1. A bio-ink comprising a host material, a cartilage acellular matrix and exosomes, wherein the host material comprises methacrylic anhydride gelatin, oxidized hyaluronic acid, dopamine modified hyaluronic acid.

2. The bio-ink according to claim 1, wherein the mass ratio of the methacrylic anhydride gelatin is 6% to 12%.

3. The bio-ink according to claim 1, wherein the oxidized hyaluronic acid is present in a proportion of 0.5% to 4% by mass.

4. The bio-ink according to claim 1, wherein the dopamine-modified hyaluronic acid is present in an amount of 0.5% to 4% by mass.

5. The bio-ink according to claim 1, wherein the cartilage acellular matrix is present in an amount of 0.5 to 5% by mass.

6. The bio-ink according to claim 1, wherein the exosome is at a concentration of 10-1000 μ g/mL.

7. The bio-ink according to claim 1, further comprising a photoinitiator, wherein the photoinitiator is present in a mass ratio of 0.1 to 0.5%.

8. The bio-ink according to claim 1, comprising 6 to 12% by mass of methacrylic anhydride gelatin, 0.5 to 4% by mass of oxidized hyaluronic acid, 0.5 to 4% by mass of dopamine-modified hyaluronic acid, 0.5 to 5% by mass of cartilage acellular matrix, and 0.1 to 0.5% by mass of photoinitiator, and exosomes at a concentration of 10 to 1000 μ g/mL.

9. A biological scaffold, wherein the bio-ink of any one of claims 1 to 8 is manufactured by 3D printing.

10. A preparation method of bio-ink is characterized by comprising the following steps:

1) weighing a proper amount of methacrylic anhydride gelatin, adding into ddH₂In O, adding oxidized hyaluronic acid after stirring and dissolving at 37 ℃, and continuously stirring and dissolving to obtain a first solution;

2) preparing acellular matrix ink, adjusting the pH to 7.4, adding dopamine-modified hyaluronic acid and photoinitiator, and stirring and dissolving at room temperature to obtain a second solution;

3) uniformly mixing the first solution and the second solution to obtain acellular matrix biological ink;

4) adding mesenchymal stem cell exosomes into the acellular matrix bio-ink to enable the final concentration of the exosomes to reach the expected concentration, so as to obtain the bio-ink;

wherein the steps 1) and 2) are not in sequence.

Background

Articular cartilage is one of the important components of the motor system, and is connected with the surface of the endosseous bone of the joint, and has smooth and elastic texture. Articular cartilage has the functions of lubricating joints, buffering vibration and impact generated by movement, improving movement and form matching between bones and is very important for maintaining normal movement functions of the joints. Cartilage damage can cause severe pain, joint swelling, decreased mobility and deterioration of surrounding cartilage and subchondral bone, and even progression to osteoarthritis, severely affecting the quality of life of the patient and placing a heavy economic burden on the individual and society. With the increasing enthusiasm of people in China in physical training, the types of sports activities are gradually expanded, and the probability of sports injury including articular cartilage injury of people is greatly increased. In the area of athletic trauma, an increasing number of patients suffer from damage to the articular cartilage. Cartilage defects are common in the clinic and studies have shown that cartilage defects are present in more than 60% of patients undergoing arthroscopic knee surgery. Cartilage tissue has no vascular, neural and lymphatic distribution, and its nutritional sources depend primarily on the supply of joint synovial fluid and blood vessels surrounding the synovial lining of the joint capsule. Thus, self-repair after cartilage damage is difficult.

Currently, the commonly used surgical strategies for cartilage defect repair mainly include Microaneurysm (MF), autologous chondrocyte transplantation (ACI), autologous cartilage tissue transplantation, allogeneic cartilage tissue transplantation, stem cell therapy, tissue engineering techniques, and the like. However, each method has certain limitations. Many clinical results indicate that the regenerated cartilage tissue repaired by MF and ACI methods is mainly fibrocartilage tissue and has biomechanical properties inferior to natural hyaline cartilage. The autologous cartilage tissue or the allogeneic cartilage tissue has good transplantation and repair effects, but the wide clinical application is limited due to the easy occurrence of complications at the material-taking part and the limited source. Cell transplantation, including ACI and stem cell therapy, often requires two phases: the first stage is to separate, culture and expand autologous chondrocytes or stem cells in vitro; the second stage is surgical implantation into the defect site. The dedifferentiation, decrease in dryness, aging, high cost, long waiting time, secondary operation and the like during the in vitro expansion of cells are the limiting factors of the clinical application of cell therapy. In addition, conventional cell transplantation is not easily retained at the defect site for a long period of time, which is also an important problem. To date, none of these treatments has been able to completely repair damaged articular cartilage.

It was confirmed that the experimental group directly injecting exosome into the tissue to be repaired has better repairing effect than the control group, but the infection risk caused by multiple injections and the dispersion of exosome suspension in the joint cavity reduce the treatment efficiency.

The traditional freeze-drying method is difficult to prepare bionic scaffolds with different spatial specificities, and the emergence of the 3D bioprinting technology provides a new method for accurately constructing a bionic structure to simulate and remold three-dimensional spatial structures of different tissues. The acellular matrix can simulate the biological and structural microenvironment of the source tissue, provides ideal conditions for regeneration, and is considered as the most ideal bionic biomaterial for tissue engineering. However, the mechanical strength of the pure acellular matrix material is low, so that the 'collapse effect' easily occurs after printing multiple layers, and the spatial arrangement of the bionic scaffold cannot be maintained. Although other biomaterials printed by 3D have certain effects of promoting chondrocyte differentiation and repairing cartilage damage, the final repairing effect is not good, and the biomaterials do not have bionic performance or have poor bionic performance.

