The synthesis and application of stimuli-responsive polymer materials have been extensively studied. Among stimuli-responsive polymers, thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) is the most widely investigated. PNIPAAm-based polymers undergo a reversible hydrophilic/hydrophobic phase transition in response to temperature. In addition, by introducing sites that are responsive to physical and chemical stimuli into PNIPAAm-based polymers, they also undergo phase transitions in response to stimuli, such as light, pH, oxidation/reduction, and enzyme activity. In this focus review, recent advancements in the applications of stimuli-responsive polymers based on PNIPAAm in biomedical fields are summarized, with an emphasis on our own research. In particular, a summary of the design of polymers for application in the separation and purification of (bio)pharmaceutical products and controlled cellular uptake is provided. First, temperature-responsive chromatography with PNIPAAm-modified silica beads is introduced. Thereafter, temperature- and pH-responsive polymers based on PNIPAAm used in imaging and drug delivery applications are discussed. Finally, the conclusions are presented, and future perspectives for the biomedical applications of stimuli-responsive polymers are discussed.
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Stuart MAC, Huck WTS, Genzer J, Müller M, Ober C, Stamm M, et al. Emerging applications of stimuli-responsive polymer materials. Nat Mater. 2010;9:101–13.
Jochum FD, Theato P. Temperature- and light-responsive smart polymer materials. Chem Soc Rev. 2013;42:7468–83.
Ulijn RV. Enzyme-responsive materials: a new class of smart biomaterials. J Mater Chem. 2006;16:2217–25.
Meng F, Hennink WE, Zhong Z. Reduction-sensitive polymers and bioconjugates for biomedical applications. Biomaterials. 2009;30:2180–98.
Hasuike E, Akimoto AM, Kuroda R, Matsukawa K, Hiruta Y, Kanazawa H, et al. Reversible conformational changes in the parallel type G-quadruplex structure inside a thermoresponsive hydrogel. Chem Commun. 2017;53:3142–4.
Kim YS, Tamate R, Akimoto AM, Yoshida R. Recent developments in self-oscillating polymeric systems as smart materials: from polymers to bulk hydrogels. Mater Horiz. 2017;4:38–54.
Tanaka T. Collapse of gels and the critical endpoint. Phys Rev Lett. 1978;40:820–3.
Osada Y, Gong J. Stimuli-responsive polymer gels and their application to chemomechanical systems. Prog Polym Sci. 1993;18:187–226.
Schild HG. Poly(N-isopropylacrylamide): experiment, theory and application. Prog Polym Sci. 1992;17:163–249.
Heskins M, Guillet JE. Solution properties of poly(N-isopropylacrylamide). J Macromol Sci Chem. 1968;2:1441–55.
Podewitz M, Wang Y, Quoika PK, Loeffler JR, Schauperl M, Liedl KR. Coil–globule transition thermodynamics of poly(N-isopropylacrylamide). J Phys Chem B. 2019;123:8838–47.
Wu C, Wang X. Globule-to-coil transition of a single homopolymer chain in solution. Phys Rev Lett. 1998;80:4092–4.
Zhang Y, Furyk S, Bergbreiter DE, Cremer PS. Specific ion effects on the water solubility of macromolecules: PNIPAM and the Hofmeister series. J Am Chem Soc. 2005;127:14505–10.
Hiruta Y, Nagumo Y, Suzuki Y, Funatsu T, Ishikawa Y, Kanazawa H. The effects of anionic electrolytes and human serum albumin on the LCST of poly(N-isopropylacrylamide)-based temperature-responsive copolymers. Colloids Surf B. 2015;132:299–304.
Hiruta Y, Shimamura M, Matsuura M, Maekawa Y, Funatsu T, Suzuki Y, et al. Temperature-responsive fluorescence polymer probes with accurate thermally controlled cellular uptakes. ACS Macro Lett. 2014;3:281–5.
Feil H, Bae YH, Feijen J, Kim SW. Effect of comonomer hydrophilicity and ionization on the lower critical solution temperature of N-isopropylacrylamide copolymers. Macromolecules. 1993;26:2496–500.
