Double-layered wound dressing based on electrospun antimicrobial Polymer

Whiting, Nicole (2017-03)

Thesis (MSc)--Stellenbosch University, 2017.


ENGLISH ABSTRACT: The design and production of novel wound dressings that address resistance of microorganisms to antimicrobial agents, has attracted considerable attention. The ability to produce polymers with specific characteristics for specific applications offers a wide variety of options for application in the biomedical field, especially polymers that exhibit antimicrobial behaviour. This thesis is thus committed to the design, synthesis and characterisation of a bi-layered wound dressing, as well as antimicrobial evaluation of the final product. The bi-layered wound dressing consists of a component that maintains a favourable moist wound environment and a second component that addresses microbial infection. For the component that maintains the favourable moist wound environment two hydrogels will be created and electrospun. For this study the hydrogels were chosen to be sodium alginate, a hydrogel already in use for wound dressings, as well as a hydrogel from poly(styrene-alt-maleic anhydride) (SMA). For the antimicrobial component, quaternary ammonium salts were synthesised, as these are known to have antimicrobial properties. SMA is a biocompatible and commercially available copolymer that can easily undergo chemical modification through the highly reactive maleic anhydride residues and therefore is an attractive polymer for the production of hydrogels and antimicrobial polymers. SMA was synthesised by conventional free radical chemistry, followed by modification to yield a hydrogel as well as modification of SMA to yield two quaternary ammonium salts, exhibiting antimicrobial activity. SMA was electrospun and treated with a heat-activated crosslinking agent, namely diethylene glycol, to yield a nanofibrous hydrogel. A second nanofibrous hydrogel was also created from a natural polymer, namely sodium alginate. SMA was also treated with 3-(N,N-dimethylamino)propyl-1-amine (DMAPA), a compound with both a primary and tertiary amine, to yield poly(styrene maleimide) (SMI). SMI was then treated with two alkyl halides (1-bromooctane and 1-bromododecane) to yield quaternary ammonium compounds (qSMI) that shows antimicrobial activity. The quarternised SMI is then also electrospun to yield an antimicrobial nanofibrous layer and heat treated to render the fibres insoluble in water and organic solvents. The bi-layered wound dressing is produced by electrospinning one layer on top of the other in the case of the SMA hydrogel, followed by heat treatment to render the fibres insoluble. In the case of the alginate hydrogel, qSMI is electrospun and heat treated, followed by electrospinning of alginate on top of the qSMI layer. The individual electrospun fibre mats as well as the bi-layered system are subjected to antimicrobial evaluation by means of confocal fluorescence microscopy as well as zone inhibition on agar plates. The organisms used for the antimicrobial evaluation were Staphylococcus aureus, a Gram-positive bacterium, and Pseudomonas aeruginosa, a Gram-negative bacterium. Confocal imaging and zone inhibition revealed that qSMI containing the C12 aliphatic side chain showed a greater antimicrobial activity towards S. aureus as compared to C8. In the case of P. aeruginosa it was not clear which of the C8 or C12 containing qSMI fibres showed greater antimicrobial activity, however confocal imaging and zone inhibition revealed that both showed antimicrobial activity towards P. aeruginosa.

AFRIKAANSE OPSOMMING: Die ontwerp en vervaardiging van oorspronklike wondbedekkings wat die weerstand van mikro-organismes tot antimikrobiese middele aanspreek geniet aansienlike navorsingsaandag. Die vermoë om polimere met spesifieke eienskappe vir spesifieke toepassings te vervaardig bied `n wye verskeidenheid opsies vir aanwending in die biomediese veld, veral vir polimere wat antimikrobiese eienskappe het. Hierdie tesis is gerig op die ontwerp, sintese en karakterisering van `n dubbellaag wondbedekking en die ondersoek van die antimikrobiese eienskappe van die eindproduk. Die dubbellaag wondbeddekking bestaan uit `n komponent wat `n gunstige vogtige wondomgewing handhaaf en `n tweede komponent wat mikrobiese infeksie aanspreek. Vir hierdie studie is twee jel matrikse gekies om die gunstige vogtige wondomgewing te handhaaf, naamlik natrium alginaat, `n jel matriks wat reeds as wondbedekking gebruik word, en poli(stireen-alt-malaïene anhidried) (SMA) as die tweede jel matriks. SMA is `n biologies-versoenbare kommersieël beskikbare kopolimeer wat maklik chemiese modifikasie ondergaan deur sy hoogs reaktiewe maleïene anhidried groepe en is dus `n aantreklike polimeer vir die vervaardiging van jel matrikse en antimikrobiese polimere. SMA is deur konvensionele vrye radikaal chemie gesintetiseer, gevolg deur wysiging om `n jel matriks te vervaardig, sowel as wysiging van SMA om `n kwaternêre ammonium sout wat antimikrobiese aktiwiteit toon, te vervaardig. SMA vesels is voorberei en behandel met `n hitte geaktiveerde bindingsagent, naamlik di-etileenglikol, om `n nano-veselagtige jel matriks te vorm. `n Tweede nano-veselagtige jel matriks is uit `n natuurlike polimeer, naamlik natrium alginaat, vervaardig. SMA is ook met 3-(N,N-dimetielamino)propiel-1-amien (DMAPA), `n molekule met beide `n primêre en tersiêre amien, behandel om poli(stireen maleïmied) (SMI) te vervaardig. SMI is gevolglik met twee alkielhaliede (1-bromo-oktaan en 1-bromododekaan) behandel om kwaternêre ammonium molekules (qSMI) wat antimikrobiese aktiwiteit toon, te vervaardig. Vesels is dan ook uit die qSMI vervaardig om `n nano-veselagtige laag te maak wat dan met hitte behandel is om die vesels onoplosbaar te maak in water en ander organiese oplosmiddels. Die dubbellaag wondbedekking word vervaardig deur een vesellaag op die ander te spin in die geval van die SMA jel matriks, gevolg deur hitte behandeling om die vesels onoplosbaar te maak. In die geval van die natrium alginaat jel matriks is die qSMI laag eerste vervaardig, met hitte behandel, gevolg deur vesel vervaardiging van die alginaat bo-op die qSMI-laag. Die onderskeie veselagtige matte en die dubbellaag sisteem is dan aan antimikrobiese evaluering blootgestel deur middel van konfokale fluoressensie mikroskopie, sowel as sone inhibisie op agar plate. Die organismes wat ondersoek is, is Staphylococcus aureus, `n Gram-positiewe bakterium, en Pseudomonas aeruginosa, `n Gram-negatiewe bakterium. Konfokale besigtiging en sone inhibisie het aangedui dat qSMI met die C12 alifatiese syketting `n groter antimikrobiese effek op S. aureus het in vergelyking met die C8 syketting. Vir P. aeruginosa was dit nie duidelik watter van die C8 of C12 syketting qSMI vesels beter antimikrobiese aktiwiteit getoon word nie, maar konfokale besigtiging en sone inhibisie het wel getoon dat beide antimikrobiese aktiwiteit teen P. aeruginosa besit.

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