Development of Vascular Inspired Electrospun Hollow Fibre Membranes for use in 3D Tissue Culture

The indispensability of two-dimensional (2D) tissue culture techniques is marred by its insufficient mimicry of cell-cell and cell-extracellular matrix (ECM) interactions. In static three-dimensional (3D) tissue culture scaffolds more than 200 m thick, the short effective range of diffusive mass transfer results in ischemic tissue damage and necrotic regions1-4.

In vivo, vasculature transports nutrients and oxygen to tissues through arteries and removes waste metabolites in veins. In leu of a native vascular network in tissue engineered constructs, hollow fibre membranes (HFMs) have been utilised to facilitate convective mass transport5-7. The rigidity and monolithic surface of existing HFMs, however, disrupts passive mechanical cues while inhibiting multimodal mechanical stimulation.
Electrospinning, a versatile technique enabling the drawing of nano-fibres from polymer solutions or melts, has enabled the development of bioactive materials which mimic the fibrous structure of the ECM8. Through the utilisation of this technique, electrospun vascular scaffolds (EVSs) have been developed to exhaustively mimic the morphology and mechanical properties of native vasculature. The methods used to produce EVSs have, however, limited their length to short sections. Recently electrospinning has also been implemented in the production of long flexible filaments with similar mechanical properties to that of tendon9. The combination of these techniques may thereby facilitate the novel production of long sections of vascular mimetic HFMs. These in turn may be used to facilitate nutrient and gas transfer while maintaining physiological mechanical cues10,11.

While trial and error fabrication has predominantly driven EVS development to date, several complications are still associated with their use. Recent developments in vascular growth and regeneration modelling techniques hold promise towards their use to expedite the identification of optimal scaffold characteristics12. Concurrently, in view of the complex interconnected nature of biological systems, mathematical modelling techniques have been used to decipher the underlying mechanisms determining; culture outcomes, optimising culture conditions and improving culture yields of several cell types13-16. By combining lessons learnt from each of these model development techniques it may thereby be possible to develop a novel model to enable the identification of optimal culture conditions within an electrospun HFM bioreactor.

Considering this current state of affairs, my research aims to answer the questions:

1) Can HF membranes be fabricated continuously by electrospinning in a reproducible way to mimic the morphological and mechanical properties of native vasculature and facilitate nutrient exchange to a tertiary scaffold in static and dynamic culture conditions?

2) Can such HFs be used as a substrate for biomedical research, potentially for the production of biomaterials intended for therapeutic application?

To answer these questions, my specific objectives are therefore:

I. Produce novel electrospun HFs which mimic the morphology and mechanical properties of native vasculature through a novel continuous process in a reproducible controllable manner.
II. Characterise the transport properties of the membranes and how they may change under mechanical loading
III. Develop a novel mathematical model to describe the transport across the electrospun HFMs
IV. Develop a static and mechanically dynamic HF bioreactor, geometrically informed from the electrospun HFM transport model
V. Evaluate the use of the electrospun HFs for tissue culture in (a) static and (b) mechanically dynamic HF bioreactor configurations

This project falls within the EPSRC Health Care Technologies research area, specifically towards the development of biomaterials and tissue engineering.