Li J, Kaku T, Tokura Y, Matsukawa K, Homma K, Nishimoto T, et al. Adsorption–desorption control of fibronectin in real time at the liquid/polymer interface on a quartz crystal microbalance by thermoresponsivity. Biomacromolecules. 2019;20:1748–55.
Yin X, Hoffman AS, Stayton PS. Poly(N-isopropylacrylamide-co-propylacrylic acid) copolymers that respond sharply to temperature and pH. Biomacromolecules. 2006;7:1381–5.
Okubo M, Ahmad H, Suzuki T. Synthesis of temperature-sensitive micron-sized monodispersed composite polymer particles and its application as a carrier for biomolecules. Colloid Polym Sci. 1998;276:470–5.
Matyjaszewski K, Spanswick J. Controlled/living radical polymerization. Mater Today. 2005;8:26–33.
Žuvela P, Skoczylas M, Jay Liu J, Ba̧czek T, Kaliszan R, Wong MW, et al. Column characterization and selection systems in reversed-phase high-performance liquid chromatography. Chem Rev. 2019;119:3674–729.
Mochida M, Nagai Y, Kumagai H, Imai H, Citterio D, Hiruta Y. A biomimetic hybrid material consisting of CaCO3 mesoporous microspheres and an alternating copolymer for reversed-phase HPLC. J. Mater Chem B. 2019;7:4771–7.
Zhang Z, Zheng Y, Chen J, Zhang Q, Ni Y, Liang X. Facile synthesis of monodisperse magnesium oxide microspheres via seed-induced precipitation and their applications in high- performance liquid chromatography. Adv Funct Mater. 2007;17:2447–54.
Nagase K, Kanazawa H. Temperature-responsive chromatography for bioseparations: a review. Anal Chim Acta. 2020;1138:191–212.
Sakata K, Ohkubo K, Hiruta Y, Ayano E, Kanazawa H. Temperature-responsive chromatography using a functional polymer modified stationary phase with molecular recognition sites. Kobunshi Ronbunshu. 2014;71:293–301.
Kanazawa H, Yamamoto K, Matsushima Y, Takai N, Kikuchi A, Sakurai Y, et al. Temperature-responsive chromatography using poly(N-isopropylacrylamide)-modified silica. Anal Chem. 1996;68:100–5.
Mikuma T, Kuroki T, Yoshikawa M, Uchida R, Hiruta Y, Kanazawa H. Analysis of psychoactive drugs by temperature-responsive chromatography. Chromatography. 2017;38:115–21.
Maekawa Y, Okamoto N, Okada Y, Nagase K, Kanazawa H. Green analytical method for the simultaneous analysis of cytochrome P450 probe substrates by poly(N-isopropylacrylamide)-based temperature-responsive chromatography. Sci Rep. 2020;10:8828.
Kanazawa H, Nishikawa M, Mizutani A, Sakamoto C, Morita-Murase Y, Nagata Y, et al. Aqueous chromatographic system for separation of biomolecules using thermoresponsive polymer modified stationary phase. J Chromatogr A. 2008;1191:157–61.
Okubo K, Ikeda K, Oaku A, Hiruta Y, Nagase K, Kanazawa H. Protein purification using solid-phase extraction on temperature-responsive hydrogel-modified silica beads. J Chromatogr A. 2018;1568:38–48.
Nomoto D, Nagase K, Nakamura Y, Kanazawa H, Citterio D, Hiruta Y. Anion species-triggered antibody separation system utilizing a thermo-responsive polymer column under optimized constant temperature. Colloids Surf B. 2021;205:111890.
Nagase K, Inanaga D, Ichikawa D, Mizutani Akimoto A, Hattori Y, Kanazawa H. Temperature-modulated cell-separation column using temperature-responsive cationic copolymer hydrogel-modified silica beads. Colloids Surf B. 2019;178:253–62.
Nagase K, Uchikawa N, Hirotani T, Akimoto AM, Kanazawa H. Thermoresponsive anionic copolymer brush-grafted surfaces for cell separation. Colloids Surf B. 2020;185:110565.
