A study of core-shell and self-crosslinked doubly cross-linked gels

Abstract

This thesis presents a study of a pH-responsive, redox-responsive, and reversible doubly cross-linked gel (DX) and their associated performance of DX gels also be introduced. The potential application of these gels in tissue engineering is also discussed. Firstly, the properties of core-shell nanogel particles are discussed in Chapter 3. The six different types of core-shell nanoparticles were prepared using emulsion polymerisation. The properties are determined by changing the monomers and crosslinkers in the core-shell structure. The copolymers of the core include poly (ethyl acrylate) (PEA), poly (methacrylic acid) (PMMA), poly (methyl methacrylate) (PMMA) and poly (ethyl glycol dimethacrylate) (PEGDMA), and the monomers of the shell are PEA, PMAA and poly (bis(2-methacryloyl)oxyethyl disulfide) (PBMAC). The nanogel properties are determined by changing the monomers and crosslinker in the core-shell structure. All six nanoparticles are spherical. A change in pH affects the state of the nanoparticles. Taking PEA-MAA-BMAC as an example, the dynamic light scattering data and UV-visible spectrum showed that the particle size of its nanoparticles would increase with the increase of pH and the optical density (OD) values would decrease with the increase of pH. Disulfide bonds are introduced into the shell by BMAC. The disulfide bonds are reduced to thiol groups by reducing agents tris(2-carboxyethyl)phosphine hydrochloride solution (TCEP). The nanogels with a disulfide bond introduced in the shell are pH-responsive and redox-responsive. A new type of doubly cross-linked gel with a core-shell structure is presented in Chapter 4. These doubly cross-linked gels are constructed from the core-shell nanoparticles described in Chapter 3. Here, the CS-NGs means that the core-shell nanogel systems. The CS-NGs nanoparticles form a physical gel after alkali treatment. The mechanical properties of these SXCS-NGs (singly crosslinked) gels are also altered depending on their ϕ_(p )values (polymer volume fractions). The freeze-dried SXCS-NGs gels show a porous structure. Through dynamic disulfide-thiol transition, a double cross-linked gel (DXCS-NGs) can be formed using a reducing agent and oxidising agent (H2O2). The crosslinker and the monomer are shown to influence the stiffness of the gels. The mechanical properties of DXCS-NGs are also change in different pH environments. In addition to this, DXCS-NGs gels can achieve a fluid-to-gel-to-fluid state transition. This transformation is reversible. At the same time, the change of state of the gel also affects its mechanical properties. Taking these data together, the DXCS-NGs gels are pH-responsive, redox-responsive, reversible, and injectable. In Chapter 5, the self-crosslinked nanogels and the self-crosslinked hydrogels are presented. These self-crosslinked nanogels were also prepared using emulsion polymerisation. Three different types of self-crosslinked gel systems were designed depending on the synthesis temperature. A common feature of all three types of gels is the use of the initiator ammonium persulfate (APS) in combination with the catalyst N,N,N’,N’- tetramethylenediamine (TEMED) to adjust self-crosslinking. In addition, a control group was also synthesised. Unlike the other three groups, the group did not incorporate TEMED. The four types of gels were studied and compared. The monomer used for all four nanogels were PEA, PMAA and PBMAC. This is the same as the core-shell structure nanogel systems reported above. Their pH-responsive properties nanoparticle dispersions were investigated. In addition, the mechanical properties of the self-crosslinked doubly cross-linked gels were also explored. Furthermore, these systems showed high swelling rates and high elasticity compared to the earlier DXCS-NGs systems. Consequently, the nanogel design affect the gel mechanical properties.

Date of Award	31 Dec 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Brian Saunders (Supervisor) & Lee Fielding (Supervisor)