Supplies

Silkworm cocoons have been generously supplied by the Chongqing Sericulture Science and Know-how Analysis Institute, positioned in Chongqing, China. The next supplies have been procured from Macklin Co.: N-(3-dimethylaminopropyl)-n′-ethylcarbodiimide hydrochloride (EDC), N-hydroxysuccinimide (NHS), polyvinyl alcohol (PVA; Molecular weight: 195,000), lithium bromide, and 2-mercaptoethanol (2-ME) (Shanghai, China). Moreover, we sourced Dulbecco’s modified eagle medium (DMEM) with excessive glucose, phosphate buffered saline (PBS) and penicillin–streptomycin (5000 U/mL) from Gibco Life Know-how Co. (USA). Foetal bovine serum (FBS) and MVs-depleted FBS have been bought from VivaCell Co. (Shanghai, China). All antibodies have been procured from Abcam Inc. (USA). The Reactive Oxygen Species Assay Package, Senescence-Related β-Galactosidase (SA-β-Gal) Stain Package and Calcein/PI Cell Viability Assay Package have been bought from Beijing Solarbio Science & Know-how Co. (Beijing, China). The BCA protein focus kits, Enhanced ATP Assay Package and Enhanced Mitochondrial Membrane Potential Assay Package with JC-1) have been obtained from Beyotime Biotechnology Co. (Shanghai, China). The RNA Extraction Package was sourced from Thermo Fisher Scientific Co. (MA, USA), and the cDNA synthesis package was acquired from MedChemExpress Co. (Shanghai, China). Each the C3H/10T1/2 cell line and ATDC5 cell line have been bought from the American Sort Tradition Middle (Manassas, VA, USA).

Extraction and characterisation of MSCs MVs/iMVs

To acquire two distinct varieties of MSCs MVs, we cultured C3H/10T1/2 cells, that are well-established mouse embryo fibroblasts serving as a mesenchymal stem cell mannequin [42,43,44]. Initially, cells have been seeded in 15-cm cell tradition plates at a density of 5 × 10⁶ cells per dish and cultivated for twenty-four h in DMEM supplemented with 10% FBS, 1% penicillin–streptomycin, and maintained in a moist ambiance with 5% CO2. For the extraction of iMVs, the addition of 10 ng/mL IFN-γ to the medium was required. Subsequently, the MV-free tradition medium was utilised for each MVs and iMVs at when the cell confluence reached 50–60%. After 48 h of continued mobile secretion of MVs and iMVs, the cell supernatant was collected.

A differential centrifugation approach was employed for the isolation of MVs and iMVs [45]. In abstract, the supernatant was centrifuged at 300g for 10 min to take away cells, adopted by centrifugation at 2000g for 10 min to take away lifeless cells. Subsequent, centrifugation at 10,000g for 30 min was carried out to discard cell particles. Lastly, the supernatant underwent ultracentrifugation at 120,000g for two h, adopted by resuspension in PBS inside sterile centrifuge tubes, and non permanent storage at 4 °C [21]. Subsequently, the characterisations of MVs and iMVs have been evaluated, with their morphology noticed utilizing scanning electron microscopy (SEM, JEM-1200EX, Japan). The particle dimension of MVs and iMVs was assessed utilizing ZetaView (Particle Metrix, Germany). Furthermore, the expression of MVs floor markers CD9, CD63, and CD81 was decided by western blotting [46].

Uptake of Exos/iExos by ATDC5

All through the research, ATDC5, a mouse chondrocyte line, was used [47]. ATDC5 cells have been seeded in ConfocalDishes containing full media. Remoted MVs/iMVs have been stained and labelled utilizing pink fluorescent dye PKH26. After cell attachment and reaching 50% confluence, MVs/iMVs have been launched, and incubation continued for 8 h. Following fixation with 4% paraformaldehyde, the cells have been labelled with phalloidin and DAPI to delineate the cytoskeleton and nucleus, respectively. The uptake of MVs/iMVs was noticed by scanning the cells utilizing a confocal laser microscope (Nikon NIE-A1plus, Japan).

