{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,30]],"date-time":"2026-07-30T02:37:41Z","timestamp":1785379061498,"version":"3.55.0"},"reference-count":48,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2026,2,1]],"date-time":"2026-02-01T00:00:00Z","timestamp":1769904000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Polymers"],"abstract":"<jats:p>Poly(hexamethylene biguanide) (PHMB) is a polycationic antimicrobial polymer exhibiting broad-spectrum activity against bacteria, fungi, and viruses, and is widely used in medical settings for infection prevention and control. However, the relationship between chemical structure and antimicrobial activity remains unclear. In this study, we synthesised and characterised a series of polymeric biguanides with systematically varied alkyl chain lengths to examine the effects of structural variation on physicochemical properties and antimicrobial activity. H NMR spectroscopy and FTIR confirmed successful polymerisation. Solubility measurements revealed a progressive decrease in aqueous solubility with increasing alkyl chain length, consistent with increased hydrophobicity. Dynamic light scattering indicated reversible folding and unfolding of polymer chains in aqueous solution, with stabilisation at higher concentrations. Diffusion-ordered spectroscopy was used to calculate hydrodynamic diameters and polydispersity indices. Antimicrobial assays against Staphylococcus aureus and Pseudomonas aeruginosa showed that polymers containing heptamethylene and octamethylene chains exhibited the highest antibacterial activity, whereas tetramethylene- and pentamethylene-containing polymers showed greater fungicidal activity against Candida albicans. Highly hydrophobic polymers showed increased aggregation, resulting in reduced antimicrobial efficacy. Overall, these results indicate that both charge density and alkyl chain length are key determinants of antimicrobial activity. This polymeric biguanide series provides a platform for further investigation of structure\u2013activity relationships and mechanisms of action against pathogenic microorganisms and their biofilms.<\/jats:p>","DOI":"10.3390\/polym18030390","type":"journal-article","created":{"date-parts":[[2026,2,2]],"date-time":"2026-02-02T12:49:44Z","timestamp":1770036584000},"page":"390","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":1,"title":["Alkyl Chain Length Governs Structure, Conformation and Antimicrobial Activity in Poly(alkylene biguanide)"],"prefix":"10.3390","volume":"18","author":[{"ORCID":"https:\/\/orcid.org\/0000-0001-6254-8432","authenticated-orcid":false,"given":"Enas","family":"Al-Ani","sequence":"first","affiliation":[{"name":"Division of Pharmacy and Optometry, University of Manchester, Manchester M13 9PL, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-3604-9861","authenticated-orcid":false,"given":"Khalid","family":"Doudin","sequence":"additional","affiliation":[{"name":"Department of Mathematical and Physical Sciences, The University of Sheffield, Sheffield S10 2TN, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5255-5425","authenticated-orcid":false,"given":"Andrew J.","family":"McBain","sequence":"additional","affiliation":[{"name":"Division of Pharmacy and Optometry, University of Manchester, Manchester M13 9PL, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zeeshan","family":"Ahmad","sequence":"additional","affiliation":[{"name":"Division of Pharmacy and Optometry, University of Manchester, Manchester M13 9PL, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3831-9151","authenticated-orcid":false,"given":"Sally","family":"Freeman","sequence":"additional","affiliation":[{"name":"Division of Pharmacy and Optometry, University of Manchester, Manchester M13 9PL, UK"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1968","published-online":{"date-parts":[[2026,2,1]]},"reference":[{"key":"ref_1","unstructured":"WHO (2025, October 29). Ten Threats to Global Health in 2019. Available online: https:\/\/www.who.int\/news-room\/spotlight\/ten-threats-to-global-health-in-2019."},{"key":"ref_2","unstructured":"WHO (2025, October 29). Antimicrobial Resistance. Available online: https:\/\/www.who.int\/news-room\/fact-sheets\/detail\/antimicrobial-resistance."