Chemical & Petroleum Engineering

Chemical Engineering
Petroleum Engineering

CPE Faculty and Staff

Stevin H. Gehrke

Professor

B.S., Chemical Engineering, Kansas State University, 1980
M.S., Chemical Engineering, University of Minnesota, 1983
Ph.D., Chemical Engineering, University of Minnesota, 1986

Room: 217 Burt Hall
Phone: (785) 864-4956
Fax: (785) 864-4967
E-mail: shgehrke@ku.edu

Research Interests

Hydrogels

Hydrogels are hydrophilic, crosslinked polymers that swell in water but cannot dissolve because of their network structure. They are fascinating materials with a wide variety of applications; everyday examples include gelatin and soft contact lenses. Hydrogels are key components of consumer products like diapers, biochemical separation techniques, pharmaceutical delivery systems and medical devices such as artificial organs. The utility of hydrogels lies in their ability to absorb large amounts of water and to influence the mass transfer of solutes.

This research involves the theoretical and experimental study of the thermodynamics, sorption and desorption kinetics, solute permeability and mechanical properties of various gels with important scientific and industrial uses. Novel gels with unique properties and applications are also synthesized and characterized; for example, gels that expand and contract with small changes in temperature and gels that can absorb solvent almost instantly have been developed in our lab. Applications of gels in pharmacy and biotechnology receive particular emphasis. Drug delivery applications are described below; gel-based techniques for protein purification examined include chromatography, gel electrophoresis, and aqueous two-phase extraction. Our research goals are to understand and improve these techniques as well as to develop novel techniques for protein isolation and purification using hydrogels.

Controlled Drug Delivery

As the patents on many established drugs expire and the costs of developing new drugs mount, pharmaceutical companies are taking a more careful look at how available drugs can be used more effectively. Most drugs work only within a rather narrow range of concentration; often, the goal of controlled drug delivery is to release a drug at a carefully controlled rate over an extended period of time (sustained release) to maintain a constant blood level. In other cases, the drug must be delivered to a specific site in the body to be effective (targeted delivery). The traditional training of chemical engineers in transport phenomena, reaction kinetics, and applied mathematics is ideal preparation for solving these nontraditional problems. Both fundamentals of mass transfer in drug delivery systems and the development of novel drug delivery devices and techniques are being investigated. Drug delivery systems based on hydrogels are emphasized. Recently, the use of hydrogel-coated catheters for the delivery of drugs directly to diseased tissues has been examined in detail, primarily in connection with balloon angioplasty catheters.

Protein-Based Biomaterials

Since the human body is composed primarily of proteins, proteins have special potential for use as bioresponsive and/or biodegradable drug delivery systems. They can also be used as cell encapsulating matrices for tissue engineering. An approach to making novel biomaterials with tremendous potential for the future is the genetically directed synthesis of new amino acid polymers or "artificial proteins." The concept is to use genetic engineering techniques to "program" cells to produce artificial proteins of a specified design. First, molecular modeling software and protein design heuristics are used to design an amino acid sequence of the desired function. Then genetic engineering techniques are used to create E. coli bacteria that will produce the artificial protein according to the design. Next, these engineered cells are grown in a fermentor; the artificial protein is then extracted from the fermentation broth. Once purified, the artificial protein is studied to understand structure-function relationships in protein-based biomaterials. These novel materials are also being examined for potential practical utility in tissue engineering, bioseparations, and pharmacy. Current research is focused on crosslinked gels made from artificial proteins based on elastin and on silk structures, and also on synthetic poly(amino acids) like poly(L-lysine). Projects on novel uses of plant proteins are under development.

Hydrogels: Synthesis and Properties

S. H. Gehrke and E. L. Cussler "Mass Transfer in pH-Sensitive Hydrogels," Chemical Engineering Science 44 559-566 (1989).

S. H. Gehrke, L. H. Lyu and M. C. Yang "Swelling, Shrinking, and Solute Permeation of Temperature-Sensitive N-isopropylacrylamide Gel," Polymer Preprints, 30 482-483 (1989).

S. H. Gehrke, M. C. Yang, B. Kabra, L. H. Lyu and M. K. Akhtar "Volume Change Kinetics of Environmentally Responsive Hydrogels," Proceedings of the International Symposium on the Controlled Release of Bioactive Materials, 16, 209-210 (1989).

D. C. Harsh and S. H. Gehrke "Characterization of Ionic Water Absorbent Polymers: Determination of Ionic Content and Effective Crosslink Density" in Absorbent Polymer Technology, Lisa Brannon-Peppas, ed., Elsevier, Amsterdam, 103-124 (1990).

D. Harsh and S. H. Gehrke "Phase Behavior of Novel Cellulose Ether Hydrogels," Proceedings of the International Symposium on the Controlled Release of Bioactive Materials, 17, 383-384 (1990).