Extraction and modification of SF

The SF preparation adopted beforehand described procedures [48]. Briefly, cleaned cocoons have been lower and boiled with 0.02 M Na₂CO₃ for 1 h, repeating this course of twice to remove sericin. The SF was washed with distilled water and dried. A selected weight of SF was collected and dissolved in lithium bromide at 55 °C. Afterward, it was dialysed in ultrapure water for 3 days to remove ions and different impurities, yielding a 5 wt.% SF answer. To switch the silk protein, the SF answer was dialysed in 0.5 M MES buffer (pH = 6.0) in a single day previous to the response. A mix of two g EDC and 5.5 g NHS was stirred right into a 100 mL SF answer for 30 min at room temperature to provoke the response. Subsequently, 1 mL of 2-ME was added to halt the response, adopted by the gradual addition of 1.5 g APBA into the answer slowly, which was stirred to dissolve, react for two h. After completion of the response, the combination was dialysed in double-distilled water for 48 h, with water modifications each 6 h. The APBA-SF answer and SF answer have been freeze-dried, and Fourier evaluation was carried out. Rework infrared spectroscopy (iS10 FT-IR spectrometer, USA) was employed to detect and analyse all three chemical compounds, together with APBA, SF, and APBA-SF.

Preparation of PVA-APBA-SF Hydrogel@MVs/iMVs

To create the PVA-APBA-SF hydrogel, MVs/iMVs suspended in PBS have been initially blended with a 5 wt.% PVA answer (molecular weight ≈ 195,000). This combination was then diluted with double-distilled water to realize a 2.5 wt.% focus and allowed to relaxation for a specified period. Subsequently, this answer with a 2.5 wt.% APBA-SF answer in a 3:1 ratio. This ensuing combination quickly fashioned the PVA-APBA-SF Hydrogel@MVs/iMVs.

Characterisation of hydrogel

The form of the hydrogel was noticed by using SEM following. Moreover, laser confocal microscopy was utilised to evaluate the distribution of PKH26 fluorescently labelled MVs inside the hydrogel, each in cross-sections and in 3D house. Dynamic rheological behaviour of the hydrogels was evaluated utilizing a rotating rheometer (Discovery HR-2, USA). A pressure scanning frequency of 1 Hzwas used, protecting a pressure vary from 0.01 to 100% to find out the vital pressure level. Moreover, cyclic small pressure (0.5%, 60 s) and huge pressure (50%, 60 s) assessments have been carried out to evaluate the self-healing potential of the hydrogel.

In vitro degradation and ROS responsiveness of hydrogels

The precisely weighed hydrogel specimens have been immersed in separate tubes containing PBS and H₂O₂ (1 mM), each supplemented with proteinase XIV to simulate the in vivo degradation setting. These tubes have been constantly shaken at 37 °C. At intervals of two days, the hydrogel was eliminated, floor moisture was absorbed utilizing filter paper, and the mass Md was recorded at completely different time factors over a complete of 21 days. Every situation at every time level had three samples. The degradation price (share) was calculated utilizing the formulation (M0−Md)/M0 × 100%.

MVs launch from hydrogels

To guage the effectivity of exosomes launch, the hydrogel was loaded right into a dialysis bag (MWCO = 1000 Da) and immersed in PBS and 1 mM H₂O₂ respectively, whereas being shaken at 37 °C. Dialysis fluid was collected and replenished at common intervals. The BCA approach was employed to quantify the MVs launch effectivity by measuring the protein content material within the dialysis answer [49].