Konishi T, Mizutani Akimoto A, Nishimoto T, Tokura Y, Tenjimbayashi M, Homma K, et al. Crosslinked poly(N-Isopropylacrylamide)-based microfibers as cell manipulation materials with prompt cell detachment. Macromol Rapid Commun. 2019;40:1900464.
Yakushiji T, Sakai K, Kikuchi A, Aoyagi T, Sakurai Y, Okano T. Effects of cross-linked structure on temperature-responsive hydrophobic interaction of poly(N-isopropylacrylamide) hydrogel-modified surfaces with steroids. Anal Chem. 1999;71:1125–30.
Nagase K, Kobayashi J, Kikuchi A, Akiyama Y, Kanazawa H, Okano T. Interfacial property modulation of thermoresponsive polymer brush surfaces and their interaction with biomolecules. Langmuir. 2007;23:9409–15.
Kanazawa H, Kashiwase Y, Yamamoto K, Matsushima Y, Kikuchi A, Sakurai Y, et al. Temperature-responsive liquid chromatography. 2. Effects of hydrophobic groups in N-isopropylacrylamide copolymer-modified silica. Anal Chem. 1997;69:823–30.
Kanazawa H, Sunamoto T, Matsushima Y, Kikuchi A, Okano T. Temperature-responsive chromatographic separation of amino acid phenylthiohydantoins using aqueous media as the mobile phase. Anal Chem. 2000;72:5961–6.
Mori H, Sutoh K, Endo T. Controlled radical polymerization of an acrylamide containing l-phenylalanine moiety via RAFT. Macromolecules. 2005;38:9055–65.
Casolaro M, Cini R, Del Bello B, Ferrali M, Maellaro E. Cisplatin/hydrogel complex in cancer therapy. Biomacromolecules. 2009;10:944–9.
Feng X, Zhang Q, Liang X, Li J, Zhao Y, Chen L. Preparation, characterization and application of a chiral thermo-sensitive membrane for phenylalanine separation of the racemic mixture. J Polym Res. 2014;21:1–9.
Kanazawa H, Ayano E, Sakamoto C, Yoda R, Kikuchi A, Okano T. Temperature-responsive stationary phase utilizing a polymer of proline derivative for hydrophobic interaction chromatography using an aqueous mobile phase. J Chromatogr A. 2006;1106:152–8.
Hiruta Y, Kanazashi R, Ayano E, Okano T, Kanazawa H. Temperature-responsive molecular recognition chromatography using phenylalanine and tryptophan derived polymer modified silica beads. Analyst. 2016;141:910–7.
Hiruta Y, Nagumo Y, Miki A, Okano T, Kanazawa H. Effects of terminal group and chain length on temperature-responsive chromatography utilizing poly(N-isopropylacrylamide) synthesized via RAFT polymerization. RSC Adv. 2015;5:73217–24.
Mikuma T, Uchida R, Kajiya M, Hiruta Y, Kanazawa H. The use of a temperature-responsive column for the direct analysis of drugs in serum by two-dimensional heart-cutting liquid chromatography. Anal Bioanal Chem. 2017;409:1059–65.
Akimaru M, Okubo K, Hiruta Y, Kanazawa H. Temperature-responsive solid-phase extraction column for biological sample pretreatment. Anal Sci. 2015;31:881–6.
Nagase K, Ishii S, Ikeda K, Yamada S, Ichikawa D, Akimoto AM, et al. Antibody drug separation using thermoresponsive anionic polymer brush modified beads with optimised electrostatic and hydrophobic interactions. Sci Rep. 2020;10:11896.
Karnebogen M, Singer D, Kallerhoff M, Ringert RH. Microcalorimetric investigations on isolated tumorous and non-tumorous tissue samples. Thermochim Acta. 1993;229:147–55.
Monti M, Brandt L, Ikomi-Kumm J, Olsson H. Microcalorimetric investigation of cell metabolism in tumour cells from patients with non-Hodgkin lymphoma (NHL). Scand J Haematol. 1986;36:353–7.
Wust P, Hildebrandt B, Sreenivasa G, Rau B, Gellermann J, Riess H, et al. Hyperthermia in combined treatment of cancer. Lancet Oncol. 2002;3:487–97.