M. Palasis and S. H. Gehrke "Controlling Permeability in Responsive Hydrogels," Proceedings of the International Symposium on the Controlled Release of Bioactive Materials, 17, 385-386 (1990).

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M. K. Akhtar and S. H. Gehrke "Volume Change Kinetics of Responsive Polymer Gels," Proceedings of the International Symposium on the Controlled Release of Bioactive Materials, 17, 168-169 (1990).

B. Kabra, S. H. Gehrke, S. T. Hwang and W. Ritschel "Modification of the Dynamic Swelling Behavior of PHEMA" Journal of Applied Polymer Science., 42, 2409-2416 (1991).

B. Kabra and S. H. Gehrke "Synthesis of Fast Response Poly(N-isopropylacrylamide) Gels," Polymer Communications, 32, 322-323 (1991).

D. C. Harsh and S. H. Gehrke "Controlling the Swelling Characteristics of Temperature-Sensitive Cellulose Ether Hydrogels," Journal of Controlled Release, 17, 175-186 (1991).

M. Palasis and S. H. Gehrke "Permeability of Temperature Sensitive Gels," Journal of Controlled Release, 18, 1-12 (1992).

S. H. Gehrke, G. Agrawal and M.-C. Yang "Moving Ion Exchange Fronts in Polyelectrolyte Gels," in Polyelectrolyte Gels, R. S. Harland and R. K. Prud’homme, Eds., ACS Symposium Series 480, Washington, D.C., 211-237 (1992).

D. Biren, B. Kabra and S. H. Gehrke "Effect of Initial Sample Anisotropy on the Solvent Sorption Kinetics of Glassy Poly(2-Hydroxyethyl methacrylate," Polymer, 33, 554-561 (1992).

B. Kabra, M. K. Akhtar and S. H. Gehrke "Volume Change Kinetics of Temperature-Sensitive Poly(vinylmethylether) Gel," Polymer, 33, 990-995 (1992).

S. H. Gehrke, M. Palasis and M. K. Akhtar "Effect of Synthesis Conditions on Properties of Poly(N-isopropylacrylamide) Gels," Polymer International, 29, 29-36 (1992).

D. C. Harsh, B. G. Kabra and S. H. Gehrke "Controlling Swelling Characteristics of Novel Cellulose Ether Hydrogels" Abstr. Pap. Am. Chem. Soc., 203, 22-CELL (1992)

D.C. Harsh and S. H. Gehrke "Modeling Swelling Behavior of Cellulose Ether Hydrogels," in Polymeric Delivery Systems, M. El-Nokaly, D. Piatt, B. Charpentier Eds., ACS Symposium Series 520, Washington, D.C., 105-134 (1993).

S. H. Gehrke "Synthesis, Equilibrium Swelling, Kinetics, Permeability and Applications of Environmentally Responsive Gels," in Responsive Gels: Volume Transitions II, K. Dusek, Ed., Advances in Polymer Science Series 110, Springer-Verlag, Heidelberg, 81-144 (1993).

B. Kabra and S. H. Gehrke "Rate Limiting Steps for Sorption by Microporous Stimuli-Sensitive Absorbent Gels," Polymeric Materials Science & Engineering, 69 , 533-534 (1993).

S. H. Gehrke, D. Biren and J. Hopkins "Evidence for Fickian Water Transport in Initially Glassy Poly(2-hydroxyethyl methacrylate)," Journal of Biomaterials Science, Polymer Edition, 6, 375-390 (1994).

B. Kabra and S. H. Gehrke "Rate Limiting Steps for Solvent Sorption and Desorption by Microporous Stimuli-Sensitive Absorbent Gels," in Superabsorbent Polymers: Science and Technology, F. L. Buchholz and N. A. Peppas Eds., ACS Symposium Series 573, Washington, D.C., 76-87 (1994).

S. Gehrke, M. Palasis, M. Lund "Interactions of Solutes with Hydrogels" Proceed. 4th Symposium on Polymer Gels- Molecular/Supramolecular Control and Their Applications, The Society of Polymer Science-Japan, Tokyo, 50-51 (1995).

S. H. Gehrke and D. C. Harsh "Environmentally Responsive Gels," in: Polymeric Materials Encyclopedia, Vol. 3, J. C. Salamone, Ed., CRC Press, Boca Raton, FL 2093-2102 (1996).

S. H. Gehrke, M. Palasis, M. Lund and J. Fisher "Factors Determining Hydrogel Permeability," Annals of the New York Academy of Sciences, 831, 179-207 (1997).

S. M. O'Connor and S. H. Gehrke "Synthesis and Characterization of Temperature-Sensitive HPMC Gel Spheres," Journal of Applied Polymer Science, 66, 1279-1290 (1997).