Evaluation of hydrogel biocompatibility in vitro

The biocompatibility of the hydrogel was assessed utilizing a co-culture mannequin of hydrogel and ATDC5 cells stablished by a Transwell equipment [50]. ATDC5 cells have been cultured within the decrease chamber, whereas Hhydrogel or Hydrogel@iMVs, together with full development medium, have been added for cell cultivation. The management group obtained no hydrogel. On days 1, 3, and 5, we the hydrogel was eliminated, and reside/lifeless assays have been carried out to tell apart between reside and lifeless cells. Pictures have been captured utilizing a fluorescent inverted microscope (Nikon Clipstie, Japan), and reside and lifeless cells have been counted. Moreover, on the identical time factors, cell viability was assessed by the CCK-8 assay by measuring absorbance, following the producer’s directions.

In vitro research of the therapeutic results of Hydrogel@MVs/iMVs on senescence in ATDC5 cells

To analyze the therapeutic results of Hydrogel@MVs/iMVs on ageing in cartilage cells, we carried out an evaluation utilizing an SA-β-Gal stain package. In abstract, ATDC5 cells have been seeded in a 6-well plate and subjected to cell ageing induction by treating them with 200 μM of H₂O₂ for 48 h in full tradition medium. Hydrogel@MVs/iMVs have been employed within the remedy, whereas the management group obtained no H₂O₂ remedy. After remedy, the cells have been mounted for 15 min at room temperature with 4% paraformaldehyde following two PBS washes. A premade SA-β-Gal staining answer was utilized to every properly, and incubated at 37 °C in a single day. Subsequently, cells have been washed with 70% ethanol, and after buying inverted microscope pictures, the variety of optimistic cells in each the ageing and regular teams was counted and analysed to calculate the speed of ageing cell positivity. Moreover, beneath the identical remedy circumstances, immunofluorescence staining of Ki67 was carried out in ATDC5 cells, and pictures have been captured utilizing a fluorescence microscope. The proportion of Ki67-positive cells was calculated, and Western Blot experiments have been carried out to evaluate the expression of RB protein and p-RPS6 protein within the cells, offering a complete analysis of the therapeutic results on cell senescence [51].

Movement cytometry

Movement cytometry was employed to evaluate the results of Hydrogel@MVs/iMVs on the cell cycle of ATDC5 cells after the induction of cell senescence. The induction and grouping of cell senescence in ATDC5 cells have been carried out as beforehand described. Cells have been handled, collected, mounted with 70% ethanol in a single day at 4 °C, after which analysed utilizing a circulation cytometer (CytoFLEX, Beckman Coulter, Fullerton, USA).

Examination of mitochondrial perform in vitro

Cells underwent the identical remedy for 48 h earlier than being rinsed with PBS and positioned in contemporary full media. Subsequently, the cells have been handled for 20 min at 37 °C with the JC-1 staining working answer and noticed beneath a fluorescence microscope. Moreover, the cells have been resuspended in JC-1 staining working answer, incubated, centrifuged, washed twice, and resuspended for evaluation utilizing a fluorescence spectrophotometer. A 490 nm excitation and 530 nm emission wavelength have been used to determine JC-1 monomers, whereas a 525 nm excitation and 590 nm emission wavelength have been employed to detect JC-1 aggregates. With a purpose to consider the potential and performance of mitochondria [52].

ATP evaluation

An appropriate variety of ATDC5 cells have been seeded right into a 6-well plate and allowed to stick and develop till they reached 50% confluency. Senescence was induced for 48 h after which Hydrogel@MVs/iMVs have been added. The management group obtained no remedy whereas the H₂O₂ group didn’t obtain any hydrogel. Following the producer’s directions, the tradition medium was eliminated, and 200 μL of lysis buffer was added to every properly to lyse the cells. The supernatant was obtained after centrifuging the lysate at 12,000g for five min at 4 °C. A 96-well plate was used, and ATP detection working answer and supernatant have been added. Fluorescence spectrophotometry was employed to measure the ATP stage in numerous cell sorts, assessing mitochondrial exercise.

