ABSTRACT
Conductive biohybrid cell-material systems have applications in bioelectronics and biorobotics. To date, conductive scaffolds are limited to those with low electrical conductivity or 2D sheets. Here, 3D biohybrid conductive systems are developed using fibroblasts or cardiomyocytes integrated with carbon nanotube (CNT) forests that are densified due to interactions with a gelatin coating. CNT forest scaffolds with a height range of 120-240 µm and an average electrical conductivity of 0.6 S/cm are developed and shown to be cytocompatible as evidenced from greater than 89% viability measured by live-dead assay on both cells on day 1. The cells spread on top and along the height of the CNT forest scaffolds. Finally, the scaffolds have no adverse effects on the expression of genes related to cardiomyocyte maturation and functionality, or fibroblast migration, adhesion, and spreading. The results show that the scaffold could be used in applications ranging from organ-on-a-chip systems to muscle actuators.
ABSTRACT
Huntsman-Merrimack MIRALON® carbon nanotubes (CNTs) are a novel, highly entangled, commercially available, and scalable format of nanotubes. As-received and acid-treated CNTs were added to aerospace grade epoxy (CYCOM® 977-3), and the composites were characterized. The epoxy resin is expected to infiltrate the network of the CNTs and could improve mechanical properties. Epoxy composites were tested for flexural and viscoelastic properties and the as-received and acid treated CNTs were characterized using Field-Emission Scanning and Transmission Electron Microscopy, X-Ray Photoelectron Spectroscopy, and Thermogravimetric Analysis. Composites containing 0.4 wt% as-received CNTs showed an increase in flexural strength, from 136.9 MPa for neat epoxy to 147.5 MPa. In addition, the flexural modulus increased from 3.88 GPa for the neat epoxy to 4.24 GPa and 4.49 GPa for the 2.0 wt% and 3.0 wt% as-received CNT/epoxy composites, respectively. FE-SEM micrographs indicated good dispersion of the CNTs in the as-received CNT/epoxy composites and the 10 M nitric acid 6 h treatment at 120 °C CNT/epoxy composites. CNTs treated with 10 M nitric acid for 6 h at 120 °C added oxygen containing functional groups (C-O, C=O, and O=C-O) and removed iron catalyst present on the as-received CNTs, but the flexural properties were not improved compared to the as-received CNT/epoxy composites.
ABSTRACT
This study proposes a new design of lightweight and cost-efficient composite materials for the aeronautic industry utilizing recycled fresh scrap rubber, epoxy resin, and graphene nanoplatelets (GnPs). After manufacturing the composites, their bending strength and fracture characteristics were investigated by three-point bending (3PB) tests. Halpin-Tsai homogenization adapted to composites containing GnPs was used to estimate the moduli of the composites, and satisfactory agreement with the 3PB test results was observed. In addition, 3PB tests were simulated by finite element method incorporating the Halpin-Tsai homogenization, and the resulting stress-strain curves were compared with the experimental results. Mechanical test results showed that the reinforcement with GnPs generally increased the modulus of elasticity as well as the fracture toughness of these novel composites. Toughening mechanisms were evaluated by SEM fractography. The typical toughening mechanisms observed were crack deflection and cavity formation. Considering the advantageous effects of GnPs on these novel composites and cost efficiency gained by the use of recycled rubber, these composites have the potential to be used to manufacture various components in the automotive and aeronautic industries as well as smart building materials in civil engineering applications.
ABSTRACT
Femoral components of hip replacements are commonly anchored in the femur with bone cement or poly(methyl methacrylate) (PMMA). Wear or fracture of bone cement can lead to loosening of the femoral component, which drastically affects the success and longevity of hip replacements. Self-reinforced composite PMMA (SRC-PMMA) has been previously developed for potential use, as a precoat material for hip replacements. The composite consists of high strength fibers that have been shown to have greatly improved mechanical properties over bulk PMMA. The goal of this work was to examine SRC-PMMA for improved wear properties, as a function of processing temperature. Pin-on-disc tests were used to characterize and rank the wear rates of SRC-PMMA and PMMA. Composites made with higher processing temperatures had significantly lower wear rates than do PMMA at a significance level of p < or = 0.05. The lowest wear rate was 8.2 microg/m, at a processing temperature of 136 degrees C, compared to a wear rate for PMMA of 13.3 microg/m. At the lowest processing temperature (105 degrees C), a wear rate higher than PMMA was found, and failure was dominated by fiber delamination. In the more completely processed samples (122 degrees C < or = T < or = 150 degrees C), wear rates were equivalent to or better than PMMA, and smoother and more homogenous wear was noted in wear tracks. Fatigue cracks were prominent at higher processing temperatures or when the wear pin was riding orthogonal to fibers. Wear particles were collected and examined. Wear particle diameter and aspect ratio showed no correlation to processing temperature, but were similar to particles retrieved from human tissue samples.
Subject(s)
Biocompatible Materials , Joint Prosthesis , Polymethyl MethacrylateABSTRACT
Poly(lactic acid) (PLA) is used for medical devices such as sutures or orthopedic screws. A standard way to determine the loss of mechanical properties of a degradable polymer would be to soak the polymer in phosphate buffered saline (PBS) and test the desired property as a function of immersion time. This method is not sensitive enough to discern changes in mechanical properties through the cross-section of the polymer and neglects the degradation that is occurring at the molecular level. This article presents results of a nanoindentation study carried out with PLA. The modulus and hardness of PLA is characterized as a function of processing method, immersion time in PBS, and location of the indent. Measuring local properties with the nanoindenter allowed detection of differences in material properties as a function of all three of these variables. The mechanical properties on the edge were lower than the interior of the sample after in vitro degradation, and changes were seen earlier for nanoindentation than for traditional flexural or tensile tests. The nanoindenter is a valuable tool for quantifying changes in material properties and may have applicability for accelerated tests to screen biomaterials.
Subject(s)
Biocompatible Materials , Lactic Acid , Nanotechnology , Polymers , Buffers , Polyesters , Sodium Chloride , Time FactorsABSTRACT
Understanding the wear characteristics of bone cement and its alternatives is critical to improving the quality and longevity of hip replacements. A novel composite material, self-reinforced composite poly(methyl methacrylate), has been previously developed for potential use as a pre-coat material for hip implants. The goal of this work was to examine the properties of self-reinforced composite poly(methyl methacrylate) as a function of processing temperature. Nanoindentation tests were performed to measure hardness and modulus of self-reinforced composite poly(methyl methacrylate) at the nanoscale. Nanoscratch tests were performed parallel, orthogonal, and longitudinal to composite fibers to measure residual scratch depths. Significant differences were found in the hardness, modulus, and residual scratch depth as a function of processing temperature when compared to poly(methyl methacrylate). As processing temperature is increased, hardness decreased and residual scratch depths increased. Data also showed that fiber orientation plays a critical role in scratch resistance. Scratching orthogonal to fiber orientation produced the least residual scratch depth ranging from 524 nm at 105 degrees C to 838 nm at 150 degrees C, compared to a residual scratch depth for poly(methyl methacrylate) of 842 nm.