B. Kabra, S. H. Gehrke and R. Spontak "Microporous Responsive HPC Gels 1. Synthesis and Microstructure," Macromolecules, 31, 2166-2173 (1998).

S.H. Gehrke and D.C. Harsh "Environmentally Responsive Gels," in: Concise Polymeric Materials Encyclopedia, J.C. Salamone, Ed., CRC Press Boca Raton, FL 428-430 (1999).

E.D. Oliveira and S.H. Gehrke, "Influence of Network Conformation on Properties of Poly (Amino Acid) Hydrogels," Polym. Prepr., 41, 745-746 (2000).

E.D. Oliveira, S.A. Hagan and S.H. Gehrke, "Mechanical Properties of Elastin-Mimetic Gels" Proceedings International Symposium Controlled Release of Bioactive Materials 28 355-356 (2001).

S. M. O'Connor and S. H. Gehrke "Particle Growth Analysis as a Characterization Method for Gels Produced in Suspension Reactors," Polymer, 42, 1541-1546, (2001).

J. P. Fisher and S. H. Gehrke "Dependence of Solute Permeability in Cellulose Ether Gels on Synthesis Conditions," submitted.

Hydrogels: Drug Delivery

B. Kabra and S. H. Gehrke "Hydrogels for Driving an Osmotic Pump," Polymer Preprints., 30 490-491 (1989).
S. H. Gehrke and P. I. Lee "Hydrogels for Drug Delivery" in Specialized Drug Delivery Systems, Manufacturing and Production Technology, Praveen Tyle, ed., Marcel Dekker, New York 333-392 (1990).
W. A. Ritschel, A. Sabouni, S. H. Gehrke, S. T. Hwang "Permeability of 3H-Water Across a Porous Polymer Matrix Used as a Rate-Limiting Shell in Compression-Coated Tablets" Journal of Controlled Release, 12, 97-102 (1990).
S. Gehrke, N. Vaid and L. Uhden "Enhanced Protein Loading of Hydrogels" Proceedings of the International Symposium on the Controlled Release of Bioactive Materials, 20, 113-114 (1993).
C.-L. Cheng, S. H. Gehrke and W. A. Ritschel "Development of an Azopolymer Based Colonic Release Capsule for Delivering Proteins/Macromolecules," Methods and Findings in Experimental and Clinical Pharmacology, 16 , 271-278 (1994).
S. Gehrke, L. Uhden, M. Schiller "Enhanced Loading and Activity Retention in Hydrogel Delivery Systems" Proceedings of the International Symposium on the Controlled Release of Bioactive Materials, 22, 145-146 (1995).

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Hydrogels: Biotechnology

S. H. Gehrke, G. P. Andrews, E. L. Cussler "Chemical Aspects of Gel Extraction," Chemical Engineering Science, 41 (1986) 2153-2160.

S. H. Gehrke, J. F. Johnson, J. Robeson and N. Vaid "Protein Separation by Selective Gel Sorption" Biotechnology Progress, 7, 355-358 (1991).

S. H. Gehrke, L.H. Lyu and K. Barnthouse "Dewatering Fine Coal Slurries by Gel Extraction," Separation Science & Technology, 33, 1467-1485 (1998).

S. H. Gehrke, N. Vaid and J. M. McBride " Protein Sorption and Recovery by Hydrogels Using Principles of Two Aqueous Phase Protein Extraction" Biotechnology & Bioengineering, 58, 416-427 (1998).

C. S. Putka, S. H. Gehrke, M. Willis, D. Stafford, J. Bryant "Recovery and Separation of Cell Lysate Proteins Using Hydrogels, Guided by Aqueous Two Phase Extraction Principles," Biotechnology & Bioengineering, accepted (2001).

Biomedical Engineering

S. M. O'Connor, S. Patuto, S. H. Gehrke and G. Retzinger "Influence of co-adsorbed surfactants on the adsorption and coagulability of fibrinogen on hydrophobic surfaces: Development of a model system," Federation of American Societies of Experimental Biology Journal, 10, 3252 (1996).

S. M. O'Connor, S. H. Gehrke, S. Patuto, and G. Retzinger "The Adsorption and Functionality of Fibrinogen on Hydrophobic Surfaces Modified with PEO/PPO/PEO Block Copolymers," Polymer Preprints, 38, 559-560 (1997).

S. M. O'Connor, S. H. Gehrke, S. Patuto, and G. Retzinger "Macrophage Adherance to Polystyrene Beads coated with Pluronic® Block Copolymers," Annals of the New York Academy of Sciences, 831, 138-144 (1997).

S. M. O'Connor, S. H. Gehrke, S. Patuto, and G. Retzinger "Macrophage Adherence to Surfaces Coated with Fibrinogen and PEO/PPO Triblock Copolymers," Proceedings of the Topical Conference on Biomaterials, N. A. Peppas, Ed., AIChE, NY, 123-125 (1997).

