An inverse analysis approach to the characterization of chemical transport in paints.

The ability to directly characterize chemical transport and interactions that occur within a material (i.e., subsurface dynamics) is a vital component in understanding contaminant mass transport and the ability to decontaminate materials. If a material is contaminated, over time, the transport of highly toxic chemicals (such as chemical warfare agent species) out of the material can result in vapor exposure or transfer to the skin, which can result in percutaneous exposure to personnel who interact with the material. Due to the high toxicity of chemical warfare agents, the release of trace chemical quantities is of significant concern. Mapping subsurface concentration distribution and transport characteristics of absorbed agents enables exposure hazards to be assessed in untested conditions. Furthermore, these tools can be used to characterize subsurface reaction dynamics to ultimately design improved decontaminants or decontamination procedures. To achieve this goal, an inverse analysis mass transport modeling approach was developed that utilizes time-resolved mass spectroscopy measurements of vapor emission from contaminated paint coatings as the input parameter for calculation of subsurface concentration profiles. Details are provided on sample preparation, including contaminant and material handling, the application of mass spectrometry for the measurement of emitted contaminant vapor, and the implementation of inverse analysis using a physics-based diffusion model to determine transport properties of live chemical warfare agents including distilled mustard (HD) and the nerve agent VX.

Direct measurement of chemical distributions in heterogeneous coatings.

Chemical warfare agents (CWA) can be absorbed by variety of materials including polymeric coatings like paints through bulk liquid contact, thus presenting touch and vapor hazards to interacting personnel. In order for accurate hazard assessments and subsequent decontamination approaches to be designed, it is necessary to characterize the absorption and distribution of highly toxic species, as well as their chemical simulant analogs, in the subsurface of engineered, heterogeneous materials. Using a combination of judicious sample preparation in concert with scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), it should be possible to directly measure the uptake and distribution of CWA simulants in the subsurface of complex multilayer coatings. Polyurethane and alkyd coatings were applied to aluminum and silicon substrates and contaminated with 2-chloroethyl ethyl sulfide (CEES) and dimethyl methylphosphonate (DMMP). The surfaces and cross-sectional interfaces of the contaminated coatings were probed with SEM-EDS to provide imaging, spectral, and elemental mapping data of the contaminant-material systems. This work demonstrated SEM-EDS capability to detect and spatially resolve unique elemental signatures of CWA simulants within military coatings. The visual and quantitative results provided by these direct measurements illustrate contaminant spatial distributions, provide order-of-magnitude approximations for diffusion coefficients, and reveal material characteristics that may impact contaminant transport into complex coating materials. It was found that contaminant uptake was significantly different between the topcoat and primer layers.

Physics-based agent to simulant correlations for vapor phase mass transport.

Chemical warfare agent simulants are often used as an agent surrogate to perform environmental testing, mitigating exposure hazards. This work specifically addresses the assessment of downwind agent vapor concentration resulting from an evaporating simulant droplet. A previously developed methodology was used to estimate the mass diffusivities of the chemical warfare agent simulants methyl salicylate, 2-chloroethyl ethyl sulfide, di-ethyl malonate, and chloroethyl phenyl sulfide. Along with the diffusivity of the chemical warfare agent bis(2-chloroethyl) sulfide, the simulant diffusivities were used in an advection-diffusion model to predict the vapor concentrations downwind from an evaporating droplet of each chemical at various wind velocities and temperatures. The results demonstrate that the simulant-to-agent concentration ratio and the corresponding vapor pressure ratio are equivalent under certain conditions. Specifically, the relationship is valid within ranges of measurement locations relative to the evaporating droplet and observation times. The valid ranges depend on the relative transport properties of the agent and simulant, and whether vapor transport is diffusion or advection dominant.

Characterization of chemical agent transport in paints.

