Polymer Chemistry Group

Hydrogels for Drug Delivery

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Polymer hydrogels based on copolymers of hydroxyethyl methacrylate (HEMA) and other methacrylate monomers have a range of potential applications in the medical fields, including use as vehicles for controlled delivery of drugs. The design philosophy we have used involves loading of drugs within monomer mixtures prior to polymerization, although more complex methodologies are being investigated. We have studied the diffusion of water and drugs in a range of copolymer of HEMA with the relatively-hydrophilic monomer tetrahydrofurfuryl methacrylate (THFMA).

When the hydrogels are exposed to water, they absorb water and swell to an extent determined by internal parameters such as hydrophilicity and crosslink density, and external parameters such as temperature, pH and ionic strenght of the solution. As an example we show the increase in mass of poly(HEMA) on exposure to distilled water.

Kinetics of swelling of PHEMA hydrogel

The red line is the best fit of the data to the equation describing Fick's second law of diffusion into a cylinder. The initial stage of the diffusion is well described by Fick's law, while a later time a slight overshoot occurs due to the relatively slow relaxation of the polymer chains compared to the rate of deformation due to swelling.

Additional insights into the diffusion processes can be gained from NMR images of the water profiles across the swelling cylinders. The image below shows the concentration of water across a cylinder of poly(HEMA) containing 5 wt. % of the model drug vitamin B12. There are two features apparent, namely an underlying Fickian profile and within the cylinder a peak in the profile due to water in cracks formed by swelling. A number of features of diffusion have been examined, including anomolous and concentration-dependent diffusion.

MRI of water ingress into a PHEMA hydrogel

In summary we have studied diffusion in:

  • Poly(HEMA)
  • Poly(HEMA-co-THFMA)
  • Poly(HEMA-co-ethoxyethyl methacrylate)
  • Poly(HEMA-co-ethyl methacrylate)
  • Poly(HEMA-co-butyl methacrylate)
  • Poly(HEMA-co-cyclohexyl methacrylate)
  • Poly(HEMA-co-MOEP)
  • Poly(NIPAM-co-DMA)

In a related project, we have investigated the structure and relaxation properties of polymer gel dosimeters. These are crosslinked polyacrylamide hydrogels polymerised under exposure to ionising radiation within a LINAC used for conformal radiotherapy. This ongoing project in collaboration with Dr. Clive Baldock of the University of Sydney, has resulted in an understanding of the molecular origins of the observed NMR relaxation behaviour of these dosimeters.