S. H. Gehrke "Review Essay: Bioethics: A Primer for Christians by Gilbert Meilaender," Logia: A Journal of Lutheran Theology, 7, 57-60 (1998).

S. M. O’Connor, S. H. Gehrke, G. Retzinger "Ordering of Poly(ethylene oxide)/Poly(propylene oxide) Triblock Copolymers in Condensed Films," Langmuir, 15, 2580-2585 (1999).

S.M. O'Connor, A.P. DeAnglis, S.H. Gehrke, G.S. Retzinger, "Adsorption of Plasma Proteins onto Poly(ethylene oxide)/Poly(propylene oxide) Triblock Copolymer Films. A Focus on Fibrinogen," Biotechnol Appl Biochem., 31, 185-196 (2000).

Patents

B. Kabra and S. Gehrke, "Superabsorbent Foams and Methods for Producing Same," U.S. Patent No. 5,573,994, Issued 11/12/96.

S. H. Gehrke, E. C. Lupton, M. E. Schiller, L. Uhden, and N. Vaid, "Enhanced Loading of Solutes Into Polymer Gels and Methods of Use," U.S. Patent No. 5,603,955, Issued 2/18/97.

S. H. Gehrke, E. C. Lupton, M. E. Schiller, L. Uhden and N. Vaid, "Compositions and Methods for Protecting Compound Activity," U.S. Patent No. 5,674,521, Issued 10/7/97.

B. Kabra and S. Gehrke, "Superabsorbent Foams and Methods for Producing Them," U.S. Patent 6,027,795, Issued 2/22/2000.

B. Kabra and S. Gehrke, "Microporous Fast Response Gels and Methods of Use," U.S. Patent 6,030,442, Issued 2/29/2000.

Invited Lectures

"Hydrogels for Drug Delivery," Center-of-Excellence for Membrane Technology, University of Cincinnati, Cincinnati, OH November 4, 1988.

"Phase Transitions in Hydrogels," 3M Company, St. Paul, MN March 3, 1989.

"Controlled Drug Delivery with Responsive Hydrogels," Michigan Technological University, Houghton, MI October 11, 1989.

"Volume Change Kinetics of Responsive Gels" Bioengineering Department, University of Washington, Seattle, WA November 13, 1989.

"Phase Transitions in Hydrogels," ACS Cincinnati Section, Colloid Chemistry Discussion Group, Cincinnati OH April 18, 1990

"Controlling Permeability of Responsive Hydrogels," Center-of-Excellence for Membrane Technology, University of Cincinnati, Cincinnati, OH May 15, 1990.

"Volume Change Kinetics of Responsive Gels" 33rd IUPAC International Symposium on Macromolecules, Montreal, Canada July 10, 1990.

"Volume Change Kinetics of Responsive Polymer Gels" Sharon Woods Technical Center, Procter and Gamble Corporation, Cincinnati, OH, October 30, 1990.

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"Environmentally Responsive Polymers for Drug Delivery" American Association of Pharmaceutical Scientists, Indianapolis/Cincinnati Discussion Group, Cincinnati, OH, March 13, 1991.

"Volume Change Kinetics of Responsive Polymer Gels" Absorbent Technology Group, Kimberly-Clark Corporation, Neenah, WI, July 25, 1991.

"Volume Change Kinetics of Polymer Gels," ACS Cincinnati Section, Polymer Discussion Group, Cincinnati OH January 15, 1992.

"Controlling Permeability of Responsive Gels," College of Pharmacy, South Dakota State University, March 18, 1992.

"Volume Change Kinetics of Polymer Gels," Department of Chemistry, South Dakota State University, March 25, 1992.

"Controlling Permeability of Responsive Gels," 3M Company, St. Paul, MN July 9, 1992.

"Properties and Applications of Hydrogels," Gel Sciences, Inc., Waltham, MA Dec. 30, 1993

"Influence of Network Structure on the Properties of Polymer Gels," Dept. of Polymer Science and Engineering, University of Massachusetts, Amherst, MA April 1, 1994

"Hydrogels for Drug Delivery," Boston Scientific, Boston, MA June 23, 1994

"Properties and Applications of Environmentally Responsive Gels," ACS Local Section, Polymer Discussion Group, Raleigh, NC October 13, 1994.

"Properties and Applications of Environmentally Responsive Gels," Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC October 14, 1994.

S. Gehrke "Funding Opportunites for Controlled Release Research with the National Science Foundation," 22th International Symposium on Controlled Release of Bioactive Materials, Seattle, WA (1995).

"Environmentally Responsive Gels- A Series of Lectures," Department of Polymer Science, University of Helsinki, Helsinki, Finland, 8/21/95 - 8/25/95.

"Interactions of Solutes with Responsive Gels," 4th Symposium on Polymer Gels and Networks (Society of Polymer Science, Japan), Tsukuba, Japan 11/29/95 - 12/1/95.

