Stock material or miscellaneous articles – Composite – Of quartz or glass
Reexamination Certificate
1999-09-30
2001-08-07
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Composite
Of quartz or glass
C428S442000
Reexamination Certificate
active
06270903
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a methods of bonding functional surface materials such as poly(N-isopropylacrylamide) (PNIPAAm) to substrates and applications in microtechnology and for anti-fouling.
BACKGROUND OF THE INVENTION
In general, functional surface materials (FSMs) may be broadly described as materials which exhibit a reversible response in response to a stimuli. The study of a variety of FSMs has attracted a great deal of attention due to the potential for exploitation of these reversible changes in a variety of uses. One good example of a FSM is poly(N-isopropylacrylamide) (PNIPAAm) which exhibits a shift from being hydrophobic to hydrophilic, or from hydrophilic to hydrophobic, in response to changes in temperature. As such, surfaces modified by PNIPAAm have attracted a great deal of research attention because of the potential for the application of the characteristics of PNIPAAm, such as molecular switching of the surface by altering interfacial properties. See Dagani, R. Chem. Eng. News, 1997, June 9, 27, and Snowdown, M.; Murray, M.; Chowdry, B. Chemistry and Industry, 1996, July 15, 531. Such uses are possible because PNIPAAm exhibits a lower critical solution temperature (LCST), and remarkable hydration-dehydration changes in response to relatively small changes in temperature, when placed in an aqueous solution. See Heskins, M.; Guillet, J. E.; James, E. J. Macromol. Sci. Chem., 1968, A2,1441. Below the LCST, PNIPAAm chains hydrate to form an expanded structure, and above LCST, PNIPAAm chains dehydrate to form a shrinkage structure. This property is due to the reversible formation and cleavage of the hydrogen bonds between the NH or C═O groups of PNIPAAm and the surrounding water molecules brought about with changes in the temperature. See Okubo, M.; Ahmad, H; Colloid Polym. Sci., 1995, 73, 817. Since PNIPAAm's physical properties are readily controlled by simply changing temperature, and without changing the chemical structure of the polymer, a broad range of potential uses for temperature-responsive PNIPAAm have been suggested. Among other uses, PNIPAAM can be employed in drug delivery systems, see Hoffman, A. S. J. Controlled Release, 1987, 6, 297, for solute separation, see Feil, H.; Bae, Y. H.; Jan, F.; Kim, S. W. J. Membrane Sci., 1991, 64, 283, in the concentration of dilute solutions, see Trank, S. J.; Johnson, D. W.; Cussler, E. L. Food Technol., 1989, June, 79, for the immobilization of enzymes, see Dong, L. C.; Hoffman, A. C. J. Controlled Release, 1986, 4, 223, for the coupling of biomolecules, see Matsukata, M.; Takei, Y.; Aoki, T.; Sanui, K.; Ogata, N.; Sakurai, Y.; Okano, T. J. Biochem, 1994, 116, 682, and for the preparation of photosensitive materials, see Suzuki, A.; Tanaka, T.; Nature, 1990, 346, 345.
In one example where PNIPAAm has been bonded to a substrate by using plasma-treated polystyrene dishes grafted with PNIPAAm, the alteration of the hydrophilic/hydrophobic properties of the surface was observed as a response to temperature change. See Okano, T.; Yamada, N.; Okuhara, M.; Sakai, H.; Sakurai. Y. Biomaterials, 1995, 16, 297. In this study, endothelial cells and hepatocytes attached and proliferated on the PNIPAAm grafted surface at 37° C., above the LCST of PNIPAAm. The cultured cells were readily detached from these surfaces by simply lowering the incubation temperature and without the usual damage associated with trypsinization. The radiation grafting utilized for this study had the advantage of being able to bind convalently the N-isopropylacrylamide (NPAAm) monomer onto a chemically inert surface without contamination by potentially hazardous catalyst fragments. However, a problem remains due to the inconvenience and expense of radiation machines and damage to the materials from radiation, especially damage to the polymer materials.
