Development of a versatile method for incorporating conductive materials into textiles could enable advances in wearable electronics and smart textiles. One area of critical importance is the ...detection of chemicals in the environment for security and industrial process monitoring. Here, the fabrication of a flexible, sensor material based on functionalized multi‐walled carbon nanotube (MWNT) films on a porous electrospun fiber mat for real‐time detection of a nerve agent simulant is reported. The material is constructed by layer‐by‐layer (LbL) assembly of MWNTs with opposite charges, creating multilayer films of MWNTs without binder. The vacuum‐assisted spray‐LbL process enables conformal coatings of nanostructured MWNT films on individual electrospun fibers throughout the bulk of the mat with controlled loading and electrical conductivity. A thiourea‐based receptor is covalently attached to the primary amine groups on the MWNT films to enhance the sensing response to dimethyl methylphosphonate (DMMP), a simulant for sarin nerve agent. Chemiresistive sensors based on the engineered textiles display reversible responses and detection limits for DMMP as low as 10 ppb in the aqueous phase and 5 ppm in the vapor phase. This fabrication technique provides a versatile and easily scalable strategy for incorporating conformal MWNT films into three‐dimensional substrates for numerous applications.
Flexible sensory material based on conformal multi‐walled carbon nanotube (MWNT) films on a porous electrospun polymeric fiber mat is constructed using a vacuum‐assisted spray layer‐by‐layer assembly. The resulting thin MWNT films coat individual electrospun fibers with controlled loading and electrical conductivity. The MWNT/electrospun fiber electrodes display reversible responses and high sensitivity for detecting DMMP in aqueous and vapor phases.
Adherence of proteins, cells, and microorganisms to the surface of biomaterials used for vascular access contribute to device failure by thrombosis, occlusions, and infections. Current technologies ...for inhibiting these complications are limited to coatings and additives that are limited in duration of efficacy and often induce adverse side effects. In this work, we developed a novel composite hydrogel structure comprising of a porous poly(vinyl alcohol) (PVA) that is impregnated with poly(acrylic acid) (PAA) and heat treated to create a physically cross-linked high-strength hydrogel material. The swelling and mechanical properties can be controlled by the temperature and duration of heat treatment to increase the cross-link density of the matrix. The heat treated composite PVA/PAA hydrogel exhibits both the mechanical strength and durability of thermoplastic polyurethanes (TPUs) and the inherently non-thrombogenic surface functionality of PVA-based hydrogels without the use of chemical cross-linking agents. The composite hydrogels were found to maintain their mechanical integrity and surface functionality after accelerated aging in a simulated-use in vitro model for 162.5 days real-time equivalent. Relative to commercial catheter materials, the composite PVA/PAA hydrogel exhibited up to an average of 97% reduction in platelet adhesion when exposed to an in vitro blood loop model and a lower rate of tip occlusion due to thrombosis. This high-strength thromboresistant hydrogel could have a major impact as a novel biomaterial for use in vascular access applications to improve patient health.
The mechanical and tribological properties of electrospun fiber mats are of paramount importance to their utility as components in a large number of applications. Although some mechanical properties ...of these mats have been reported previously, reports of their tribological properties are essentially nonexistent. In this work, electrospun nanofiber mats of poly(trimethyl hexamethylene terephthalamide) (PA 6(3)T) with average fiber diameter of 463 ± 64 nm are characterized mechanically and tribologically. Post-spin thermal annealing was used to modify the properties of the fiber mats. Morphological changes, in-plane tensile response, friction coefficient and wear rate were characterized as functions of the annealing temperature. The Young's moduli, yield stresses and toughnesses of the nonwoven mats improved by two- to ten-fold when annealed slightly above the glass transition temperature, but at the expense of mat porosity. The coefficient of friction and the wear rate decrease by factors of two and ten, respectively, under the same conditions. The wear rate correlates with the yield properties of the mat, in accord with a modified Ratner–Lancaster model. The variation in mechanical and tribological properties of the mats with increasing annealing temperature is consistent with the formation of fiber-to-fiber junctions and a mechanism of abrasive wear that involves the breakage of fibers between junctions.
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Compressibility of electrospun fiber mats Choong, Looh Tchuin; Mannarino, Matthew M.; Basu, Sandip ...
Journal of materials science,
11/2013, Letnik:
48, Številka:
22
Journal Article
Recenzirano
Odprti dostop
Compressive properties of electrospun fiber mats are reported for the first time. Mats of bisphenol-A polysulfone (PSU) and of poly(trimethyl hexamethylene terephthalamide) PA 6(3)T were electrospun ...and annealed over a range of temperatures spanning the glass transition temperature of each polymer. The data for applied stress versus mat solidity were found to be well-described by a power law of the form
σ
zz
=
kE
(
ϕ
n
−
ϕ
0
n
)
, where
σ
zz
is the applied stress and
ϕ
is solidity, in accord with the analysis of Toll (Polym Eng Sci 38(8):1337,
2004
). The values of
n
range from 3.2 to 6 for PSU and from 8.0 to 20 for PA 6(3)T. The lowest values in each case were exhibited by mats annealed near the glass transition temperature of the fiber material. The values of
n
are independent of fiber diameter. The higher values of
n
are attributed to fiber slippage via a mechanism analogous to that of work hardening of metals. The values of
kE
can vary by an order of magnitude and were difficult to determine precisely, due to the nature of the power law and the inhomogeneity of the mats. The compressibility of electrospun mats in response to an applied stress is sufficiently large that it cannot be neglected in applications where large pressures may be involved, such as filtration or membrane separations. In addition to the initial solidity of the mats, the material compressibility and the operating pressure relevant to the application are important to describe the structure of electrospun mats quantitatively under conditions of use.