"Solute Interactions with Poly(N-isopropylacrylamide) Gel," Pacifichem ’95 Conference, Honolulu, HI 12/21/95.

"Influence of Steric and Hydrophobic Interactions on Permeation of Solutes Hydrogels," Dept. of Pathology and Lab Medicine, University of Cincinnati 2/1/96.

"Interactions of Solutes with Responsive Polymer Gels," Dept. of Materials Science and Engineering, University of Cincinnati 5/17/96.

"Influence of Steric and Hydrophobic Interactions on Permeation of Solutes Hydrogels," Engineering Foundation Conference "Bioartificial Organs", Nashville, TN 7/23/96.

"Solute Permeability of Responsive Polymer Gels," Depts. of Chemistry and Chemical Engineering, University of Alabama-Huntsville, Huntsville, AL 10/25/96.

"Gel Biotechnology: New Developments in the Sorption and Immobilization of Active Enzymes," Department of Biological Sciences, University of Exeter, Exeter UK 6/20/97.

"Advances in Organic Materials Science," Gordon Research Conference on Biomaterials: Biocompatibility and Tissue Engineering, Holderness School, Holderness, NH 7/21/97.

"Synthesis and Properties of Cellulose Ether Hydrogels," BF Goodrich, Cleveland, OH 10/28/97

"Advances in Polymer Gel Technology and Applications," SCA Mölnlycke, Gothenberg, Sweden 12/10/97.

"Environmentally Responsive Gels Workshop," Department of Physical Chemistry, Lund University, Lund, Sweden, 12/12/97.

"Review of the PhD of Olof Rosen," Department of Physical Chemistry, Lund University, Lund, Sweden, 12/13/97.

"Solute Permeability of Responsive Polymer Gels," Department of Pharmacy, University of Toronto, Toronto, Canada, 2/19/98.

"Synthesis and Properties of Cellulose Ether Hydrogels," Materials in the Heartland Conference, Carbondale, IL, 10/30/98.

"Synthesis, Properties and Drug Delivery Applications of Cellulose Ether Hydrogels," Department of Chemical Engineering, University of Kansas, Lawrence, KS, 3/17/99.

"Synthesis, Properties and Applications of Responsive Cellulose Ether Hydrogels," Department of Chemistry, Pittsburg State University, Pittsburg, KS, 11/11/99.

"Biosynthesis of protein polymers for tissue engineering and other biomedical applications," Department of Biochemistry, Kansas State University, Manhattan, KS, 11/22/99.

"Synthesis, Properties and Biomedical Applications of Cellulose Ether Hydrogels," Department of Chemical Engineering, University of Oklahoma, Norman, OK, 12/2/99.

"Influence of Microstructure on the Permeability of Hydrogels," E.V. Murphree Award Symposium Honoring J. Larry Duda, Annual ACS Meeting, San Francisco, CA, (2000).

"Synthesis, Properties and Drug Delivery Applications of Cellulose Ether Hydrogels," Department of Pharmaceutical Sciences, University of Kansas, Lawrence, KS, 4/25/00.

"Synthesis, Properties and Applications of Hydrogels," PowderJect Technologies, Inc., Fremont, CA, 6/12/01.

"Synthesis, Properties and Applications of Hydrogels," Procter & Gamble, Cincinnati, 7/24/02.

"Influence of Microstructure on the Permeability and Modulus of Responsive Biopolymer Gels," Sensitive Polymers and Smart Gels Symposium Honoring Toyoichi Tanaka, 7th Pacific Polymer Conference, Oaxaca, Mexico, 12/5/01.

"Influence of Microstructure on the Permeability and Modulus of Responsive Biopolymer Gels," University of Minnesota, Minneapolis, MN 2/5/03.

"Influence of Microstructure on the Permeability of Hydrogels," E.V. Murphree Award Symposium Honoring E.L. Cussler, Annual ACS Meeting, Orlando, Fl, 4/7/02.

"Influence of Microstructure on the Permeability and Modulus of Responsive Biopolymer Gels," Asian Biomaterials and Drug Delivery Symposium, Taipei, Taiwan, 4/14/02.

"Synthesis, Properties and Drug Delivery Applications of Cellulose Ether Hydrogels," National Taiwan University, Taipei, Taiwan, 4/17/02.

"Biosynthesis and Applications of Biomimetic Proteins," Yuan Ze Univ., Chung-Li, Taiwan, 4/18/02.

"Influence of Microstructure on the Permeability and Modulus of Responsive Biopolymer Gels," Department of Chemical Engineering, Kansas State University, Manhattan, KS 10/17/02.

Conference Presentations and Posters

B. Kabra and S. H. Gehrke "Controlling Hydrogel Swelling Kinetics," 1988 Annual National AIChE Meeting, Washington, D.C. (1988).

