Living organisms exhibit unique homeostatic abilities, maintaining tight control of their local environment through inter-conversions of chemical and mechanical energy and selfregulating feedback loops organized hierarchically across many length scales 1-7 . In contrast, most synthetic materials are incapable of undergoing continuous self-monitoring and self-regulating behavior due to their limited single-directional chemo-mechanical 7-12 or mechano-chemical 13, 14 modes. Applying the concept of homeostasis to the design of autonomous materials 15 would have transformative impacts in areas ranging from medical implants that help stabilize bodily functions to smart materials that regulate energy usage 2, 16, 17 . Here we present a versatile strategy for creating self-regulating, self-powered, homeostatic materials capable of precisely tailored chemo-mechano-chemical feedback loops at the nano/microscale. We design a bilayer system with hydrogel-supported, catalyst-bearing microstructures, which are separated from a reactant-containing "nutrient" layer. Reconfiguration of the gel in response to a stimulus induces the reversible actuation of the microstructures in and out of the nutrient layer and serves as a highly precise "on/off" switch for chemical reactions. We apply this design to trigger organic, inorganic and biochemical reactions that undergo reversible, repeatable cycles synchronized with the motion of the microstructures and the driving external chemical stimulus. By exploiting a continuous feedback loop between various exothermic catalytic reactions in the nutrient layer and the mechanical action of the temperature-responsive gel, we then create exemplary autonomous, self-sustained homeostatic systems that maintain a user-defined parameter-temperature-in a narrow range. The experimental results were validated using computational modeling that qualitatively captured the essential features of the self-regulating behavior and provided additional criteria for the optimization of the homeostatic function, subsequently confirmed experimentally. This design is highly customizable due to the broad choice of chemistries, tunable mechanics, and physical simplicity, thus promising exciting applications in autonomous systems with chemomechano-chemical transduction at their core.The survival of organisms relies on homeostatic functions such as the maintenance of stable body temperature, blood pressure, pH, and sugar levels 1,3,[5][6][7] . This remarkable self-

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Light-responsive, spiropyran-functionalized hydrogels have been used to create reversibly photoactuated structures for applications ranging from microfluidics to nonlinear optics. Tailoring a spiropyran-functionalized hydrogel system for a particular application requires an understanding of how co-monomer composition affects the switching dynamics of the spiropyran chromophore. Such gels are frequently designed to be responsive to different stimuli such as light, temperature, and pH. The coupling of these influences can significantly alter spiropyran behavior in ways not currently well understood. To better understand the influence of responsive co-monomers on the spiropyran isomerization dynamics, we use UV−vis spectroscopy and time-dependent fluorescence intensity measurements to study spiropyran-modified hydrogels polymerized from four common hydrogel precursors of different pH and temperature responsivity: acrylamide, acrylic acid, N-isopropylacrylamide, and 2-(dimethylamino)ethyl methacrylate. In acidic and neutral gels, we observe unusual nonmonotonic, triexponential fluorescence dynamics under 405 nm irradiation that cannot be explicated by either the established spiropyran−merocyanine interconversion model or hydrolysis. To explain these results, we introduce an analytical model of spiropyran interconversions that includes H-aggregated merocyanine and its light-triggered disaggregation under 405 nm irradiation. This model provides an excellent fit to the observed fluorescence dynamics and elucidates exactly how creating an acidic internal gel environment promotes the fast and complete conversion of the hydrophilic merocyanine speciesto the hydrophobic spiropyran form, which is desired in most light-sensitive hydrogel actuators. This can be achieved by incorporating acrylic acid monomers and by minimizing the aggregate concentration. Beyond spiropyranfunctionalized gel actuators, these conclusions are particularly critical for nonlinear optical computing applications.

Next-generation photonics envisions circuitry-free, rapidly reconfigurable systems powered by solitonic beams of self-trapped light and their particlelike interactions. Progress, however, has been limited by the need for reversibly responsive materials that host such nonlinear optical waves. We find that repeatedly switchable self-trapped visible laser beams, which exhibit strong pairwise interactions, can be generated in a photoresponsive hydrogel. Through comprehensive experiments and simulations, we show that the unique nonlinear conditions arise when photoisomerization of spiropyran substituents in pH-responsive poly(acrylamide-co-acrylic acid) hydrogel transduces optical energy into mechanical deformation of the 3D cross-linked hydrogel matrix. A Gaussian beam self-traps when localized isomerization-induced contraction of the hydrogel and expulsion of water generates a transient waveguide, which entraps the optical field and suppresses divergence. The waveguide is erased and reformed within seconds when the optical field is sequentially removed and reintroduced, allowing the self-trapped beam to be rapidly and repeatedly switched on and off at remarkably low powers in the milliwatt regime. Furthermore, this opto-chemo-mechanical transduction of energy mediated by the 3D cross-linked hydrogel network facilitates pairwise interactions between self-trapped beams both in the short range where there is significant overlap of their optical fields, and even in the long range––over separation distances of up to 10 times the beam width––where such overlap is negligible.

