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Explainable artificial intelligence (XAI) aims to reduce the opacity of AI-based decision-making systems, allowing humans to scrutinize and trust them. Unlike prior work that attributes the responsibility for an algorithm's decisions to its inputs as a purely associational concept, we propose a principled causality-based approach for explaining black-box decision-making systems. We present the demonstration of Lewis, a system that generates explanations for black-box algorithms at the global, contextual, and local levels, and provides actionable recourse for individuals negatively affected by an algorithm's decision. Lewis makes no assumptions about the internals of the algorithm except for the availability of its input-output data. The explanations generated by Lewis are based on probabilistic contrastive counterfactuals, a concept that can be traced back to philosophical, cognitive, and social foundations of theories on how humans generate and select explanations. We describe the system layout of Lewis wherein an end-user specifies the underlying causal model and Lewis generates explanations for particular use-cases, compares them with explanations generated by state-of-the-art approaches in XAI, and provides actionable recourse when applicable. Lewis has been developed as open-source software; the code and the demonstration video are available at lewis-system.github.io.

Experimental Data fromthe paper 'Spatiotemporal characterization of the field-induced insulator-to-metal transition' by Javier del Valle et al.

Many correlated systems feature an insulator-to-metal transition that can be triggered by an electric field. Although it is known that metallization takes place through filament formation, the details of how this process initiates and evolves remain elusive. We use in-operando optical reflectivity to capture the growth dynamics of the metallic phase with space and time resolution. We demonstrate that filament formation is triggered by nucleation at hotspots, with a subsequent expansion over several decades in time. By comparing three case studies (VO2, V3O5, and V2O3), we identify the resistivity change across the transition as the crucial parameter governing this process. Our results provide a spatiotemporal characterization of volatile resistive switching in Mott insulators, which is important for emerging technologies, such as optoelectronics and neuromorphic computing.

Metasurfaces are two-dimensional nanostructures that allow unprecedented control of light through engineering the amplitude, phase, and polarization across meta-atom resonators. Adding tunability to metasurface components would boost their potential and unlock a vast array of new application possibilities such as dynamic beam steering, tunable metalenses, and reconfigurable meta-holograms, to name a few. We present here high-index meta-atoms, resonators, and metasurfaces reconfigured by thermal effects, across the near to mid-infrared spectral ranges. We study thermal tunability in group IV and group IV–VI semiconductors, as well as in phase-transition materials, and demonstrate large dynamic resonance frequency shifts accompanied by significant amplitude and phase modulation in metasurfaces and resonators. We highlight the importance of high-Q resonances along with peak performance of thermal and thermo-optic effects, for efficient and practical reconfigurable devices. This paper paves the way to efficient high-Q reconfigurable and active infrared metadevices.

Dielectric-resonator-based nanophotonic devices show promise owing to their low intrinsic losses, support of multipolar resonances, and efficient operation in both reflection and transmission confi...

Metasurfaces allow unprecedented control of light through engineering the amplitude, phase and polarization across arrays of meta-atom resonators. Adding dynamic tunability to metasurface components would boost their potential and unlock a vast array of new application possibilities such as dynamic beam steering, LIDAR, tunable metalenses and reconfigurable meta-holograms, to name a few. We present here high-index reconfigurable metaatoms, resonators and metasurfaces that can dynamically and continuously tune their frequency, amplitude and phase, across the near to mid-infrared spectral ranges. We highlight the importance of narrow linewidth resonances along with peak performance of tunable mechanisms for efficient and practical reconfigurable devices.