S. H. Gehrke, L. H. Lyu and M. C. Yang "Swelling, Shrinking, and Solute Permeation of Temperature-Sensitive N-isopropylacrylamide Gel," 1989 Spring National ACS Meeting, Dallas, TX (1989).

B. Kabra and S. H. Gehrke "Hydrogels for Driving an Osmotic Pump," 1989 Spring National ACS Meeting, Dallas, TX (1989).

S. H. Gehrke, M. C. Yang, B. Kabra, L. H. Lyu and M. K. Akhtar "Volume Change Kinetics of Environmentally Responsive Gels," 16th International Symposium on Controlled Release of Bioactive Materials, Chicago, IL (1989).

S. H. Gehrke, M. C. Yang, B. Kabra, L. H. Lyu and M. K. Akhtar "Volume Change Kinetics of Environmentally Responsive Gels," 1989 Summer National AIChE Meeting, Philadelphia, PA. (1989).

D. Biren, B. Kabra and S. H. Gehrke "Anomalous Solvent Sorption in Glassy PHEMA" 1989 Annual National AIChE Meeting, San Francisco, CA (1989).

L.H. Lyu and S. H. Gehrke "Dewatering Fine Coal Slurry by Gel Extraction" 1989 Annual AIChE Meeting, San Francisco, CA (1989).

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D. Harsh and S. H. Gehrke "Phase Behavior of Novel Cellulose Ether Hydrogels," 17th International Symposium on Controlled Release of Bioactive Materials, Reno, NV (1990).

M. Palasis and S. H. Gehrke "Controlling Permeability in Responsive Hydrogels," 17th International Symposium on Controlled Release of Bioactive Materials, Reno, NV (1990).

M. K. Akhtar and S. H. Gehrke "Volume Change Kinetics of Responsive Polymer Gels," 17th International Symposium on Controlled Release of Bioactive Materials, Reno, NV (1990).

D. Harsh and S.H. Gehrke "Phase Behavior of Novel Cellulose Ether Hydrogels," 76th Annual Meeting of the Kentucky Acadamy of Sciences, Northern Kentucky University, November 9, 1990.

M. Palasis and S. H. Gehrke "Controlling Permeability in Responsive Hydrogels," 76th Annual Meeting of the Kentucky Acadamy of Sciences, Northern Kentucky University, November 9, 1990.

D. Harsh and S. H. Gehrke "Phase Behavior of Novel Cellulose Ether Hydrogels," 1990 Annual National AIChE Meeting, Chicago, IL (1990).

M. Palasis and S. H. Gehrke "Controlling Permeability in Responsive Hydrogels," 1990 Annual National AIChE Meeting, Chicago, IL (1990).

M. K. Akhtar and S. H. Gehrke "Volume Change Kinetics of Responsive Polymer Gels," 1990 Annual National AIChE Meeting, Chicago, IL (1990).

D. Harsh and S. H. Gehrke "Controlling the Swelling Characteristics of Cellulose Ether Hydrogels," 1991 Annual National AIChE Meeting, Los Angeles, CA (1991).

M. Palasis and S. H. Gehrke "Solute Permeability of Responsive Poly(N-isopropylacrylamide) Gel," 1991 Annual National AIChE Meeting, Los Angeles, CA (1991).

B. Kabra and S. H. Gehrke "Synthesis and Characterization of Fast Response Temperature Sensitive Gels," 1991 Annual National AIChE Meeting, Los Angeles, CA (1991).

D. Harsh, B. Kabra and S. H. Gehrke "Controlling Swelling Characteristics of Novel Cellulose Ether Hydrogels," 1992 Spring National ACS Meeting, San Francisco, CA (1992).

D. Harsh and S. H. Gehrke "Controlling Swelling Characteristics of Novel Cellulose Ether Hydrogels," Regional ACS Meeting, Cincinnati, OH (1992).

M. Palasis and S. H. Gehrke "Controlling Permeability in Responsive Hydrogels," Regional ACS Meeting, Cincinnati, OH (1992).

M. K. Akhtar and S. H. Gehrke "Volume Change Kinetics of Responsive Polymer Gels," Regional ACS Meeting, Cincinnati, OH (1992).

N. Vaid and S. H. Gehrke "Protein Isolation by Solution-Controlled Gel Sorption" 1992 Annual National AIChE Meeting, Miami Beach, FL (1992).

S. Gehrke, N. Vaid and L. Uhden "Enhanced Protein Loading of Hydrogels" 20th International Symposium on Controlled Release of Bioactive Materials, Washington, DC (1993).

B. Kabra and S. H. Gehrke "Rate Limiting Steps for Sorption by Stimuli-Responsive Absorbent Gels," 1993 Summer National ACS Meeting, Chicago, IL (1993).

