This paper introduces a new class of amphiphilic block copolymers created by combining two polymers: polylactic acid (PLA), a biocompatible and biodegradable hydrophobic polyester used for cargo encapsulation, and a hydrophilic polymer composed of oligo ethylene glycol chains (triethylene glycol methyl ether methacrylate, TEGMA), which provides stability and repellent properties with added thermo-responsiveness. The PLA-b-PTEGMA block copolymers were synthesized using ring-opening polymerization (ROP) and reversible addition-fragmentation chain transfer (RAFT) polymerization (ROP-RAFT), resulting in varying ratios between the hydrophobic and hydrophilic blocks. Standard techniques, such as size exclusion chromatography (SEC) and 1H NMR spectroscopy, were used to characterize the block copolymers, while 1H NMR spectroscopy, 2D nuclear Overhauser effect spectroscopy (NOESY), and dynamic light scattering (DLS) were used to analyze the effect of the hydrophobic PLA block on the LCST of the PTEGMA block in aqueous solutions. The results show that the LCST values for the block copolymers decreased with increasing PLA content in the copolymer. The selected block copolymer presented LCST transitions at physiologically relevant temperatures, making it suitable for manufacturing nanoparticles (NPs) and drug encapsulation-release of the chemotherapeutic paclitaxel (PTX) via temperature-triggered drug release mechanism. The drug release profile was found to be temperature-dependent, with PTX release being sustained at all tested conditions, but substantially accelerated at 37 and 40 °C compared to 25 °C. The NPs were stable under simulated physiological conditions. These findings demonstrate that the addition of hydrophobic monomers, such as PLA, can tune the LCST temperatures of thermo-responsive polymers, and that PLA-b-PTEGMA copolymers have great potential for use in drug and gene delivery systems via temperature-triggered drug release mechanisms in biomedicine applications.

Institute of Macromolecular Chemistry CAS Heyrovského nám 2 162 06 Prague Czech Republic

See more in PubMed

Ruiz A.L., Ramirez A., McEnnis K. Single and Multiple Stimuli-Responsive Polymer Particles for Controlled Drug Delivery. Pharmaceutics. 2022;14:421. doi: 10.3390/pharmaceutics14020421. PubMed DOI PMC

Urbánek T., Jäger E., Jäger A., Hrubý M. Selectively biodegradable polyesters: Nature-inspired construction materials for future biomedical applications. Polymers. 2019;11:1061. doi: 10.3390/polym11061061. PubMed DOI PMC

Wells C.M., Harris M., Choi L., Murali V.P., Guerra F.D., Jennings J.A. Stimuli-responsive drug release from smart polymers. J. Funct. Biomater. 2019;10:34. doi: 10.3390/jfb10030034. PubMed DOI PMC

Roy S.G., De P. pH responsive polymers with amino acids in the side chains and their potential applications. J. Appl. Polym. Sci. 2014;131:41084. doi: 10.1002/app.41084. DOI

Saravanakumar G., Kim J., Kim W.J. Reactive-Oxygen-Species-Responsive Drug Delivery Systems: Promises and Challenges. Adv. Sci. 2017;4:1600124. doi: 10.1002/advs.201600124. PubMed DOI PMC

Bordat A., Boissenot T., Nicolas J., Tsapis N. Thermoresponsive polymer nanocarriers for biomedical applications. Adv. Drug Deliv. Rev. 2019;138:167–192. doi: 10.1016/j.addr.2018.10.005. PubMed DOI

Hruby M., Štěpánek P., Pánek J., Papadakis C.M. Crosstalk between responsivities to various stimuli in multiresponsive polymers: Change in polymer chain and external environment polarity as the key factor. Colloid Polym. Sci. 2019;297:1383–1401. doi: 10.1007/s00396-019-04576-5. DOI

Liu F., Urban M.W. Recent advances and challenges in designing stimuli-responsive polymers. Prog. Polym. Sci. 2010;35:3–23. doi: 10.1016/j.progpolymsci.2009.10.002. DOI

Zarrintaj P., Jouyandeh M., Ganjali M.R., Hadavand B.S., Mozafari M., Sheiko S.S., Vatankhah-Varnoosfaderani M., Gutiérrez T.J., Saeb M.R. Thermo-sensitive polymers in medicine: A review. Eur. Polym. J. 2019;117:402–423. doi: 10.1016/j.eurpolymj.2019.05.024. DOI

