Three-Dimensional Imaging and Quantitative Analysis of Blood Vessel Distribution in The Meniscus of Transgenic Mouse after Tissue Clearing.

OBJECTIVE: Blood supply to the meniscus determines its recovery and is a reference for treatment planning. This study aimed to apply tissue clearing and three-dimensional (3D) imaging in exploring the quantitative distribution of blood vessels in the mouse meniscus. MATERIALS AND METHODS: In this experimental study, tissue clearing was performed to treat the bilateral knee joints of transgenic mice with fluorescent vascular endothelial cells. Images were acquired using a light sheet microscope and the vascular endothelial cells in the meniscus was analysed using 3D imaging. Quantitative methods were employed to further analyse the blood vessel distribution in the mouse meniscus. RESULTS: The traditional three-equal-width division of the meniscus is as follows: the outer one-third is the red-red zone (RR), the inner one-third is the white-white zone (WW), and the transition area is the red-white zone (RW). The division revealed significant signal differences between the RW and WW (P<0.05) zones, but no significant differences between the RR and RW zones, which indicated that the division might not accurately reflect the blood supply of the meniscus. According to the modified division (4:2:1) in which significant differences were ensured between the adjacent zones, we observed that the width ratio of each zone was 38 ± 1% (RR), 24 ± 1% (RW), and 38 ± 2% (WW). Furthermore, the blood supply to each region was verified. The anterior region had the most abundant blood supply. The fluorescence count in the anterior region was significantly higher than in the central and posterior regions (P<0.05). The blood supply of the medial meniscus was superior to the lateral meniscus (P<0.05). CONCLUSION: Analysis of the blood supply to the mouse meniscus under tissue clearing and 3D imaging reflect quantitative blood vessel distribution, which would facilitate future evaluations of the human meniscus and provide more anatomical references for clinicians.

Regional Alterations of Macroscopy and Histology in Meniscus in an ACL Transection Rabbit Model.

BACKGROUND: Although meniscal injury is common after anterior cruciate ligament (ACL) injury, the underlying process in different meniscal regions remains unclear. PURPOSE: To investigate macroscopic and histological alterations in different meniscal regions in an ACL transection (ACLT) rabbit model. STUDY DESIGN: Controlled laboratory study. METHODS: ACLT was performed on New Zealand White rabbits. Both the medial meniscus (MM) and the lateral meniscus (LM) of the ACLT knees were obtained at 8 (n = 6) and 26 (n = 6) weeks postoperatively. MM and LM collected from nonoperated knees were considered 0 weeks (n = 6) postoperatively. Menisci were then divided into posterior, central, and anterior regions for macroscopic (width) and histological (hematoxylin and eosin, safranin O/fast green, collagen type 2 [COL2]) analysis. RESULTS: The macroscopic widths of MM and LM increased and then decreased over 26 weeks postoperatively, with all 3 MM widths at 8 weeks significantly wider than at 0 weeks (posterior: P < .01; central: P < .05; anterior: P < .05). In the MM, chondrocyte-like cell density increased and then decreased postoperatively, whereas in the LM, it decreased and then remained almost unchanged. Cell density was significantly higher in the central MM region at 8 weeks than at 0 weeks (P < .05). Glycosaminoglycan (GAG) and COL2 percentages of MM and LM decreased from 0 to 8 weeks and then returned to nearly normal levels at 26 weeks postoperatively. In the MM, the GAG percentage in the posterior (P < .05) and central (P < .01) regions and the COL2 percentage in the posterior region (P < .05) was significantly lower at 8 weeks than at 0 weeks. CONCLUSION: After ACLT in rabbit meniscus, the extracellular matrix (ECM) initially decreased and then increased to almost normal. Additionally, there were significant differences in the ECM percentage in the posterior and central regions of the MM in comparison with other meniscal regions between 0 and 8 weeks postoperatively. CLINICAL RELEVANCE: The results indicate that the time for meniscal injury after ACL injury is important, and attention should be paid to the posterior and central regions of the MM after ACLT.

