Use this URL to cite or link to this record in EThOS:
Title: The development and characterisation of biocompatible emulsion templated foams for additive manufacturing
Author: Sherborne, Colin
ISNI:       0000 0004 5922 8333
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2015
Availability of Full Text:
Access from EThOS:
Access from Institution:
A High internal phase emulsion (HIPE), contains a high volume ratio between two immiscible liquids which form an emulsion comprising of a droplet phase, and a continuous one. The water volume ratio has to exceed 74% to be classified as a HIPE. When the continuous phase is a polymerizable monomer, a porous polymeric material can be created by emulsion templating of the HIPE to create a highly porous foam called a PolyHIPE. This thesis will address the growing need to manufacture complex 3D tissue engineering scaffolds from synthetic biocompatible polymeric materials. The PolyHIPEs inherent porous nature is an attractive material for this application. The highly porous interconnected network of the PolyHIPE architecture can provide the basic cellular support, porosity and interconnectivity for cell ingrowth and nutrient/waste removal. The ability to tailor these features by altering the conditions of the initial emulsion, or adjusting the monomer formulation means that the scaffold can be tuned to control the cell material interaction and mimic the native physiological environment of the cells. The development of a Poly e-caprolactone (PCL) based PolyHIPE opens up another material that can be used for this application, and may be more suitable for future cell based studies. In this thesis I demonstrate the incorporation of both additive, and subtractive manufacturing techniques to the PolyHIPE material. This is used to introduce a secondary, macroscopic level of porosity on top of the inherent micro-porosity from the templating of water droplets. Projection and scanning stereolithography polymerises the HIPE in a layer-by-layer fashion to produce bespoke porous 3D scaffolds. Laser etching is used to introduce a macro porosity within a PolyHIPE sheet, this is a technique that can be adapted to a range of biomaterials for a high throughput fabrication process. The underlying methodology, characterisation and logistics of using these advanced fabrication techniques to customize the PolyHIPE into novel bespoke porous structures is demonstrated. This method of processing the HIPE has not previously been reported on in the literature to the best of my knowledge, therefore the characterisation presents the groundwork for this structuring methodology for the PolyHIPE. The first section of this thesis I introduce the stereolithographic fabrication of the PolyHIPE material. This is a hybrid technique where the micro porosity is dictated by the initial emulsion conditions, such as water volume ratio, and the macro structure is dictated by the selective polymerisation of the HIPE. Adjusting the laser intensity has an effect on both the size and structural stability of the polymerised structures, and a fabrication time for basic structures takes only seconds. Proof of concept designs are initially fabricated to demonstrate this approach and characterise the processing parameters. The PolyHIPEs internal morphology is unaffected by the stereolithography fabrication process over its bulk polymerisation counterpart. The second section focuses on the identification, characterisation and elimination of a surface skin effect that forms around the outside of the polymerised PolyHIPE surfaces. The generation of the surface skin was experimentally shown to occur during the washing stages as the outer surface collapses upon itself. The underlying mechanism behind this comes from the gradual scattering and decrease in polymerizable energy of the Ultraviolet Light (UV) as it is absorbed. Separate polymerised regions that overlap formed connecting bridges from this UV scattering effect and the addition of a light absorber is shown to significantly increase both the surface porosity and increase the achievable resolution of the stereolithography approach. The mechanical properties of the PolyHIPE are tailored by altering either the monomer blend or water volume ratio. This demonstrated the tunability of the PolyHIPEs so that it can potentially be tailored for specific cellular applications. Finally the last chapter focuses on the methodical development of a PCL based PolyHIPE. This is the first example of a photocurable PCL PolyHIPE in the literature to my knowledge. This section is presented as a systematic methodology to identify the key emulsion stability parameters for a stable PCL based emulsion though experimental means, and tailor them to increase emulsion stability. A blend between the PCL and thiolene was initially used as a stepping stone for the pure PCL PolyHIPE. The emulsion stability was found to be highly sensitive to a solvent blend, as well as a particular surfactant. The protocol for a stable PCL based HIPE was eventually established for the now routine development of a PCL PolyHIPE.
Supervisor: Frederik, Claeyssens ; Sheila, MacNeil Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available