Manouras T., Vamvakaki M. Field responsive materials: Photo-, electro-, magnetic- and ultrasound-sensitive polymers. Polym. Chem. 2017;8:74–96. doi: 10.1039/C6PY01455K. DOI

Sedlacek O., Hoogenboom R. Drug Delivery Systems Based on Poly(2-Oxazoline)s and Poly(2-Oxazine)s. Adv. Ther. 2020;3:1900168. doi: 10.1002/adtp.201900168. DOI

Zhang C., Sanchez R.J.P., Fu C., Clayden-Zabik R., Peng H., Kempe K., Whittaker A.K. Importance of Thermally Induced Aggregation on 19 F Magnetic Resonance Imaging of Perfluoropolyether-Based Comb-Shaped Poly(2-oxazoline)s. Biomacromolecules. 2019;20:365–374. doi: 10.1021/acs.biomac.8b01549. PubMed DOI

Sedlacek O., de la Rosa V.R., Hoogenboom R. Poly(2-oxazoline)-protein conjugates. Eur. Polym. J. 2019;120:109246. doi: 10.1016/j.eurpolymj.2019.109246. DOI

Schmaljohann D. Thermo- and pH-responsive polymers in drug delivery. Adv. Drug Deliv. Rev. 2006;58:1655–1670. doi: 10.1016/j.addr.2006.09.020. PubMed DOI

Ward M.A., Georgiou T.K. Thermoresponsive polymers for biomedical applications. Polymers. 2011;3:1215–1242. doi: 10.3390/polym3031215. DOI

Doberenz F., Zeng K., Willems C., Zhang K., Groth T. Thermoresponsive polymers and their biomedical application in tissue engineering-A review. J. Mater. Chem. B. 2020;8:607–628. doi: 10.1039/C9TB02052G. PubMed DOI

Wan Z., Zhang P., Liu Y., Lv L., Zhou Y. Four-dimensional bioprinting: Current developments and applications in bone tissue engineering. Acta Biomater. 2020;101:26–42. doi: 10.1016/j.actbio.2019.10.038. PubMed DOI

Aseyev V., Tenhu H., Winnik F.M. Non-ionic Thermoresponsive Polymers in Water. Adv. Polym. Sci. 2010;242:29–89. doi: 10.1007/12_2010_57. DOI

Halperin A., Kröger M., Winnik F.M. Poly(N-isopropylacrylamide) Phase Diagrams: Fifty Years of Research. Angew. Chemie-Int. Ed. 2015;54:15342–15367. doi: 10.1002/anie.201506663. PubMed DOI

Rusu M., Wohlrab S., Kuckling D., Möhwald H., Schönhoff M. Coil-to-globule transition of PNIPAM graft copolymers with charged side chains: A1H and2H NMR and spin relaxation study. Macromolecules. 2006;39:7358–7363. doi: 10.1021/ma060831a. DOI

Schild H.G. Poly(N-isopropylacrylamide): Experiment, theory and application. Prog. Polym. Sci. 1992;17:163–249. doi: 10.1016/0079-6700(92)90023-R. DOI

Spěváček J., Konefał R., Čadová E. NMR Study of Thermoresponsive Block Copolymer in Aqueous Solution. Macromol. Chem. Phys. 2016;217:1370–1375. doi: 10.1002/macp.201600025. DOI

Jana S., Uchman M. Poly(2-oxazoline)-based stimulus-responsive (Co)polymers: An overview of their design, solution properties, surface-chemistries and applications. Prog. Polym. Sci. 2020;106:101252. doi: 10.1016/j.progpolymsci.2020.101252. DOI

Hoogenboom R., Schlaad H. Thermoresponsive poly(2-oxazoline)s, polypeptoids, and polypeptides. Polym. Chem. 2017;8:24–40. doi: 10.1039/C6PY01320A. DOI

Roy D., Brooks W.L.A., Sumerlin B.S. New directions in thermoresponsive polymers. Chem. Soc. Rev. 2013;42:7214–7243. doi: 10.1039/c3cs35499g. PubMed DOI

Constantinou A.P., Tall A., Li Q., Georgiou T.K. Liquid–liquid phase separation in aqueous solutions of poly(ethylene glycol) methacrylate homopolymers. J. Polym. Sci. 2022;60:188–198. doi: 10.1002/pol.20210714. DOI

