TECHNOLOGY FOCUS - INSTRUMENTATION AND TESTING - Preferred Components: The valve is operable in a pH range of 2-7.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The acid is acrylic acid (preferred), methacrylic acid, 2-ethylacrylic acid, 2-propylacrylic acid, 2-(trifluoromethyl)acrylic acid, 2-(bromomethyl)acrylic acid, 2-bromacrylic acid, vinylsulfonic acid, 4-styrenesulfonic acid, 2-acrylamido-2-methyl-1-propanesulfonic acid, or vinylphosphonic acid. The crosslinking agent is N,N'-methylenebisacrylamide, N,N'-ethylenebisacrylamide, butanediol diacrylate, hexanediol diacrylate, poly(ethylene glycol) diacrylate, or poly(propylene glycol) diacrylate. The N-isopropylacrylamide is present in an amount of 100 mole%. The benzospiropyran acrylate is present in an amount of 1-3 mole%. The acrylic acid is present in an amount of 1-15 mole%. The N,N'-methylenebisacrylamide is present in an amount of 0.1-3 mole%. The initiator comprises a white light photo-initiator and a UV-initiator. The white light photo-initiator comprises phenylbis(2 4 6-trimethylbenzoyl)phosphine oxide. The organic solvent is 1,4-dioxane, ethanol, acetone, tetrahydrofuran, dimethyl sulfoxide, and/or water.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The hydrogel exhibits photo-induced shrinking upon white light irradiation. The polymerizable derivative of benzospiropyran comprises at least one acrylate group and benzospiropyran acrylate. The copolymers comprise acrylic acid-co-benzospiropyran acrylate-co-N-isopropylacrylamide-co-N,N'-methylenebisacrylamide of formula (I). The gel shrinks by an amount of 1-90%, preferably 5-20% upon white light irradiation for a period of 0.01 seconds to 30 minutes or 1-20 minutes. The gel comprises 1 mol% of benzospiropyran acrylate and re-swells to 95-100% or greater than or equal to 50% of its initial diameter upon exposure to water, preferably in darkness, for a period of 15-60 minutes. The mixture comprises a pore-forming agent. The pore-forming agent comprises poly(ethylene glycol) having a molecular weight of 2000-20000 g/mole.x, y, z, c = a value of repeating units, where a ratio of z+y+z+c is 5:1:100:3.Preferred Process: The process further comprises the step of adding the pore-forming agent to the organic solvent prior to step (b). EXAMPLE - 0.5 g of Trimethyl-6-hydroxyspiro-(2H-1-benzopyran-2,2'indoline) was dissolved in 20 ml of an anhydrous dichloromethane in 100 ml round bottom flask. The flask was cooled with an ethanol-liquid nitrogen bath. 0.6 ml of Triethylamide was added to the cooled mixture followed by 0.2 ml of acryloyl chloride. The mixture was allowed to reach room temperature and was left stirring for 48 hours. After this time the dichloromethane solution was washed by liquid-liquid extraction using brine and sodium bicarbonate solution. The product was separated using silica column chromatography with hexane and ethyl acetate in a ratio of 8:1. 200 mg of N-Isopropylacrylamide was mixed with 3 mole% of N,N'-methylenebisacrylamide, 1 mole% of acrylic acid and 1 mole% of benzospiropyran acrylate, these were then dissolved in 500 mu l of 1,4-dioxane/water mixture in a volume ratio of 4:1. To this mixture, 50 mu l of the initiator solution was added (76 mg of piperonyl butoxide in 500 mu l of acetone). This mixture was poured onto a polydimethylsiloxane mold containing circular pits with various sizes, covered with a glass microscope slide and polymerized for 30 minutes with white light. The polymerized gels were swollen in deionized water that was changed twice. After 24 hours the gels were swollen and equilibrated and cut into 3 mm circles.