## 1 Introduction  
The demand for tissue and organ replacement, repair, and regeneration is growing due to increasing traumatic injury or disease cases, limited sources of donor organs, and immune rejection of donor tissues, which are such that demand exceeds supply [1]. Therefore, this has promoted researches in tissue engineering and regenerative medicine, especially the emerging hotspot of biological scaffolds [2, 3, 4]. Nowadays, an emerging 3D printing technology can compensate for the shortcomings of traditional manufacturing methods. It is an additive manufacturing method that uses biomaterials to print precise, bionic, and personalized scaffold structures in a layer-by-layer manner, with the ability to modify the shape, size, structure, and porosity of the scaffold [5, 6]. In order to obtain suitable scaffolds, various methods including selective laser sintering (SLS) [7], fused deposition modeling (FDM) [8, 9], laminated object manufacturing (LOM) [10, 11], stereolithography apparatus (SLA) [12, 13], and others were developed. Among these, FDM is one of the most common and easily-implemented 3D printing processes [14]. PCL is a biodegradable biomaterial with good biocompatibility, mechanical strength and durability, good thermo-plasticity, easy processing, and low melting point, which makes PCL widely used in tissue engineering [15, 16, 17]. There are two main challenges for PCL as a tissue engineering material. One is hydrophobicity, as studies have shown that cells are more likely to adsorb, grow and migrate on hydrophilic scaffolds [18], which can be solved by blending PCL with hydrophilic polymers [19, 20]. Secondly, mechanical strength limits its application in tissue engineering such as skin, blood vessels, tendons, and bones, which require sufficient mechanical strength, and one effective way is to add nanofillers [21]. Cellulose nanocrystal, as a new functional polymeric material [22; 23], has been extensively studied to show that composites with CNC as the reinforcing phase not only improve the material properties but also achieve controllable properties of composites, compared to single-component materials [24]. CNC isolated from plant cellulose have attracted considerable attention due to their high aspect ratio, high strength, abundant hydroxyl groups, low cost, widely available, and good biocompatibility. At present, there are two main sources of nanocellulose, one is from plants, the other is from bacterial metabolites. Moreover, it's more economical and convenient to get it from plants. The design of the scaffold must have a porous structure and suitable porosity to obtain the desired mechanical function and mass flow [25]. The results indicate [26; 27; 28] that cell viability and proliferation can be enhanced by varying the microporous geometry and porosity of the scaffold. High porosity and pore size benefit in nutrient and oxygen delivery or allow more cells to grow inward, but the mechanical properties of the scaffold will be compromised due to the large pore volume. Therefore, the microporous structure and porosity of the scaffold should be considered during scaffold design and fabrication to achieve a good balance between mechanical properties and mass transfer [28; 29]. To address the above issues, the introduction of CNC into PCL nanofibers is utilized to prepare CNC/PCL composites, and the influence of the physicochemical properties and cytocompatibility of CNC/PCL composites is explored in order to obtain composites with good mechanical properties, as well as the cytocompatibility for their applications in tissue engineering. The properties of different pore shapes were tested by varying the pore shape of the printed scaffold. In addition, three different orthogonal, triangular, and concave hexagon pore shapes were compared, in combination with software simulation to analyze the mechanical properties of the different pore shapes and the flow of liquid in the scaffold.