a useful method to improve alloy biocompatibility.     

In vitro and in vivo degradability,biocompatibility and antimicrobial characteristics of Cu added iron-manganese alloy

In recent years,iron(Fe)based degradable metal is explored as an alternative to permanent fracture fixation devices.In the present work,copper(Cu)is added in Fe-Mn system to enhance the degradation rate and antimicrobial properties.Fe-Mn-xCu(x=0.9,5 and 10 wt.％)alloys are prepared by the melting-casting-forging route.XRD analysis confirms austenite phase stabilization due to the presence of Mn and Cu.As predicted by Thermo-Calc calculations,Cu rich phase precipitations are noticed along the austen-ite grain boundaries.Degradation behaviours of Cu added Fe-Mn alloys are investigated through static immersion and electrochemical polarization where enhanced degradation is found for higher Cu added alloys.When challenged against E.Coli bacteria,the Fe-Mn-Cu alloy media extract shows a significant bac-tericidal effect compare to the base alloy.In vitro cytocompatibility studies,as determined using MG63 and MC3T3-E1 cell lines,indicate increased cell density as a function of time for all the alloys.When implanted in rabbit femur,the newly developed alloy does not show any kind of tissue necrosis around the implants.Better osteogenesis and higher new bone formation are observed with Fe-Mn-10Cu alloy as evident from micro-computed tomography(μ-CT)and fluorochrome labelling.     

双层结构纳米羟基磷灰石/硅橡胶复合材料的制备及性能

纳米羟基磷灰石/硅橡胶与硅橡胶在同时硫化的条件下制备出了双层结构的纳米羟基磷灰石/硅橡胶复合材料,利用XRD、SEM、MTT和力学性能测试等手段对复合材料进行表征.结果表明,两层材料的界面结合紧密,材料的细胞相容性好,力学性能与硅橡胶的力学性能相近,能够达到医用植入硅橡胶材料的要求.     

High electrical performance of carbon nanotubes/rubber composites with low percolation threshold prepared with a rotation-revolution mixing technique

The present study demonstrates a novel mixing approach for achieving a good dispersion of carbon nanotubes (CNTs) in a styrene-butadiene rubber (SBR), which leads to a significant improvement in electrical properties. Our mixing technique consists of (1) pretreatment by ultrasonication to disentangle the bundles of CNTs in organic solvent and (2) “rotation-revolution” mixing of the CNTs with SBR without mechanical shear, which prevents CNTs from collapsing during the mixing process. The present mixing method does not require the addition of any dispersing agents (amphiphilic molecules) or chemical modification of the CNTs to obtain a good dispersion. Compared with a conventional Banbury mixing technique, our method leads to a significant decrease in the percolation threshold (less than 1 phr), where the electrical conductivity suddenly increases due to the formation of percolation networks of CNTs in SBR. This is because the aspect ratio of the CNTs was maintained even after the mixing process, whereas CNTs were broken during the conventional Banbury mixing. The effect of using different types of CNTs on electrical conductivity was also investigated. The results show that the percolation threshold is largely related to the structural quality (graphitization) of the CNTs as well as their aspect ratio.     

In vitro evaluation and in vivo performance of lyophilized gliclazide

Enhancement of the dissolution rate of the poorly water-soluble hypoglycemic agent, gliclazide, by the aid of lyophilization was investigated. Mannitol, sodium lauryl sulfate (SLS) and polyvinyl pyrrolidone (PVP-k-30) were employed in different weight ratios (43%, 56% and 64% w/w, respectively) as water-soluble excipients in the formulation. Lyophilized systems were found to exhibit extremely higher in vitro dissolution rate compared to the unprocessed drug powder. Solid state characterization of the lyophilized systems using X-ray powder diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry techniques revealed that dissolution enhancement was attributable to transformation of gliclazide from the crystalline to an amorphous state in the solid dispersion formed during the lyophilization process. The gastrointestinal absorption and hypoglycemic effect of the lyophilized gliclazide/SLS system were investigated following oral administration to Albino rabbits. C_max and area under the plasma concentration–time curve of gliclazide (AUC_0–12) after administration of the lyophilized formulations were significantly higher than those obtained after administration of the unprocessed gliclazide.     

Mechanical properties, fire performance and thermal stability of magnesium hydroxide sulfate hydrate whiskers flame retardant silicone rubber

Halogen-free flame retardant silicone rubber (SR) composites, using magnesium hydroxide sulfate hydrate (MHSH) whiskers as flame retardant have been prepared by a two-roll mill. Moreover, microencapsulated red phosphorus (MRP) was used as a synergist. Mechanical tests were performed to determine the tensile strength, elongation at break, and shore hardness of the composites. The morphology of fracture surface was observed by environmental scanning electron microscopy (ESEM). The results showed MHSH slightly reduced the tensile strength of the composites, but had obvious influence on the elongation at break. Meanwhile, Shore A hardness presented uptrend with increasing MHSH content. The addition of vinyl silicone fluid (VSF) could improve the compatibility of the MHSH whiskers in SR matrix, and therefore improved the mechanical properties of composites. The flammability properties of composites were investigated by limited oxygen index (LOI), UL-94 tests, and cone calorimetry experiments. It is found that MHSH whiskers can effectively improve the flame retardancy of SR composites due to the endothermic degradation of MHSH whiskers accompanied with the release of water vapor, and the formation of fibrous magnesia acting as a barrier layer. The incorporation of MRP in SR/MHSH whiskers system had a synergic fire retardant effect in the condensed and gas phase. In addition, thermogravimetric analysis (TGA) indicated the presence of MRP enhanced thermal stability of the SR/MHSH composites at higher temperature range, and remarkably promoted char residue yield.