Antifungal Activity of Polyhexamethyleneguanidine Derivatives Introduced into Biodegradable Polymers

For the past few years, intensive research has been carried out in the field of environmentally friendly biodegradable and biocompatible polymers such as polyesters, polyanhydrides, poly(ester amide)s, and biodegradable polyurethanes [ 1 ]. Polycaprolactone, polyglycolide, polylactide and polybutylene adipate-co-terephalate find applications in various fields, for example, food packaging [ 2 , 3 , 4 ], compost bags, medical sutures, nanoscale or microscale drug delivery vehicles, and temporary scaffolds for tissue regeneration [ 5 , 6 , 7 ]. A serious threat to these polymers is the ability to form biofilms. For a few years, the polymer has been modified by introducing different biocidal substances. Introducing antimicrobial substances into polymers by covalent linkages is possible using different methods. According to Jao et al. [ 8 ] the antibacterial polymers can be grafted on biodegradable polymers, as shown for grafting of chitosan on polybutyleneadipate-co-terephthalate. Research is being conducted on a number of biocidal substances that potentially can be introduced into polymers. For example, direct contact of N -halamine acts as a biocidal on E. coli and Staphylococcus aureus [ 9 ]. Polyhexamethyleneguanidine (PHMG) is a biocidal, cationic polymer based guanidine salt, synthesized from hexamethylenediamine and guanidine HCl [ 10 ]. This polymer is stable over a wide range of pH 1–10, non-flammable, and has a high thermal resistance. PHMG is able to eliminate bacteria and some viruses, fungi and unicellular algae. The mechanism of action is that PHMG destabilises the osmotic equilibrium and destructs the cytoplasmic membrane in bacteria or fungi [ 11 ]. It was also reported a cooperative binding between guanidine derivatives and DNA, and inhibition the activity of enzyme systems, indicating that antibacterial effect might be also related to other interaction [ 12 , 13 ]. PHMG and its derivatives are becoming increasingly popular due to its broad range of antibacterial activity and relatively low toxicity. Currently guanidine derivatives with biocidal activity are mainly used as disinfectant in human eye infections and wound care, as water treatmentsand in swimming pools, the disinfection of various solid surfaces, and the impregnation of fabrics [ 14 , 15 ]. PHMG has been proposed too as a safe and highly effective fungicide and disinfectant in fruits challenged with mould [ 11 , 16 ]. PHMG derivatives insoluble in water are used as resin and paint coatings or as additives to plastics such as polycarbonate and polyamide [ 17 ]. Research into the introduction of PHMG and its derivatives into polymeric materials such as polycaprolactone, polylactide or polyamide has led to the development of the packaging industry. Polyamide 12 film (PA 12) modified polyhexamethylene guanidine dodecylbenzenesulfonate (PHMG-DBS) almost completely inhibited the growth of moulds [ 18 ]. Yeasts, moulds and mycotoxins are a serious threat because they are, for example, a cause of many food poisonings [ 19 ]. The introduction of biocidal substances into packaging materials could protect the food against fungal infections. The fungicidal activity of PHMG is shown by Feng et al. [ 20 ]. However, it is not known whether PHMG after incorporation into the polymers also has a biocidal effect. So far, studies have been carried out on the bactericidal properties of PHMG derivatives introduced into polymers. Hence, the purpose of our study was to investigate whether PHMG derivatives introduced in biodegradable polymers have fungicidal properties and the effect of the derivatives on extracellular hydrolytic enzymes.