Accordingly, there is a need for a method and product that addresses all or a portion of the above problems.

Disclosure of Invention

A first aspect of the present invention provides a bio-ink comprising a host material, a cartilage acellular matrix and exosomes, the host material comprising methacrylic anhydride gelatin (GelMA), Oxidized Hyaluronic Acid (OHA) and dopamine-modified hyaluronic acid (HA-DA);

optionally, the mass ratio of GelMA is 6-12%, the mass ratio of OHA is 0.5-4%, the mass ratio of HA-DA is 0.5-4%, and the mass ratio of acellular matrix is 0.5-5%;

the exosome is mesenchymal stem cell exosome, preferably the exosome is derived from adipose mesenchymal stem cells (ADSCs), and the final concentration of the exosome is 10-1000 mug/mL; preferably 100. + -. 50. mu.g/mL, most preferably 100. mu.g/mL;

optionally, the bio-ink of the invention further comprises a photoinitiator, and the mass ratio of the photoinitiator is 0.1-0.5%.

In one embodiment, the bio-ink of the present invention preferably comprises 9% by mass of GelMA, 2% by mass of OHA, 2% by mass of HA-DA, 2% by mass of acellular matrix, and 0.4% by mass of photoinitiator, and exosomes at a final concentration of 100 μ g/mL.

A second aspect of the present invention provides a biological scaffold fabricated by a 3D printing method using the bio-ink of the present invention.

The third aspect of the invention provides a preparation method of bio-ink, which comprises the following steps:

1) weighing appropriate amount of GelMA, adding into ddH₂In O, adding OHA after stirring and dissolving at 37 ℃, and continuously stirring and dissolving to obtain a first solution;

2) preparing 4% acellular matrix ink, adjusting the pH value to 7.4, adding HA-DA and a photoinitiator, and stirring at room temperature for dissolving to obtain a second solution;

3) uniformly mixing the first solution and the second solution to obtain acellular matrix biological ink;

4) adding mesenchymal stem cell exosomes into the acellular matrix bio-ink to enable the final concentration of the exosomes to reach the expected concentration, so as to obtain the bio-ink;

wherein the steps 1) and 2) are not in sequence.

Further, in one embodiment, the method of preparing a bio-ink proceeds as follows:

1) 0.9 g of methacrylic anhydride gelatin was weighed into 5 mL of ddH₂In O, stirring and dissolving at 37 ℃, adding 0.2 g of oxidized hyaluronic acid, and continuously stirring and dissolving;

2) preparing 5 mL of 4% cartilage acellular matrix ink, adjusting the pH to 7.4, adding 0.2 g of dopamine-modified hyaluronic acid and 0.04 g of photoinitiator, and stirring at room temperature for dissolution;

3) uniformly mixing the two solutions to obtain the cartilage acellular matrix biological ink;

4) adding exosomes to the cartilage acellular matrix bio-ink to a final concentration of 100 μ g/mL;

the preparation of the cartilage acellular matrix ink comprises the following steps:

a) weighing 15 mg of pepsin, adding the pepsin into 5 mL of 0.1M hydrochloric acid solution, and stirring for 30 minutes at room temperature;

b) 150 mg of cartilage acellular matrix powder is weighed, the hydrochloric acid solution containing pepsin is added, and the mixture is hermetically stirred at room temperature for 72 hours to obtain the cartilage acellular matrix ink. The amount of the reagent to be used is determined by the total amount, and the aforementioned mass is merely a specific example and can be scaled up or down.

The masses in this example are only examples and it is known to those skilled in the art that different desired ink volumes can be prepared in the same proportions.

The invention has the advantages that:

1. the biological ink and the biological scaffold can simulate the joint cartilage microenvironment and realize bionic repair;

2. the aldehyde group in the OHA added into the biological scaffold can react with amino in GelMA and acellular matrix to realize dynamic covalent crosslinking, and the aldehyde group is combined with the dopamine active group in HA-DA to achieve better slow-release repairing effect of exosome;

3. the slow-release exosome keeps the biological activity and can promote the proliferation of mesenchymal stem cells and the chondrogenic differentiation;

4. the absorption rate of the bracket in vivo is matched with the tissue regeneration rate, the cartilage generation effect is good, and the efficiency is high.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention. In the drawings:

FIG. 1 is a 1H NMR analysis of a gel material in one embodiment of the invention. FIG. 1A is an alignment of gelatin and GelMA; FIG. 1B is an alignment analysis of HA, OHA and HA-DA.

FIG. 2 is a characterization of a cartilage acellular matrix prepared according to a method of one embodiment of the present invention, showing gross appearance, HE staining and DAPI staining before and after cartilage decellularization;

fig. 3 is a characterization of a cartilage acellular matrix prepared according to a method of one embodiment of the present invention, fig. 3a. DNA content assay. Figure 3b. GAG content detection; FIG. 3℃ collagen (collagen) content assay;

fig. 4 is a characterization of a cartilage acellular matrix prepared according to a method of one embodiment of the present invention, fig. 4a. acellular matrix bio-ink gelation assay; fig. 4b rheology measurements. n = 3, P < 0.01, P < 0.001.