},{"key":"ref_3","doi-asserted-by":"crossref","unstructured":"Paleczny, J., Junka, A., Bro\u017cyna, M., Dydak, K., Oleksy-Wawrzyniak, M., Ciecholewska-Ju\u015bko, D., Dziedzic, E., and Bartoszewicz, M. (2021). The high impact of Staphylococcus aureus biofilm culture medium on in vitro outcomes of antimicrobial activity of wound antiseptics and antibiotic. Pathogens, 10.","DOI":"10.3390\/pathogens10111385"},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"63","DOI":"10.1089\/wound.2016.0701","article-title":"The role of topical antiseptic agents within antimicrobial stewardship strategies for prevention and treatment of surgical site and chronic open wound infection","volume":"6","author":"Roberts","year":"2017","journal-title":"Adv. Wound Care"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"113726","DOI":"10.1016\/j.ejmech.2021.113726","article-title":"Biguanides drugs: Past success stories and promising future for drug discovery","volume":"224","author":"Grytsai","year":"2021","journal-title":"Eur. J. Med. Chem."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"63","DOI":"10.1080\/15685551.2021.1900025","article-title":"Synthesis of antibacterial polyether biguanide curing agent and its cured antibacterial epoxy resin","volume":"24","author":"Li","year":"2021","journal-title":"Des. Monomers Polym."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"26S","DOI":"10.1177\/1091581820958683","article-title":"Safety assessment of polyaminopropyl biguanide (polyhexamethylene biguanide hydrochloride) as used in cosmetics","volume":"39","author":"Johnson","year":"2020","journal-title":"Int. J. Toxicol."},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"3","DOI":"10.1684\/ejd.2013.2198","article-title":"A comparison of the irritant and allergenic properties of antiseptics","volume":"24","author":"Lachapelle","year":"2014","journal-title":"Eur. J. Dermatol."},{"key":"ref_9","unstructured":"Rose, F.L., and Swain, G. (1953). Polymeric Diguanides. (US Patent 2,643,232 A)."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"3973","DOI":"10.1016\/S0032-3861(96)00969-X","article-title":"Polybiguanides: Synthesis and characterization of polybiguanides containing hexamethylene groups","volume":"38","author":"East","year":"1997","journal-title":"Polymer"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"4928","DOI":"10.1002\/app.24915","article-title":"Characterization of the biocide polyhexamethylene biguanide by matrix-assisted laser desorption ionization time-of-flight mass spectrometry","volume":"102","author":"Hassan","year":"2006","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"655","DOI":"10.1177\/11206721221124684","article-title":"Polyhexamethylene biguanide hydrochloride (PHMB)-properties and application of an antiseptic agent. A narrative review","volume":"33","author":"Niro","year":"2023","journal-title":"Eur. J. Ophthalmol."},{"key":"ref_13","unstructured":"Gray, D., Barrett, S., Battacharyya, M., Butcher, M., Enoch, S., Fumerola, S., Stephen-Haynes, J., Edwards-Jones, V., Leaper, D., and Strohal, R. (2010). PHMB and Its Potential Contribution to Wound Management, Wounds UK."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"12","DOI":"10.31436\/imjm.v23i01.2249","article-title":"A systematic review on multiple purpose solution of contact lens ingredients: Benefits and risks","volume":"23","author":"Ibrahim","year":"2024","journal-title":"IIUM Med. J. Malays."},{"key":"ref_15","unstructured":"European Pharmaceutical Review (2025, September 29). European Commission Licenses First Treatment for Acanthamoeba Keratitis. Available online: https:\/\/www.europeanpharmaceuticalreview.com\/news\/232657\/european-commission-licenses-first-treatment-for-acanthamoeba-keratitis\/."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"62","DOI":"10.1016\/j.ejpb.2020.11.001","article-title":"Cellular gene delivery via poly (hexamethylene biguanide)\/pDNA self-assembled nanoparticles","volume":"158","author":"Chivu","year":"2021","journal-title":"Eur. J. Pharm. Biopharm."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"128707","DOI":"10.1016\/j.cej.2021.128707","article-title":"Covalently construction of poly (hexamethylene biguanide) as high-efficiency antibacterial coating for silicone rubber","volume":"412","author":"Peng","year":"2021","journal-title":"Chem. Eng. J."},{"key":"ref_18","doi-asserted-by":"crossref","unstructured":"Zwicker, P., Geist, N., G\u00f6bler, E., Kulke, M., Schmidt, T., Hornschuh, M., Lembke, U., Prinz, C., Delcea, M., and Kramer, A. (2021). Improved adsorption of the antimicrobial agent poly (hexamethylene) biguanide on Ti-Al-V alloys by NaOH treatment and Impact of mass coverage and contamination on cytocompatibility. Coatings, 11.","DOI":"10.3390\/coatings11091118"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"277","DOI":"10.1016\/j.ophtha.2023.09.031","article-title":"The orphan drug for acanthamoeba keratitis (ODAK) trial: PHMB 0.08%(polihexanide) and placebo versus PHMB 0.02% and propamidine 0.1%","volume":"131","author":"Dart","year":"2024","journal-title":"Ophthalmology"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"S18","DOI":"10.12968\/bjon.2020.29.18.S18","article-title":"Maintenance of indwelling urinary catheters with a novel polyhexanide-based solution: User experience","volume":"29","author":"Andersen","year":"2020","journal-title":"Br. J. Nurs."