Polymer electrolyte films are deposited onto highly porous electrospun mats using layer‐by‐layer (LbL) processing to fabricate composite proton conducting membranes. By simply changing the assembly ...conditions for generation of the LbL film on the nanofiber mat substrate, three different and unique composite film morphologies can be achieved in which the electrospun mats provide mechanical support; the LbL assembly produces highly conductive films that coat the mats in a controlled fashion, separately providing the ionic conductivity and fuel blocking characteristics of the composite membrane. Coating an electrospun mat with the LbL dipping process produces composite membranes with “webbed” morphologies that link the fibers in‐plane and give the composite membrane in‐plane proton conductivities similar to that of the pristine LbL system. In contrast, coating an electrospun mat using the spray‐LbL process without vacuum produces a uniform film that bridges across all of the pores of the mat. These membranes have methanol permeability similar to free‐standing poly(diallyl dimethyl ammonium chloride)/sulfonated poly(2,6‐dimethyl 1,4‐phenylene oxide) (PDAC/sPPO) thin films. Coating an electrospun mat with the vacuum‐assisted spray‐LbL process produces composite membranes with conformally coated fibers throughout the bulk of the mat with nanometer control of the coating thickness on each fiber. The mechanical properties of the LbL‐coated mats display composite properties, exhibiting the strength of the glassy PDAC/sPPO films when dry and the properties of the underlying electrospun polyamide mat when hydrated. By combining the different spray‐LbL fabrication techniques with electrospun fiber supports and tuning the parameters, mechanically stable membranes with high selectivity can be produced, potentially for use in fuel cell applications.
Polymer electrolyte films are deposited onto highly porous electrospun mats using layer‐by‐layer (LbL) processing to fabricate composite proton conducting membranes. Various dip and spray processing techniques are investigated for different and unique composite film morphologies. By combining the different spray‐LbL fabrication techniques with electrospun fiber supports and tuning the parameters, mechanically stable membranes with high selectivity can be produced.
Composite membranes composed of highly conductive and selective layer-by-layer (LbL) films and electrospun fiber mats were fabricated and characterized for mechanical strength and electrochemical ...selectivity. The LbL component consists of a proton-conducting, methanol-blocking poly(diallyl dimethyl ammonium chloride)/sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (PDAC/sPPO) thin film. The electrospun fiber component consists of poly(trimethyl hexamethylene terephthalamide) (PA 6(3)T) fibers in a nonwoven mat of 60–90% porosity. The bare mats were annealed to improve their mechanical properties, which improvements are shown to be retained in the composite membranes. Spray LbL assembly was used as a means for the rapid formation of proton-conducting films that fill the void space throughout the porous electrospun matrix and create a fuel-blocking layer. Coated mats as thin as 15 μm were fabricated, and viable composite membranes with methanol permeabilities 20 times lower than Nafion and through-plane proton selectivity five and a half times greater than Nafion are demonstrated. The mechanical properties of the spray coated electrospun mats are shown to be superior to the LbL-only system and possess intrinsically greater dimensional stability and lower mechanical hysteresis than Nafion under hydrated conditions. The composite proton exchange membranes fabricated here were tested in an operational direct methanol fuel cell. The results show the potential for higher open circuit voltages (OCV) and comparable cell resistances when compared to fuel cells based on Nafion.
The mechanical and tribological properties of electrospun fiber mats are of paramount importance to their utility in a large number of applications. In this work, mats of electrospun fibers of ...poly(hexamethylene adipamide) (PA 6,6) with average fiber diameter of 238±22nm are characterized for their crystal structure as well as their mechanical and tribological properties. Post-spin thermal annealing was used to modify the fiber morphology and crystallinity within the fibers. Morphological changes, in-plane tensile response, friction coefficient and wear rate were characterized as functions of the annealing temperature. The mechanical and tribological properties of the thermally annealed PA 6,6 fiber mats exhibited significant improvements through the Brill transition temperature, comparable to the improvements observed for amorphous polyamide electrospun mats annealed near the glass transition temperature. The effective wear rate of the electrospun fiber mats is well-described by a previously proposed modification of the Ratner-Lancaster relationship that relates wear to the yield behavior of these nonwoven mats.
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•Poly(hexamethylene adipamide) fibers with diameters of 238±22nm were electrospun.•Post-spin thermal annealing improves tensile stiffness and wear resistance of mats.•Brill transition signals major changes in crystal morphology and mat properties.•Wear rate is well described by a modified Ratner-Lancaster model.