T. D. Reynolds, A. S. Hussain, S. H. Gehrke and L. S. Shenouda "Preliminary Study on the Water Uptake of Various Grades of Hydroxypropylmethylcellulose (HPMC)," Pharm. Res. 10(10): S-274 (1993); 1993 Annual AAPS Meeting (1993).

M. Palasis, S. H. Gehrke and E. E. Brooks "Influence of Hydrophobicity on Diffusion of Amino Acids in Responsive PNIPAAm Gels Measured by PGSE NMR" 1993 Annual National AIChE Meeting, St. Louis, MO (1993).

M. Palasis, S. H. Gehrke and E. E. Brooks "Studies of Drug Interactions with Temperature-Sensitive Poly(N-isopropylacrylamide) Gel using PGSE-NMR," Polymers in Biosystems Gordon Research Conference, Oxnard, CA (1994).

S. Gehrke and L. Uhden "Enhanced Protein Loading of Hydrogels" 1994 Annual National AIChE Meeting, San Francisco, CA (1994).

T. D. Reynolds, A. S. Hussain, S. H. Gehrke and L. S. Shenouda "A Study on the Swelling Characteristics of Hydroxypropylmethylcellulose (HPMC) Matrices Using Optical Microscopy," Pharm. Res. 11(10): S-306 (1994); 1994 Annual AAPS Meeting, (1994).

S. Gehrke, J. Braun, V. Conticello, D. Tirrell, E. Cantor, M. Fournier, T. Mason "Biosynthesis of Model Protein Compounds for Hydrogel Transport Studies," 1994 Annual National AIChE Meeting, San Francisco, CA (1994).

S. Gehrke, L. Uhden, M. Schiller "Enhanced Loading and Activity Retention in Hydrogel Delivery Systems" 22th International Symposium on Controlled Release of Bioactive Materials, Seattle, WA (1995).

T. D. Reynolds, A. S. Hussain, S. H. Gehrke and L. S. Shenouda "A Gravimetric Study to Simultaneously Evaluate Water Uptake and Polymer Erosion of Various Grades of Hydroxypropylmethylcellulose (HPMC) Matrices," Pharm. Res. 12(9): S-249 (1995); 1995 Annual AAPS Meeting, Miami Beach, FL (1995).

T. D. Reynolds, A. S. Hussain, S. H. Gehrke and L. S. Shenouda "Swelling and Release Characteristics of an Experimental Grade of HPMC, Methocel K700," Pharm. Res. 12(9): S-250 (1995); 1995 Annual AAPS Meeting, Miami Beach, FL (1995).

S. M. O'Connor and S. H. Gehrke "Synthesis and Characterization of Thermally Responsive Gel Beads" 1995 Annual National AIChE Meeting, Miami Beach, FL (1995).

S. M. O'Connor, S. J. Patuto, G. S. Retzinger, S. H. Gehrke "The Influence of Pre-adsorbed Surfactants on the Adsorption of Fibrinogen: Development of a Model System," Federation of American Societies for Experimental Biology (FASEB), Experimental Biology ’96, Washington D.C. (1996).

S. M. O'Connor, S. J. Patuto, G. S. Retzinger, S. H. Gehrke "The Influence of Pre-adsorbed Surfactants on the Adsorption of Fibrinogen: Development of a Model System," Engineering Foundation Conference "Bioartificial Organs", Nashville, TN (1996).

S. Gehrke, L. Uhden, M. Schiller "Enhanced Loading and Activity Retention in Hydrogel Delivery Systems" 1996 Annual National AIChE Meeting, Chicago, IL (1996).

S. M. O'Connor, S. J. Patuto, G. S. Retzinger, S. H. Gehrke "The Influence of Pre-adsorbed Surfactants on the Adsorption of Fibrinogen: Development of a Model System," 1996 Annual National AIChE Meeting, Chicago, IL (1996).

J. F. McBride, J. Fisher, S. H. Gehrke "The Permeability of Temperature-Responsive Gels," 1996 Annual National AIChE Meeting, Chicago, IL (1996).

S. H. Gehrke, J. F. McBride, S. M. O'Connor, H. Zhu, J. P. Fisher "Gel-Coated Catheters as Drug Delivery Systems," 1997 Spring National ACS Meeting, San Francisco, CA (1997).

S. M. O'Connor, S. H. Gehrke, S. Patuto, and G. Retzinger "Adsorption of Pluronic Triblock Copolymers to Polystyrene Beads," 1997 Spring National ACS Meeting, San Francisco, CA (1997).

S. H. Gehrke, J. F. McBride, S. M. O'Connor, H. Zhu, J. P. Fisher "Drug Delivery from Hydrogel-Coated Catheters," 24th International Symposium on Controlled Release of Bioactive Materials, Stockholm, Sweden (1997).

