Abstract: Preparation and expansion methods for human pluripotent stem cell-derived human retinal pigment epithelial cells are provided. The preparation method includes the following steps: collecting 3D-PRE spheroids derived from human pluripotent stem cells, performing mechanical separation to remove non-RPE cells and clusters which are non-pigmented and retain a pigmented RPE cell sheet, enzymatically digesting the pigmented RPE cell sheet to obtain an RPE single cell suspension, and thereby the human pluripotent stem cell-derived human retinal pigment epithelial cells are obtained. The expansion method includes centrifuging the RPE single cell suspension and removing a supernatant, resuspending in an RPE cell medium and seeding into a cell culture container precoated with extracellular matrix to allow primary culture, and subculturing the cells after cells spread out.

Abstract: A finishing gear hob whose shape is of a worm includes a working side with cutting edges K, which are in the form of a continuous equally-rising spaced cylindrical helix, and edges K are formed by the intersection of the rake faces A, i.e. the top surfaces of the worm, and the flanks B, i.e. the working sides of the worm. The number of cutting edges K equals to the thread number i of the worm, where i is a positive integer. The normal pitch P.sub.n of the working side of the worm is equal to the normal base pitch t.sub.b of the machined gear .pi.m.sub.n COS.alpha..sub.n where m.sub.n is the normal module of the machined gear; and .alpha..sub.n is the normal pressure angle at the reference circle of the machined gear. The lead angle .lambda. of the helix cutting edge is calculated by the formula Sin.lambda.=(im.sub.n COS.alpha..sub.n)/2R where R is the radius of cylindrical helix cutting edge K, and the helix lead P of the helix cutting edge P=(i.pi.m.sub.n COS.alpha..sub.n)/COS.lambda..