A REVIEW ON RECENT ADVANCES IN HYDROGELS AS DRUG DELIVERY SYSTEM

AYA M. GHANEM; SONDOS AHMAD ASHOUR; RUAA M. HUSSIEN

doi:10.22159/ijap.2025v17i1.51987

Authors

AYA M. GHANEM Department of Applied Science, Faculty of Aqaba college, Al-Balqa Applied University, Salt-19117, Jordan https://orcid.org/0000-0002-4246-7640
SONDOS AHMAD ASHOUR Department of Pharmacy, University of Medical Sciences and Technology, Khartoum-Sudan https://orcid.org/0000-0002-6039-9709
RUAA M. HUSSIEN Department of Clinical Pharmacy, University of Jordan, Amman-Jordan https://orcid.org/0009-0006-6792-8614

DOI:

https://doi.org/10.22159/ijap.2025v17i1.51987

Keywords:

Hydrogels, Networks, Hydrophilic, Drug targeting, Drug delivery, Crosslinking

Abstract

Hydrogels are hydrophilic three-dimensional polymeric networks which has the capability to absorb water or biological fluids. These polymeric network is formulated through chemical crosslinking or physical crosslinking mechanisms. Several polymers of synthetic and natural origin can be used to form hydrogels. Mechanical properties, swelling and biological properties are about the most significant hydrogels properties that can affect their morphology and structure. Hydrogels are promising biomaterials due to their significant properties as hydrophilicity, biodegradability, biocompatibility and non-toxicity. These characteristics make hydrogels appropriate for medical and pharmaceutical application. This review discusses the types of hydrogels, their properties, mechanism of preparation and applications of hydrogels as drug delivery system.

Downloads

Download data is not yet available.

References

Ahmed EM. Hydrogel: preparation characterization and applications: a review. J Adv Res. 2015 Mar;6(2):105-21. doi: 10.1016/j.jare.2013.07.006, PMID 25750745.

Chamkouri H. A review of hydrogels their properties and applications in medicine. AJBSR. 2021 Feb 3;11(6):485-93. doi: 10.34297/AJBSR.2021.11.001682.

Sanchez Cid P, Jimenez Rosado M, Romero A, Perez Puyana V. Novel trends in hydrogel development for biomedical applications: a review. Polymers. 2022 Jul 26;14(15):3023. doi: 10.3390/polym14153023, PMID 35893984.

Giordano S, Gallo E, Diaferia C, Rosa E, Carrese B, Borbone N. Multicomponent peptide based hydrogels containing chemical functional groups as innovative platforms for biotechnological applications. Gels. 2023 Nov 15;9(11):903. doi: 10.3390/gels9110903, PMID 37998993.

Karoyo AH, Wilson LD. A review on the design and hydration properties of natural polymer based hydrogels. Materials (Basel). 2021 Feb 26;14(5):1095. doi: 10.3390/ma14051095, PMID 33652859.

Cao H, Duan L, Zhang Y, Cao J, Zhang K. Current hydrogel advances in physicochemical and biological response driven biomedical application diversity. Signal Transduct Target Ther. 2021 Dec 16;6(1):426. doi: 10.1038/s41392-021-00830-x, PMID 34916490.

HO TC, Chang CC, Chan HP, Chung TW, Shu CW, Chuang KP. Hydrogels: properties and applications in biomedicine. Molecules. 2022 May 2;27(9):2902. doi: 10.3390/molecules27092902.

Cai MH, Chen XY, FU LQ, DU WL, Yang X, Mou XZ. Design and development of hybrid hydrogels for biomedical applications: recent trends in anticancer drug delivery and tissue engineering. Front Bioeng Biotechnol. 2021 Feb 17;9:630943. doi: 10.3389/fbioe.2021.630943, PMID 33681168.

Catoira MC, Fusaro L, DI Francesco D, Ramella M, Boccafoschi F. Overview of natural hydrogels for regenerative medicine applications. J Mater Sci Mater Med. 2019 Oct 10;30(10):115. doi: 10.1007/s10856-019-6318-7, PMID 31599365.

LU L, Yuan S, Wang J, Shen Y, Deng S, Xie L. The formation mechanism of hydrogels. Curr Stem Cell Res Ther. 2018;13(7):490-6. doi: 10.2174/1574888X12666170612102706, PMID 28606044.