Resistive switching, a phenomenon in which the resistance of a device can be modified by applying an electric field1–5, is at the core of emerging technologies such as neuromorphic computing and resistive memories6–9. Among the different types of resistive switching, threshold firing10–14 is one of the most promising, as it may enable the implementation of artificial spiking neurons7,13,14. Threshold firing is observed in Mott insulators featuring an insulator-to-metal transition15,16, which can be triggered by applying an external voltage: the material becomes conducting (‘fires’) if a threshold voltage is exceeded7,10–12. The dynamics of this induced transition have been thoroughly studied, and its underlying mechanism and characteristic time are well documented10,12,17,18. By contrast, there is little knowledge regarding the opposite transition: the process by which the system returns to the insulating state after the voltage is removed. Here we show that Mott nanodevices retain a memory of previous resistive switching events long after the insulating resistance has recovered. We demonstrate that, although the device returns to its insulating state within 50 to 150 nanoseconds, it is possible to re-trigger the insulator-to-metal transition by using subthreshold voltages for a much longer time (up to several milliseconds). We find that the intrinsic metastability of first-order phase transitions is the origin of this phenomenon, and so it is potentially present in all Mott systems. This effect constitutes a new type of volatile memory in Mott-based devices, with potential applications in resistive memories, solid-state frequency discriminators and neuromorphic circuits. Mott materials feature scale-less relaxation dynamics after the insulator-to-metal transition that make its electric triggering dependent on recent switching events.

We report the existence of two competing mechanisms in the current-driven electrical breakdown of vanadium sesquioxide (${\mathrm{V}}_{2}{\mathrm{O}}_{3}$) and vanadium dioxide ($\mathrm{V}{\mathrm{O}}_{2}$) nanodevices. Our experiments and simulations show that the competition between a purely electronic (PE) mechanism and an electrothermal (ET) mechanism, suppressed in nanoscale devices, explains the current-driven insulator-to-metal phase transition (IMT). We find that the relative contribution of PE and ET effects is dictated by thermal coupling and resistivity, a discovery which disambiguates a long-standing controversy surrounding the physical nature of the current-driven IMT in vanadium oxides. Furthermore, we show that the electrothermally driven IMT occurs through a nanoscopic surface-confined filament. This nanoconfined filament has a very large thermal gradient, thus generating a large Seebeck-effect electric field.

GLUT1, and to a lesser extent, GLUT3, appear to be interesting targets in the treatment of glioblastoma multiforme. The current review aims to give a brief history of the scientific community’s understanding of these glucose transporters and to relate their importance to the metabolic changes that occur as a result of cancer. One of the primary changes that occurs in cancer, the Warburg Effect, is characterized by an extreme shift toward glycolysis from the usual reliance on oxidative phosphorylation and is currently being investigated to target the upstream and downstream factors responsible for Warburg-induced changes. Further, it aims to explain the differential expression of GLUT1 and GLUT3 in glioblastoma tissue, and how these modulations in expression can serve as targets to restore a more normal metabolism. Additionally, hypoxia-induced factor-1α’s (HIF1α) role in a number of transcriptional changes typical to GBM will be discussed, including its role in GLUT upregulation. Finally, the four known subtypes of GBM [proneural, neural, mesenchymal, and classical] will be characterized in order to discuss how metabolic changes differ in each subtype. These changes have the potential to be selectively targeted in order to provide specificity to the clinical treatment options in GBM.

Sustained-release implants for insulin can be made by compressing a powder admixture with palmitic acid as the excipient. At less than 20%, insulin does not disperse uniformly in the admixture. The size distribution of the excipient particles obtained after grinding for 15 min does not affect the sustained release action. When tested in a 33 d period, an 1/8-size piece (approximately 25 mg) implant cut from a pellet disc containing 20% insulin which is 13 mm in diameter and 1.5 mm thick released 0.12-0.17 mg insulin/d in diabetic Wistar rats. The 1/8-size piece containing 20% insulin or a rod of similar weight with a diameter of 3 mm, which can be inserted by a trocar, was optimal for the implant to provide a service-life of 49 +/- 7 d. The service-life decreased with progressive reduction in implant size. The implant functioned just as well subcutaneously or intraperitoneally and was eroded subcutaneously by 33.6-53.1% in 33 d. The glycosylated haemoglobin contents of diabetic animals on implant therapy which had a blood glucose level of 4.7 +/- 2.5 mmol/l were in a range of 6.2-8.9% compared to the control value of greater than 13% with chronic hyperglycemia. The overall results indicated that the implant was a promising alternative to daily insulin injections.