Webb BA, Chimenti M, Jacobson MP, Barber DL. Dysregulated pH: a perfect storm for cancer progression. Nat Rev Cancer. 2011;11:671–7.
Yuba E. Development of functional liposomes by modification of stimuli-responsive materials and their biomedical applications. J Mater Chem B. 2020;8:1093–107.
Bordat A, Boissenot T, Nicolas J, Tsapis N. Thermoresponsive polymer nanocarriers for biomedical applications. Adv Drug Deliv Rev. 2019;138:167–92.
Akimoto J, Nakayama M, Okano T. Temperature-responsive polymeric micelles for optimizing drug targeting to solid tumors. J Control Release. 2014;193:2–8.
Kono K, Hayashi H, Takagishi T. Temperature-sensitive liposomes: liposomes bearing poly (N-isopropylacrylamide). J Control Release. 1994;30:69–75.
Cammas S, Suzuki K, Sone C, Sakurai Y, Kataoka K, Okano T. Thermo-responsive polymer nanoparticles with a core-shell micelle structure as site-specific drug carriers. J Control Release. 1997;48:157–64.
Chung JE, Yokoyama M, Yamato M, Aoyagi T, Sakurai Y, Okano T. Thermo-responsive drug delivery from polymeric micelles constructed using block copolymers of poly(N-isopropylacrylamide) and poly(butylmethacrylate). J Control Release. 1999;62:115–27.
Kono K, Henmi A, Yamashita H, Hayashi H, Takagishi T. Improvement of temperature-sensitivity of poly(N-isopropylacrylamide)-modified liposomes. J Control Release. 1999;59:63–75.
Kono K, Nakai R, Morimoto K, Takagishi T. Temperature-dependent interaction of thermo-sensitive polymer-modified liposomes with CV1 cells. FEBS Lett. 1999;456:306–10.
Akimoto J, Nakayama M, Sakai K, Okano T. Temperature-induced intracellular uptake of thermoresponsive polymeric micelles. Biomacromolecules. 2009;10:1331–6.
Akimoto J, Nakayama M, Sakai K, Okano T. Thermally controlled intracellular uptake system of polymeric micelles possessing poly(N-isopropylacrylamide)-based outer coronas. Mol Pharmaceutics. 2010;7:926–35.
Hamai C, Yang T, Kataoka S, Cremer PS, Musser SM. Effect of average phospholipid curvature on supported bilayer formation on glass by vesicle fusion. Biophys J. 2006;90:1241–8.
Yamada A, Hiruta Y, Wang J, Ayano E, Kanazawa H. Design of environmentally responsive fluorescent polymer probes for cellular imaging. Biomacromolecules. 2015;16:2356–62.
Kanai Y, Segawa H, Miyamoto K-I, Uchino H, Takeda E, Endou H. Expression cloning and characterization of a transporter for large neutral amino acids activated by the heavy chain of 4F2 antigen (CD98). J Biol Chem. 1998;273:23629–32.
Matsuura M, Ohshima M, Hiruta Y, Nishimura T, Nagase K, Kanazawa H. LAT1-targeting thermoresponsive fluorescent polymer probes for cancer cell imaging. Int J Mol Sci. 2018;19:1646.
Ju XJ, Liu L, Xie R, Niu CH, Chu LY. Dual thermo-responsive and ion-recognizable monodisperse microspheres. Polymer. 2009;50:922–9.
Jochum FD, Zur Borg L, Roth PJ, Theato P. Thermo- and light-responsive polymers containing photoswitchable azobenzene end groups. Macromolecules. 2009;42:7854–62.
Hiruta Y, Funatsu T, Matsuura M, Wang J, Ayano E, Kanazawa H. pH/temperature-responsive fluorescence polymer probe with pH-controlled cellular uptake. Sens Actuators B Chem. 2015;207:724–31.
Kolate A, Baradia D, Patil S, Vhora I, Kore G, Misra A. PEG—a versatile conjugating ligand for drugs and drug delivery systems. J Control Release. 2014;192:67–81.
Hatakeyama H, Akita H, Harashima H. A multifunctional envelope type nano device (MEND) for gene delivery to tumours based on the EPR effect: a strategy for overcoming the PEG dilemma. Adv Drug Deliv Rev. 2011;63:152–60.
