title: Fabrication of fluorescent composite hydrogel using in situ synthesis of upconversion nanoparticles.
abstract: Fluorescent composite hydrogels have found widespread applications, especially in spatial and temporal monitoring of in vivo hydrogel behaviors via the emitting optical signal. However, most existing fluorescent composite hydrogels suffer from limited capability of deep tissue imaging and complicated fabrication routes. We herein report a facile method for fabricating fluorescent composite hydrogels based on the in situ synthesis of NaYF4:Yb, Er upconversion nanoparticles (UCNPs). This approach employs polyacrylamide (PAAm) hydrogels as a template, where the interconnected pores within the hydrogel act as nanoreactors to confine the growth of nanocrystals. We then obtained a fluorescent composite hydrogel exhibiting upconversion fluorescence and enhanced mechanical properties. The fluorescence spectra show that the fluorescence intensity decreases with decreasing size of the UCNPs. We investigated the relationship between the optical properties of the fluorescent composite hydrogel and the incorporated UCNPs based on the morphology, size, and distribution of the UCNPs by using scanning electron microscopy and transmission electron microscopy. In addition, we demonstrated the applicability of the synthesized hydrogel for deep tissue imaging through an in vitro tissue penetration experiment. Compressive and dynamic rheological testing reveal enhanced mechanical properties with increasing UCNP concentration. The fabricated upconversion fluorescent composite hydrogel may pave the way for monitoring the in vivo behavior of biomimetic materials via deep tissue imaging.
authors.affiliation: State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.|The MOE Key Laboratory of Biomedical Information Engineering, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.
authors.forename: Yuqing
authors.initials: Y
authors.lastname: Dong
authors.affiliation: The MOE Key Laboratory of Biomedical Information Engineering, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.|Bioinspired Engineering and Biomechanics Center (BEBC), Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.
authors.forename: Min
authors.initials: M
authors.lastname: Lin
authors.affiliation: The MOE Key Laboratory of Biomedical Information Engineering, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.|Bioinspired Engineering and Biomechanics Center (BEBC), Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.
authors.forename: Guorui
authors.initials: G
authors.lastname: Jin
authors.affiliation: School of Chemical Engineering, Chonnam National University, Gwangju 61186, Republic of Korea.
authors.forename: Yong
authors.initials: Y
authors.lastname: Il Park
authors.affiliation: The MOE Key Laboratory of Biomedical Information Engineering, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.|Bioinspired Engineering and Biomechanics Center (BEBC), Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.
authors.forename: Mushu
authors.initials: M
authors.lastname: Qiu
authors.affiliation: The MOE Key Laboratory of Biomedical Information Engineering, School of Life Science and Technology, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.|Bioinspired Engineering and Biomechanics Center (BEBC), Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhao
authors.affiliation: School of Life Sciences, Northwestern Polytechnical University, Xi'an 710072, People's Republic of China.
authors.forename: Hui
authors.initials: H
authors.lastname: Yang
authors.affiliation: Key Laboratory of Shaanxi Province for Craniofacial Precision Medicine Research, College of Stomatology, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.
authors.forename: Ang
authors.initials: A
authors.lastname: Li
authors.affiliation: Bioinspired Engineering and Biomechanics Center (BEBC), Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.
authors.forename: Tian
authors.initials: T
authors.lastname: Jian Lu