Peng W, LI D, Dai K, Wang Y, Song P, LI H. Recent progress of collagen chitosan alginate and other hydrogels in skin repair and wound dressing applications. Int J Biol Macromol. 2022 May 31;208:400-8. doi: 10.1016/j.ijbiomac.2022.03.002, PMID 35248609.

Chen M, Wang Y, Zhang J, Peng Y, LI S, Han D. Stimuli responsive DNA based hydrogels for biosensing applications. J Nanobiotechnology. 2022 Jan 21;20(1):40. doi: 10.1186/s12951-022-01242-x, PMID 35062945.

Jiang Y, Wang Y, LI Q, YU C, Chu W. Natural polymer based stimuli responsive hydrogels. Curr Med Chem. 2020;27(16):2631-57. doi: 10.2174/0929867326666191122144916, PMID 31755377.

Wang C, Zhang J. Recent advances in stimuli responsive DNA based hydrogels. ACS Appl Bio Mater. 2022 May 16;5(5):1934-53. doi: 10.1021/acsabm.1c01197, PMID 35138079.

Das S, Kumar V, Tiwari R, Singh L, Singh S. Recent advances in hydrogels for biomedical applications. Asian J Pharm Clin Res. 2018 Nov;11(11):62-8. doi: 10.22159/ajpcr.2018.v11i11.27921.

Amsden B. Solute diffusion within hydrogels. Mechanisms and models. Macromolecules. 1998 Nov 1;31(23):8382-95. doi: 10.1021/ma980765f.

Ghasemiyeh P, Mohammadi Samani S. Hydrogels as drug delivery systems; pros and cons. Trends Pharmacol Sci. 2019 Mar 1;5(1):7-24.

Gerecht S, Townsend SA, Pressler H, Zhu H, Nijst CL, Bruggeman JP. A porous photocurable elastomer for cell encapsulation and culture. Biomaterials. 2007;28(32):4826-35. doi: 10.1016/j.biomaterials.2007.07.039, PMID 17692371.

Ganji F, Vasheghani FS, Vasheghani FE. Theoretical description of hydrogel swelling: a review. Iranian Polymer Journal. 2010;19(5):375-98.

Yin L, Fei L, Cui F, Tang C, Yin C. Superporous hydrogels containing poly(acrylic acid-co-acrylamide)/O-carboxymethyl chitosan interpenetrating polymer networks. Biomaterials. 2007 Feb 1;28(6):1258-66. doi: 10.1016/j.biomaterials.2006.11.008, PMID 17118443.

Lima CS, Balogh TS, Varca JP, Varca GH, Lugao AB, A Camacho Cruz L. An updated review of macro micro and nanostructured hydrogels for biomedical and pharmaceutical applications. Pharmaceutics. 2020 Oct;12(10):970. doi: 10.3390/pharmaceutics12100970, PMID 33076231.

Hafezi Moghaddam R, Dadfarnia S, Shabani AM, Moghaddam ZH, Tavakol M. Electron beam irradiation synthesis of porous and non porous pectin based hydrogels for a tetracycline drug delivery system. Mater Sci Eng C Mater Biol Appl. 2019 Sep 1;102:391-404. doi: 10.1016/j.msec.2019.04.071, PMID 31147010.

Garg S, Garg A. Hydrogel: classification properties preparation and technical features. Asian J Biomater Res. 2016 Sep 4;2:163-70.

Holback H, Yeo Y, Park K. 1-Hydrogel swelling behavior and its biomedical applications. Rimmer S, editor. Woodhead Publishing Series in Biomaterials Biomedical Hydrogels; 2011. p. 3-24.

Sornkamnerd S, Okajima MK, Kaneko T, Kaneko T. Tough and porous hydrogels prepared by simple lyophilization of LC gels. ACS Omega. 2017 Aug 31;2(8):5304-14. doi: 10.1021/acsomega.7b00602, PMID 31457799.

Luo R, WU J, Dinh ND, Chen CH. Gradient porous elastic hydrogels with shape-memory property and anisotropic responses for programmable locomotion. Adv Funct Materials. 2015;25(47):7272-9. doi: 10.1002/adfm.201503434.

DE France KJ, XU F, Hoare T. Structured macroporous hydrogels: progress challenges and opportunities. Adv Healthc Mater. 2018;7(1):1700927. doi: 10.1002/adhm.201700927, PMID 29195022.

