Extreme wetting surfaces have been the significant subject of surface engineering field. A superhydrophillc surface has an exceptionally strong affinity to water and provides outstanding properties such as self-cleaning, anti-fogging, which offers a broad range of potential applications in many fields. Compared with superhydrophobic surfaces, superhydrophilic surfaces have received relatively few attentions, and some problems still exist in both academic and application. In this review, the controversy about the definition of superhydrophilic surfaces is introduced, then we analyze the mechanism of superhydrophilic phenomenon. The preparation methods and practical application are also discussed. Furthermore, some challenges and the current international new research tendency of superhydrophilic surfaces are highlighted. The review aims to provide an introductory yet comprehensive overview about superhydrophilic surfaces.

Contents
1 Introduction
2 Definition and mechanism
2.1 Definition of superhydrophilic surfaces
2.2 Mechanism of superhydrophilic phenomenon
3 Fabrication and application
3.1 Fabrication of superhydrophilic surfaces
3.2 Application of superhydrophilic surfaces
4 Problem and progress
4.1 Existing problems