The needs for high-resolution, well-defined and complex 3D microstructures in diverse fields call for the rapid development of novel 3D microfabrication techniques. Among those, two-photon polymerization (TPP) attracted extensive attention owing to its unique and useful characteristics. As an approach to implementing additive manufacturing, TPP has truly 3D writing ability to fabricate artificially designed constructs with arbitrary geometry. The spatial resolution of the manufactured structures via TPP can exceed the diffraction limit. The 3D structures fabricated by TPP could properly mimic the microenvironment of natural extracellular matrix, providing powerful tools for the study of cell behavior. TPP can meet the requirements of manufacturing technique for 3D scaffolds (engineering cell culture matrices) used in cytobiology, tissue engineering and regenerative medicine. In this review, we demonstrated the development in 3D microfabrication techniques and we presented an overview of the applications of TPP as an advanced manufacturing technique in complex 3D biomedical scaffolds fabrication. Given this multidisciplinary field, we discussed the perspectives of physics, materials science, chemistry, biomedicine and mechanical engineering. Additionally, we dived into the principles of tow-photon absorption (TPA) and TPP, requirements of 3D biomedical scaffolders, developed-to-date materials and chemical approaches used by TPP and manufacturing strategies based on mechanical engineering. In the end, we draw out the limitations of TPP on 3D manufacturing for now along with some prospects of its future outlook towards the fabrication of 3D biomedical scaffolds.

In this report, the surface topography of crescent array in the Nepenthes slippery zone is measured and bionic fabricated by two‐photon polymerization (TPP) technology. A subregion outside‐in scanning method (SOSM) is proposed to solve the photoresist converge and large area surface positioning problem existing in bionic crescent array surface (BCAS) fabrication. The geometric parameters of BCAS, including area fraction, height, offset, and outer–inner radius ratio, are systematically investigated to reveal their effects on the hydrophobic performance. Perfluorinated polyether oil and fluorocarbon solvent were used to increase the hydrophobicity and homogeneity of bionic surface. The contact angles of BCASs coated with and without the solution are measured. The maximum contact angle can reach to 152.1°. What's more, considering the anisotropy of BCAS, anisotropic wetting research is conducted. Offset and outer–inner radius ratio are found to have obvious effects on the contact angle differences between convexity and concavity directions. The maximum contact angle difference can reach to 5.1°. Spreading and pinning phenomenon caused by droplet anisotropic wetting are observed and explained. This work is expected to provide references for the BCAS to be applied in super‐hydrophobic and droplets motion fields.

Objective: Two-photon polymerization (TPP) utilizes an optical nonlinear absorption process to initiate the polymerization of photopolymerizable materials. To date, it is the only technique capable of fabricating complex 3D microstructures with finely adjusted geometry on the cell and sub-cell scales. TPP shows a very promising potential in biomedical applications related to high-resolution features, including drug delivery, tissue engineering, microfluidic devices, and so forth. Therefore, it is of high significance to grasp the global scientific achievements in this field. An analysis of publications concerning the applications of TPP in the biomedical field was performed, and the knowledge domain, research hotspots, frontiers, and research directions in this topic were identified according to the research results.Methods: The publications concerning TPP applications in biomedical field were retrieved from WoSCC between 2003 and 2022, Bibliometrics and visual analysis employing CiteSpace software and R-language package Bibliometrix were performed in this study.Results: A total of 415 publications regarding the TPP applications in the biomedical field were retrieved from WoSCC, including 377 articles, and 38 review articles. The studies pertaining to the biomedical applications of TPP began back in 2003 and showed an upward trend constantly. Especially in the recent 5 years, studies of TPP in biomedical field have increased rapidly, with the number of publications from 2017 to 2021 accounting for 52.29% of the total. In terms of output, China was the leading country and Chinese Acad Sci, Tech Inst Phys and Chem was the leading institution. The United States showed the closest cooperation with other countries. ACS applied materials and interfaces was the most prolific journal (n = 13), followed by Biofabrication (n = 11) and Optics express (n = 10). The journals having the top cited papers were Biomaterials, Advanced materials, and Applied physic letters. The most productive author was Aleksandr Ovsianikov (27 articles). Meanwhile, researchers who had close cooperation with other researchers were also prolific authors. “cell behavior”, " (tissue engineering) scaffolds”, “biomaterials,” and “hydrogel” were the main co-occurrence keywords and “additional manufacturing”, “3D printing,” and “microstructures” were the recent burst keywords. The Keyword clusters, “stem cells,” and “mucosal delivery”, appeared recently. A paper reporting unprecedented high-resolution bull models fabricated by TPP was the most locally cited reference (cited 60 times). “Magnetic actuation” and “additive manufacturing” were recently co-cited reference clusters and an article concerning ultracompact compound lens systems manufactured by TPP was the latest burst reference.Conclusion: The applications of TPP in biomedical field is an interdisciplinary research topic and the development of this field requires the active collaboration of researchers and experts from all relevant disciplines. Bringing up a better utilization of TPP as an additive manufacturing technology to better serve the biomedical development has always been the research focus in this field. Research on stem cells behaviors and mucosal delivery based on microstructures fabricated using TPP were becoming new hotspots. And it can be predicted that using TPP as a sourcing technique to fabricate biomedical-related structures and devices is a new research direction. In addition, the research of functional polymers, such as magnetic-driven polymers, was the frontier topic of TPP biomedical applications.

Microlens arrays have been widely used in the fields of micro-optics because of the advantages of their high diffraction efficiency, high fill factor, and wide operating band. However, the microlens array still has problems with its smaller field of view (FOV) and lower utilization of light energy. In this paper, a 3D compound eye system consisting of a microlens array and a pinhole array was designed according to the optical principle of insect compound eye. The artificial compound eye structure was processed in two-photon polymerization processing technology. Ray tracing and optical system simulation of the designed artificial compound eye structure were performed. The results showed that the artificial compound eye structure had a wider FOV and higher light energy utilization than a conventional 2D microlens array. This thesis may lay a theoretical foundation for the structural optimization design of microlens arrays.

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