Am R, Prabhu SS, JD JR, Sundaram SK, RM, TK V. Hydrogel formulation from calotropis gigantea plant extract against foot ulcer causing bacteria in diabetes. Asian J Pharm Clin Res. 2021 Nov 7;14(11):96-9.

Gemeinhart RA, Park H, Park K. Pore structure of superporous hydrogels. Polym Adv Technol. 2000;11(8-12):617-25. doi: 10.1002/1099-1581(200008/12)11:8/12<617::AID-PAT12>3.0.CO;2-L.

Thakur S, Thakur VK, Arotiba OA. History classification properties and application of hydrogels: an overview. In: Hydrogels recent advances. Thakur VK, Thakur MK, editors. Gels Horizons: From Science to Smart Materials: 2018. p. 29-50. doi: 10.1007/978-981-10-6077-9_2.

Zhan Y, FU W, Xing Y, MA X, Chen C. Advances in versatile anti-swelling polymer hydrogels. Mater Sci Eng C Mater Biol Appl. 2021 Aug 1;127:112208. doi: 10.1016/j.msec.2021.112208, PMID 34225860.

Peppas NA, Bures P, Leobandung W, Ichikawa H. Hydrogels in pharmaceutical formulations. Eur J Pharm Biopharm. 2000 Jul 3;50(1):27-46. doi: 10.1016/s0939-6411(00)00090-4, PMID 10840191.

Lin CC, Metters AT. Hydrogels in controlled release formulations: network design and mathematical modeling. Adv Drug Deliv Rev. 2006 Nov 30;58(12-13):1379-408. doi: 10.1016/j.addr.2006.09.004, PMID 17081649.

Kim D, Park K. Swelling and mechanical properties of superporous hydrogels of poly (acrylamide-co-acrylic acid)/polyethylenimine interpenetrating polymer networks. Polymer. 2004 Jan 1;45(1):189-96. doi: 10.1016/j.polymer.2003.10.047.

Gemeinhart RA, Chen J, Park H, Park K. pH-sensitivity of fast responsive superporous hydrogels. J Biomater Sci Polym Ed. 2000 Jan 1;11(12):1371-80. doi: 10.1163/156856200744390, PMID 11261878.

Huglin MB, Liu Y, Velada J. Thermoreversible swelling behaviour of hydrogels based on N-isopropylacrylamide with acidic comonomers. Polymer. 1997 Nov 1;38(23):5785-91. doi: 10.1016/S0032-3861(97)00135-3.

Brannon Peppas L, Peppas NA. Equilibrium swelling behavior of pH-sensitive hydrogels. Chem Eng Sci. 1991 Jan 1;46(3):715-22. doi: 10.1016/0009-2509(91)80177-Z.

Kasai RD, Radhika D, Archana S, Shanavaz H, Koutavarapu R, Lee DY. A review on hydrogels classification and recent developments in biomedical applications. Int J Polym Mater Polym Biomater. 2023;72(13):1059-69. doi: 10.1080/00914037.2022.2075872.

Younis MK, Tareq AZ, Kamal IM. Optimization of swelling drug loading and release from natural polymer hydrogels. IOP Conf Ser Mater Sci Eng. 2018 Dec;454(1):012017. doi: 10.1088/1757-899X/454/1/012017.

Ovadia M, Silverstein MS. High porosity responsive hydrogel copolymers from emulsion templating. Polym Int. 2016;65(3):280-9. doi: 10.1002/pi.5052.

Huang T, XU HG, Jiao K, Zhu LP, Brown H, Wang H. A novel hydrogel with high mechanical strength: a macromolecular microsphere composite hydrogel. Adv Mater. 2007 May 15;19(12):1622-6. doi: 10.1002/adma.200602533.

Gong JP. Why are double network hydrogels so tough? Soft Matter. 2010 Jun 8;6(12):2583-90. doi: 10.1039/b924290b.

Haque MA, Kurokawa T, Kamita G, Gong JP. Lamellar bilayers as reversible sacrificial bonds to toughen hydrogel: hysteresis self-recovery fatigue resistance and crack blunting. Macromolecules. 2011 Nov 22;44(22):8916-24. doi: 10.1021/ma201653t.