FIG. 5 shows the microscopic morphology of a Hydrogel scaffold and a Hydrogel-DCM scaffold prepared according to an embodiment of the present invention under a scanning electron microscope.

Fig. 6 is a graph of swelling, degradation rate, and fourier transform infrared spectroscopy analysis of a Hydrogel scaffold, a Hydrogel-DCM scaffold prepared according to a method of an embodiment of the present invention, fig. 6a. degradation rate of scaffold, n = 5, fig. 6b. swelling of scaffold, n = 3, hours (h), fig. 6c. fourier transform infrared spectroscopy analysis, transmittance (transmittince), wave number (wavenumber).

FIG. 7 shows the biocompatibility test of the Hydrogel scaffold and the Hydrogel-DCM scaffold prepared by the method according to one embodiment of the invention. FIG. 7A Live/Dead (Live/Dead) staining of bone marrow mesenchymal stem cells (BMSCs) seeded on scaffolds for 24 h; FIG. 7B cytoskeletal staining of BMSCs on scaffolds cultured for 72 h. i and ii: 3D (three-dimensional) graph; iv and v: an overlay; vii and viii: a partial enlarged view.

Fig. 8 shows the results of the human infrapatellar adipose mesenchymal stem cells (ADSCs) trilineage differentiation potency assay obtained using the method described in the present specification.

FIG. 9 shows the detection of ADSCs surface markers using flow cytometry using the methods described in the present specification.

FIG. 10 shows the identification of exosomes derived from human ADSCs. FIG. 10A. Transmission Electron microscopy observations; fig. 10b nano particle size analysis, concentration (concentration), particles (particles), size (nanometers (nm)); figure 10c western blot detection of exosome markers.

FIG. 11 shows the distribution and performance of exosomes in a scaffold according to one embodiment of the present invention, FIG. 11A shows the distribution of exosomes in a scaffold observed using confocal laser microscopy; FIG. 11B 3D distribution effect of exosomes; figure 11c. slow release profile of exosomes; n = 3.

FIG. 12 shows the results of using CCK-8 to test the viability of BMSCs cells on scaffolds. n = 5, P < 0.01, P < 0.001.

Figure 13 shows the assessment of in vitro chondrogenic differentiation of BMSCs on respective sets of scaffolds fabricated according to the methods of the present invention. Fig. 13A-fig. 13d. mRNA expression analysis of cartilage-associated genes ACAN, COL II, SOX9, COL X induced to cartilage differentiation 7d and 14 d in vitro, n = 5; fig. 13e. COL II and SOX9 protein expression assay after induction of chondrogenic differentiation to 14 d, n = 3. P < 0.05, P < 0.01, P < 0.001, relative fold change.

Detailed Description

The preferred embodiments of the present invention will be described in conjunction with the accompanying drawings, and it will be understood that they are described herein for the purpose of illustration and explanation and not limitation.

First, experiment method

1.1 chondrogenic induced differentiation

(1) When second generation adipose mesenchymal stem cells (ADSCs) were grown to 90% density, 2 mL of 0.25% trypsin digest was added and cell morphology was observed under an inverted microscope for 1 ‒ 2 minutes (min). When cells were found to retract, round, interstitial larger and suspended, digestion was stopped by adding an equal volume of complete medium.

(2) Transferring the cell suspension to a centrifuge tube, rotating at 800 r/min, and centrifuging for 5 min.

(3) The cell suspension was counted using an automatic cell counter and the cell density was adjusted to 1.0X 10⁷one/mL, 5. mu.L of the cell suspension was gently dropped onto a 24-well cell culture plate and allowed to stand in a cell culture chamber at 37 ℃ for 4 hours (h).

(4) Adding complete culture medium for chondrogenesis induction differentiation, and placing in a cell culture box at 37 ℃. The differentiation induction medium was replaced with fresh medium every 3 days.

(5) After inducing differentiation for 21 days, the medium was discarded, carefully washed with a PBS solution, and fixed with 10% neutral formaldehyde for 30 min.

(6) The PBS solution was carefully washed 2 times and stained with Alisine blue stain for 30 min at room temperature.

(7) The dye solution was aspirated and washed 3 times with PBS.

(8) Observed under a microscope and photographed.

1.2 osteogenic Induction of differentiation

(1) When the second generation ADSCs were grown to 90% density, 2 mL of 0.25% trypsin digest was added and cell morphology was observed under an inverted microscope at 1 ‒ 2 min. When cells were found to retract, round, interstitial larger and suspended, digestion was stopped by adding an equal volume of complete medium.

(2) Transferring the cell suspension to a centrifuge tube, rotating at 800 r/min, and centrifuging for 5 min.

(3) The cell suspension was counted using an automatic cell counter and the cell density was adjusted to 0.5X 10⁵2 mL of cell suspension drop 6-well cell culture plate (coated with 0.1% gelatin in advance) is taken and incubated in a cell culture box at 37 ℃ for 12 h to ensure that the cells are fully attached.

(4) After the medium was aspirated, the medium was washed with PBS solution 2 times, and after the medium was added to the medium, the medium was placed in a 37 ℃ cell incubator. The solution was changed 1 time every 3 days.

(5) After inducing differentiation for 21 days, the medium was discarded, carefully washed with a PBS solution, and fixed with 10% neutral formaldehyde for 30 min.

(6) The PBS solution was carefully washed 2 times and stained with alizarin red stain for 30 min at room temperature.

