Ex vivo evaluation of a multilayered sealant patch for watertight dural closure: cranial and spinal models.

Cerebrospinal fluid leakage is a frequent complication after cranial and spinal surgery. To prevent this complication and seal the dura watertight, we developed Liqoseal, a dural sealant patch comprising a watertight polyesterurethane layer and an adhesive layer consisting of poly(DL-lactide-co-ε-caprolactone) copolymer and multiarmed N-hydroxylsuccinimide functionalized polyethylene glycol. We compared acute burst pressure and resistance to physiological conditions for 72 h of Liqoseal, Adherus, Duraseal, Tachosil, and Tisseel using computer-assisted models and fresh porcine dura. The mean acute burst pressure of Liqoseal in the cranial model (145 ± 39 mmHg) was higher than that of Adherus (87 ± 47 mmHg), Duraseal (51 ± 42 mmHg) and Tachosil (71 ± 16 mmHg). Under physiological conditions, cranial model resistance test results showed that 2 of 3 Liqoseal sealants maintained dural attachment during 72 hours as opposed to 3 of 3 for Adherus and Duraseal and 0 of 3 for Tachosil. The mean burst pressure of Liqoseal in the spinal model (233 ± 81 mmHg) was higher than that of Tachosil (123 ± 63 mmHg) and Tisseel (23 ± 16 mmHg). Under physiological conditions, spinal model resistance test results showed that 2 of 3 Liqoseal sealants maintained dural attachment for 72 hours as opposed to 3 of 3 for Adherus and 0 of 3 for Duraseal and Tachosil. This novel study showed that Liqoseal is capable of achieving a strong watertight seal over a dural defect in ex vivo models.

On calculation of thermal conductivity from Einstein relation in equilibrium molecular dynamics.

In equilibrium molecular dynamics, Einstein relation can be used to calculate the thermal conductivity. This method is equivalent to Green-Kubo relation and it does not require a derivation of an analytical form for the heat current. However, it is not as commonly used as Green-Kubo relationship. Its wide use is hindered by the lack of a proper definition for integrated heat current (energy moment) under periodic boundary conditions. In this paper, we developed an appropriate definition for integrated heat current to calculate thermal conductivity of solids under periodic conditions. We applied this method to solid argon and silicon based systems; compared and contrasted with the Green-Kubo approach.

Thermal conductivity of Si-Ge quantum dot superlattices.

Quantum dot superlattices (QDSLs) have been proposed for thermoelectric applications as a means of increasing thermal conductivity, σ, and reducing the lattice thermal conductivity, κ(l), to increase the dimensionless thermoelectric figure of merit, ZT. To fully exploit the thermoelectric potential of Si-Ge quantum dot superlattices (QDSLs), we performed a thorough study of the structural interplay of QDSLs with κ(l) using Green-Kubo theory and molecular dynamics. It was found that the resulting κ(l) has less dependence on the arrangement of the dots than to dot size and spacing. In fact, regardless of arrangement or concentration, QDSLs show a minimum κ(l) at a dot diameter of 1.4-1.6 nm and can reach values as low as 0.8-1.0 W mK⁻¹, increasing ZT by orders of magnitude over bulk Si and Ge. The drastic reduction of thermal conductivity in such a crystalline system is shown to be the result of both the stress caused by the dots as well as the quality of the Si-Ge interface.