EPSRC Portfolio Partnership in Complex Fluids and Complex Flows

The Production of 3-D Porous Polymeric Structures with Bespoke Morphologies for Applications from Tissue Engineering to Data Storage

Production of Highly Regular Porous Structures over a Large Surface Area

The development of a reliable method of fabricating large areas of uniformly micropatterned porous structures is a challenging problem. In addressing this issue, we have studied a process that eschews the conventional templating approach to micropatterning, relying instead on the formation of ordered arrays of moisture droplets called 'breath figures'.

Breath figures form when a cold solid or a liquid surface is brought in contact with moist air. Moisture condensation forms growing water droplets, which give rise to distinct patterns on the surface. These water droplets are then incorporated within the solution leading to the formation of porous solid polymer films. Under appropriate conditions, highly regular, 2-D monolayers or 3-D hexagonally-packed multilayered scaffolds result from this process. An interesting feature of this process is that the non-coalescing water droplets assemble into an ordered, hexagonally-packed array by a process of self-organisation. The benefits of self-organisation are that it can provide the highly regular pore size and ordered spatial geometry required for specialised applications.

SEM image (left) and an AFM topographical image (right) depicting regularly spaced pores produced by a breath figure template.

The porous structures were prepared inside a flow chamber by casting a volatile polymer solution onto a surface exposed to an air stream of regulated humidity, this typically being 55% RH at 21°C.

A Kodak Ektapro 4540mx high speed digital video camera system was attached to an Olympus microscope providing remote observation of the formation

mechanisms.

Schematic Representation of the Equipment Used to Make the Scaffolds

6

13

3 4 5

8

1 Flowmeter 9 Glass Slide

2 Humidifier 10 Objective Lens

3 Buffer Flask 11 Supplementary Lens

4 Thermometer 12 Digital Video Camera

5 Hygrometer 13 Camera Processor

6 Valve 14 Computer

7 Flow Chamber 15 Monitor

8 Positioning Stage

79

10

11

12

14

15

vent

2

1

Formation of a ‘breath figure’

Multilayer morphology of the scaffolds

AFM image of a smart scaffold, a section of the upper surface has been removed to reveal the sub - surface structure

SEM image of a multilayer.

Srinivasarao et al (2001).

Left: mobile layer of water droplets packed near the surface of the polymer solution. Highlighted - close packing of the droplets was disrupted by ‘defects’.

Right: AFM scan showing the distinctive defect pattern preserved within the solid polymer after evaporation.

Future work will further develop the use of bio polymer - solvent systems and the incorporation of simple embedded functional networks. These studies will further develop recent work which has successfully superimposed ordered structure around encapsulated micro wires and capillaries. The incorporation of wires has potential applications in

the controlled development of scaffold morphlogy ab initio and in facilitating the functionality of the polymer construct.

SEM images of a 5m thermocouple wire incorporated into the polymer scaffold

The Incorporation of Actuators and Sensors Within the Scaffold with no Disruption of the Surrounding Scaffold Morphology

Application of Bio-mimetic Surfaces

Right: AFM force measurement showing the interaction of a biomimetic surface (yeast cell probe) with a planar surface in a relevant aqueous environment

Development of Bio-mimetic Surfaces

Scaffold formed on a 40 m silica sphere

Fluorescence Image of Fibroblasts on Smart Scaffold

Development of Scaffolds for Tissue Engineering

Production of Connected or Isolated Chambers Within the Scaffold

Sub-micron Structures Within the Final Polymer Scaffold

Nanoscale structures within the final polymer scaffold also exhibit regular and controllable structure

Colloid probe (silica)

PRIFYSGOL CYMRU ABERTAWE

UNIVERSITY OF WALES SWANSEA