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"4487","DOI":"10.1021\/acs.jpcb.0c02609","article-title":"Insights into the polyhexamethylene biguanide (PHMB) mechanism of action on bacterial membrane and DNA: A molecular dynamics study","volume":"124","author":"Carbone","year":"2020","journal-title":"J. Phys. Chem. B"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"703","DOI":"10.1111\/j.1365-2672.2005.02664.x","article-title":"Cationic antiseptics: Diversity of action under a common epithet","volume":"99","author":"Gilbert","year":"2005","journal-title":"J. Appl. Microbiol."},{"key":"ref_23","doi-asserted-by":"crossref","unstructured":"Duprat, F., Ploix, J.-L., Aubry, J.-M., and Gaudin, T. (2023). Fast and accurate prediction of refractive index of organic liquids with graph machines. Molecules, 28.","DOI":"10.3390\/molecules28196805"},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"126286","DOI":"10.1016\/j.molliq.2024.126286","article-title":"Thermodynamic insight of DMSO-DMA and DMSO-DMF binary mixtures across varying temperatures","volume":"415","author":"Singh","year":"2024","journal-title":"J. Mol. Liq."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"85","DOI":"10.1021\/je60048a006","article-title":"Density and viscosity of deuterium oxide solutions from 5\u201370. deg","volume":"16","author":"Millero","year":"1971","journal-title":"J. Chem. Eng. Data"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"169","DOI":"10.1016\/j.jmr.2011.06.020","article-title":"Polydispersity index of polymers revealed by DOSY NMR","volume":"212","author":"Tanty","year":"2011","journal-title":"J. Magn. Reson."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"7849","DOI":"10.1021\/acs.analchem.2c05531","article-title":"Polymer molecular weights via DOSY NMR","volume":"95","author":"Ruzicka","year":"2023","journal-title":"Anal. Chem."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"5","DOI":"10.1093\/jac\/48.suppl_1.5","article-title":"Determination of minimum inhibitory concentrations","volume":"48","author":"Andrews","year":"2001","journal-title":"J. Antimicrob. Chemother."},{"key":"ref_29","doi-asserted-by":"crossref","unstructured":"Swebocki, T., Barras, A., and Kocot, A.M. (2023). Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) Assays Using Broth Microdilution Method, IEMN NanoBioInterfacest.","DOI":"10.17504\/protocols.io.5qpvo3x6dv4o\/v1"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"13899","DOI":"10.1039\/D4SC03420A","article-title":"Conformational modulation and polymerization-induced folding of proteomimetic peptide brush polymers","volume":"15","author":"Oktawiec","year":"2024","journal-title":"Chem. Sci."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"928","DOI":"10.3390\/polym3020928","article-title":"Physical and chemical characterization of poly(hexamethylene biguanide) hydrochloride","volume":"3","author":"Netto","year":"2011","journal-title":"Polymers"},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"1401","DOI":"10.1016\/j.chemosphere.2008.04.074","article-title":"Log D: Lipophilicity for ionisable compounds","volume":"72","author":"Kah","year":"2008","journal-title":"Chemosphere"},{"key":"ref_33","first-page":"e202403573","article-title":"Effect of Hydrophobic Acrylic Monomers with Different Alkyl Side Chain Lengths on Reducing the Glistening of Hydrophobic Acrylic Intraocular Lens Materials","volume":"9","author":"Kim","year":"2024","journal-title":"Chem. Sel."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"23796","DOI":"10.1039\/D1CP02802B","article-title":"The impact of the length of alkyl chain on the behavior of benzyl alcohol homologues\u2013the interplay between dispersive and hydrogen bond interactions","volume":"23","author":"Soszka","year":"2021","journal-title":"Phys. Chem. Chem. Phys."