Li Q., Constantinou A.P., Georgiou T.K. A library of thermoresponsive PEG-based methacrylate homopolymers: How do the molar mass and number of ethylene glycol groups affect the cloud point? J. Polym. Sci. 2021;59:230–239. doi: 10.1002/pol.20200720. DOI

Liu G., Li Y., Yang L., Wei Y., Wang X., Wang Z., Tao L. Cytotoxicity study of polyethylene glycol derivatives. RSC Adv. 2017;7:18252–18259. doi: 10.1039/C7RA00861A. DOI

Lutz J.F. Thermo-switchable materials prepared using the OEGMA-platform. Adv. Mater. 2011;23:2237–2243. doi: 10.1002/adma.201100597. DOI

Lutz J.F., Hoth A. Preparation of ideal PEG analogues with a tunable thermosensitivity by controlled radical copolymerization of 2-(2-methoxyethoxy)ethyl methacrylate and oligo(ethylene glycol) methacrylate. Macromolecules. 2006;39:893–896. doi: 10.1021/ma0517042. DOI

Han S., Hagiwara M., Ishizone T. Synthesis of Thermally Sensitive Water-Soluble Polymethacrylates by Living Anionic Polymerizations of Oligo(ethylene glycol) Methyl Ether Methacrylates. Macromolecules. 2003;36:8312–8319. doi: 10.1021/ma0347971. DOI

Szweda D., Szweda R., Dworak A., Trzebicka B. Thermoresponsive poly[oligo(ethylene glycol) methacrylate]s and their bioconjugates-Synthesis and solution behavior. Polimery/Polymers. 2017;62:298–310. doi: 10.14314/polimery.2017.298. DOI

Yao Z.L., Tam K.C. Temperature induced micellization and aggregation of biocompatible poly (oligo(ethylene glycol)methyl ether methacrylate) block copolymer analogs in aqueous solutions. Polymer. 2012;53:3446–3453. doi: 10.1016/j.polymer.2012.06.002. DOI

Zuppardi F., Chiacchio F.R., Sammarco R., Malinconico M., Gomez d’Ayala G., Cerruti P. Fluorinated oligo(ethylene glycol) methacrylate-based copolymers: Tuning of self assembly properties and relationship with rheological behavior. Polymer. 2017;112:169–179. doi: 10.1016/j.polymer.2017.01.080. DOI

Guo Y., Dong X., Ruan W., Shang Y., Liu H. A thermo-sensitive OEGMA-based polymer: Synthesis, characterization and interactions with surfactants in aqueous solutions with and without salt. Colloid Polym. Sci. 2017;295:327–340. doi: 10.1007/s00396-016-4006-4. DOI

Maeda Y., Nakamura T., Ikeda I. Hydration and phase behavior of poly(N-vinylcaprolactam) and poly(N-vinylpyrrolidone) in water. Macromolecules. 2002;35:217–222. doi: 10.1021/ma011034+. DOI

Diab C., Akiyama Y., Kataoka K., Winnik F.M. Microcalorimetric Study of the Temperature-Induced Phase Separation in Aqueous Solutions of Poly(2-isopropyl-2-oxazolines) Macromolecules. 2004;37:2556–2562. doi: 10.1021/ma0358733. DOI

Maeda Y. IR Spectroscopic Study on the Hydration and the Phase Transition of Poly(vinyl methyl ether) in Water. Langmuir. 2001;17:1737–1742. doi: 10.1021/la001346q. DOI

Martinez-Moro M., Jenczyk J., Giussi J.M., Jurga S., Moya S.E. Kinetics of the thermal response of poly(N-isopropylacrylamide co methacrylic acid) hydrogel microparticles under different environmental stimuli: A time-lapse NMR study. J. Colloid Interface Sci. 2020;580:439–448. doi: 10.1016/j.jcis.2020.07.049. PubMed DOI

Kadlubowski S., Matusiak M., Jenczyk J., Olejniczak M.N., Kozanecki M., Okrasa L. Radiation-induced synthesis of thermo-sensitive, gradient hydrogels based on 2-(2-methoxyethoxy)ethyl methacrylate. Radiat. Phys. Chem. 2014;100:23–31. doi: 10.1016/j.radphyschem.2014.03.014. DOI