Hydrogels prepared by crosslinking of natural or synthetic polymers have many biomedical applications. In the treatment of severe skin defects caused by disease or accidents, it is desirable to have the hydrogel surface modified to support cell growth which may enhance healing. To prepare and test such an hydrogel in vitro, 5 g of poly (vinyl alcohol) granules were suspended in 40 mL ethanol for reaction with 9 g of glycidyltrimethyl ammonium chloride at 60°C for 6 hr to graft the trimethyl-2-hydroxyaminopropyl (abbrev. TMHAP) function onto some of the hydroxyl groups. The 5 g of modified poly(vinyl alcohol) granules was then dissolved in 35 mL of water and 3.6 mL of 10 N sodium hydroxide for crosslinking by 2.8 g of epichlorohydrin to form a gel sheet in 20 hr having about 2% solids content. The amount of TMHAP groups thereon was determined by exchange of the chloride ions with a 10% sodium sulfate solution, followed by titration with silver nitrate using potassium chromate as indicator. Hydrogels with about 0.15 mM TMHAP group/g dry solid and diameter of 3.5 cm were inoculated with about 2 × 105 cells. On the next day, 20% of the cells attached thereto grew to 1.6, 3.1, and 6.5 × 105 cells on days 3, 5, and 7, respectively. The growth depended on the pre-conditioning of the hydrogel in culture medium and frequency of its change, but much less on cell inoculation density.

The construction and characterization of a simple hygrometer system for the measurement of evaporative loss from rodent skin are described. The performance of the present system is comparable to instruments of more complex design and higher cost.

Insulin dispersed in a pellet disk made by compressing an admixture with cholesterol was found to reduce hyperglycemia in streptozocin-induced diabetic Wistar rats. I evaluated the effect of insulin content. At 3% insulin, two pieces of quarter-disk implant (approximately 50 mg each) lowered blood glucose levels from greater than 22 mM to 17.5 mM for only 3 days. Normalization of hyperglycemia was sustained from approximately 10 days for the implant with 6% insulin content and to 24 +/- 5 days for 8-10% insulin in the composition. Insulin content up to 50% resulted in hypoglycemia and shorter implant service life. Not all of the pellet disks prepared were active, especially those with 3% insulin content. However, when broken further into 1-mm3 chips, all became active, with onset of action in less than 2 h, and the extent of hyperglycemia reduction was reproducible. Three successive subcutaneous insertions of approximately 80 mg chips with 10% insulin maintained normoglycemia for 2.5 mo. Because the implant materials are constituents of tissue, no biocompatibility problem is expected.

When implanted in Wistar rats with streptozotocin-induced diabetes, the release of insulin from an admixture with cholesterol which had been compressed into a pellet disc was previously found to continue for about 30 days. Several common fatty acids, their anhydrides, and glycerides were evaluated for similar suitability as a component of the implant in this study. Stearic acid and palmitic acid were found to be very promising. Especially with palmitic acid, a 25 mg piece containing 20% insulin reduced hyperglycemia to 3.7 ± 0.8 mmol/1 for 43.5 ± 6.5 days when implanted subcutaneously in diabetic rats. The stable blood glucose leve followed a regular food consumption pattern. But under scheduled feeding, the level varied from 2.4 ± 0.3 to 6.2 ± 0.5 mmol/1. However, hypoglycemic convulsion did not occur even after fasting for 16 h. Therefore, the rat model study indicates that palmitic acid can be a useful adjunct in sustaining the release of insulin from an implant.

Dextran and its crosslinked beads have many biomedical applications. If the stirring to maintain the epichlorohydrin emulsion is stopped in aboutseven minutes, crosslinked dextran gel sheets can be prepared. The elastic sheet obtained afterwashing in water, followed by treatment with propylene glycol containing 15% isopropanol, is suitable as a covering on rodent skin wound. Antibacterial agents can be dispersed into the sheet or admixed in the paste form of dextran gel.