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"845","DOI":"10.1016\/0040-4020(72)84044-4","article-title":"Spectrophotometric (UV) investigation on biguanide and substituted biguanides","volume":"28","author":"Nandi","year":"1972","journal-title":"Tetrahedron"},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"110","DOI":"10.1016\/j.molliq.2012.02.011","article-title":"Calculation of spectral shifts in UV\u2013visible region and photo stability of thermotropic liquid crystals: Solvent and alkyl chain length effects","volume":"169","author":"Praveen","year":"2012","journal-title":"J. Mol. Liq."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"57","DOI":"10.1016\/j.saa.2017.07.061","article-title":"Chain length effects on the vibrational structure and molecular interactions in the liquid normal alkyl alcohols","volume":"189","author":"Kiefer","year":"2018","journal-title":"Spectrochim. Acta Part A Mol. Biomol. Spectrosc."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"333","DOI":"10.4028\/www.scientific.net\/SSP.268.333","article-title":"EIS and FTIR Characterisation of NaI-NaN (CN) 2 Solid Electrolyte Prepared by Mechanical Milling","volume":"268","author":"Yusof","year":"2017","journal-title":"Solid State Phenom."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"1329","DOI":"10.1007\/s11095-022-03468-8","article-title":"Direct assessment of oligomerization of chemically modified peptides and proteins in formulations using DLS and DOSY-NMR","volume":"40","author":"Wang","year":"2023","journal-title":"Pharm. Res."},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"3730","DOI":"10.1021\/acs.jpclett.6b01631","article-title":"Unexpected like-charge self-assembly of a Biguanide-based antimicrobial polyelectrolyte","volume":"7","author":"Zaki","year":"2016","journal-title":"J. Phys. Chem. Lett."},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"33","DOI":"10.1038\/pj.2017.72","article-title":"Antimicrobial cationic polymers: From structural design to functional control","volume":"50","author":"Yang","year":"2018","journal-title":"Polym. J."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"733","DOI":"10.1021\/acsmacrolett.3c00182","article-title":"Correlation between Self-Folding Behavior of Amphiphilic Polymers and Their Molecular Flexibility","volume":"12","author":"Nagao","year":"2023","journal-title":"ACS Macro Lett."},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"247","DOI":"10.1021\/ma801929g","article-title":"2H NMR studies of polymer multilayer capsules, films, and complexes","volume":"42","author":"Reven","year":"2009","journal-title":"Macromolecules"},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"111745","DOI":"10.1016\/j.colsurfb.2021.111745","article-title":"Membrane perturbation, altered morphology and killing of Staphylococcus epidermidis upon contact with a cytocompatible peptide-based antibacterial surface","volume":"203","author":"Lekka","year":"2021","journal-title":"Colloids Surf. B Biointerfaces"},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"1279","DOI":"10.1002\/mabi.201200052","article-title":"Poly(ethylene imine)s as antimicrobial agents with selective activity","volume":"12","author":"Gibney","year":"2012","journal-title":"Macromol. Biosci."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"23121","DOI":"10.1038\/srep23121","article-title":"The antimicrobial polymer PHMB enters cells and selectively condenses bacterial chromosomes","volume":"6","author":"Chindera","year":"2016","journal-title":"Sci. Rep."},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"1252","DOI":"10.1093\/jac\/dkv474","article-title":"Bactericidal effects of polyhexamethylene biguanide against intracellular Staphylococcus aureus EMRSA-15 and USA 300","volume":"71","author":"Kamaruzzaman","year":"2016","journal-title":"J. Antimicrob. Chemother."},{"key":"ref_48","doi-asserted-by":"crossref","unstructured":"Karpi\u0144ski, T.M., Korbecka-Paczkowska, M., Stasiewicz, M., Mrozikiewicz, A.E., W\u0142odkowic, D., and Cielecka-Piontek, J. (2025). Activity of Antiseptics Against Pseudomonas aeruginosa and Its Adaptation Potential. Antibiotics, 14.","DOI":"10.3390\/antibiotics14010030"}],"container-title":["Polymers"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/2073-4360\/18\/3\/390\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,2,2]],"date-time":"2026-02-02T12:52:26Z","timestamp":1770036746000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/2073-4360\/18\/3\/390"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,2,1]]},"references-count":48,"journal-issue":{"issue":"3","published-online":{"date-parts":[[2026,2]]}},"alternative-id":["polym18030390"],"URL":"https:\/\/doi.org\/10.3390\/polym18030390","relation":{},"ISSN":["2073-4360"],"issn-type":[{"value":"2073-4360","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,2,1]]}}}