Spěváček J. NMR investigations of phase transition in aqueous polymer solutions and gels. Curr. Opin. Colloid Interface Sci. 2009;14:184–191. doi: 10.1016/j.cocis.2008.10.003. DOI

Hofmann C.H., Schönhoff M. Dynamics and distribution of aromatic model drugs in the phase transition of thermoreversible poly(N-isopropylacrylamide) in solution. Colloid Polym. Sci. 2012;290:689–698. doi: 10.1007/s00396-011-2577-7. DOI

Kouřilová H., Šťastná J., Hanyková L., Sedláková Z., Spěváček J. 1H NMR study of temperature-induced phase separation in solutions of poly(N-isopropylmethacrylamide-co-acrylamide) copolymers. Eur. Polym. J. 2010;46:1299–1306. doi: 10.1016/j.eurpolymj.2010.03.006. DOI

Zhang C., Peng H., Whittaker A.K. NMR investigation of effect of dissolved salts on the thermoresponsive behavior of oligo(ethylene glycol)-methacrylate-based polymers. J. Polym. Sci. Part A Polym. Chem. 2014;52:2375–2385. doi: 10.1002/pola.27252. DOI

Zhang C., Peng H., Li W., Liu L., Puttick S., Reid J., Bernardi S., Searles D.J., Zhang A., Whittaker A.K. Conformation Transitions of Thermoresponsive Dendronized Polymers across the Lower Critical Solution Temperature. Macromolecules. 2016;49:900–908. doi: 10.1021/acs.macromol.5b02414. DOI

Repasky E.A., Evans S.S., Dewhirst M.W. Temperature Matters ! And Why It Should Matter to Tumor Immunologists. 2013;1:210–217. doi: 10.1158/2326-6066.CIR-13-0118. PubMed DOI PMC

Gomes I.P., Duarte J.A., Maia A.L.C., Rubello D., Townsend D.M., de Barros A.L.B., Leite E.A. Thermosensitive nanosystems associated with hyperthermia for cancer treatment. Pharmaceuticals. 2019;12:171. doi: 10.3390/ph12040171. PubMed DOI PMC

Jäger A., Gromadzki D., Jäger E., Giacomelli F.C., Kozlowska A., Kobera L., Brus J., Íhová B., El Fray M., Ulbrich K., et al. Novel “soft” biodegradable nanoparticles prepared from aliphatic based monomers as a potential drug delivery system. Soft Matter. 2012;8:4343–4354. doi: 10.1039/c2sm07247e. DOI

Themistou E., Battaglia G., Armes S.P. Facile synthesis of thiol-functionalized amphiphilic polylactide- methacrylic diblock copolymers. Polym. Chem. 2014;5:1405–1417. doi: 10.1039/C3PY01446K. DOI

García-Peñas A., Biswas C.S., Liang W., Wang Y., Yang P., Stadler F.J. Effect of Hydrophobic Interactions on Lower Critical Solution Temperature for. Polymers. 2019;11:991. doi: 10.3390/polym11060991. PubMed DOI PMC

Konefał R., Spěváček J., Mužíková G., Laga R. Thermoresponsive behavior of poly(DEGMA)-based copolymers. NMR and dynamic light scattering study of aqueous solutions. Eur. Polym. J. 2020;124:109488. doi: 10.1016/j.eurpolymj.2020.109488. DOI

Zeng F., Tong Z., Feng H.N.m.r. investigation of phase separation in poly(N-isopropyl acrylamide)/water solutions. Polymer. 1997;38:5539–5544. doi: 10.1016/S0032-3861(97)00118-3. DOI

Spěváček J., Konefał R., Dybal J., Čadová E., Kovářová J. Thermoresponsive behavior of block copolymers of PEO and PNIPAm with different architecture in aqueous solutions: A study by NMR, FTIR, DSC and quantum-chemical calculations. Eur. Polym. J. 2017;94:471–483. doi: 10.1016/j.eurpolymj.2017.07.034. DOI

Hanykova L., Radecki M. NMR and thermodynamic study of phase transition in aqueous solutions of thermoresponsive amphiphilic polymer. Chem. Lett. 2012;41:1044–1046. doi: 10.1246/cl.2012.1044. DOI