(7) Alizarin red staining solution was aspirated and washed 3 times with PBS.

(8) Observed under a microscope and photographed.

1.3 adipogenic Induction of differentiation

(1) When the second generation ADSCs were grown to 90% density, 2 mL of 0.25% trypsin digest was added and cell morphology was observed under an inverted microscope at 1 ‒ 2 min. When cells were found to retract, round, interstitial larger and suspended, digestion was stopped by adding an equal volume of complete medium.

(2) Transferring the cell suspension to a centrifuge tube, rotating at 800 r/min, and centrifuging for 5 min.

(3) Counting the cell suspension by using an automatic cell counter and adjustingWhole cell density to 0.5X 10⁵2 mL of cells are taken to be suspended in a 6-hole cell culture plate and incubated in a 37 ℃ cell culture box for 12 h to ensure that the cells are fully attached to the wall.

(4) After the culture medium is sucked out, washing the culture medium for 2 times by using a PBS solution, adding a complete adipogenic differentiation induction culture medium A liquid to induce differentiation for 3 days, and then changing the culture medium A liquid to a B liquid to induce differentiation for 1 day.

(5) The induction was performed 4 times alternately with solution A and solution B, and the culture was continued for 5 days with solution B, with replacement every 3 days.

(6) After inducing differentiation for 21 days, the medium was discarded, carefully washed with a PBS solution, and fixed with 10% neutral formaldehyde for 30 min.

(7) The PBS solution was carefully washed 2 times and stained with oil red O stain for 30 min at room temperature.

(8) The oil red O dye was aspirated and washed 3 times with PBS.

(9) Observed under a microscope and photographed.

1.4 flow cytometry

(1) When the second generation ADSCs were grown to 90% density, cells were digested with 2 mL of 0.25% trypsin digest for 1 ‒ 2 min, observed for cell morphology, and when cells were found to retract, round, interstitial larger and suspended, an equal volume of complete medium was added to stop the digestion.

(2) Transferring the cell suspension to a centrifuge tube, and centrifuging for 5 min at the rotating speed of 300 g/min.

(3) The cells were gently pipetted by adding 5 mL of PBS and step (2) was repeated.

(4) Cells were resuspended using 400 μ L PBS, all according to 1:100, adding CD29, CD34, CD45, CD90 and CD105 antibodies respectively, and incubating for 1h in the absence of light.

(5) Centrifuge at 300 g/min for 5 min and resuspend the cells using 400. mu.L PBS.

(6) Filtering the cell suspension by using a cell sieve to obtain a single cell suspension, and detecting on a machine.

(7) Data were analyzed using FlowJo software.

1.5 statistical analysis

Statistical analysis was performed using SPSS 22.0 software and results are expressed as (mean ± standard deviation). The comparison between the two groups was analyzed using independent sample T-test. When three groups or more are compared, the homogeneity of variance is firstly tested, and single-way analysis of variance (ANOVA) is adopted when the variance is uniform; non-parametric tests are used when the variance is irregular. When P < 0.05, the results were considered statistically different.

1.6 Primary isolation and culture of BMSCs

80 ‒ 100g male SD rats were sacrificed and soaked in 75% ethanol for 30 min. The tibia and femur at the knee joint were removed and the metaphysis exposed, and the marrow cavity was flushed using syringe aspiration PBS and bone marrow aspirate collected. Centrifuging at 800 rpm/min for 5 min, adding MEM-alpha, suspending the bottom cell mass, and adding 5% CO₂The BMSCs were obtained at 1 ‒ 2 weeks by culturing the cells at 37 ℃ for 5 days and then replacing the medium every 3 days. When the cells grow to 80 ‒ 90% density, the cells are expanded by passage at a ratio of 1:3 ‒ 1:4 or frozen.

1.7 extraction of exosomes

Sufficient cells need to be expanded to extract the exosomes from the MSCs, and Falcon multi-layer cell culture flasks (875 cm) from corning were used to ensure expansion efficiency and reduce dedifferentiation of MSCs²) Three MSCs were amplified. When the cells had grown to about 80% density, the culture supernatant was discarded, washed 2 times with PBS, replaced with 5% exosome-free FBS-containing MEM- α medium, and cultured for another 48 hours, and the cell supernatant, i.e., conditioned medium, was collected. The conditioned medium was then treated as follows:

(1) the conditioned medium was centrifuged at 300 Xg for 10 min and the supernatant was collected.

(2) The supernatant was collected by centrifugation at 2,000 Xg for 10 min.

(3) The supernatant was collected by centrifugation at 10,000 Xg for 30 min.

(4) Using tangential flow technology, the supernatant was concentrated by centrifugation at 3,500 Xg using a filtration membrane system containing a molecular weight cut-off of 100 kDa (Centricon Plus-70, Millipore).

(5) The supernatant was filtered using a 0.22 μm pore size filter.

(6) Centrifuge at 100,000 Xg for 2 h at 4 ℃ and carefully aspirate the supernatant and resuspend the pellet in pre-cooled PBS.

(7) Centrifugation was carried out at 100,000 Xg for 2 h at 4 ℃ and the PBS was carefully aspirated, 100 ‒ 200 μ L of precooled PBS was added to resuspend the bottom pellet, which was then frozen at ‒ 80 ℃ for storage.

