Cell Growth Behavior On Polymer-based Patterned Substrates With Micro-and Nano-scaled Hierarchical Structures

Tissue engineering is one of the modern strategies to provide a functional biological tissue equivalent to restore,replace,maintain or improve the function of human tissues that lost by disease,traumatic events,or congenital abnormalities.The most basic essential factor in tissue engineering is appropriate scaffold.With a specific composition,structure and physical properties,each organ and tissue is a unique three-dimensional(3D)bioreactor,and they provide special biochemical and biophysical microenvironments to cells and tissues to direct or regulate the specific biological functions that the human body needs.The scaffolds are the artificially constructed microenvironment for cell growth,and the interaction between cell and scaffold is paying more attention in the study of tissue engineering.The composition,surface topography,3D geometrical features and mechanical properties of scaffold can provide bioactive cues that act together to synergistically direct or regulate cells behavior.Biodegradable polymers as useful scaffolds or ideal implant devices in tissue engineering has been widely used due to their advantages,including ease of processing,variety of physical and mechanical properties,favorable tissue response and biodegradation kinetics and compatibility with nanofabrication techniques.These researches on the biodegradable polymers scaffold mainly focuses on two aspects to control or regulate cells behaviors:the development of new biodegradable polymers with improved biological responses;the construction of biomimetic hierarchical structures with specific surface topography.Poly(?-caprolactone)(PCL)and poly(lactide)(PLA)aretwo of the most common used biodegradable synthetic polymers for 3D scaffolds in tissue engineering due to their excellent biocompatibility,while the scaffold structure varies according to the purpose of use and the fabrication technique.However,most studies focused on the effects of micropatterned or nanopatterned scaffolds on cell behavior separately,and the study on the effects of patterned hierarchical structure with both micro-and nano-scaled features is not too much.Based on these facts,in this paper,we will investigate the relationship between the three factors:patterned structure,polymer composition and cell type.In this work,a template method was proposed for the preparation of patterned structures.This method shows advantages of simplicity,efficiency,nonuse of solvent and good controllability.The most attractive advantage is that the customized hierarchical structure with both micro-and nano-scale features can be prepared in one step.Thus,a series of customized hierarchical structure was prepared.PCL substrates with different structural hierarchy can be fabricated by the selection and combination of templates.Microisland substrates(Microisland)with micro-scale feature can be obtained by using Al grid as a template;NW substrates with nano-scale feature can be obtained by using A AO membrane as a template;hierarchical substrates with both micro-and nano-scale features can be obtained by using both A1 grid and AAO membrane as double templates.The pattern geometry(hexagonal or strip),island spacing and island size of substrates can be regulated.Based on this,cells behavior of MG-63 on the patterned substrates shows that the Microisland and pNW substrates exert different influence on cells behavior,including cell density,distribution,proliferation,morphogenesis,cellular alignment and elongation.Compared with island size,island spacing plays a dominant role in controlling cell growth.The substrates with pNW structure show a more effective role in promoting cell proliferation and the cells show the extended state with many filopodia on pNW surface,indicating the good interaction between cells and substrates with nanowire structure surface after second day's incubation.In terms of pattern geometry,the island size of pNW with hexagonal shape has an influence on cellular elongation,while the patterned substrates with strip shape(including Microisland and pNW)show the stronger ability for guiding cellular alignment,especially those pNW substrates with smaller size and more narrow spacing.The surface morphology of the substrates can be regulated by changing the chemical composition of copolymers.In our experiment,the patterned substrates with different surface morphology were fabricated based on di-,tri,pentablock copolymers.The results show that patterned substrates with different surface morphology can be prepared by using PCL-b-PLLA with different composition,and patterned substrates with similar surface morphology can be prepared by using polymers with similar composition.The growth behavior of MG-63 on these patterned substrates shows that cell response is mainly dominated by the surface morphology of patterned substrates.That is to say surface morphology of patterned substrates plays a more important role than polymer composition for the growth of MG-63.Finally,the investigation of different cell on the patterned substrate shows that different cell performed different response to the substrates.