A combination of vacuum-based vapor emission measurements with a mass transport model was employed to determine the interaction of chemical warfare agents with various materials, including transport parameters of agents in paints. Accurate determination of mass transport parameters enables the simulation of the chemical agent distribution in a material for decontaminant performance modeling. The evaluation was performed with the chemical warfare agents bis(2-chloroethyl) sulfide (distilled mustard, known as the chemical warfare blister agent HD) and O-ethyl S-[2-(diisopropylamino)ethyl] methylphosphonothioate (VX), an organophosphate nerve agent, deposited on to two different types of polyurethane paint coatings. The results demonstrated alignment between the experimentally measured vapor emission flux and the predicted vapor flux. Mass transport modeling demonstrated rapid transport of VX into the coatings; VX penetrated through the aliphatic polyurethane-based coating (100 µm) within approximately 107 min. By comparison, while HD was more soluble in the coatings, the penetration depth in the coatings was approximately 2× lower than VX. Applications of mass transport parameters include the ability to predict agent uptake, and subsequent long-term vapor emission or contact transfer where the agent could present exposure risks. Additionally, these parameters and model enable the ability to perform decontamination modeling to predict how decontaminants remove agent from these materials.

Treatment of atrophic diaphyseal humeral nonunions with compressive locked plating and augmented with an intramedullary strut allograft.

OBJECTIVE: The aim of this study was to evaluate the effectiveness of thorough debridement and locked compression plating augmented with an intramedullary fibular allograft for the treatment of atrophic diaphyseal humeral nonunions. DESIGN: The study involved a level 4 retrospective case series. SETTING: This study was conducted at a level 1 university trauma center. PATIENTS: Twenty patients with painful atrophic nonunions of the humeral diaphysis were examined. INTERVENTION: This involved a thorough debridement and locked compression plating augmented with an intramedullary fibular allograft. MAIN OUTCOME MEASURES: These were union rate, shoulder range of motion, visual analog scale (VAS) pain, VAS function, patient satisfaction, and American Shoulder and Elbow Surgeons score at latest follow-up. METHODS: Clinical and radiographic examinations were performed preoperatively and postoperatively. VAS pain and function scores were collected preoperatively and postoperatively. Patient satisfaction and ASES scores were recorded at the time of the most recent follow-up. RESULTS: : Bony union was achieved in 19 of 20 patients (95%). The patients demonstrated an average improvement in forward elevation from 65 to 144° (P = 0.001), abduction from 48 to 133° (P < 0.001), external rotation from 34 to 70° (P = 0.05), and internal rotation from S1 to T12 (P = 0.025). VAS pain scores improved from 6.05 to 1.88 (P = 0.032). VAS function scores improved from 2.06 to 7.75 (P = 0.003). The average postoperative ASES score was 76, and the average patient satisfaction was rated 9.3/10. CONCLUSIONS: Atrophic nonunions of the humerus can be successfully treated with debridement of the nonunion, coupled with the use of a fibular allograft and locked compression plating. This technique leads to predictable healing without the morbidity associated with autograft. LEVEL OF EVIDENCE: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

The use of the reverse shoulder arthroplasty for treatment of failed total shoulder arthroplasty.

BACKGROUND: This study evaluated the outcomes of patients with failed total shoulder arthroplasty (TSA) who were treated with conversion to reverse shoulder arthroplasty (RSA). MATERIALS AND METHODS: We performed a retrospective case series of 24 consecutive patients with failed TSA who were treated with conversion to RSA. Twenty-two patients (16 women, 6 men) had a minimum 2-year clinical and radiographic follow-up. The average age at the time of revision was 68 years (range, 51-84 years). Indications for conversion to RSA included failure of TSA from glenohumeral instability in 19, mechanical failure of the humeral or glenoid component in 10, and infection in 2. RESULTS: The median total American Shoulder and Elbow Surgeons score improved from 38.5 preoperatively to 67.5 (P < .001). Visual analog scale pain scores decreased from 5 to 1.5 (P < .001), and function improved from 2 to 6.5 (P < .001). The median Simple Shoulder Test improved from 1 to 5 (P = .006). Forward flexion improved from 50° to 130° (P < .001), abduction from 45° to 100° (P < .001), and external rotation from 12.5° to 49.5° (P = .056). Internal rotation improved from a spinal level of S2 to L3 (P = .064). Fourteen patients rated their outcome as excellent, 3 as good, 3 as satisfactory, and 2 as unsatisfactory. The overall complication rate was 22.7% (5 of 22). CONCLUSION: RSA can be an effective treatment for failed TSA by decreasing pain and improving shoulder function. However, RSA in the revision setting is associated with a higher complication rate.