In this thesis two types of silica hollow core microstructured fibres - the Negative Curvature Fibre and the Photonic Bandgap Fibre - are presented as a novel solution for the flexible delivery of Er:YAG laser radiation. The Negative Curvature Fibre and Photonic Bandgap Fibre had attenuations of 0.06 dB/m and 1.1 dB/m at 2.94 μm wavelength, respectively. This is an important wavelength regime for medical applications, specifically surgery, due to the existence of a strong absorption peak for water around 3 μm. The guidance of high energy pulses of the order of 195 mJ and 14.4 mJ respectively is demonstrated. These energies are sufficient to ablate soft and hard biological tissue. As verification, porcine bone was ablated in air and submerged in water to simulate practical application of a surgical device. The presented fibres are compared to alternative state-of-the-art solid and hollow core fibres, in respect of the fabrication, attenuation, pulse energy delivery capability, bend sensitivity and the output beam profile. The fabrication and characterisation of a novel sapphire endtip is also presented, which seals the hollow cores of the fibres from contamination and therefore increases the usability significantly. The endtip was shown to be mechanically robust, provide a hermetic seal and able to survive practical tissue ablation in air and water. These encapsulated fibres provide a new fully flexible delivery system for high energy Er:YAG laser radiation and hence will open up the possibility of new minimally invasive surgical procedures.