In a previous study of the dextran gel sphere model system, a possible correlation between cell deformability and agglutinability by concanavalin A was indicated. Cell deformability was evaluated as filtrability, using polycarbonate membrane filtration. With 25-mm diameter filters and 5-ml cell suspensions at (0.8-16) X 10(5) cells/ml, the filtrability at a given filter pore size was highly reproducible and was not affected by variations in cell population, viability, washings of cells retained on filter, or temperature. The filtrability of EDTA-dissociated 3T3 cells through 12-micron pore size filter was 8%, and a suspension of 10(6) cells/ml was not agglutinated by 600 micrograms concanavalin A. The filtrability of trypsin-dissociated 3T3 cells was 95%, and these cells were agglutinated by 200 micrograms of the lectin. EDTA-dissociated SV-3T3 cells had a filtrability of 73% and were also highly agglutinable. Formalin fixation reduced the high filtrability to 6%, and also abolished the agglutinability. As a further test of the correlation, trypsin-dissociated 3T3 cells were admixed with the fixed cells. The agglutinability varied with the proportions of the two cell components, and the admixtures could be separated according to filtrability into the original components with distinctly different agglutinability. Furthermore, 25% of a random population of EDTA-dissociated SV-3T3 cells retained by the filter were found to be non-agglutinable. The separated SV-3T3 cell fractions could also form admixtures of different agglutinability. It is concluded that the agglutinability of mouse 3T3 and SV-3T3 cells by concanavalin A can be correlated with and predicted by cell filtrability.

Previous work in this series has shown that some aromatic and n-alkyl isocynates can significantly improve the adhesion of a fast-setting polyurethane prepolymer to internal tissue. In the present study, several acyl or aroyl anhydrides, chlorides, and a triaryl chloroalkane have been found to effect various degrees of improvement in the adhesion of fast-setting prepolymer to tissue. To determine the influence of minor structural changes on adhesion, the isomers of methyl phenyl isocynate and chlorobenzoyl chloride were investigated. The isomers were found to give the same extent of improvement in adhesion of the prepolymer as the parent compound without the methyl or chloro substituents. Among all the reactive monofunctional compounds studied, benzoyl chloride and its chlorobenzoyl derivatives are the most effective. When primed on tissue or admixed as little as a 3% additive in some polymer preparations, these aroyl chlorides can promote the adhesion of many ordinary adhesives to internal tissue. The effectiveness is attributed to the modification of hydrophilic tissue surface by the hydrophobic benzoyl group attached to tissue after reaction. The prosthetic benzoyl group makes the tissue/polymer interface more compatible and the compatibility results in good adhesion.

Solvent-extracted white birch, kept near 20° in liquid ammonia under pressure for 72 h and then extracted with methanol to remove acetamide, retained 0.25% of amide nitrogen. Extraction of the very finely ground residual wood with hot water yielded 21% as a 4-O-methylglucuronoxylan containing 0.53% of amide nitrogen. Alkaline hydrolysis removed the amide absorption in the infrared and restored the normal xylan spectrum. These results, supported by various control experiments, showed that amide groups in the ammonia-treated wood were derived from lactone or ester groups in the original 4-O-methylglucuronoxylan. Some of the uronic acid groups in the native wood presumably existed as ester crosslinks.

Conventional polyurethane prepolymers have been shown to adhere to living biological tissues. However, their setting is not sufficiently expedient to permit convenient applications in vivo. A prepolymer prepared from the highly reactive 6-chloro-2,4,5-trifluoro-1,3-phenylene diisocyanate, castor oil, and a trace of pyridine has afforded an adhesive which sets in about 2 min in vivo. The fast setting has resulted in poor adhesion on biological tissue. The bonding has been improved by the inclusion of tolylene diisocyanate in the composition without affecting the fast curing rate of the prepolymer. The dispersion of the adhesive and its cohesion after solidification have been adjusted by other minor additives. Preliminary evaluation on animals indicates that this adhesive is most useful as a hemostatic coating in hepatic lacerations.