1.8 identification of exosomes

1.8.1 Transmission Electron microscope Observation

10 mu L of freshly separated exosome was diluted with PBS and dropped onto a copper mesh, and negatively stained with 2% phosphotungstic acid at room temperature for 2 min. Observations were made using a JEOL-1400 transmission electron microscope (JEOL, Tokyo, Japan).

1.8.2 analysis of the particle size at nm

The size and concentration of exosomes were determined by nanoparticle tracking analysis using the NanoSight NS300 system (Malvern Instruments). And (3) diluting 2 mu L of freshly separated exosome with PBS (phosphate buffer solution) to 1 mL, placing the diluted exosome into an injector, injecting a sample into an instrument by an automatic mechanical pump at a constant speed, and tracking and analyzing through Brownian motion of particles to calculate the size and the concentration of the nanoparticles.

1.8.3 Western blotting experiment

(1) Preparation of cell and exosome protein samples

Extracting cell protein: when the cells were grown to 90% density on a 10 cm diameter cell culture dish, the supernatant was discarded, after washing 2 times with precooled PBS, the remaining PBS was sufficiently blotted using a pipette, RIPA lysate containing protease inhibitor was added on ice, and the lysate was rapidly collected with a cell scraper. After incubation on ice for 30 min, the supernatant was centrifuged at 10,000 Xg for 15 min at 4 ℃ to obtain a cell protein extract.

Exosome protein extraction: mixing exosome and RIPA lysate containing protease inhibitor according to the volume ratio of 1:1, incubating on ice for 30 min, and centrifuging at 4 ℃ and 10,000 Xg for 15 min to obtain supernatant, namely the protein extract of exosome.

(2) Protein concentration determination

The protein concentration was measured by the BAC method according to the protocol of protein quantification kit (BCA method) of Thermo corporation, as follows:

1) preparing a working solution: and uniformly mixing the reagent A and the reagent B according to the volume ratio of 50:1 to prepare working solution. The working solution needs to be prepared at present.

2) Preparing a standard solution: standard solutions of different concentrations (1500, 1000, 750, 500, 250, 125 and 0 μ g/mL) were obtained by dilution using PBS and protein standard solutions (2000 μ g/mL). 25 μ L of each concentration standard was added to a 96-well plate.

3) 2.5. mu.L of each sample was added to a 96-well plate, and PBS was added to make up the sample volume to 25. mu.L.

4) Add 200. mu.L of working solution to 96-well plate and mix gently to avoid air bubbles.

5) Incubate in a constant temperature box at 37 ℃ for 30 min in the dark.

6) And detecting the absorbance value at the wavelength of 562 nm by using a multifunctional microplate reader.

7) And establishing a standard curve according to the concentration of each standard solution and the measured absorbance value, and calculating the protein concentration of each sample through the standard curve.

(3) Western blot experiment

1) Preparing 10% separation gel, wherein the proportion of each component is as follows:

30% acrylamide solution	3.3 mL
		Gel separation buffer	2.5 mL
ddH2O	4.1 mL
		10% APS	0.1 mL
TEMED	4 μL

After mixing evenly, pouring the separation glue between the clean glass plates, and adding ddH₂O makes the separation gel level. After standing at room temperature for 30 min, a clear boundary was visible between water and the separation gel.

2) 5 percent of concentrated glue is prepared, and the proportion of each component is as follows:

30% acrylamide solution	0.68 mL
		Concentrated gel buffer	1.0 mL
ddH2O	2.28 mL
		10% APS	40 μL
TEMED	4 μL

Carefully discard ddH from the upper layer of the separation gel₂And O, adding the concentrated glue to the top of the glass plate, inserting a comb, standing at room temperature for 30 min, and then pulling out the comb.

3) Loading: after 1 Xelectrophoresis buffer was added to the electrophoresis chamber, equal amounts of protein samples were added to each well of the concentrated gel according to the protein concentration measured, and the protein marker was pre-stained for 6. mu.L.

4) Electrophoresis: and (3) using 80V constant voltage electrophoresis, adjusting the voltage to 120V after the sample enters the separation gel, continuing electrophoresis, and ending electrophoresis when bromophenol blue reaches the bottom of the separation gel.

5) Glue removing: one glass plate was removed carefully and the sample-free portion of the concentrated gel and the gel was cut off, and corner cut marked.

6) Film transfer: measuring the size of the residual glue, cutting a PVDF film according to the corresponding size, soaking the PVDF film in methanol for 3 min to balance the PVDF film, and placing the PVDF film in an electric rotating tank according to the sequence of black glue and white film. Switching on a power supply, setting the current to be 250 mA constant current, and carrying out ice bath or film conversion at 4 ℃ for 2 h.

7) Sealing and primary antibody incubation: the membranes were rinsed 3 times in TBST, blocked with 5% skim milk powder or 5% BSA at room temperature for 1h, and primary antibody was added, and placed on a shaker at 4 ℃ overnight.

8) And (3) secondary antibody incubation: rinsing with TBST 3 times at room temperature for 10 min, adding secondary antibody, and incubating at room temperature for 1 h.

9) Luminescence: and rinsing the sample by TBST for 3 times at room temperature, each time for 10 min, dripping a proper amount of luminous liquid for chemical color development, and collecting images.

Second, embodiment: preparation of exosome-containing scaffold by using 3D printing and performance detection method thereof

2.1 Experimental animals

The present invention was carried out in accordance with The "The Guide for The Care and Use of Laboratory Animals" (1996 edition) published by The national institutes of health, and The animal protocol was approved by The animal ethics committee of The department of medicine of Beijing university.

