Polymer Gel Based Bioadhesives

Abstract

There is a need for materials to replace or augment the use of sutures and staples in surgical procedures. Currently available commercial surgical adhesives provide either high bond strength with biological toxicity or polymer and protein-based products that are biologically acceptable but have much reduced bond strength. It is desirable to provide novel biocompatible and biodegradable surgical adhesives/sealants capable of high strength with minimal immune or inflammatory response. In this project, the synthesis of different branched PEO-derivatives having aldehyde and amine end groups using efficient synthetic routes is reported. These synthesised gel-precursors were then characterised using different analytical methods such as microanalysis, GPC (Gel Permeation Chromatography), FTIR (Fourier Transform Infra-Red), 1H, 13C NMR (Nuclear Magnetic Resonance), ESI-MS (Electron Spray Ionisation) and MALDI-TOF (Matrix Assisted Laser Desorption Ionisation – Time of Flight) spectroscopy. These PEO-derivatives were further utilised for preparing covalently crosslinked gels by Schiff-base chemistry. The viscoelastic, mechanical, adhesive and cytotoxic evaluation of the prepared gels were also carried out. Branched PEOs having different molecular weights were employed, for the evaluation of the effect of molecular weights and chain length on different gel properties. This gave us a better understanding of the gel properties such as gel time, crosslink density, elasticity and toughness of these gels. Since these properties are crucial to determine the stability of the gel when used for surgical purpose, the main aim was the selection of a suitable gel candidate that would have enough strength to hold two surfaces together without being too hard/stiff or too brittle.

Chapter 1 provides a general introduction and a review of literature for the currently available adhesives and sealants in use. The chapter also presents the objective of the thesis. Chapter 2 deals with the end group functionalization of low molecular weight PEOs and their characterisation. Schiff-base gels were prepared utilising these PEO-derivatives and their setting times, swelling behaviour, and viscoelastic properties were evaluated. Chapter 3 provides the synthesis and characterisation of the bottle-brush PEO with aldehyde end groups. The synthetic route involves anionic polymerisation of ethylene oxide (EO) with a protected initiator to yield a mono-ol with a protected aldehyde group. This mono-ol is converted to a macromonomer by reacting with 4-vinylbenzyl chloride. Polymerisation of the macromonomer yields a PEO bottle-brush polymer with protected aldehyde ends, which is deprotected in the next step to produce the desired bottle-brush PEO with aldehyde end groups. Unfortunately, these PEO-aldehydes could not be utilised for making gels due to self-crosslinking of the aldehyde groups. Attempts were also made towards branched PEO with amine end groups employing similar synthetic strategy but were unsuccessful. Chapter 4 discusses the end group derivatization of high molecular weight gel precursors and their characterisation. Schiff-base gels were prepared utilising these high molecular weight PEO aldehyde and amine derivatives. The physical, viscoelastic and adhesive properties were studied using various methods described earlier. Cytotoxic evaluation of the prepared gels was also carried out. Chapter 5 presents a brief introduction to the various instruments and methods of characterisation such as FTIR, 1H and 13C NMR spectroscopy for the end group and number average molecular weight (Mn NMR) determination, GPC analysis for Mn GPC and ESI-MS as well as MALDI-TOF for absolute molecular weight determination. It also describes different methods used for the characterisation and evaluation of the gel properties such as swelling, viscoelastic properties, adhesive lap-shear strength and cytotoxicity studies. Chapter 6 includes the final results and conclusions along with the future directions of the project.