Clay Nanotube/Poly(methyl methacrylate) Bone Cement Composites with Sustained Antibiotic Release

Orthopedic‐grade PMMA bone cement, admixed with prophylactic antibiotics, is widely used in hip and knee replacement surgery. There is a critical need to improve its structural integrity and to control antibiotic release. In this study, clay nanotubes are loaded with the antibiotic gentamicin sulfate and the cement is doped with 5–8 wt% nanotubes. The halloysite nanotubes isolate the drug from the cement monomers and serve as nanocontainers for sustained release of the antibiotic. Gentamicin‐loaded clay nanotubes admixed in PMMA cement provide sustained release up to 300–400 h and with enhanced release at cement cracks. The PMMA/halloysite/gentamicin composite tensile strength does not deteriorate as compared with pure cement and its adhesion to bone is significantly increased.

     

Halloysite clay nanotubes for controlled release of protective agents

Halloysite is a naturally occurring clay mineral with submicron sized hollow cylindrical morphology. Halloysite morphology, structure and properties were characterized by using SEM, TEM, XRD, FT-IR spectroscopy, surface electrokinetic (zeta) potential and nitrogen adsorption isotherms. Comparison of the halloysite structure with imogolite was also provided. Halloysite toxicological studies revealed that it is environmentally friendly and biocompatible material. Due to its unique tubular shape and availability in thousands of tons halloysite has potential to be applied as nanocontainers for encapsulation of chemically and biologically active agents such as medicines, pharmaceuticals, antiseptics, corrosion inhibitors, antifouling agents, and doped with them plastics producing smart polymeric nanocomposites with improved mechanical strength. Finally possibility to synthesize metal nanorods within the halloysite lumen was demonstrated.     

Ionic conductivity and dielectric relaxation in γ-irradiated TlGaTe2 crystals

The switching effect, field and temperature dependences of the permittivity and conductivity of TlGaTe₂ crystals subjected to various γ-irradiation doses are studied. Under rather low electric fields, the phenomenon of threshold switching with an S-shaped current-voltage characteristic containing a portion with negative differential resistance is observed in the crystals. In the region of critical voltages, current and voltage oscillations and imposed modulation are observed. Possible mechanisms of switching, ionic conductivity, disorder, and electrical instability in TlGaTe₂ crystals are discussed.     

Electrical and Optical Properties of Unrelaxed InAs1 –xSbx Heteroepitaxial Structures

Semiconductors - The electrical and galvanomagnetic properties of unrelaxed heteroepitaxial InAs1 –xSbx structures (x = 0.43 and 0.38) in a wide temperature range of 5–300 K and...     

Specific features of conductivity of γ-irradiated TlGaTe<Subscript>2</Subscript> crystals with nanochain structure

Temperature dependences of electrical conductivity σ(T) and current-voltage characteristics of one-dimensional TlGaTe₂ single crystals subjected to various doses of γ-ray radiation in both geometries of the experiment-along nanochains parallel to the tetragonal axis of the crystal (σ_|) and perpendicular to these nanochains (σ_⊥)-are studied. It is shown that the dependence σ(T) measured in the ohmic region of the current-voltage characteristic is the shape typical of the hopping mechanism and can be described in terms of the Mott approximation. The values of the densities of localized states N _F, the activation energy E _a, the hop lengths R, the difference between the energies of states ΔE in the vicinity of the Fermi level, and the concentrations of deep traps N _t are determined. The current-voltage characteristics in the region of a more abrupt increase in the current are also studied. It is shown that this region of current-voltage characteristics is described in the context of the Pool-Frenkel thermal-field effect. Concentrations of ionized centers N _f , the free-path lengths λ, the Frenkel coefficients β, and the shape of the potential well in initial and irradiated (with 250 Mrad) TlGaTe₂ crystals are determined. It is shown that anisotropy of electrical conductivity changes under the effect of irradiation, which brings about translational ordering of nanochains.     

Enhanced flame retardancy of latex coating doped with clay nanotubes

Halloysite clay nanotubes of 0.5–1 μm length and 0.05 μm diameter are cheap and abundantly available natural materials which may be used as an additive for paint formulations. Its admixing at 5 wt% enhances latex paint flame-retardancy and did not change paint color, surface roughness and adhesion to the substrate. Tested according to the ASTM E84 standard, 5 wt% halloysite doping was the best formulation evaluated on the flame spread and smoke developed. Halloysite decomposition resulting in degradation and release of water molecule is believed to be a reason for the decreasing rate of combustion.     

Superionic conductivity in TlGaTe<Subscript>2</Subscript> crystals

Temperature dependences of electrical conductivity σ(T) and permittivity ɛ(T) of one-dimensional (1D) TlGaTe₂ single crystals are investigated. At temperatures higher than 305 K, superionic conductivity of the TlGaTe₂ is observed and is related to diffusion of Tl⁺ ions via vacancies in the thallium sublattice between (Ga³⁺Te₂^{2− −} nanochains. A relaxation character of dielectric anomalies is established, which suggests the existence of electric charges weakly bound to the crystal lattice. Upon the transition to the superionic state, relaxors in the TlGaTe₂ crystals are Tl⁺ dipoles ((Ga³⁺Te₂²⁻)⁻ chains) that arise due to melting of the thallium sublattice and hops of Tl⁺ ions from one localized state to another. The effect of a field-induced transition of the TlGaTe₂ crystal to the superionic state is detected.     

Superionic conductivity and switching effect with memory in TlInSe<Subscript>2</Subscript> and TlInTe<Subscript>2</Subscript> crystals

The temperature dependences of the conductivity σ(T) and the switching and memory effects in one-dimensional TlInSe₂ and TlInTe₂ single crystals have been studied. A specific feature is found in the dependence σ(T) above 333 K, which is related to the transition of crystals to the state with superionic conductivity. It is suggested that the ion conductivity is caused by the diffusion of Tl⁺ ions over vacancies in the thallium sublattice between (In³⁺Te₂²⁻)⁻ and (In³⁺Se₂²⁻)⁻ nanochains (nanorods). S-type switching and memory effects are revealed in TlInSe₂ and TlInTe₂ crystals, as well as voltage oscillations in the range of negative differential resistance. It is suggested that the switching effect and voltage oscillations are related to the transition of crystals to the superionic state, which is accompanied by “melting” of the Tl sublattice. The effect of electric-field-induced transition of TlInSe₂ and TlInTe₂ crystals to the superionic state is found.