Šťastná J., Ivaniuzhenkov V., Hanyková L. External Stimuli-Responsive Characteristics of Poly(N,N′-diethylacrylamide) Hydrogels: Effect of Double Network Structure. Gels. 2022;8:586. doi: 10.3390/gels8090586. PubMed DOI PMC

Konefał R., Černoch P., Konefał M., Spěváček J. Temperature behavior of aqueous solutions of poly(2-oxazoline) homopolymer and block copolymers investigated by NMR spectroscopy and dynamic light scattering. Polymers. 2020;12:1879. doi: 10.3390/polym12091879. PubMed DOI PMC

Aubrecht K.B., Grubbs R.B. Synthesis and characterization of thermoresponsive amphiphilic block copolymers incorporating a poly(ethylene oxide-stat-propylene oxide) block. J. Polym. Sci. Part A Polym. Chem. 2005;43:5156–5167. doi: 10.1002/pola.21007. DOI

Riley T., Stolnik S., Heald C.R., Xiong C.D., Garnett M.C., Illum L., Davis S.S., Purkiss S.C., Barlow R.J., Gellert P.R. Physicochemical evaluation of nanoparticles assembled from poly(lactic acid)-poly(ethylene glycol) (PLA-PEG) block copolymers as drug delivery vehicles. Langmuir. 2001;17:3168–3174. doi: 10.1021/la001226i. DOI

Konefał R., Spěváček J., Jäger E., Petrova S. Thermoresponsive behaviour of terpolymers containing poly(ethylene oxide), poly(2-ethyl-2-oxazoline) and poly(ε-caprolactone) blocks in aqueous solutions: An NMR study. Colloid Polym. Sci. 2016;294:1717–1726. doi: 10.1007/s00396-016-3930-7. DOI

Loukotová L., Bogomolova A., Konefal R., Špírková M., Štěpánek P., Hrubý M. Hybrid κ-carrageenan-based polymers showing “schizophrenic” lower and upper critical solution temperatures and potassium responsiveness. Carbohydr. Polym. 2019;210:26–37. doi: 10.1016/j.carbpol.2019.01.050. PubMed DOI

Yamamoto S.-I., Pietrasik J., Matyjaszewski K. The effect of structure on the thermoresponsive nature of well-defined poly(oligo(ethylene oxide) methacrylates) synthesized by ATRP. J. Polym. Sci. Part A Polym. Chem. 2008;46:194–202. doi: 10.1002/pola.22371. DOI

Benoit C., Talitha S., David F., Michel S., Anna S.J., Rachel A.V., Patrice W. Dual thermo- and light-responsive coumarin-based copolymers with programmable cloud points. Polym. Chem. 2017;8:4512–4519. doi: 10.1039/C7PY00914C. DOI

Weber C., Hoogenboom R., Schubert U.S. Temperature responsive bio-compatible polymers based on poly(ethylene oxide) and poly(2-oxazoline)s. Prog. Polym. Sci. 2012;37:686–714. doi: 10.1016/j.progpolymsci.2011.10.002. DOI

Zhang C., Peng H., Puttick S., Reid J., Bernardi S., Searles D.J., Whittaker A.K. Conformation of hydrophobically modified thermoresponsive poly(OEGMA-co-TFEA) across the LCST revealed by NMR and molecular dynamics studies. Macromolecules. 2015;48:3310–3317. doi: 10.1021/acs.macromol.5b00641. DOI

Wang F., Porter M., Konstantopoulos A., Zhang P., Cui H. Preclinical development of drug delivery systems for paclitaxel-based cancer chemotherapy. J. Control. Release. 2017;267:100–118. doi: 10.1016/j.jconrel.2017.09.026. PubMed DOI PMC

Kim S.C., Kim D.W., Shim Y.H., Bang J.S., Oh H.S., Kim S.W., Seo M.H. In vivo evaluation of polymeric micellar paclitaxel formulation: Toxicity and efficacy. J. Control. Release. 2001;72:191–202. doi: 10.1016/S0168-3659(01)00275-9. PubMed DOI

Salvioni L., Rizzuto M.A., Bertolini J.A., Pandolfi L., Colombo M., Prosperi D. Thirty Years of Cancer Nanomedicine: Success, Frustration, and Hope. Cancers. 2019;11:1855. doi: 10.3390/cancers11121855. PubMed DOI PMC