Previously, a small implant of compressed insulin in palmitic acid provided a basal dose to reduce hyperglycaemia for 42 +/- 12 d in rats with induced diabetes. This study describes a silicone implant that can be used for preprandial dose supplements. The device consists of two compartments assembled by attaching a 9 mm diameter foam ring to a 6 mm diameter ring of the same material. The assembly is then enclosed between two membranes, and an annular external wall. Before sealing, a 6 mg piece of compressed insulin (Zn) is inserted into the smaller ring with 2 mg tetracycline to hinder microbial growth. The top membrane is pierced once with an 18 gauge needle, and the device is tested by implanting under the abdominal skin of diabetic rats. Serous fluid soon enters to fill the 141 microliter internal volume through the orifice and dissolves some of the insulin which does not leak out. Sidewise compression weekly over the skin fold of the unanesthetized animal shows that the insulin remained potent until used up after 154 d. When compressed daily, the insulin supply lasted for 24 +/- 4 d and maintained the blood glucose consistently at 3.4 +/- 1.1 mM/l for 6-8 h each day. The dependable device is refillable percutaneously by injection of an insulin suspension.

Bioactive polypeptides are susceptible to inactivation by proteolytic enzymes in body fluids. Instead of many injections, these polypeptides may be specially formulated to prolong their action in vivo to several months by entrapment in a polymer mixture. In a recent fundamental study on implant for drug delivery, it was found in this laboratory that a polymer support component was not mandatory and pharmacologically active macromolecules could be readily delivered on a sustained basis. Consequently, when 10% insulin (Zn) was admixed with cholesterol and then compressed, the hormone action was extended to about 20 days when tested subcutaneously in Wistar rats with streptozotocin-induced diabetes. Evaluation of other lipids has shown that with palmitic acid as the excipient, the 8-hr action of insulin can be extended to about 40 days. The same type of sustained delivery implant containing insulin or pituitary growth hormone can enhance growth in normal Wistar rats. Since no synthetic materials were used, biocompatibility problem is not expected. Further, the fatty acid excipient is gradually eroded in vivo, and explantation of the implant will not be necessary as well. This approach shall be particularly useful in special formulations of other pharmaceutical proteins such as the rDNA-produced somatotropin analog used in growth enhancement of farm animals raised for consumer food products.

Dextran and its crosslinked beads have many biomedical applications. If stirring to maintain the epichlorohydrin emulsion is stopped in about 7 minutes, crosslinked dextran gel sheets can be prepared. The elastic sheet obtained after washing in water, followed by treatment with propylene glycol containing 15% isopropanol is suitable as a covering on rodent skin wound. Antibacterial agents can be dispersed into the sheet or admixed in the paste form of the gel.In standard tests, a 4 cm × 4 cm surface wound on the back of a 400-g Wistar rat was covered with the dextran gel material. The evaporation loss was found to reduce immediately from 94 mg H20/cm2/hr to 1/2 of this value which became 12.5 mg H20/cm2hr in 18 hours. Such a covered wound healed in 10–17 days with 10–15% distortion, while the controls were delayed to 25 ± 7 days with >65% wound contraction.Another modification of the gel material involves the surface attachment of the positively charged 2-diethylaminoethyl function (DEAE). Although up to 2.41 mM DEAE groups/g gel can be introduced, only 3 to 2 × 105 cells/cm2. Therefore, the gel material may have potential as a substrate for dermal cells as well for later transfer.

Generally, a polymer implant may release a drug by diffusion at the same time with dissolution of the polymer component without depolymerization (Type A) or by erosion involving depolymerization (Type B). The Type A material induces immune response while the Type B polymer may lead to toxicity problems. It is proposed that a combination of the two types of polymer may attenuate the intensity of the biological responses, because the presence of one in an implant of the same weight reduces the amount of the other. However, it is important to know if sustained delivery may be achieved by such an implant. In this study, partially hydrolyzed poly(vinyl acetate) (PVA) and polycaprolactone (PCL) were chosen as the model Type A. and B polymers, respectively, to evaluate this objective first in vitro with methylene blue (MB) as a model drug. Results show that sustained delivery can be effected, but PCL erosion did not occur as intended. Therefore, PCL served only as a passive component of the implant. while PVA was eroded with the release of MB. Consequently, it was inferred that a polymer may not be required as a passive component. Tests with insulin in a compressed solid admixture with palmitic acid showed that reduction of hyperglycemia in diabetic Wistar rat could be effected repro-ducibly for at least 5 weeks. Thus, the present study, originally planned to test a proposed concept, indicates that non-polymeric materials of known biocompatibility may be suitable for delivery of many bioactive polypeptides as well.

