|M.Sc Student||Avraham Liraz|
|Subject||Renewable-Resource-Based Emulsion-Templated Porous|
|Department||Department of Materials Science and Engineering||Supervisor||Professor Michael Silverstein|
|Full Thesis text|
PolyHIPEs are highly porous, emulsion-templated polymer monoliths typically synthesized via free radical polymerization within high internal phase emulsions (HIPEs) with more than 74 vol % internal phase. The advantages of polyHIPEs include high porosities, low densities, and the ability to absorb relatively large amounts of liquids. Recent work has demonstrated that poly(urethane urea) (PUU) polyHIPEs can be synthesized through step-growth polymerization (SGP) within water-in-oil HIPEs. It should be possible to generate PUU polyHIPEs through interfacial SGP within oil-in-water (O/W) HIPEs. Moreover, it should be possible to incorporate renewable resource polymers (RRPs), such as polysaccharides (PSacs), into these polyHIPEs by adding them to the external aqueous phase. Such RRP-containing porous polyHIPEs may be of interest for tissue engineering (TE) applications.
The objectives of this research were to synthesize RRP-containing PUU polyHIPEs, characterize their structures and properties, and evaluate their potential for TE applications. The RRP-containing polyHIPEs were synthesized through interfacial SGP within O/W HIPEs containing either a polysaccharide (chitosan, pectin, dextran, or alginate) or a polyphenol (tannic acid (TA)) in the external phase and hexamethylene diisocyanate (HDI) in the internal phase. The RRP is expected either to react with the HDI or to form a coating on the polyHIPE surface. The porous structures and the mechanical properties were characterized and the potential for TE was evaluated through cell growth.
The HDI content, the effectiveness of the polysaccharide as a HIPE stabilizer, and the type of catalyst all affected the porous morphology and properties. Increasing the HDI content and increasing the stability of the emulsion increased the tendency to form capsule-like structures. Chitosan was the most effective stabilizer among the PSacs and chitosan-containing polyHIPEs exhibited open-cell structures. Dextran was the least effective stabilizer and dextran-containing polyHIPEs exhibited the greatest tendency to form closed-cell structures. The densities of the open-cell polyHIPEs were low compared to those of the close-cell structures. The mechanical behavior was more strongly influenced by the morphology than by the HDI content. The open-cell polyHIPEs exhibited stress-strain behaviors of typical polyHIPEs with relatively low stresses at 70 % strain, s70. The closed-cell polyHIPEs exhibited stress-strain behaviors typical of closed-cell foams containing a gas and relatively high s70. The catalyst type affected the HIPE stability, morphology, and cell growth. Changing the catalyst from dibutyltin dilaurate to N,N,N’,N’-tetramethylethylenediamine seemed to reduce the HIPE stability, but significantly enhanced the cell growth.
Since TA reacted with typical surfactants, TA-containing HIPEs could only be stabilized using silane-modified silica NPs and forming Pickering HIPEs or by adding alginate. Unexpectedly, the TA-based-polyHIPE from a Pickering HIPE exhibited the best potential for TE applications. Moreover, truly closed-cell “green materials” with potential for organic liquid encapsulation for “release under stress/strain” applications, were synthesized within HIPEs containing TA and Alg.
Novel polyHIPEs were produced using an innovative synthesis methodology. For the first time, RRP-containing polyHIPEs were successfully synthesized within O/W HIPEs through interfacial step-growth polymerization. A breakthrough in the field of encapsulation was achieved through the successful synthesis of monoliths containing large amounts of encapsulated organic solvents.