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Publications

1. P. Ghi, D.J.T. Hill, P.J. Pomery and A.K. Whittaker, "The copolymerization of hydroxyl-ethyl methacrylate and tetrahydrofurfyrl methacrylate", Polym. Gels Networks, 4, 253-267 (1996).
2. P. Ghi, D.J.T. Hill, D. Maillet and A.K. Whittaker, "NMR imaging of diffusion of water into poly(tetrahydrofurfurly methacrylate-co-hydroxethyl methacrylate), Polymer Commun., 38, 3985-3989 (1997).
3. R.M. Hodge, G.P. Simon, M.R. Whittaker, D.J.T. Hill, and A.K. Whittaker, "Free volume and water uptake in a copolymer hydrogel series", J Polym. Sci. B, Polym. Phys., 36, 463-471 (1998).
4. P.Y. Ghi; D.J.T. Hill; A.K. Whittaker. Diffusion of water in poly(hydroxyethyl methacrylate) hydrogels. Chem. Aust. (1999), 66(1), 37-39.
5. D.J.T. Hill, M.C.H. Lim and A.K. Whittaker, "Water diffusion in hydroxyethyl methacrylate (HEMA)-based hydrogels formed by -radiolysis", Polym. Int., 48, 1046-1052 (1999).
6. P.Y. Ghi, D.J.T. Hill and A.K. Whittaker, "A study of the copolymerization of hydroxyethyl methacrylate and tetrahydrofurfuryl methacrylate", J. Polym. Sci., Polym. Chem. Ed., 37, 3730-3737, (1999).
7. D.J.T. Hill, N.G. Moss, P.J. Pomery and A.K. Whittaker, "Copolymer hydrogels of hydroxyethyl methacrylate with n-butyl methacrylate and cyclohexyl methacrylate: synthesis, characterization and water up-take", Polymer, 41, 1287-1296 (2000).
8. 13C-NMR, 1H-NMR, and FT-raman study of radiation-induced modifications in radiation dosimetry polymer gels. Lepage, M.; Whittaker, A. K.; Rintoul, L.; Baldock, C. J. Appl. Polym. Sci. (2000), 79(9), 1572-1581.
9. Water sorption by poly(tetrahydrofurfuryl methacrylate-co-2-hydroxyethyl methacrylate). Part 1. A mass-uptake study. Ghi, Phuong; Hill, David J. T.; Whittaker, Andrew K. J. Polym. Sci., Part B: Polym. Phys. (2000), 38(14), 1939-1946.
10. Imaging of water sorption into poly(hydroxyethyl methcarylate-co-tetrahydrofurfuryl methacrylate) Ghi, P.Y.; Hill, D.J.T.; Whittaker, A.K.. Biomacromolecules, (2001), 2, 504-510.
11. Modeling of post-irradiation events in polymer gel dosimeters. Lepage, M.; Whittaker, A.K.; Rintoul, L.; Bäck, S.A.J.; Baldock, C.. Phys. Med. Biol., (2001), 46, 2827-2839.
12. The relationship between radiation-induced chemical processes and transverse relaxation times in polymer gel dosimeters. Lepage, M.; Whittaker, A.K.; Rintoul, L.; Bäck, S.A.J.; Baldock, C.. Phys. Med. Biol., ( 2001), 46, 1061-1074.
13. The copolymerization of N-vinyl-2-pyrrolidone with 2-hydroxyethyl methacrylate. Faragalla, M.M.; Hill, D.J.T.; Pomery, P.J.; Whittaker, A.K.. Polym. Bull, (2002), 47, 421-427.
14. Ultrasound evaluation of polymer gel dosimeters, Mather, M.L., Whittaker, A.K. and Baldock, C. Phys. Med. Biol, 2002, 47, 1449-1458.
15. Mather, M.L.; De Deene, Y.; Whittaker, A.K.; Simon, G.P.; Rutgers, R.; Baldock, C., Investigation of ultrasonic properties of PAG and MAGIC polymer gel dosimeters, Phys. Med. Biol., (2002), 47, 4397-4409.
16. Ghi, Phuong Y.; Hill, David J. T.; Whittaker, Andrew K.. 1H NMR Study of the States of Water in Equilibrium Poly(HEMA-co-THFMA) Hydrogels. Biomacromolecules (2002), 3(5), 991-997.
17. Ghi, Phuong Y.; Hill, David J. T.; Whittaker, Andrew K.. PFG-NMR Measurements of the Self-Diffusion Coefficients of Water in Equilibrium Poly(HEMA-co-THFMA) Hydrogels. Biomacromolecules (2002), 3(3), 554-559.
18. Malak, Mark; Hill, David J. T.; Whittaker, Andrew K.. Water sorption into poly[(2-hydroxyethyl methacrylate)-co-(1-vinyl-2-pyrrolidone)]at 310 K. Polymer International (2003), 52(11), 1740-1748.
19. Mather, Melissa L.; Collings, Anthony F.; Bajenov, Nick; Whittaker, Andrew K.; Baldock, Clive. Ultrasonic absorption in polymer gel dosimeters. Ultrasonics (2003), 41(7), 551-559.
20. Zainuddin, T.V. Chirila, D.J.T. Hill, A.K. Whittaker, Study of the calcification of PHEMA hydrogels using a two compartment permeation cell, J. Mol. Struct., accepted, May 04.
21. Chowdhury, Mohammad A.; Hill, David J. T.; Whittaker, Andrew K.. NMR Imaging of the Diffusion of Water at 37 oC into Poly(2-hydroxyethyl methacrylate) Containing Aspirin or Vitamin B12. Biomacromolecules (2004), 5(3), 971-976.
22. Hill, David J. T.; Chowdhury, Mohammad; Ghi, Phuong Y.; Moss, Naomi G.; Whittaker, Andrew K.. Water diffusion in methacrylate based copolymer hydrogels of 2-hydroxyethyl methacrylate. Macromolecular Symposia (2004), 207(Fundamentals and Applications of Polymer Gels), 111-123.
23. Chowdhury, Mohammad A.; Hill, David J. T.; Whittaker, Andrew K.; Braden, Michael; Patel, Mangala P. NMR Imaging of the Diffusion of Water at 310 K into Semi-IPNs of PEM and Poly(HEMA-co-THFMA) with and without Chlorhexidine Diacetate. Biomacromolecules (2004), 5(4), 1405-1411.
24. George, Karina A.; Wentrup-Byrne, Edeline; Hill, David J. T.; Whittaker, Andrew K. Investigation into the Diffusion of Water into HEMA-co-MOEP Hydrogels Biomacromolecules (2004), 5(4), 1194-1199.

Collaborators

Traian Chirila, Queensland Eye Institute
Edeline Wentrup-Byrne, Queensland University of Technology
Clive Baldock, University of Sydney

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