A manufacturable smart dressing with oxygen delivery and sensing capability for chronic wound management

Chronic non-healing wounds, impact over 6.5 million Americans, costs in excess of $25 billion to treat on an annual basis and its incidence is predicted to rise due to the prevalence of obesity and type-2 diabetes. One of the primary complications often associated with chronic wounds is the improper functionality of the peripheral vasculature to deliver O2-rich blood to the tissue which leads to wound hypoxia. Although hyperbaric oxygen therapy are widely used and accepted as an effective approach to bolster tissue O2 levels in hypoxic chronic wounds, most of such treatments require bulky equipment and often expose large areas of the body to unnecessarily elevated oxygen concentrations that can damage healthy tissue. In this paper, we present a smart low-cost wound dressing with integrated oxygen sensor and delivery for locally generating and delivering oxygen to selected hypoxic regions on the wound. The dressing is fabricated on a biocompatible water resistant/hydrophobic paper-based substrate with printed optical oxygen sensors and patterned catalytic oxygen generating regions that are connected to a flexible microfluidic systems. Oxygen generation occurs by flowing H2O2 through the channels and chemical decomposition at the catalyst printed regions on the paper substrate. The hydrophobic paper provides structural stability and flexibility while simultaneously offering printability, selective gaseous filtering, and physical/chemical protection. The fabrication process take advantage of scalable manufacturing technologies including laser processing, inkjet printing, and lamination

Kinetics of UV Irradiation Induced Chain Scission and Cross-Linking of Coumarin-Containing Polyester Ultrathin Films

Photoresponsive thin films are commonly encountered as high performance coatings as well as critical component, photoresists, for microelectronics manufacture. Despite intensive investigations into the dynamics of thin glassy polymer films, studies involving reactions of thin films have typically been limited by difficulties in decoupling segregation of reacting components or catalysts due to the interfaces. Here, thin films of coumarin polyesters overcome this limitation where the polyester undergoes predominately cross-linking upon irradiation at 350 nm, while chain scission occurs with exposure to 254 nm light. Spectroscopic ellipsometry is utilized to track these reactions as a function of exposure time to elucidate the associated reaction kinetics for films as thin as 15 nm. The cross-linking appears to follow a second order kinetic rate law, while oxidation of the coumarin that accompanies the chain scission and enables this reaction to be tracked spectroscopically appears to be a first order reaction in coumarin concentration. Because of the asymmetry in the coumarin diol monomer and the associated differences in local structure that result during formation of the polyester, two populations of coumarin are required to fit the reaction kinetics; 10–20% of the coumarin is significantly more reactive, but these groups appear to undergo chain scission/oxidation at both wavelengths. These reaction rate constants are nearly independent (within 1 order of magnitude) of film thickness down to 15 nm. There is maximum rate at a finite thickness for the 254 nm exposure, which we attribute to constructive interference of the UV radiation within the polymer film, rather than typical confinement effects; no thickness dependence in reaction rates is observed for the 350 nm exposure. The utilization of a single polymer with two distinct reactions enables unambiguous investigation of thickness effects on reactions

Development of a Fluorinated Graphene-Based Resistive Humidity Sensor

This work presents the development of novel fluorinated graphene (FG)-based resistive humidity sensor. The humidity sensor was fabricated by drop-casting FG suspension, as the humidity sensing material, on silver (Ag)-based interdigitated electrodes (IDEs). The silver-based IDEs were screen printed on a flexible polyimide substrate. The FG suspension was synthesized by uniform dispersion of FG in isopropyl alcohol (IPA), using the ultra-sonication process. The resistive response of the fabricated humidity sensors towards varying relative humidity (RH) levels was investigated, when the RH was varied from 20% to 80%, in steps of 10%, and at a temperature of 24 \ub0C. A relative resistance change of 13.3% was observed when the RH was changed from 20% to 80%, with a sensitivity of 0.22%/%RH for the FG-based humidity sensor. Response time and recovery time of 82 s and 125 s, respectively, was obtained for the fabricated sensor. In addition, the effect of varying operating temperatures on the response of the fabricated humidity sensors was investigated. The average temperature coefficient of resistance of sensors was obtained as approximately -0.3%/\ub0C. A linear relation between the temperature and the relative resistance change of sensors was observed. Further, first-principles study, employing density functional theory calculations, was performed to investigate interactions between the fluorine atom and graphene substrate, as well as humidity sensing behavior of the FG. DFT calculations showed that hydrogen atoms of the water molecule move towards the fluorine atom of the FG during the relaxation process, confirming the hydrogen bonding between FG and water molecules. The Eads of -0.50 eV was calculated for the adsorption of water molecule on the FG, demonstrating the strong humidity sensing property of the FG. The results demonstrate that FG, a highly stable derivative of graphene, is a potential material for humidity sensing applications