HU J, Hiwatashi K, Kurokawa T, Liang SM, WU ZL, Gong JP. Microgel reinforced hydrogel films with high mechanical strength and their visible mesoscale fracture structure. Macromolecules. 2011 Oct 11;44(19):7775-81. doi: 10.1021/ma2016248.

Suekama TC, HU J, Kurokawa T, Gong JP, Gehrke SH. Double network strategy improves fracture properties of chondroitin sulfate networks. ACS Macro Lett. 2013 Feb 19;2(2):137-40. doi: 10.1021/mz3006318, PMID 35581775.

Chen Q, Chen H, Zhu L, Zheng J. Fundamentals of double network hydrogels. J Mater Chem B. 2015 Mar 31;3(18):3654-76. doi: 10.1039/c5tb00123d, PMID 32262840.

Chen Y, Dong K, Liu Z, XU F. Double network hydrogel with high mechanical strength: performance progress and future perspective. Sci China Technol Sci. 2012 Aug 1;55(8):2241-54. doi: 10.1007/s11431-012-4857-y.

Argenta DF, Dos Santos TC, Campos AM, Caon T. Chapter 3-hydrogel nanocomposite systems: physic chemical characterization and application for drug delivery systems. Mohapatra SS, Ranjan S, Dasgupta N, Mishra RK, Thomas S, editors. Elsevier: Nanocarriers for drug delivery; 2019. p. 81-131. doi:10.1016/B978-0-12-814033-8.00003-5.

Haraguchi K, Takehisa T. Nanocomposite hydrogels: a unique organic–inorganic network structure with extraordinary mechanical optical and swelling/de-swelling properties. Adv Mater. 2002 Aug 16;14(16). doi: 10.1002/1521-4095(20020816)14:16<1120::AID-ADMA1120>3.0.CO;2-9.

XU K, Wang J, Xiang S, Chen Q, Yue Y, SU X. Polyampholytes superabsorbent nanocomposites with excellent gel strength. Compos Sci Technol. 2007 Dec 1;67(15-16):3480-6. doi: 10.1016/j.compscitech.2007.02.009.

Das D, Kar T, Das PK. Gel nanocomposites: materials with promising applications. Soft Matter. 2012 Feb 2;8(8):2348-65. doi: 10.1039/C1SM06639K.

Kabiri K, Omidian H, Hashemi SA, Zohuriaan Mehr MJ. Synthesis of fast-swelling superabsorbent hydrogels: effect of crosslinker type and concentration on porosity and absorption rate. Eur Polym J. 2003 Jul 1;39(7):1341-8. doi: 10.1016/S0014-3057(02)00391-9.

Chavda H, Patel C. Effect of crosslinker concentration on characteristics of superporous hydrogel. Int J Pharm Investig. 2011;1(1):17-21. doi: 10.4103/2230-973X.76724, PMID 23071915.

Kabiri K, Zohuriaan Mehr MJ. Porous superabsorbent hydrogel composites: synthesis morphology and swelling rate. Macro Materials & Eng. 2004;289(7):653-61. doi: 10.1002/mame.200400010.

Annabi N, Mithieux SM, Boughton EA, Ruys AJ, Weiss AS, Dehghani F. Synthesis of highly porous crosslinked elastin hydrogels and their interaction with fibroblasts in vitro. Biomaterials. 2009 Sep 1;30(27):4550-7. doi: 10.1016/j.biomaterials.2009.05.014, PMID 19500832.

Pandey M, Mohd Amin MC, Ahmad N, Abeer MM. Rapid synthesis of superabsorbent smart swelling bacterial cellulose/acrylamide based hydrogels for drug delivery. Int J Polym Sci. 2013 Aug 28;2013:1-10. doi: 10.1155/2013/905471.

Gupta NV, Shivakumar HG. Preparation and characterization of superporous hydrogels as pH-sensitive drug delivery system for pantoprazole sodium. Curr Drug Deliv. 2009 Oct 1;6(5):505-10. doi: 10.2174/156720109789941722, PMID 19863492.

Haque MD A, Kurokawa T, Gong JP. Super tough double network hydrogels and their application as biomaterials. Polymer. 2012 Apr 17;53(9):1805-22. doi: 10.1016/j.polymer.2012.03.013.