2.2 isolation and culture of MSCs

2.2.1 isolation and characterization of rat BMSCs

Rat BMSCs isolated and identified using the method described in 1.6.

2.2.2 isolation, culture and identification of human ADSCs

The protocol for the selection and testing of human adipose tissue specimens was approved by the ethical committee of the third hospital of Beijing university. The patient signs an informed consent. Human adipose tissue specimens were derived from the waste infrapatellar adipose pad tissue in arthroscopic descending knee joint cruciate ligament reconstruction. Immediately putting the obtained tissue into sterile physiological saline, and conveying the tissue to a laboratory for primary cell culture by using a low-temperature ice box special for clinical specimens. The 2 nd generation ADSCs are identified by three-line differentiation (see 1.1-1.3) and flow cytometry (see 1.4).

2.3 extraction and identification of exosomes

See 1.7 and 1.8.

2.4 Material preparation and characterization

2.4.1 preparation of gelatin-methacrylic anhydride

(1) 6 g of gelatin was weighed into 60 mL volume of PBS, and dissolved in a water bath at 50 ℃ with stirring.

(2) Methacrylic anhydride 300. mu.L was added dropwise using a pipette.

(3) Stirring is continuously carried out for 1h in a water bath at 50 ℃ in the dark.

(4) The reaction was stopped by adding 200 mL of PBS at 37 ℃ and stirred rapidly for 10 min.

(5) Transferring to dialysis bag, sealing, and adding ddH₂Dialyzing in a large beaker of O in an oven at 37 ℃ for 3 days, and replacing ddH at intervals of 12 h₂O。

(6) Freeze-drying, and storing at ‒ 20 deg.C for use.

2.4.2 preparation of oxidized hyaluronic acid

(1) Hyaluronic acid 1 g was weighed and added to ddH in a volume of 100 mL₂In O, dissolve with magnetic stirring at room temperature.

(2) 550 mg of sodium periodate are weighed out and dissolved in a volume of 5 mL of ddH₂And (4) in O.

(3) The sodium periodate solution was added dropwise to the hyaluronic acid solution using a pipette and stirred at room temperature for 2 h.

(4) Transferring to dialysis bag, sealing, and adding ddH₂Dialyzing in O big beaker for 3 days, and replacing ddH every 12 h₂O。

(5) Freeze-drying, and storing at ‒ 20 deg.C for use.

2.4.3 hyaluronic acid-dopamine preparation

(1) Hyaluronic acid 1 g was weighed and added to ddH in a volume of 100 mL₂In O, dissolve with magnetic stirring at room temperature.

(2) 575 mg of EDC and 345 mg of NHS were added and stirred at room temperature for 20 min.

(3) 569 mg of dopamine hydrochloride is added and stirred for 3 h in the absence of light, during which time the pH is maintained in the range of 5 ‒ 6, and the reaction is continued for 21 h.

(4) Filling into dialysis bag and sealing, and applying ddH with pH of 3 ‒ 4₂After 2 days of O dialysis, ddH was continued₂O dialysis for 1 day, during which ddH was replaced at 12 h intervals₂O。

(5) Freeze-drying, and storing at ‒ 20 deg.C for use.

2.4.4 NMR spectroscopy

Preparing 1% gelatin, 1% GelMA, 0.8% HA, 0.8% OHA and 0.8% HA-DA hydrogel by using heavy water, fully stirring uniformly, transferring into a cylindrical nuclear magnetic resonance spectroscopy (NMR) glass sample tube, and detecting on a machine while paying attention to avoid bubbles.

2.5 acellular matrix preparation

Fresh specimens of 6-month old femurs of pigs were used to remove surrounding soft tissues such as fat, muscle, fascia, etc. A cartilage acellular matrix (DCM) was prepared as follows.

2.5.1 cartilage acellular matrix preparation

(1) The cartilage at the distal trochlear of the femur was carefully dissected using a surgical blade, into cartilage pieces approximately 1 mm thick, taking care not to dissect the subchondral bone.

(2) The cartilage pieces were placed in a 50 mL centrifuge tube, frozen with liquid nitrogen, then subjected to a 37 ℃ water bath for 6 cycles.

(3) The washing was carried out 4 times at 37 ℃ for 6 h with 0.25% trypsin solution (containing EDTA).

(4) The cells were washed for 4 h at 37 ℃ with DPBS containing 10 mM Trizma-HCl, DNase (50U/mL) and RNase A (1U/mL).

(5) 10 mM Trizma-HCl wash 24 h.

(6) DPBS wash with 0.5% SDS for 24 h.

(7) The DPBS solution containing 1% Triton X-100 was washed for 24 h.

(8) DPBS wash until foam disappeared.

(9) Freeze drying, grinding into powder with ball mill, and storing at ‒ 20 deg.C for use.

2.6 characterization of the acellular matrix

2.6.1H & E staining of tissue sections

(1) Dewaxing and hydrating:

xylene substitute I	10 min
		Xylene substitute II	10 min
Xylene substitute III	10 min
		Anhydrous ethanol I	5 min
Anhydrous ethanol II	5 min
		95% ethanol	5 min
85% ethanol	5 min
		75% ethanol	5 min
Distilled water	3 min

(2) Dyeing:

1) staining with hematoxylin for 4 min, and washing off with distilled water.

2) The mixture is separated in 1% ethanol hydrochloride differentiation solution for 10 s and washed with distilled water.

