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Stimuli Responsive Polymers

Stimuli Responsive Polymers. Mustafa Yorulmaz Koç University Material Science and Engineering. Outline. Introduction Types of stimuli responsive polymers: pH-sensitive polymers Temperature responsive polymers Applications of these polymers: Drug delivery systems

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Stimuli Responsive Polymers

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  1. Stimuli Responsive Polymers Mustafa Yorulmaz Koç University Material Science and Engineering

  2. Outline • Introduction • Types of stimuli responsive polymers: • pH-sensitive polymers • Temperature responsive polymers • Applications of these polymers: • Drug delivery systems • Cell adhesion control system • Conclusions Koç University, Material Science and Engineering

  3. Introduction • Responding external stimuli • Undergo a physical change • Under controlled conditions (‘smart’ or ‘intelligent’) • External stimuli: • pH • Temperature • Ionic strength, electric field, magnetic field, light, etc. • Very promising applications in biomedical field as biomaterials. Koç University, Material Science and Engineering

  4. pH-sensitive polymers • Respond to the changes in the pH of surrounding medium • Expand or collapse depending on the pH of the environment • Due to presence of certain functional groups in the polymer chain • Acidic group (-COOH, -SO3H ) • Basic group (-NH2 ) • After ionization of these groups: hydrodynamic volume increase due to electrostatic repulsion • Drug delivery systems and biomimetics PDMAEMA PDEAEMA poly(acrylic acid) (PAA) poly(methacrylic acid) Y. Qiu, and K. Park, “Environment-sensitive hydrogels for drug delivery”, Adv. Drug Deliver Rev., Vol.53, 2001; 321-329 Koç University, Material Science and Engineering

  5. Temperature responsive polymers • Respond to temperature changes • A critical solution temperature: • Phase of the polymer and solution is changed • Phase of the polymers and solution is changed • Types: • TRP which shows UCST • One phase above certain temp • Phase separation below it • TRP which shows LCST • Monophasic below a specific temp • Biphasic above this temp • Find applications again as biomaterials mostly Koç University, Material Science and Engineering

  6. Temperature responsive polymers • The first established LCST is 32oC for poly(N-isopropylacrylamide) (PNIPAAm) in water solution • At this temp: • Undergoes a sharp coil-globule transition • Changes from hydrophilic state to hydrophobic state as temperature is increases • In aqueous solutions, it is soluble below LCST and less soluble above it PNIPAAm X. Zhang, R. Zhuo, Y. Yang, “Using mixed solvent to synthesize temperature sensitive poly(N-isopropylacrylamide) gel with rapid dynamic properties”, Biomaterials, Vol.26, 2002; 1313 C. H. Alarcon, S. Pennadam and C. Alexander, “Stimuli responsive polymers for biomedical applications”, Chem. Soc. Rev. Vol.34, 2005; 276 Koç University, Material Science and Engineering

  7. Drug release systems • Controlled release of insulin • Hydrogel works as insulin containing reservoir within (P(MAA-g-EG)) copolymer in which glucose oxidase was immobilized. • The surface of polymer contains a series of molecular entraces for delivery of insulin • When pH drops, there occurs the release of protons causing the gates to be opened for transportation of insulin. C. H. Alarcon, S. Pennadam and C. Alexander, “Stimuli responsive polymers for biomedical applications”, Chem. Soc. Rev. Vol.34, 2005; 276 Koç University, Material Science and Engineering

  8. Drug release systems • The reversible collapse and expansion behavior • PNIPAAm incoroprated into cross-linked polymer gel above the LCST of the hompolymer • At low temperatures, swollen PNIPAAm hydrogels kept in drug solutions and at elevated temperatures, rapid initial drug release is observed as a result of fast matrix contraction • Pulsatile release of prostaglandin H2 synthase-1 inhibitor, indomethacin and sodium salt of salicylic acid C. H. Alarcon, S. Pennadam and C. Alexander, “Stimuli responsive polymers for biomedical applications”, Chem. Soc. Rev. Vol.34, 2005; 276 Koç University, Material Science and Engineering

  9. Cell adhesion control • Platelets on PEG-grafted (tissue culture of polystyrene) TCPS retain a rounded shape at 37oC • The platelets exhibit rounded and unspread morphology at 12oC on PNIPAAm-grafted TCPS • By contrast, platelets on PNIPAAm-grafted TCPS dramatically change their behavior depending on temperature as platelets adhere, spread and develop characteristic pseudopodia on PNIPAAm-grafted TCPS at 37oC • Hydrophilic/hydrophobic switching of PNIPAAm-grafted surfaces on TCPS K. Uchida, K. Sakai, E. Ito, O. H. Kwon, A. Kikuchi, M. Yamato and T. Okano, “Temperature-dependent modulation of blood platelet movement and morphology on poly(N-isopropylacrylamide)-grafted surfaces”, Biomaterials, Vol.21, 2000, 923 Koç University, Material Science and Engineering

  10. Conclusions • Most used and important types of stimuli responsive polymers: • pH sensitive • Temperature responsive • Drug delivery systems and cell adhesion control mechanism • Temperature responsive polymers will be mostly focused on for their uses in biomedical applications. Koç University, Material Science and Engineering

  11. Thanks.. • Questions?? Koç University, Material Science and Engineering

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