LI X, Wang H, LI D, Long S, Zhang G, WU Z. Dual ionically cross linked double-network hydrogels with high strength toughness swelling resistance and improved 3D printing process ability. ACS Appl Mater Interfaces. 2018 Sep 19;10(37):31198-207. doi: 10.1021/acsami.8b13038, PMID 30148345.

Mishra RK, Datt M, Banthia AK. Synthesis and characterization of pectin/PVP hydrogel membranes for drug delivery system. AAPS Pharm Sci Tech. 2008 Jun 1;9(2):395-403. doi: 10.1208/s12249-008-9048-6, PMID 18431673.

Sharma S, Jain P, Tiwari S. Dynamic imine bond based chitosan smart hydrogel with magnified mechanical strength for controlled drug delivery. Int J Biol Macromol. 2020 Oct 1;160:489-95. doi: 10.1016/j.ijbiomac.2020.05.221, PMID 32479933.

Pourjavadi A, Kurdtabar M, Mahdavinia GR, Hosseinzadeh H. Synthesis and super swelling behavior of a novel protein based superabsorbent hydrogel. Polym Bull. 2006 Oct 1;57(6):813-24. doi: 10.1007/s00289-006-0649-5.

Zahra Q, Minhas MU, Khan S, WU PC, Suhail M, Iqbal R. Fabrication of polyethylene glycol hydrogels with enhanced swelling; loading capacity and release kinetics. Polym Bull. 2022 Jul 1;79(7):5389-415. doi: 10.1007/s00289-021-03740-8.

Lazaridou M, Nanaki S, Zamboulis A, Papoulia C, Chrissafis K, Klonos PA. Super absorbent chitosan based hydrogel sponges as carriers for caspofungin antifungal drug. Int J Pharm. 2021 Sep 5;606:120925. doi: 10.1016/j.ijpharm.2021.120925, PMID 34303816.

Cai B, Luo Y, Guo Q, Zhang X, WU Z. A glucose sensitive block glycopolymer hydrogel based on dynamic boronic ester bonds for insulin delivery. Carbohydr Res. 2017 Jun 5;445:32-9. doi: 10.1016/j.carres.2017.04.006, PMID 28395252.

Zhang J, Zhao D, LU K. Mechanisms and influencing factors of peptide hydrogel formation and biomedicine applications of hydrogels. Soft Matter. 2023 Oct 11;19(39):7479-93. doi: 10.1039/d3sm01057k, PMID 37756117.

Parhi R. Cross linked hydrogel for pharmaceutical applications: a review. Adv Pharm Bull. 2017 Dec;7(4):515-30. doi: 10.15171/apb.2017.064, PMID 29399542.

Pragya A, Mutalik S, Younas MW, Pang SK, SO PK, Wang F. Dynamic cross-linking of an alginate acrylamide tough hydrogel system: time resolved in situ mapping of gel self assembly. RSC Adv. 2021 Mar 10;11(18):10710-26. doi: 10.1039/d0ra09210j, PMID 35423570.

Bashir S, Hina M, Iqbal J, Rajpar AH, Mujtaba MA, Alghamdi NA. Fundamental concepts of hydrogels: synthesis properties and their applications. Polymers. 2020 Nov 16;12(11):2702. doi: 10.3390/polym12112702, PMID 33207715.

Berger J, Reist M, Mayer JM, Felt O, Gurny R. Structure and interactions in chitosan hydrogels formed by complexation or aggregation for biomedical applications. Eur J Pharm Biopharm. 2004 Jan;57(1):35-52. doi: 10.1016/s0939-6411(03)00160-7, PMID 14729079.

Xue X, HU Y, Wang S, Chen X, Jiang Y, SU J. Fabrication of physical and chemical crosslinked hydrogels for bone tissue engineering. Bioact Mater. 2022;12:327-39. doi: 10.1016/j.bioactmat.2021.10.029, PMID 35128180.

Naranjo Alcazar R, Bendix S, Groth T, Gallego Ferrer G. Research progress in enzymatically cross linked hydrogels as injectable systems for bioprinting and tissue engineering. Gels. 2023 Mar 15;9(3):230. doi: 10.3390/gels9030230, PMID 36975679.

Badali E, Hosseini M, Mohajer M, Hassanzadeh S, Saghati S, Hilborn J. Enzymatic crosslinked hydrogels for biomedical application. Polym Sci A. 2022 Feb;63:S1-S22.