3) Return to blue was observed in 0.5 ‒ 1% ammonia for 10 seconds(s), rinsed with distilled water.

4) Eosin staining for 40 s, and washing with distilled water to remove loose color.

(3) And (3) dehydrating and transparency:

dehydration with 95% ethanol I	20 s
		95% ethanol dehydration II	20 s
Dehydration with anhydrous ethanol I	20 s
		Dehydration with anhydrous ethanol II	20 s
Clear xylene substitute after dyeing I	3 min
		Clear xylene substitute after dyeing II	3 min

(4) The neutral gum was encapsulated, air dried and observed under a microscope and photographed.

2.6.2 tissue section DAPI staining

(1) Dewaxing and hydrating: see 2.6.1.

(2) DAPI staining: the DAPI stain was dropped onto the specimen and incubated for 10 min at room temperature in the dark.

(3) PBS wash 3 times, each 3 min.

(4) After mounting, images were taken using a fluorescence microscope.

2.6.3 DNA content detection

(1) Preparing papain lysate: papain 125. mu.g/mL, 5 mM Na2-EDTA, 5 mM L-cysteine, 0.1M sodium acetate, adjusted to pH 6.2.

(2) 10 mg of the freeze-dried normal cartilage and DCM powder are respectively added into 1 mL of papain lysate, and the papain lysate is placed in an oven at 60 ℃ for lysis for 24 h.

(3) 200 mu.L of Hoechst 33258 working solution (2 mu g/ml) is added into a 96-well plate, and then 20 uL of sample lysate or calf thymus DNA standard substance with each concentration is added into each well, and the incubation is carried out for 1h in a incubator at 37 ℃ in the dark.

(4) 100. mu.L of the mixture was added to a 96-well plate, and the fluorescence value was measured using a multifunctional microplate reader (excitation light: 360 nm, emission light: 460 nm).

(5) Drawing a DNA standard curve, and calculating the DNA concentration of each sample.

2.6.4 GAG content detection

(1) Adding 200 mu L of 1, 9-dimethyl methylene blue (DMMB) solution into a 96-well plate, adding 20 mu L of the sample lysate or chondroitin sulfate standard substances with different concentrations, and fully and uniformly mixing.

(2) Incubate at room temperature in dark for 30 min.

(3) The absorbance value at 525 nm was measured using a multifunctional microplate reader.

(4) Draw standard curve, calculate GAG concentration of each sample.

2.6.5 hydroxyproline content assay

The hydroxyproline detection kit produced by Nanjing institute of bioengineering is used for evaluating the change of the collagen content before and after cell removal by measuring the hydroxyproline content. The oxidation product generated by hydroxyproline under the action of an oxidant can react with dimethylaminobenzaldehyde to show purple red, and the content is calculated according to the absorbance value of the oxidation product.

(1) Reagent one, reagent two and reagent three were prepared according to the instructions.

(2) Respectively taking 200 mu L ddH₂O, the standard substance and the above-mentioned sample lysate are added to an EP tube containing 100. mu.L of the first reagent, mixed well and then left to stand for 10 min.

(3) Adding 100 mu L of reagent II, mixing uniformly and standing for 5 min.

(4) Adding 100 μ L of reagent III, mixing, and heating in water bath at 60 deg.C for 15 min.

(5) 3500 rpm/min, 10 min of centrifugation.

(6) 100 μ L of the supernatant was added to a 96-well plate, and the absorbance at a wavelength of 550 nm was measured using a multifunctional microplate reader.

(7) And calculating the hydroxyproline content in the sample according to the concentration of the standard substance.

2.6.6 gelling Capacity test

(1) Preparing DCM ink:

1) 15 mg of pepsin was weighed into 5 mL of a 0.1M hydrochloric acid solution, and stirred at room temperature for 30 min.

2) 150 mg of DCM powder is weighed, added with the hydrochloric acid solution containing pepsin and sealed and stirred at room temperature for 72 h to obtain DCM ink.

3) The DCM ink was placed on ice and the pH was carefully adjusted to 7.4 using sodium hydroxide solution, taking care to add small amounts multiple times to avoid pH above 7.4.

(2) Adding a proper amount of DCM ink into a glass tube, putting the glass tube into an incubator at 37 ℃ for incubation for 30 min, and then, inverting to observe whether the glass tube is gelatinized or not and photographing.

(3) The dynamic changes in elastic modulus G 'and viscous modulus G' of DCM inks with temperature changes were examined using a rheometer.

2.7 printing and characterization of stents

2.7.1 hydrogel Bio-ink preparation

(1) Preparing Hydrogel biological ink:

1) 0.9 g GelMA was weighed into 5 mL ddH₂In O, 0.2 g of OHA was added after dissolving the compound at 37 ℃ with stirring, and the solution was further dissolved with stirring.

2) 0.2 g HA-DA and 0.04 g photoinitiator were weighed out and 5 mL of double distilled water (ddH) was added₂O), the mixture was dissolved at room temperature with stirring.

3) And uniformly mixing the two solutions to obtain the Hydrogel biological ink.

(2) Preparing Hydrogel-DCM biological ink:

1) 0.9 g GelMA was weighed into 5 mL ddH₂In O, 0.2 g of OHA was added after dissolving the compound at 37 ℃ with stirring, and the solution was further dissolved with stirring.

