| The fully compliant-haptic intraocular lens(IOL) is a novel IOL which is combined with compliant mechanisms. Because of the design of flexure hinge and micro-displacement amplification mechanisms to transfer movement, the problem of lack of accommodative capacity can be thoroughly solved, which efficiently improves the optical power of IOL. Thus, it is one of the frontier topics in the field of cataract surgery and artificial organs. To date, most of the researches devote to the development and manufacturing of biomedical materials with great morphology change, and the structure design and deformation analysis of IOL haptics with micro-displacement. The benefits of the replacement of traditional haptics using spatial compliant micro-displacement amplification mechanisms have not been revealed.The IOL was studied in this paper based on the research of the structural properties, peripheral tissue morphology, physiological features, physical behavior of human lens, as well as the principle of refractive accommodation. The optical lens and haptics of IOL were respectively surveyed in the aspects of structural parametric geometry model, material properties analysis, principle of refractive accommodation of IOL, design of flexure hinge, spatial compliant micro-displacement amplification mechanisms based on experience and topological technology.Modelling: The structural parametric geometry model of human lens and IOL, material properties analysis and finite element analysis of refractive model were presented. In terms of vivo human lens obtained from the peripheral tissue morphology and physiological features of different sources and different individuals, a parametric 3D geometry model of human crystalline lens was established. Then the parametric 3D geometry model of IOL was proposed, which can be expressed by a function with independent variable of age and dependent variables of the diameter, thickness, radius of curvature at frontier and back poles of capsular bag and core.Designing: Firstly, the optical lens of IOL fabricated of PDMS was presented to investigate the relationship between accommodative amplitude, morphology change, and optical power based on gradient refractive index model and refractive model. Secondly, the haptics of IOL depending on experiences were created. To solve the problem of lack of accommodative ability, the compliant joints were formed according to the bending theory and elliptical centrifugal angle theory. An integral formula for elliptical arc flexure hinge was deduced and simplified by defining the intermediate parameter, after which the connection between the performances of hinges, the geometry of incision, dimension, and minimum thickness was concluded. Thirdly, the haptics of IOL depending on topological technology were provided. Taking maximum output displacement and minimum structural weight as optimization objectives, a mathematical model was established for optimal topology design using finite element analysis and topological technology. After that, rigid geometric model and compliant geometric model were reconstructed connected with optimal topology module of Hypermesh. The results show that it is available to improve the displacement by increasing flexure hinges and changing dimension of bars. The output displacement is 1~4 times to that using the former method, and further improves 3 times later using the latter method. Thus, the magnification ratio is promoted. In addition, different structures designed in various domains were acquired and the law between configuration and domain were also provided by changing the height of the design domain. In the same domain, the relationship of configuration and magnification ration was summarized. And the parametric geometry model with various magnification ratios was also presented.Fabricating: The manufacturing processes of optical lens and haptics were proposed. A PDMS bio-convex lens with varied surface curvatures was obtained in terms of surface tension, wet ability between materials, heat-assisted method, gravity method, and hanging drop method through controlling the temperature, volume and time. Four kinds of micro-displacement amplification mechanisms were manufactured by 3D printing technology without any mechanical fabricating processes and modules. By means of exchanging 3D model designed by Solid Edge to STL files, and then introduced them into the slice software, followed by adjusting the operation parameters, the structures were amplified into 5 times, after which the preparation process was finished. As shown in the measuring results, the corner with minimum accuracy of 0.5mm can be completely printed; hence the manufacturing error is less than 5%.Experiment: The experimental study of optical property and morphology change of optical lens, displacement change of haptics, and the refractive accommodation of IOL was conducted. At first, the optical power of PDMS lens tested by the focal length measuring system based on drive system is around 277.001 D, which is similar to that of the ideal results with the error of only 2.2%. From which, it shows that the focal length measuring system is correct and effective. And the minimum resolvable feature size is approximately 1.38μm. The measurement of optical power and magnification ratio is in process later. Compared to 0D, the minimum focal length can be declined to 3.01 mm, which result in the maximum optical power of 327.226 D. The actual magnification ratio falls to around 50% comparing with that of the ideal data of level structure and triangle structure. While the results of optimal topology design are quite related. Further, the optical system model is established based on the working principle of optical system for human lens. In the water, the maximum optical power is about 23.02 D, which reaches and even exceed the initial goal of 8.0D. Obviously, the accommodative amplitude remarkably boosts, by which the design idea, that is changing the morphology of optical lens and replacing the traditional haptics to fully compliant micro-displacement amplification mechanisms, is proved in this paper. |
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