MA H, Peng Y, Zhang S, Zhang Y, Min P. Effects and progress of photo-crosslinking hydrogels in wound healing improvement. Gels. 2022 Sep 23;8(10):609. doi: 10.3390/gels8100609, PMID 36286110.

Czarnecki S, Rossow T, Seiffert S. Hybrid polymer network hydrogels with tunable mechanical response. Polymers. 2016;8(3):82. doi: 10.3390/polym8030082, PMID 30979176.

XU J, Zhu X, Zhao J, Ling G, Zhang P. Biomedical applications of supramolecular hydrogels with enhanced mechanical properties. Adv Colloid Interface Sci. 2023 Nov;321:103000. doi: 10.1016/j.cis.2023.103000, PMID 37839280.

Palmese LL, Thapa RK, Sullivan MO, Kiick KL. Hybrid hydrogels for biomedical applications. Curr Opin Chem Eng. 2019 Jun;24:143-57. doi: 10.1016/j.coche.2019.02.010, PMID 31844607.

Villalba Rodriguez AM, Martinez Gonzalez S, Sosa Hernandez JE, Parra-Saldivar R, Bilal M, Iqbal HM. Nanoclay/polymer based hydrogels and enzyme-loaded nanostructures for wound healing applications. Gels. 2021 May 14;7(2):59. doi: 10.3390/gels7020059, PMID 34068868.

Zhang Y, Huang Y. Rational design of smart hydrogels for biomedical applications. Front Chem. 2020;8:615665. doi: 10.3389/fchem.2020.615665, PMID 33614595.

Golmohamadi M, Davis TA, Wilkinson KJ. Diffusion and partitioning of cations in an agarose hydrogel. J Phys Chem A. 2012 Jun 28;116(25):6505-10. doi: 10.1021/jp212343g, PMID 22394244.

Lacroce E, Rossi F. Polymer based thermoresponsive hydrogels for controlled drug delivery. Expert Opin Drug Deliv. 2022 Oct;19(10):1203-15. doi: 10.1080/17425247.2022.2078806, PMID 35575265.

Moriya G, Mazumder R, Padhi S, Mishra R. Gastrorententive hydrogels responsive to external stimuli for novel drug delivery. Int J App Pharm. 2024 Jul 7;16(4):1-14. doi: 10.22159/ijap.2024v16i4.51051.

Kakkar V, Narula P. Role of molecularly imprinted hydrogels in drug delivery a current perspective. Int J Pharm. 2022 Sep 25;625:121883. doi: 10.1016/j.ijpharm.2022.121883, PMID 35870667.

Ghanem AM. A review on recent advances in transdermal drug delivery systems of tamsulosin. Int J App Pharm. 2024 Mar;16(2):28-33. doi: 10.22159/ijap.2024v16i2.49950.

Khan F, Atif M, Haseen M, Kamal S, Khan MS, Shahid S. Synthesis classification and properties of hydrogels: their applications in drug delivery and agriculture. J Mater Chem B. 2022 Jan 5;10(2):170-203. doi: 10.1039/d1tb01345a, PMID 34889937.

Dimatteo R, Darling NJ, Segura T. In situ forming injectable hydrogels for drug delivery and wound repair. Adv Drug Deliv Rev. 2018 Mar 1;127:167-84. doi: 10.1016/j.addr.2018.03.007, PMID 29567395.

MO F, Jiang K, Zhao D, Wang Y, Song J, Tan W. DNA hydrogel based gene editing and drug delivery systems. Adv Drug Deliv Rev. 2021 Jan;168:79-98. doi: 10.1016/j.addr.2020.07.018, PMID 32712197.

Andriano K. Controlled release of highly water soluble drugs from the SQZ gel oral drug delivery system. Drug Deliv Technol. 2010 Jan;10(1):42.

https://www.rxlist.htm#description.Com/metrogel-vaginal-drug. [Last accessed on 20 Feb 2024].

https://www.accessdata.fda.gov/drugsatfda_docs/nda/2009/125277s000PharR_P1.pdf. [Last accessed on 20 Aug 2024].

https://www.drugs.com/pro/maxidex.html. [Last accessed on 23 Apr 2023].

https://www.medicines.org.uk/emc/product/135/smpc#gref. [Last accessed on 15 Mar 2024].

https://www.supprelinla.com. [Last accessed on 15 Mar 2024].