Chemistry: molecular biology and microbiology – Carrier-bound or immobilized enzyme or microbial cell;... – Enzyme or microbial cell is immobilized on or in an...
Reexamination Certificate
1999-05-27
2004-06-29
Naff, David M. (Department: 1651)
Chemistry: molecular biology and microbiology
Carrier-bound or immobilized enzyme or microbial cell;...
Enzyme or microbial cell is immobilized on or in an...
C424S400000, C424S484000, C435S004000, C435S177000, C435S283100, C435S287100, C435S289100, C435S803000, C436S527000, C530S412000, C530S811000
Reexamination Certificate
active
06756217
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to composite materials that react to stimuli from the environment in which they are placed. Such materials are generally referred to as “smart” materials. More particularly, then, the present invention relates to environmentally sensitive “smart” glass composite materials.
BACKGROUND ART
A continuing aim of current science and technology is to mimic nature for assembly of different functional materials, with synthetic control at the molecular level. Natural systems are extremely efficient, and perform to their optimum under very mild conditions. Thus, a new scientific-technical field has developed around artificial “molecular mechanical systems”, as suggested by Osada et al. (1993)
Progress in Polymer Science
, 18:187-226. Such systems are structural-functional assemblies which convert energy from one form to another through changes in the structure or function. It is therefore desirable but somewhat problematic, to synthesize such materials with precise control at a molecular level such that changes in structure or structural interactions can cause an energy difference, resulting in a function or movement of the molecular mechanical system or assembly. Such molecular mechanical systems or assemblies have application in micro- and macro-intelligent systems, in controlled drug release, as artificial implants, as optical shutters, in molecular separation systems, and the like.
As pointed out by Osada (May 1993)
Scientific American
, pp. 82-87, unlike natural materials, which are usually soft and wet, most industrial materials like metals, ceramics and plastics are dry and hard and so, cannot be used to make soft, bio-mimetic, and flexible materials. One class of materials, polymer gels, comes closer to natural systems in terms of soft-wet character. Polymer gels usually include an elastic, three dimensionally cross-linked network (provided by covalent bonds, physical entanglements, hydrogen bonding, Van der Waals forces, or hydrophobic interactions), and a fluid filling the interstitial space in the network. Their mechanical characteristics, optical properties, surface properties, sorption capacities, degree of swelling, etc., give them the ability to adapt to changes in their environment, thereby making them useful for various applications. Such materials that are capable of sensing a change in their environment and responding to them by altering one or more of their property coefficients are termed as “smart materials”. Gehrke, S. H. (1993)
Advances in Polymer Science
, 110:80-144 states that this “smart” ability can be finely tuned for a wide variety of applications, including switches, sensors, electromechanical-chemomechanical actuators, drug delivery devices, recyclable absorbents, specialized separation systems, bioreactors, bioassay systems, artificial muscles and display items, including light emitting diodes (LEDs), TV monitors, and the like.
The polymeric backbone of the polymer gel can be an organic or an inorganic network containing functional groups that are ionizable, amenable to red-ox reactions, photoactive, or capable of swelling by reversibly exchanging monovalent and divalent ions, as stated by Rossi et al. (1992)
Journal of Intelligent Material System and Structure
3:75-95. The polymeric network can thus generate force by swelling or shrinking; or can undergo a reversible change in its volume in response to a change in its environment, temperature, solvent composition, mechanical strain, electric field, exposure to light, or the like, with no inherent limits in lifetime.
Extensive work has been done, and continues to be done with organic polymer gels having a hydrocarbon backbone which comprises a variety of functional groups, including -amine, -hydroxy, -amide, and -carboxyl. Gehrke, S. H. (1993)
Advances in Polymer Science
, 110:80-144 described the synthesis of organic polymer gels by techniques including co-polymerization/cross-linking of monomers, cross-linking of linear polymers by treatment with chemicals or gamma (&ggr;) radiation, and chemical conversion of one gel type to another.
Polymers made out of a single monomer have been used in a number of applications. For example, a neutral polymer gel of poly (vinyl alcohol) with water as a mobile component has been shown to undergo swelling, and to perform the mechanical work of lifting a load. Additionally, poly(silamine) telechelic oligomers, consisting of alternating 3,3-dimethyl-3-silapentane and N,N-diethylene units have been synthesized for use as high performance stimulus-sensitive materials, and as a poly(silamine) brush on glass and gold surfaces, as described by Nagasaki (March 1997)
ChemTech
, 23-29.
One of the most intensively studied responsive polymer gels has been cross-linked poly(N-isopropylacrylamide) (PNIPAAm). A number of environmental stimuli, including solvent, pH, temperature, electric fields, or electromagnetic radiation have been used to collapse or swell hydrogels made out of PNIPAAm, for use in various applications.
For example, PNIPAAm polymer gels were used by Feil et al. (July 1991)
Journal of Membrane Science
, 64:283-294 in molecular separation by thermosensitive membranes. PNIPAAm hydrogel membranes have been used to separate dextrans of molecular weights of 150,000 and 4,400 g/mol, respectively; and to separate uranine of molecular weight of 376 g/mol. The swelling characteristics can be influenced by an appropriate hydrophobic/hydrophilic balance in the hydrogel. Thus, this ratio has been used to vary the degree of swelling of these membranes. Such hydrogels also demonstrated a negative thermosensitivity, with the material showing dehydration at high temperature induced by hydrophobic interactions in the hydrogel. Thus, the hydrogel swelled under low temperature conditions and shrunk at higher temperatures. These swelling characteristics provided for permeability of the small molecules (uranine) at all temperatures (−27° C.), followed by the 4,400 dextran at 23° C., and the 150,000 dextran at less than 20° C., thereby achieving separation of a mixture of molecules having a distinct difference in molecular size.
PNIPAAm hydrogels were characterized by Hoffman et al. (1986)
Journal of Controlled Release
4:213-222 as thermally reversible hydrogels. Particularly, PNIPAAm hydrogels have been observed to show, at a fixed pH, reversible shrinking and expansion at 50° C. and 4° C., respectively. The shrinking and expansion provides for the releasing and absorbing of biomolecules, including myoglobin and vitamin B 12; and organic molecules, including Methylene Blue.
PNIPAAm hydrogels have also been applied as comb-type grafted hydrogels with rapid de-swelling response to temperature changes, as described by Yoshida et al. (Mar. 16, 1995)
Nature
374:240-242. Hydrogels made of PNIPAAm with a comb structure undergo changes in volume in response to external stimuli like temperature. They collapse from their hydrated form to dehydrated form with increasing temperature because of hydrophobic interactions between the polymeric network.
PNIPAAm hydrogels have also been utilized in the synthesis and application of modulated polymer gels, as described by Hu et al. (July 1995)
Science
269:525-527. Polymeric gels made of polyacrylamide interpenetrated by NIPAAm network have been made into a bagel strip, a shape memory gel, and a gel “hand”. Each of these structures respond to environmental changes, such as change in temperature or change in acetone concentration.
To modify the properties of PNIPAAm polymers so as to tune their applicability, they have been co-polymerized with different monomers. For example, thermally responsive polymers for drug permeation and release have been described by Okano et al. (1990)
Journal of Controlled Release
11:255-265. Polymers of PNIPAAm cross-linked with butyl-methacrylate and interpenetrating networks of polytetramethyleneetherglycol (PTMEG) show shrinking with increasing temperature. Particularly, the surface of the membrane shrinks, rather than the bulk, thereby regulating
Dave Bakul C.
Rao Mukti S.
Naff David M.
Southern Illinois University
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