Extensive skin loss resulting from thermal injuries poses traumatic and life threatening problems. The major causes of death are from bacterial infection and excessive fluid loss developed post-burn. Victims who manage to survive these early threats are, nonetheless, permanently damaged psychologically and physically by the disfiguring scars which arise from wound contraction. The absence of a template for cell propagation retards epithelialization and subsequent wound closure. Previous studies on hydrogels prepared from non-immunogenic dextran (mol. wt. 151,000) and impregnated with bacteriostatic agents have shown them to be effective in controlling infection. Therefore, it is desirable to modify these hydrogels such that they will also support the growth of cells. Since positively charged groups such as 2-diethyl-aminoethyl (DEAE) have been shown to facilitate cell attachment and growth in commercial microcarriers, we investigated the binding of DEAE groups onto preformed gels. A preliminary evaluation of the DEAD-treated hydrogels indicated that DEAE-binding significantly facilitates the propagation and growth of cells on the hydrogel surface.

An implant may release a drug either by diffusion concurrent with dissolution of the polymeric implant material without depolymerization (Type A) or by bioerosion involving depolymerization (Type B). The Type A material may induce immune response, while the erosion of Type B polymer releases fragments which could cause toxicity problems. It is proposed that a combination of the two types of polymers may attenuate the intensity of immune response and toxicity, because the presence of one in an implant of the same weight reduces the amount of the other. However, it is important to determine first, if sustained delivery may be achieved by such an implant. In this study, partially hydrolyzed poly(vinyl acetate) (PVA) and polycaprolactone (PCL) were chosen as the model Type A, and B polymers, respectively, to evaluate this objective in vitro. Pellet discs were prepared to assess the effects of compression, proportion of PVA to PCL, acetyl content of PVA, PCL hydrolysis catalyst and drug loading, using methylene blue (MB) as a model drug. Results showed that sustained delivery could be effected, but PCL erosion did not occur as planned. Therefore, PCL served only as a passive component of the implant, while PVA was eroded with the release of MB. Consequently, it was inferred that a polymer may not be required as a passive component, which suggested the use of other compounds of known biocompatibility. Tests with insulin in a compressed solid admixture with cholesterol showed that reduction of hyperglycemia in diabetic Wistar rat could be effected reproducibly for at least 2 weeks. Thus, the present study, originally planned to test a proposed concept, indicates that many nonpolymeric materials of known biocompatibility may be suitable for drug delivery implants as well.

Accidental injury with loss of skin is considered to be a “neglected disease”, partly because of the superficial nature of damage to the protective layer of the body. Surveys conducted in the U.S. show that such injury is among the principal causes of death in North America between ages 1 and 44 [1]. In the Canadian province of Ontario, there were over 50,000 people suffered loss of skin in 1977 due to trauma (including surgical autograft), disease (e.g., ulceration) or burns from electrical, chemical or thermal agents. Patients often must change their occupations or alter their normal activities, and in addition many working or school days are lost annually through lengthy stays in hospital as well as re-admission for revision of scars. Besides pain and the high incidence of bacterial infection, loss of skin is followed by excessive evaporation of vital body fluids which initiates a series of physiological responses as illustrated schematically in the following diagram

Dextran is a polysaccharide which can interact with concanavalin A, and insolubilized dextran spheres are available with different degrees of swelling in water. One grade of these dextran gel spheres can be agglutinated extensively by concanavalin A, while another grade with the same binding constant is not affected. Photomicrographs and measurement by capillary suction show that deformability and good contact between these gel spheres can be correlated with their agglutinability.