Fluorescence imaging in vivo will pave an important way for the evaluation of biomaterials. The major advantage of fluorescence imaging compared to other imaging modalities is the possibility of tracking two or more fluorescence probes simultaneously with multispectral fluorescence imaging. It is essential to elucidate the location, erosion, drug release and resection of implanted biomaterials in vivo. Herein, a thermosensitive hydrogel with a protoporphyrin core based on a PEG and PCL copolymer (PCL-PEG-PPOR-PEG-PCL) was synthesized by ring-opening polymerization using protoporphyrin as a fluorescence tag. The optical properties of the hydrogel were investigated by UV-vis and fluorescence spectroscopy in vitro and by fluorescence imaging system in vivo. The hydrogel erosion and drug delivery in vivo were monitored and tracked by multispectral fluorescence imaging system in nude mice. The results show that the thermosensitive hydrogel exhibits fluorescence and injectability in vivo with good biocompatibility. Through the modality of fluorescence imaging, the status of the hydrogel is reflected in situ in vivo including its location and erosion. Multispectral analysis separates the autofluorescence signals from the specific label and provides the ability to locate the drug and carrier. The protoporphyrin incorporated thermosensitive hydrogel can be a potential visiable biomedical implant for tissue repair or drug delivery.

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Visualization of a drug delivery system could reveal the pharmacokinetic properties, which is essential for the design of a novel drug delivery system. In vivo optical imaging offers an advanced tool to monitor the drug release process and the therapeutic effect by the combination of fluorescence imaging and bioluminescence imaging. Multispectral fluorescence imaging can separate the drug and the carrier without interference. Herein, a dual fluorescent anti-tumor drug delivery system was monitored with the doxorubicin-loaded hydrogel to further explore the application of the porphyrin-incorporated hydrogel with four-arm PEG-PCL copolymer as a drug carrier, based on the beneficial fluorescence and good biocompatibility of the porphyrin incorporated hydrogel. Using nude mice bearing luciferase expressed hepatic tumor as models, the whole process from the drug delivery to the tumor therapeutic effects were real time visualized simultaneously after administration at interval from 0 to 18 d. The imaging results suggest that the fluorescence signals of the drug and the carrier can be separated and unmixed from the drug-loaded hydrogel successfully, avoiding the interference of the fluorescence signals. The tumor growth or inhibition can be real time tracked and analyzed quantitatively by bioluminescence imaging. Noninvasive continuous tracking the in vivo drug delivery process simultaneously is a potential trend for the precise drug delivery and treatment.

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