Miguel R.d.A., Hirata A.S., Jimenez P.C., Lopes L.B., Costa-Lotufo L.V. Beyond Formulation: Contributions of Nanotechnology for Translation of Anticancer Natural Products into New Drugs. Pharmaceutics. 2022;14:1722. doi: 10.3390/pharmaceutics14081722. PubMed DOI PMC

Anselmo A.C., Mitragotri S. Nanoparticles in the clinic: An update post COVID-19 vaccines. Bioeng. Transl. Med. 2021;6:e10246. doi: 10.1002/btm2.10246. PubMed DOI PMC

Moore T.L., Rodriguez-Lorenzo L., Hirsch V., Balog S., Urban D., Jud C., Rothen-Rutishauser B., Lattuada M., Petri-Fink A. Nanoparticle colloidal stability in cell culture media and impact on cellular interactions. Chem. Soc. Rev. 2015;44:6287–6305. doi: 10.1039/C4CS00487F. PubMed DOI

de Oliveira F.A., Albuquerque L.J.C., Riske K.A., Jäger E., Giacomelli F.C. Outstanding protein-repellent feature of soft nanoparticles based on poly(N-(2-hydroxypropyl) methacrylamide) outer shells. J. Colloid Interface Sci. 2020;574:260–271. doi: 10.1016/j.jcis.2020.04.048. PubMed DOI

Giacomelli F.C., Stepánek P., Giacomelli C., Schmidt V., Jäger E., Jäger A., Ulbrich K. PH-triggered block copolymer micelles based on a pH-responsive PDPA (poly[2-(diisopropylamino)ethyl methacrylate]) inner core and a PEO (poly(ethylene oxide)) outer shell as a potential tool for the cancer therapy. Soft Matter. 2011;7:9316–9325. doi: 10.1039/c1sm05992k. DOI

Chan J.M., Zhang L., Yuet K.P., Liao G., Rhee J.W., Langer R., Farokhzad O.C. PLGA-lecithin-PEG core-shell nanoparticles for controlled drug delivery. Biomaterials. 2009;30:1627–1634. doi: 10.1016/j.biomaterials.2008.12.013. PubMed DOI

Jäger E., Venturini C.G., Poletto F.S., Colomé L.M., Pohlmann J.P.U., Bernardi A., Battastini A.M.O., Guterres S.S., Pohlman A.R. Sustained release from lipid-core nanocapsules by varying the core viscosity and the particle surface area. J. Biomed. Nanotechnol. 2009;5:130–140. doi: 10.1166/jbn.2009.1004. PubMed DOI

Petrova S., Venturini C.G., Jäger A., Jäger E., Černoch P., Kereïche S., Kováčik L., Raška I., Štěpánek P. Novel thermo-responsive double-hydrophilic and hydrophobic MPEO-b-PEtOx-b-PCL triblock terpolymers: Synthesis, characterization and self-assembly studies. Polymer. 2015;59:215–225. doi: 10.1016/j.polymer.2015.01.009. DOI

Petrova S., Venturini C.G., Jäger A., Jäger E., Hrubý M., Pavlova E., Štěpánek P. Supramolecular self-assembly of novel thermo-responsive double-hydrophilic and hydrophobic Y-shaped [MPEO-b-PEtOx-b-(PCL)2] terpolymers. RSC Adv. 2015;5:62844–62854. doi: 10.1039/C5RA08298F. DOI

Sánchez-Moreno P., de Vicente J., Nardecchia S., Marchal J.A., Boulaiz H. Thermo-sensitive nanomaterials: Recent advance in synthesis and biomedical applications. Nanomaterials. 2018;8:935. doi: 10.3390/nano8110935. PubMed DOI PMC

Maeda H., Nakamura H., Fang J. The EPR effect for macromolecular drug delivery to solid tumors: Improvement of tumor uptake, lowering of systemic toxicity, and distinct tumor imaging in vivo. Adv. Drug Deliv. Rev. 2013;65:71–79. doi: 10.1016/j.addr.2012.10.002. PubMed DOI

Microfluidic Controlled Self-Assembly of Polylactide (PLA)-Based Linear and Graft Copolymers into Nanoparticles with Diverse Morphologies

Effect of polymer concentration on the morphology of the PHPMAA-g-PLA graft copolymer nanoparticles produced by microfluidics nanoprecipitation