S. M. O'Connor, S. H. Gehrke, and G. Retzinger "Surface Properties of Triblock Copolymers and Their Influence on Protein Adsorption," 1997 Gordon Conference on Biomaterials, Holderness School, Holderness, NH.

J. P. Fisher and S. H. Gehrke,"Influence of Microstructure on the Permeability of Hydrogels used for Drug Delivery Systems," 1997 Annual AIChE Meeting, Los Angeles, CA (1997).

S. M. O'Connor, S. Patuto, G. Retzinger, and S. H. Gehrke "Fibrinogen-Dependent Adherence of Macrophages to Surfaces Coated with PEO/PPO Triblock Copolymers," 1997 Annual AIChE Meeting, Los Angeles, CA (1997).

J.P. Fisher, J.F. McBride, N.E. Nevers, S.H. Gehrke, "Hydrogel Coatinsh for Drug Delivery," 1999 Gordon Conference on Polyelectrolytes, Salve Regina University, Newport, RI.

E. Oliveira and S.H. Gehrke, "Construction and Characterizaton of Novel Polypeptide Hydrogels," 1999 Gordon Conference on Polyelectrolytes, Salve Regina University, Newport, RI.

J.P. Fisher, J.F. McBride, N.E. Nevers and S.H. Gehrke, "Hydrogel Coatings for Drug Delivery," 26th International Symposium on Controlled Release of Bioactive Materials, Boston, MA, (1999).

E.D. Oliveira and S.H. Gehrke, Construction and Characterization of Designed Polypeptide Hydrogels, 1999 Annual AIChE Meeting, Dallas, TX (1999).

S.H. Gehrke, S.Rao, J. Fisher, N. Nevers, "Temperature-Triggered Solute Release from Hydrogels: Contributions of Diffusion and Convection," 1999 Annual AIChE Meeting, Dallas, TX (1999).

J.P. Fisher, J.F. McBride, N.E. Nevers, S.H. Gehrke, "Hydrogel Coatings for Drug Delivery," Enhancing Materials Research in Kansas Conference, Emporia State University, Emporia, KS.

E.D. Oliveira and S.H. Gehrke, "Influence of Network Conformation on Properties of Poly(Amino Acid) Hydrogels," National ACS Meeting, San Francisco (2000).

E.D. Oliveira, S.A. Hagan and S.H. Gehrke, "Mechanical Properties of Elastin-Mimetic Gels" 28th International Symposium on Controlled Release of Bioactive Materials, San Diego, CA (2001).

E.D. Oliveira, S.A. Hagan and S.H. Gehrke, "Influence of Polymer Conformation on Properties of Poly(Amino) Hydrogels" 2000 Annual AIChE Meeting, Los Angeles (2000).

E.D. Oliveira, S.A. Hagan and S.H. Gehrke, "Mechanical Properties of Elastin-Mimetic Gels" 28th International Symposium on Controlled Release of Bioactive Materials, San Diego, CA (2001).

E.D. Oliveira, S.A. Hagan and S.H. Gehrke, "Influence of Polymer Conformation on Properties of Poly(Amino Acid) Hydrogels" 2001 Annual AIChE Meeting, Reno, NV (2001).

E.D. Oliveira and S.H. Gehrke, "Effects of Rigid Secondary Structure on the Elastic Properties of Polypeptide Hydrogels," 6th Annual Brazilian Polymer Conference/IX International Macromolecular Colloquium, Gramado, Rio Grande do Sul, Brazil, 11/11-15/2001.

E.D. Oliveira, S.A. Hagan and S.H. Gehrke, "Swelling and Mechanical Properties of Elastin-Mimetic Hydrogels" 6th Annual Brazilian Polymer Conference/IX International Macromolecular Colloquium, Gramado, Rio Grande do Sul, Brazil, 11/11-15/2001.

E.D. Oliveira, S.A. Hagan and S.H. Gehrke, "Mechanical Performance of Elastin-Mimetic Gels" 31st Annual Biochemical Engineering Symposium, Manhattan, KS 9/8/01.

S.A. Hagan and S.H. Gehrke, "Mechanical Performance of Biomimetic Hydrogels" 2002 Annual AIChE Meeting, Indianapolis, IN 11/5/02.

S.A. Hagan, E.D. Oliveira, V.P. Conticello and S.H. Gehrke, "Effect of Polymer Chain Interactions on the Mechanical Performance of Biomimetic Hydrogels," Conference on Creating Value for Biobased Resources, K-State Agricultural Utilization Products Forum, Kansas City, MO 11/12/02.

S. A. Hagan, E.D. Oliveira, V.P. Conticello and S.H. Gehrke, "Effects of Polymer Chain Interactions on the Mechanical Performance of Biomimetic Hydrogels" ACS Workshop on Polymers in Medicine and Biology, Roehnert Park, Ca 11/13-16/02.