To determine distal lung pathology and physiology, custom miniaturised optical fibres are being developed to enable clinicians to enter, image and sense in the distal gas-exchanging regions (alveoli) of the human lung.
The multifunctional bundle will be comprised of three different fibres, one each for imaging, sensing and fluid delivery. We will design and fabricate the three fibres and package them together in one biocompatible tube to form a single, rugged multi-fibre entity, that also allows for accurate inter-fibre positioning and alignment. We are currently using prototypes of this technology to gather advanced sensing measurements in ex vivo lungs.
- To enter and deliver: The delivery fibre is a simple capillary with an inner diameter of 250 µm, which will controllably inject a fluid containing Smartprobes deep into the distal lung, and possibly even extract samples of alveolar fluid for later analysis outside the body.
- To image: The fibre must have sufficient resolution and a multi-wavelength capability. Our prototype high-resolution imaging fibre includes over 50,000 closely-spaced cores, each guiding a single image pixel. Our prototype has allowed us to develop the intricate fabrication techniques needed to make a fibre suitable for use in human patients.
- To sense: Our sensing fibre offers the unique ability to combine different reporter molecules for individual cores. These reporter molecules are excited with a pump laser, and will give signals that inform the user about the environment around them. However, a key issue with optical sensing is an unwanted background signal generated by the fibre itself that obscures the important information from the reporter molecules, To overcome this limitation, separate cores held parallel within one fibre can deliver the pump laser input and collect the return. This will greatly improve signal-to-noise ratio, and enable chemical and biological targets in the lung to be sensed to the required accuracy.
Each of these requirements necessitates careful design and synthesis. In order to enter the distal lung without causing damage, the entire bundle of fibres must be less than 1.4mm in diameter which requires advanced packaging techniques for the distal end. To do this, we have used the unique fabrication capabilities of ‘ultrafast laser inscription’ to develop precision ‘end-caps’ that accommodate each fibre.
The fibre bundle can also feature components that provide enhanced functionality, such as waveguides for suppression of the fibre-optic background, machined areas for probe deposition, or lenses for advanced distal optics.