The purposes of this study were (1) to evaluate the initial setup accuracy and intrafraction motion for spine stereotactic body radiation therapy (SBRT) using stereotactic body frames (SBFs) and (2) ...to validate an in-house-developed SBF using a commercial SBF as a benchmark.
Thirty-two spine SBRT patients (34 sites, 118 fractions) were immobilized with the Elekta and in-house (BHS) SBFs. All patients were set up with the Brainlab ExacTrac system, which includes infrared and stereoscopic kilovoltage x-ray-based positioning. Patients were initially positioned in the frame with the use of skin tattoos and then shifted to the treatment isocenter based on infrared markers affixed to the frame with known geometry relative to the isocenter. ExacTrac kV imaging was acquired, and automatic 6D (6 degrees of freedom) bony fusion was performed. The resulting translations and rotations gave the initial setup accuracy. These translations and rotations were corrected for by use of a robotic couch, and verification imaging was acquired that yielded residual setup error. The imaging/fusion process was repeated multiple times during treatment to provide intrafraction motion data.
The BHS SBF had greater initial setup errors (mean±SD): -3.9±5.5mm (0.2±0.9°), -1.6±6.0mm (0.5±1.4°), and 0.0±5.3mm (0.8±1.0°), respectively, in the vertical (VRT), longitudinal (LNG), and lateral (LAT) directions. The corresponding values were 0.6±2.7mm (0.2±0.6°), 0.9±5.3mm (-0.2±0.9°), and -0.9±3.0mm (0.3±0.9°) for the Elekta SBF. The residual setup errors were essentially the same for both frames and were -0.1±0.4mm (0.1±0.5°), -0.2±0.4mm (0.0±0.4°), and 0.0±0.4mm (0.0±0.4°), respectively, in VRT, LNG, and LAT. The intrafraction shifts in VRT, LNG, and LAT were 0.0±0.4mm (0.0±0.3°), 0.0±0.5mm (0.0±0.4°), and 0.0±0.4mm (0.0±0.3°), with no significant difference observed between the 2 frames.
These results showed that the combination of the ExacTrac system with either SBF was highly effective in achieving both setup accuracy and intrafraction stability, which were on par with that of mask-based cranial radiosurgery.
Stereotactic radiosurgery (SRS) is frequently used in the management of brain metastases, but concerns over potential toxicity limit applications for larger lesions or those in eloquent areas. ...Fractionated stereotactic radiation therapy (SRT) is often substituted for SRS in these cases. We retrospectively analyzed the efficacy and toxicity outcomes of patients who received SRT at our institution. Seventy patients with brain metastases treated with SRT from 2006–2012 were analyzed. The rates of local and distant intracranial progression, overall survival, acute toxicity, and radionecrosis were determined. The SRT regimen was 25 Gy in 5 fractions among 87 % of patients. The most common tumor histologies were non-small cell lung cancer (37 %), breast cancer (20 %) and melanoma (20 %), and the median tumor diameter was 1.7 cm (range 0.4–6.4 cm). Median survival after SRT was 10.7 months. Median time to local progression was 17 months, with a local control rate of 68 % at 6 months and 56 % at 1 year. Acute toxicity was seen in 11 patients (16 %), mostly grade 1 or 2 with the most common symptom being mild headache. Symptomatic radiation-induced treatment change was seen on follow-up MRIs in three patients (4.3 %). SRT appears to be a safe and reasonably effective technique to treat brain metastases deemed less suitable for SRS, though dose intensification strategies may further improve local control.
Patients with limited brain metastases are often candidates for stereotactic radiosurgery (SRS) or whole brain radiotherapy (WBRT). Among patients who receive SRS, the likelihood and timing of ...salvage WBRT or SRS remains unclear. We examined rates of salvage WBRT or SRS among 180 patients with 1–4 newly diagnosed brain metastases who received index SRS from 2008–2013. Competing risks multivariable analysis was used to examine factors associated with time to WBRT. Patients had non-small cell lung (53 %), melanoma (23 %), breast (10 %), renal (6 %), or other (8 %) cancers. Median age was 62 years. Patients received index SRS to 1 (60 %), 2 (21 %), 3 (13 %), or 4 (7 %) brain metastases. Median survival after SRS was 9.7 months (range, 0.3–67.6 months). No further brain-directed radiotherapy was delivered after index SRS in 55 % of patients. Twenty-seven percent of patients ever received salvage WBRT, and 30 % ever received salvage SRS; 12 % of patients received both salvage WBRT and salvage SRS. Median time to salvage WBRT or salvage SRS were 5.6 and 6.1 months, respectively. Age ≤60 years (adjusted hazard ratio AHR = 2.80; 95 % CI 1.05–7.51;
P
= 0.04) and controlled/absent extracranial disease (AHR = 6.76; 95 % CI 1.60–28.7;
P
= 0.01) were associated with shorter time to salvage WBRT. Isolated brain progression caused death in only 11 % of decedents. In summary, most patients with 1–4 brain metastases receiving SRS never require salvage WBRT or SRS, and the remainder do not require salvage treatment for a median of 6 months.
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