Abstract
Postoperative complications are the main cause of morbidity and mortality following surgery and therefore have a significant impact on healthcare resources. Recently, polymers have gained considerable attention for use in barrier based systems to prevent postoperative adhesions. A new hydrogel, which is based on the interactions of amine groups of succinyl chitosan (SC) and the aldehyde groups of dextran aldehyde (DA), was developed in our laboratory and has shown promising results in endoscopic sinus surgery. The main objective of this thesis is to describe the biological interactions of the CD hydrogel and its ability to act as an aid in endoscopic sinus surgery.
Chitosan was succinylated by succinic anhydride and hydrolysed in strong base at 60°C to obtain the desirable SC with effective cross-linking and solubility. Dextran was oxidised by sodium periodate to prepare DA with 168% oxidation. General properties of the polymeric compounds were characterised by microanalysis and NMR spectroscopy.
The CD hydrogel was studied in two distinct phases. The first stage consisted of examining the antimicrobial activity of CD hydrogel and its components in vitro by broth microdilution procedure against a range of pathogenic nosocomial microorganisms. Minimum inhibitory concentrations (MIC), minimum bactericidal concentrations (MBC) and minimum fungicidal concentrations (MFC) values were determined on various Gram-negative, Gram-positive, and one fungal species that frequently causes postoperative infections. The CD hydrogel and DA alone were found to inhibit and kill all investigated Gram-positive species in lower concentration as compared to Gram-negative bacteria. None of the tested microorganisms were susceptible to SC alone. In addition, time-dependent killing efficacy of DA for two bacterial species was tested.
The antimicrobial results led to an investigation into the mode of action, specificity and effectiveness of the CD hydrogel. Scanning and transmission electron microscopy showed a change in the bacterial membrane after being incubated with CD hydrogel and DA below the MBC. In addition, motility and chemotaxis test results showed that DA at 32,000 mg L⁻¹ concentration had more inhibitory action than the concentration of 16,000 mg L⁻¹ on the bacterial flagella and movement.
The second stage consisted of investigating the biocompatibility of CD hydrogel and its components in vitro, aiming to be used as a surgical barrier on humans in endoscopic sinus surgery. The cytotoxicity of CD hydrogel and its components was evaluated by the xCELLigence system, crystal violet, and light microscopy methods, on human cell lines. SC was revealed to be non-toxic, while DA was the toxic and the active component of the CD hydrogel. The results of Ames testing with S. Typhimurium strains in the presence and absence of S9 fraction indicated that CD hydrogel and DA were non-mutagenic.
To reduce possible problems with regulatory approval regarding the cytotoxity, the DA concentration was reduced to 3% instead of 5% in the early work. In addition, the DA oxidation degree was reduced to 39% instead of 168%.
An in vitro assessment of potential pro-inflammatory nature of CD hydrogel and its components on human cell lines by ELISA was performed. The obtained results in these tests were comparable to the negative control, which indicated that the CD hydrogel and its components did not elicit cell activation and suggested that these materials may not stimulate an inflammatory immune response when implanted in vivo.
The effect of CD hydrogel and its components on the wound healing process was evaluated in vitro using ibidi culture insert on a human nasopharyngeal epithelial cell line. The percentage of wound closure of extra dialysed CD hydrogel was less than the control to prevent scar formation by an over-zealous tissue healing response which can potentially be advantageous after surgery.
Taken together the results of the antimicrobial and biocompatibility studies demonstrated that the CD hydrogel should be considered as a postoperative aid in endoscopic sinus surgery. The development of a surgical hydrogel that is haemostatic, antimicrobial, and prevents adhesions would have immense benefits allowing for faster healing and eliminating the need for additional surgery in order to remove adhesions.