Spatio-temporally deciphering peripheral nerve regeneration in vivo after extracellular vesicle therapy under NIR-II fluorescence imaging.

Extracellular vesicles (EVs) show potential as a therapeutic tool for peripheral nerve injury (PNI), promoting neurological regeneration. However, there are limited data on the in vivo spatio-temporal trafficking and biodistribution of EVs. In this study, we introduce a new non-invasive near-infrared fluorescence imaging strategy based on glucose-conjugated quantum dot (QDs-Glu) labeling to target and track EVs in a sciatic nerve injury rat model in real-time. Our results demonstrate that the injected EVs migrated from the uninjured site to the injured site of the nerve, with an increase in fluorescence signals detected from 4 to 7 days post-injection, indicating the release of contents from the EVs with therapeutic effects. Immunofluorescence and behavioral tests revealed that the EV therapy promoted nerve regeneration and functional recovery at 28 days post-injection. We also found a relationship between functional recovery and the NIR-II fluorescence intensity change pattern, providing novel evidence for the therapeutic effects of EV therapy using real-time NIR-II imaging at the live animal level. This approach initiates a new path for monitoring EVs in treating PNI under in vivo NIR-II imaging, enhancing our understanding of the efficacy of EV therapy on peripheral nerve regeneration and its mechanisms.

NIR-II live imaging study on the degradation pattern of collagen in the mouse model.

The degradation of collagen in different body parts is a critical point for designing collagen-based biomedical products. Here, three kinds of collagens labeled by second near-infrared (NIR-II) quantum dots (QDs), including collagen with low crosslinking degree (LC), middle crosslinking degree (MC) and high crosslinking degree (HC), were injected into the subcutaneous tissue, muscle and joints of the mouse model, respectively, in order to investigate the in vivo degradation pattern of collagen by NIR-II live imaging. The results of NIR-II imaging indicated that all tested collagens could be fully degraded after 35 days in the subcutaneous tissue, muscle and joints of the mouse model. However, the average degradation rate of subcutaneous tissue (k = 0.13) and muscle (k = 0.23) was slower than that of the joints (shoulder: k = 0.42, knee: k = 0.55). Specifically, the degradation rate of HC (k = 0.13) was slower than LC (k = 0.30) in muscle, while HC showed the fastest degradation rate in the shoulder and knee joints. In summary, NIR-II imaging could precisely identify the in vivo degradation rate of collagen. Moreover, the degradation rate of collagen was more closely related to the implanted body parts rather than the crosslinking degree of collagen, which was slower in the subcutaneous tissue and muscle compared to the joints in the mouse model.

Real-Time In Vivo Detection and Monitoring of Bacterial Infection Based on NIR-II Imaging.

Treatment according to the dynamic changes of bacterial load in vivo is critical for preventing progression of bacterial infections. Here, we present a lead sulfide quantum dots (PbS QDs) based second near-infrared (NIR-II) fluorescence imaging strategy for bacteria detection and real-time in vivo monitoring. Four strains of bacteria were labeled with synthesized PbS QDs which showed high bacteria labeling efficiency in vitro. Then bacteria at different concentrations were injected subcutaneously on the back of male nude mice for in vivo imaging. A series of NIR-II images taken at a predetermined time manner demonstrated changing patterns of photoluminescence (PL) intensity of infected sites, dynamically imaging a changing bacterial load in real-time. A detection limit around 102-104 CFU/ml was also achieved in vivo. Furthermore, analysis of pathology of infected sites were performed, which showed high biocompatibility of PbS QDs. Therefore, under the guidance of our developed NIR-II imaging system, real-time detection and spatiotemporal monitoring of bacterial infection in vivo can be achieved, thus facilitating anti-infection treatment under the guidance of the dynamic imaging of bacterial load in future.