In another study involving a glass substrate, temperature sensitive surfaces were prepared by coupling either PNIPAAm with a terminal carboxyl end group or random copolymers of PNIPAAm and acrylic acid, with the amino group on the glass surface by a water soluble carbodiimide, such as 1-ethyl-3-(3-dimethyamino-propyl) carbodiimide hydrochloride. See Okano, T.; Kikuchi, A.; Sakurai, Y.; Takei, Y.; Ogata, N. J. Controlled Release, 1995, 36, 125. In this study, each PNIPAAm-grafted surface showed completely hydrophilic nature below 20° C. and a hydrophobic nature above the critical temperature. The coupling of amine and carboxyl groups involves the intermediary formation of the activated O-acylurea derivative of the carbodiimide. A subsequent nucleophilic attack by the primary nitrogen of the amino compound brings about the formation of the amide linkage with release of the soluble substituted urea. The formation of O-acylurea occurs optimally at pH 4-5. The intermediate has an extremely short life and rapidly undergoes hydrolysis or gives the N-acylurea adduct. The primary amino group of the nucleophile is predominantly protonated at this low pH and is rather unreactive. One the other hand, since it is an inhomogeneous reaction system, that is, the fact that reaction between the amine groups on the glass surface competes with the carboxyl groups on the polymer chains in solution, increases the difficulty of reaction. This limitation can severally restrict the yield of product under a variety of conditions. See Sehgal, D.; Vijay, I. K. Analytical Biochemistry, 1994,218,87.
Hydrogels, or water-swollen polymer gels, are one type of FSM which have attracted a great deal of attention in both theoretical studies and for real applications. See D. DeRossi, K. Kajiwara, Y. Osada and A. Yamauchi, Ed., Polymer Gels, Plenum Press, New York, 1989; P. S. Russo, Ed., Reversible Polymeric Gels and Related Systems, ACS Symposium Series 350, ACS, Washington, D.C., 1987; and N. A. Peppas, Ed, Hydrogels in Medicine and Pharmacy, Vol. 1, CRC Press, Boca Raton, Fla., 1986. These polymer gels can be divided into two kinds, those which do not exhibit significant sensitivity to environmental changes, and those which change their properties in response to a variety of environmental stimuli including pH, See K. Kataoka, H. Koyo and T. Tsurrta, Macromolecules, 28, 3336 (1995); and S. Nishi and T. Kotaka, Macromolecules, 19, 978 (1986), temperature, see Y. Kaneko, K. Sakai, A. Kikuchi, R. Yoshida, Y. Sakural and T. Okano, Macromolecules, 28, 7717 (1995); and T. Aoki, Y. Nagao, K. Sanui, N. Ogata, A. Kikuchi, Y. Sakurai, K. Kataoka and T. Okano, Polymer. J, 28, .371 (1996); photo, A. Suzuki and T. Tanaka, Nature, 346, 345 (1990); and A. Fissi, O. Pieroni, G. Ruggeri and F. Ciardelli, Macromolecules, 28, 302 (1995), pressure, See D. W. Urry, L. C. Hayes, T. M. Parker, R. D. Harris, Chem. Phys. Lett., 201, 336 (1993), and electrical fields, See T. Tanaka, I. Nishio, S. T. Sun and S. U. Nishio, Science, 29,218 (1982). Among these, the temperature sensitive polymer gel, poly(N-isopropylacryamide) (PNIPAAm) has been of great interest because PNIPAAm demonstrates a lower critical solution temperature (LCST) and the temperature-dependent characteristics. See R. Dagani, Chem. Eng. News, June, 27 (1997); H. G. Schild, Prog; Polym. Sci., 17, 163 (1992); and M. Heskins, J. E. Guillet and E. James, J. Macromol. Sci., Chem., A2 (8), 1441 (1968). It swells with an extended chain conformation in aqueous solution below 32° C. and deswells with a compact chain conformation in aqueous solutions above 32° C. The phenomenon is caused by reverse formation and cleavage of the hydrogen bond between water molecules and hydrophobic molecular groups of PNIPAAm. The pentagonal water structure is suggested to be generated among water molecules adjacent to the hydrophobic molecular groups of PIPAAm. See D. W. Urry, Scientific American, Jan., 64 (1995). Since the pentagonal structure is stable at low temperature and unstable at high temperature, the reverse swelling-deswelling process can be observed with the variation of environmental temperature. As the volume phase transition brings about dramatic changes in the
Feng Xiangdong
Liang Liang
Liu Jun
Battelle (Memorial Institute)
May Stephen R.
Nakarani D. S.
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