A TUNABLE MORPHING POLYELECTROLYTE SYSTEM FOR SMART OCULAR APPLICATIONS Ansu Sun, Sreepathy Sridhar, Xue Chen, Yifan Li*, and Ben B. Xu* 1 Department of Mechanical and Construction Engineering, Northumbria University, Newcastle upon Tyne, United Kingdom Yifan.li@northumbria.ac.uk Ben.xu@northumbria.ac.uk ABSTRACT For the first time, a focal-length tunable intra-ocular lens (IOL) device has been realized by a standard-shaped, homogeneous “one material” system. Different to existing technologies, this poly(N-isopropylacrylamide) gel (PNIPAM) based polyelectrolyte system doesn’t require any additional materials (e.g. metal electrodes, movable mechanical structures) to achieve a controllable lens shape transformation for the focal-length shifting actuation. The designed morphological deformation mechanism employs ionic-strength responsive mechanical buckling via controlled swelling of PNIPAM in phosphate buffered saline (PBS) with similar concentration to human eye liquid. This unique approach will unlock great potential in a wide range of smart ocular applications. KEYWORDS PNIPAM, PNIPAAm, responsive polymer, intra- ocular lens, focal length, swelling; INTRODUCTION The crystalline lens (CL) is the main functional part for the focusing control mechanism of human eyes, directing the light coming through the cornea towards the retina. Cataract is a common eye disease that affects the human eye via CL opacification. It comprises around half of the world blindness, while the number of patients will continue to increase with the aging population [1-3]. Since the invention of modern cataract surgery with artificial Intra Ocular Lenses (IOLs), it has been developed significantly into an effective way to cure this problem [4, 5]. One desirable property is the switchable focal length, where adaptive vision correction is needed when eye conditions change [6, 7]. While existing multifocal IOL designs provide a benefit for near and intermediate vision for some cases, they do not allow dynamic focus length shifting in a continuous fashion. Technical innovations towards new generation of eye implants are therefore desired in terms of improving patient experiences as well as driving efficiencies in public healthcare expenditure. Meanwhile, latest manufacturing technologies have enabled advanced materials for smart ocular system applications, such as 3D printed artificial cornea [8], customized ocular prosthesis [9], 3D printed iris [10], smart contact lenses with ocular pressure sensing [11,12]. Looking beyond human ocular applications, tunable bio- optical configurations in other advanced devices have been achieved in recent developments, which no longer require complicated mechanical units [13 – 15]. Some of the recently developed smart polymer achieve tunable optical focal length, responding to and controlled by external stimulation such as pH-responsive [16], electric field [17], and ion concentration [18] with mechanical confinement structures or electrical interconnects. However, limited efforts have been found on developing easy-to-implant artificial ocular device with responsive focal shifting, since the above devices may require non-compatible materials (e.g. metal electrodes), liquid/solid interactions and stimuli for actuation are hard to fulfil in in-vivo, as in the human eyes. With these regards, we proposed and demonstrated a new polyelectrolyte system based on PNIPAM (also named PIPAAM or PNIPAAm), to advance the robust optical implant technology with focal shifting. For the first time, tunable morphological deformation has been realized by a homogeneous “one-material” polyelectrolyte system with either freestanding (this abstract’s focus), or edge-confined configurations. Figure 1: (a) Proposed focal length shifting mechanism: mechanical buckling of the dual-curved IOL shape change; (b) Low cost and facile fabrication process of the PNIPAM tunable IOLs The designed morphological deformation mechanism is to be achieved by responsive mechanical buckling, which is a common phenomenon in thin, soft structures that may yield rapid out-of-plane deformation (Fig. 1a). Such out-of-plane deformation results in dynamic changes in designed IOL morphology parameters therefore achieving