Wang M, Thanou M. Targeting nanoparticles to cancer. Pharmacol Res. 2010;62:90–9.
Meyer DE, Shin BC, Kong GA, Dewhirst MW, Chilkoti A. Drug targeting using thermally responsive polymers and local hyperthermia. J Control Release. 2001;74:213–24.
Hiruta Y, Nemoto R, Kanazawa H. Design and synthesis of temperature-responsive polymer/silica hybrid nanoparticles and application to thermally controlled cellular uptake. Colloids Surf B. 2017;153:2–9.
Hiruta Y, Kanda Y, Katsuyama N, Kanazawa H. Dual temperature- and pH-responsive polymeric micelle for selective and efficient two-step doxorubicin delivery. RSC Adv. 2017;7:29540–9.
Nemoto R, Fujieda K, Hiruta Y, Hishida M, Ayano E, Maitani Y, et al. Liposomes with temperature-responsive reversible surface properties. Colloids Surf B. 2019;176:309–16.
Wang J, Ayano E, Maitani Y, Kanazawa H. Tunable surface properties of temperature-responsive polymer-modified liposomes induce faster cellular uptake. ACS Omega. 2017;2:316–25.
Wang J, Ayano E, Maitani Y, Kanazawa H. Enhanced cellular uptake and gene silencing activity of siRNA using temperature-responsive polymer-modified liposome. Int J Pharm. 2017;523:217–28.
Maekawa-Matsuura M, Fujieda K, Maekawa Y, Nishimura T, Nagase K, Kanazawa H. LAT1-targeting thermoresponsive liposomes for effective cellular uptake by cancer cells. ACS Omega. 2019;4:6443–51.
Lutz J-F. Polymerization of oligo(ethylene glycol) (meth)acrylates: toward new generations of smart biocompatible materials. J Polym Sci Part A: Polym Chem. 2008;46:3459–70.
Hao J, Servello J, Sista P, Biewer MC, Stefan MC. Temperature-sensitive aliphatic polyesters: synthesis and characterization of γ-substituted caprolactone monomers and polymers. J Mater Chem. 2011;21:10623–8.
Weber C, Hoogenboom R, Schubert US. Temperature responsive bio-compatible polymers based on poly(ethylene oxide) and poly(2-oxazoline)s. Prog Polym Sci. 2012;37:686–714.
Deng H, Liu J, Zhao X, Zhang Y, Liu J, Xu S, et al. PEG-b-PCL copolymer micelles with the ability of pH-controlled negative-to-positive charge reversal for intracellular delivery of doxorubicin. Biomacromolecules. 2014;15:4281–92.
Sano K, Kanada Y, Takahashi K, Ding N, Kanazaki K, Mukai T, et al. Enhanced delivery of radiolabeled polyoxazoline into tumors via self-aggregation under hyperthermic conditions. Mol Pharmaceutics. 2018;15:3997–4003.
Cheng Y, Hao J, Lee LA, Biewer MC, Wang Q, Stefan MC. Thermally controlled release of anticancer drug from self-assembled gamma-substituted amphiphilic poly(epsilon-caprolactone) micellar nanoparticles. Biomacromolecules. 2012;13:2163–73.
Sano K, Umemoto K, Miura H, Ohno S, Iwata K, Kawakami R, et al. Feasibility of using poly[oligo(ethylene glycol) methyl ether methacrylate] as tumor-targeted carriers of diagnostic drugs. ACS Appl Polym Mater. 2022;4:4734–40.
This study was partly supported by a Grant-in-Aid for Scientific Research for Research Activity-Career Scientists (Grant No. 19K16339), Grant-in-Aid for Scientific Research (C) (Grant No. 21K06495) from the Japan Society for the Promotion of Science (JSPS), and by the Program for the Advancement of Next Generation Research Projects (Type C) at Keio. I would like to thank Editage (www.editage.jp) for their English language editing services.
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Hiruta, Y. Poly(N-isopropylacrylamide)-based temperature- and pH-responsive polymer materials for application in biomedical fields. Polym J 54, 1419–1430 (2022). https://doi.org/10.1038/s41428-022-00687-z