Stimuli-responsive materials typically contain responsive molecular units that couple an external trigger to a defined macroscale response. Ongoing efforts to boost the versatility and complexity of these responses increasingly focus on multi-stimuli-responsive molecular units and crosslinkers, as these bear the potential to impart self-regulatory behaviors building on cooperative effects and feedback mechanisms. Herein, we study a stimuli-responsive platform consisting of polyacrylamide-based hydrogels with well-known multi-responsive spiropyrans covalently bound as pendant groups or ´non-innocent´ crosslinkers. Surprisingly, as compared to their appended counterparts, spiropyran crosslinkers cause up to two-fold larger hydrogel swelling in methylenebisacrylamide-crosslinked poly(acrylamide-co-acrylic acid) hydrogels, despite their increased relative crosslinking density. We seek the origin of this unexpected behavior by employing nanoindentation, swelling studies, and UV-vis spectroscopy to study changes in mechanical properties and in spiropyran isomer distribution as a function of solution pH, co-monomer chemistry, and swelling-induced polymer strain. We then estimate the osmotic counterion pressures as a function of spiropyran isomer distribution but find that such pressures alone are insufficient to explain the observed behavior. Charge complexation, cooperative effects between the hydrogel´s mechanics and chemistry, and aggregate formation may all be invoked to explain features of the observed ´non-innocence´ of spiropyran crosslinkers. Taken together, these insights will aid rational implementation of such responsive crosslinkers in materials design and extend the functionality of existing polymeric materials towards more complex and better tunable behaviors.

Stimuli-responsive materials typically contain responsive molecular units that couple an external trigger to a defined macroscale response. Ongoing efforts to boost the versatility and complexity of these responses increasingly focus on multi-stimuli-responsive molecular units and crosslinkers, as these bear the potential to impart self-regulatory behaviors building on cooperative effects and feedback mechanisms. Herein, we study a stimuli-responsive platform consisting of polyacrylamide-based hydrogels with well-known multi-responsive spiropyrans covalently bound as pendant groups or ´non-innocent´ crosslinkers. Surprisingly, as compared to their appended counterparts, spiropyran crosslinkers cause up to two-fold larger hydrogel swelling in methylenebisacrylamide-crosslinked poly(acrylamide-co-acrylic acid) hydrogels, despite their increased relative crosslinking density. We seek the origin of this unexpected behavior by employing nanoindentation, swelling studies, and UV-vis spectroscopy to study changes in mechanical properties and in spiropyran isomer distribution as a function of solution pH, co-monomer chemistry, and swelling-induced polymer strain. We then estimate the osmotic counterion pressures as a function of spiropyran isomer distribution but find that such pressures alone are insufficient to explain the observed behavior. Charge complexation, cooperative effects between the hydrogel´s mechanics and chemistry, and aggregate formation may all be invoked to explain features of the observed ´non-innocence´ of spiropyran crosslinkers. Taken together, these insights will aid rational implementation of such responsive crosslinkers in materials design and extend the functionality of existing polymeric materials towards more complex and better tunable behaviors.

Objectives: To evaluate the correlation between Glycosy lated Haemoglobin (HbA1c) level and central foveal thickness measured by Optical coherence tomography (OCT) in patients with type 2 diabetes mellitus. Materials and methods: This was a retrospective single center study of 6 month duration including patients of pre-proliferative stage of type 2 diabetes mellitus. Clinically significant macular oedema (CSME) was diagnosed by using OCT. OCT examination by 'RT optovue, Fremont, CA' and HbA1c measured by specific high-pressure liquid chromatography methods. If patient have both eye macular oedema, eye with thicker macular oedema was used for statistical analysis. Exclusion of patients who received intraocular surgery, cataract surgery, pars plana vitrectomy, Severe vitreous haemorrhage, etc. Results: One hundred four eyes of 104 patients were included in this cross-sectional study. The mean Age ±SD was 62.3±8.1 years (range, 40-77 years). Mean value of HbA1c was 7.8%±1.4% (range, 5.1%-12.1%). Mean DM duration was 11.2±5.5 years (range, 1-30 years). Mean central retinal thickness was 257.1±79.3 μm (range, 151-526 μm). Univariate analysis was significant with HbA1C level (7 or over) (P=0.005). Not statistically significant with Sex (P=0.78), Right or left eye (P=0.59). Conclusion: Patients with HbA1c of 7% or above had an increase in macular thickness as measured by OCT in shorter DM duration (< 10 years). Its association with macular oedema is statistically significant. Good sugar control decreased the risk of diabetic macular oedema.

Background: Involvement of the ocular system in pregnancy is a common finding in females having PIH (pregnancy-induced hypertension). Aim: To judge the association between pregnancy-induced hypertension changes in the fundus and fetal outcomes. Methods: In 306 pregnant females with a confirmed diagnosis of pregnancy-induced hypertension, fundus changes were assessed along with fetal outcomes. The fetal outcomes included neonatal death, stillbirth, 1-minute Apgar scores, birth weight, and gestational age. Collected data were subjected to an ANOVA test and SPSS software to assess any association. Results: Among 306 subjects, 42 subjects had fundus changes and 264 subjects had no fundus changes. Mean systolic blood pressure (BP) was 182.88±33.62 in subjects with fundus changes and 150.74±12.84 mmHg in subjects without any fundus changes which was significantly higher in fundus changes. Diastolic pressure was also significantly higher, 125.26±21.34 mmHg in subjects with fundus changes compared to 100.09±9.49 mmHg in subjects without fundus changes. Fetal outcomes were comparable in subjects with or without fundus changes. A significant association was seen between optic nerve head and retinal changes with low birth weight (p<0.05). Conclusion: Low birth weight has an association with changes in the optic nerve head and retina.