Impact of Different Ratios of Fluorine, Oxygen, and Hydroxyl Surface Terminations on Ti3C2T x MXene as Ammonia Sensor: A First-Principles Study

A first-principles study was successfully employed to investigate the impact of different ratios of functional groups such as fluorine (-F), oxygen (-O), and hydroxyl (-OH) on ammonia (NH3) sensing of titanium carbide Mxene. Density functional theory (DFT) calculations were performed for studying the adsorption energy (Eads) and charge transfer (CT) between different gases (NH3, CO 2 , NO, H2S and SO 2 ) and TbC2T x material with a high ratio of fluorine surface functional groups, TbC2(OH)o.44Fo.ssO0.66. DFT calculations showed more sensitivity to NH3, with the highest CT (0.098 e) and the lowest Eads (-0.36 eV) among the mentioned gases. The adsorption of NH3 on TbC2T x MXene with a high and low ratios of fluorine surface functional groups, TbC2(OH)o.44Fo.ssOO.66 (Substrate 1) and TbC2(OH)o.66Fo.2201.11 (Substrate 2) respectively, resulted in adsorption energies of -0.36 eV and -0.49 eV, revealing a stronger adsorption of NH3 on Substrate 2 with low ratios of fluorine. In addition, the isosurfaces representation of charge difference illustrated that fluorine atoms have smaller charge transfer than oxygen atoms when interacting with NH3 molecules. The Bader charge difference for the closest oxygen and fluorine atoms to NH3 molecule showed that oxygen atoms have 60% to 180% larger Bader charge difference, when compared to fluorine atoms, supporting that TbC2T x sensor with a lower ratio of fluorine surface termination has a stronger interaction with NH3 gas molecules

Humidity Sensing Properties of Halogenated Graphene: A Comparison of Fluorinated Graphene and Chlorinated Graphene

This work presents a comparison of humidity sensing properties of fluorinated graphene (FG) and chlorinated graphene (ClG), using experimental data and atomic-level ab-initio simulations. The fabrication of the humidity sensor included drop-casting FG and ClG suspensions on silver (Ag)based interdigitated electrodes (IDEs) to form the sensing layer. The sensitivity of FG and ClG to humidity variations was investigated by measurement of relative resistance change (\u394 R/Rb) of the fabricated humidity sensors when the relative humidity (RH) was changed from 20% to 80%, in steps of 10%, at a constant temperature of 24\ub0 C. For RH transition from 20% to 80%, the \u394 R/Rb of the FG-based and the ClG-based humidity sensors were measured as 13.3% and 10.8%, respectively, resulting in a sensitivity of 0.22%/%RH and 0.18%/%RH, respectively. Density functional theory (DFT) calculations showed adsorption energy (Eads) of-0.50 eV and-0.43 eV for the physisorption of water molecules on the FG and ClG, respectively, demonstrating the higher sensitivity of the FG to humidity. The density of states (DOS) calculations showed that the water-adsorbed FG has a larger DOS near the Fermi level when compared to water-adsorbed ClG, which can be attributed to the stronger interaction and more effective charge transfer between the FG and the water molecule

Micropatterned Coumarin Polyester Thin Films Direct Neurite Orientation

Guidance and migration of cells in the nervous system is imperative for proper development, maturation, and regeneration. In the peripheral nervous system (PNS), it is challenging for axons to bridge critical-sized injury defects to achieve repair and the central nervous system (CNS) has a very limited ability to regenerate after injury because of its innate injury response. The photoreactivity of the coumarin polyester used in this study enables efficient micropatterning using a custom digital micromirror device (DMD) and has been previously shown to be biodegradable, making these thin films ideal for cell guidance substrates with potential for future in vivo applications. With DMD, we fabricated coumarin polyester thin films into 10 × 20 μm and 15 × 50 μm micropatterns with depths ranging from 15 to 20 nm to enhance nervous system cell alignment. Adult primary neurons, oligodendrocytes, and astrocytes were isolated from rat brain tissue and seeded onto the polymer surfaces. After 24 h, cell type and neurite alignment were analyzed using phase contrast and fluorescence imaging. There was a significant difference (<i>p</i> < 0.0001) in cell process distribution for both emergence angle (from the body of the cell) and orientation angle (at the tip of the growth cone) confirming alignment on patterned surfaces compared to control substrates (unpatterned polymer and glass surfaces). The expected frequency distribution for parallel alignment (≤15°) is 14% and the two micropatterned groups ranged from 42 to 49% alignment for emergence and orientation angle measurements, where the control groups range from 12 to 22% for parallel alignment. Despite depths being 15 to 20 nm, cell processes could sense these topographical changes and preferred to align to certain features of the micropatterns like the plateau/channel interface. As a result this initial study in utilizing these new DMD micropatterned coumarin polyester thin films has proven beneficial as an axon guidance platform for future nervous system regenerative strategies