Respiratory chain complicated assay

After treating ATDC5 chondrocytes with H₂O₂, H₂O₂ + Hydrogel@MVs/iMVs, or management for 48 h, the cells have been lysed with RIPA buffer to extract proteins for Western Blot evaluation. This evaluation aimed to find out the content material of mitochondrial respiratory chain complexes in numerous teams. Protein bands have been imaged and analysed utilizing the ChemiDoc MP imaging system and ImageJ (Wayne Rasband, NIH, USA).

Analysis of the intracellular antioxidant impression of MVs/iMVs in vitro

Following 48 h of senescence-inducing remedy for ATDC5 cells, contemporary full medium was launched. Then, PKH26 fluorescent dye-labelled Hydrogel@MVs/iMVs have been individually added and incubated for twenty-four h. After the removing of the cell tradition media, the DCFH-DA probe was launched. The cells have been incubated at 37 °C for 20 min in a cell tradition incubator. Extra DCFH-DA that had not penetrated the cells was eliminated by washing them with serum-free cell tradition media. An inverted fluorescent microscope was used to watch and report the cells. ImageJ was employed to measure the fluorescence depth of DCFH-DA to evaluate the antioxidant exercise of the MVs.

RT-PCR

Complete RNA was remoted from every remedy group of ATDC5 cells utilizing an RNA extraction package after which reverse transcribed into cDNA. Actual-time fluorescence quantitative PCR was used to measure mRNA expression ranges. CT values (ΔΔCT) comparisons have been utilised to calculate the relative ranges of mRNA expression. The primer sequences (P16, P21, P53, OPA1, MFN1, MFN2, FIS1, DRP1, GAPDH) are supplied in Extra file 1: Desk S1.

Osteoarthritis rat mannequin institution

To guage the therapeutic results of Hydrogel@iMVs in vivo, we used 12-week-old male Sprague Dawley rats weighing 400 ± 20 g to ascertain an OA mannequin by destabilisation of the medial meniscus (DMM) together with anterior cruciate ligament transection (ACLT) surgical procedure. After 1 week of adaptation, and three weeks post-modelling, the OA rats have been randomly divided into 4 teams of 5 rats every. The joint cavity was injected with both PBS, hydrogel, iMVs, or Hydrogel@iMVs. To make sure sterility, all rats obtained an intramuscular dose of penicillin (2000 μ/kg) earlier than and after the process. All animal procedures have been carried out beneath sterile circumstances and have been permitted by the Institutional Animal Care and Use Committee (IACUC) of Chongqing Medical College.

Histological assays

After 5 weeks of remedy, the animals have been euthanised, and the knee joints have been dissected. The joint tissue was mounted in 4% paraformaldehyde in a single day at 4 °C and subsequently decalcified utilizing a gradual decalcification answer. Following dehydration and paraffin embedding, the tissue was sectioned within the sagittal aircraft (5 mm). Histological evaluation was carried out utilizing haematoxylin and eosin H&E and Quick Pink O-Safranin Inexperienced stains. Major antibodies, P12 and P53, produced from rabbits, have been used, and the sections have been subsequently incubated with a goat anti-rabbit secondary antibody for 1 h. DAB reagent was used for staining. Moreover, the sections have been stained for rabbit-derived DRP1, OPA1, MFN1, MFN2, and FIS1 utilizing the corresponding fluorescently labelled secondary antibodies and DAPI. All staining was noticed and recorded utilizing a microscope, and quantitative evaluation of relative expression ranges or fluorescence depth was carried out utilizing Picture J.

Statistical evaluation

All in vitro experiments have been carried out with three organic replicates and in vivo experiments have been carried out with 5 replicates. The info are offered as means ± customary deviations. Statistical evaluation was carried out utilizing one-way evaluation of variance and Tukey’s post-hoc take a look at in GraphPad Prism (9.0). Statistical significance was outlined as a P-value lower than 0.05, denoted as *P < 0.05, **P < 0.01, ***P < 0.001 and ****P < 0.0001.