Efficacy of a Bioresorbable Matrix in Healing Complex Chronic Wounds: An Open-Label Prospective Pilot Study

OBJECTIVE: The goal of this prospective clinical study was to assess the effectiveness of a novel bioresorbable polymeric matrix impregnated with ionic and metallic silver as a primary wound contact dressing in healing stagnant or deteriorating chronic wounds. MATERIALS AND METHODS: Thirty-two patients with a total of 35 chronic wounds undergoing treatment at the Wound Healing and Hyperbaric Center at Mission Hospital were recruited under a protocol approved by the institutional review board. The wounds included venous stasis ulcers, diabetic foot ulcers, postoperative surgical wounds, burn wounds, and chronic, nonpressure lower extremity ulcers. At baseline, all wounds were nonhealing (ie, stagnant or deteriorating) for a median of 39 weeks (range, 3-137 weeks) and suspected of persistent microbial colonization that had not responded to traditional antimicrobial products and/or antibiotics. The aforementioned matrix was applied to wounds once every 3 days and covered with a secondary dressing. Previously prescribed protocols of care, such as debridement or compression wraps, were continued, but prior antimicrobial dressings or antibiotics were replaced with the matrix. Wound assessments at 3 weeks and 12 weeks post intervention are reported. RESULTS: Three patients were excluded due to patients lost to follow-up after initial application. At 3 weeks, 72% of wounds (22/32) had significantly improved healing with an average wound area reduction of 66%. By 12 weeks, 91% of wounds (29/32) either healed completely (ie, fully reepithelialized) or improved significantly with an average wound area reduction of 73%. The matrix was well tolerated; no patient reported discomfort with the application of the matrix. CONCLUSIONS: The micrometer-thick bioresorbable matrix presents a new form factor to wound management, conforming intimately to the underlying wound bed to exert localized and sustained antimicrobial action of noncytotoxic levels of silver. The application of the matrix on the wound surface in protocols of care was safe and well tolerated, and it facilitated improvements in healing of a majority of the stagnant or deteriorating complex chronic wounds.

Estimating error in diffusion coefficients derived from molecular dynamics simulations.

The computationally expensive nature of molecular dynamics simulation limits the access to length (nanometer) and time scales (nanosecond) that are orders of magnitude smaller than the experiment it models. This limitation warrants a careful estimation of statistical uncertainty associated with the properties calculated from these simulations. The assumption that a simulation is long enough so that the ergodic hypothesis applies is often invoked in the literature for the computation of properties of interest from a single molecular dynamics simulation. Here, we demonstrate that making this assumption without validation results in poor estimates of the self-diffusion coefficient from a single molecular dynamics simulation of Lennard-Jones fluid. This problem is shown to be even more severe when the diffusion coefficient of macromolecules is calculated from a single molecular dynamics simulation. We have shown that conducting multiple independent simulations is necessary to obtain reliable estimates of diffusion coefficients and their associated statistical uncertainties. We show that even a "routine" calculation of the self-diffusion coefficient for a Lennard-Jones fluid, as determined from a linear fit of the mean squared displacement of particles as a function of time, violates the key assumptions of linear regression. A rigorous approach for addressing these issues is presented.

Molecular dynamics simulation of fractal aggregate diffusion.

The diffusion of fractal aggregates constructed with the method by Thouy and Jullien [J. Phys. A 27, 2953 (1994)] comprised of N(p) spherical primary particles was studied as a function of the aggregate mass and fractal dimension using molecular dynamics simulations. It is shown that finite-size effects have a strong impact on the apparent value of the diffusion coefficient (D), but these can be corrected by carrying out simulations using different simulation box sizes. Specifically, the diffusion coefficient is inversely proportional to the length of a cubic simulation box, and the constant of proportionality appears to be independent of the aggregate mass and fractal dimension. Using this result, it is possible to compute infinite dilution diffusion coefficients (D(o)) for aggregates of arbitrary size and fractal dimension, and it was found that D(o)∝N(p)(-1/df), as is often assumed by investigators simulating brownian aggregation of fractal aggregates. The ratio of hydrodynamic radius to radius of gyration is computed and shown to be independent of mass for aggregates of fixed fractal dimension, thus enabling an estimate of the diffusion coefficient for a fractal aggregate based on its radius of gyration.