2) 5 mL of 4% DCM ink was prepared as described in 2.6.6, and after adjusting the pH to 7.4, 0.2 g of HA-DA and 0.04 g of photoinitiator were added and dissolved with stirring at room temperature.

3) And uniformly mixing the two solutions to obtain the Hydrogel-DCM ink biological ink, wherein the two solutions are not arranged in sequence.

(3) Preparing Hydrogel-DCM-Exos biological ink: after being prepared, the Hydrogel-DCM biological ink is added with the ADSCs exosomes, and the final concentration is 100 mug/mL.

In order to study the effect of different variable concentrations on bio-ink, the inventors performed several sets of control experiments based on this example, and the specific changes of the experimental variables are shown in the following table:

variable names	First group	Second group	Third group	Unit of
					GelMA	6%	9%	12%	Mass percent
OHA	0.50%	2%	4%	Mass percent
					HA-DA	0.50%	2%	4%	Mass percent
DCM	0.50%	2%	4%	Mass percent
					Photoinitiator	0.10%	0.20%	0.40%	Mass percent
Final concentration of exosomes	10	100	1000	μg/mL

A specific value was chosen for each variable as an experimental group, for example:

GelMA (6%), OHA (0.5%), HA-DA (0.5%), DCM (0.5%), photoinitiator (0.1%) and mesenchymal stem cell exosome with the final concentration of 10 mug/mL are taken as an experimental group, and by analogy, 729 specific experimental schemes are counted.

2.7.2 printing of stents

Stent printing was performed using a 3D-Bioplotter (envisionTEC) bioprinter. The height of the set layer, the line width and the line spacing are all 320 mu m, the printing pressure is 2.5 ‒ 3.5.5, the printing speed is 8 ‒ 15 mm/s, the platform temperature is 10 ℃, and the ink cabin temperature is 18 ‒ 22 ℃. In vitro experiments each scaffold was printed in 6 layers. The printed scaffolds were placed on ice and UV irradiated for 20 min to fully crosslink.

2.7.3 characterization of the Stent

(1) Observation by scanning electron microscope

1) The Hydeogel, Hydeogel-DCM scaffolds were freeze dried.

2) And placing the three brackets on black conductive adhesive, and carrying out gold spraying treatment on the surface.

3) The microstructure of the scaffold was observed and photographed using a scanning electron microscope (JSM-7900F, JEOL, Japan).

(2) Fourier Infrared Spectroscopy

1) Two scaffolds, gelatin, GelMA, HA, OHA, HA-DA, DCM and Hydeogel, Hydeogel-DCM, were freeze dried and ground into powder.

2) Mixing with potassium bromide solid according to the mass ratio of 1:100, fully grinding and pressing into slices.

3) 4000-400 cm^-1Scanning wavenumber of range and 4 cm^-1And (3) analyzing the secondary structure of the protein by Fourier infrared spectroscopy.

(3) Degradation rate detection of stents

1) Each rack was printed in the same size and after freeze drying, each rack was weighed to have a dry weight Wi.

2) The scaffolds were placed into round-bottom centrifuge tubes containing 1 mL of PBS, respectively, and placed in an incubation shaker at 37 ℃ and 30 rpm/min.

3) PBS was changed every 3 days, scaffolds were removed at predetermined times, ddH₂O washes 2 times, after freeze drying the measurement stand was weighed as Wt.

4) Degradation rate = (Wt-Wi)/Wi × 100%.

(4) Swelling Rate detection of scaffolds

The same size of each stand was printed and the filter paper was weighed as Wi to wick away surface moisture. Placed into a round bottom centrifuge tube containing 1 mL PBS and incubated in an incubator at 37 ℃. Removing holders, ddH, at predetermined times₂O washes were performed 2 times and the filter paper was weighed as Wt after absorbing surface water. Swelling ratio = (Wt-Wi)/Wi × 100%.

(5) Exosome release

The same weighed quantity of Hydrogel-DCM, Hydrogel-DCM-Exos, scaffold was placed in the upper chamber (8 μm) of a different Transwell, 150 μ L of PBS was added to the lower chamber, and the mixture was incubated in a 37 ℃ incubator. At predetermined times, 15. mu.L of PBS was removed from the lower chamber and an equal volume of PBS was added. The protein content of PBS removed at each time point was measured using the micro BCA kit, and the percentage of exosomes released was calculated.

2.8 biocompatibility of the scaffold

2.8.1 cells were seeded on scaffolds

(1) The UV-irradiated scaffolds were placed in MEM-alpha complete medium containing 10% exosome-free FBS and incubated at 37 ℃ for 24 h in a cell culture chamber.

(2) Rat BMSCs from passage 3 were digested with 0.25% trypsin for about 2 min, centrifuged at 800 rpm/min for 3 min, and the cells were resuspended in complete media of 10% exosome-free FBS in MEM- α.

(3) Adjusting the cell suspension density to 1 × 10⁷and/mL, dropwise adding 100 mu L of the suspension onto a bracket, placing the bracket in a cell culture box at 37 ℃ for incubation for 4 h, replacing a culture medium, and continuing to culture or inducing differentiation.

2.8.2 Activity of cells on scaffolds

(1) After plating the cells on the scaffolds as described in 2.8.1 above, culture was continued for 24 h.

(2) Preparing Live/Dead cell activity detection working solution: mu.L of Live reagent was mixed into 499 ul of PBS, 1. mu.L of Dead reagent was mixed into 499 ul of another PBS, and the mixture was homogenized to obtain Live/Dead working solution. Live/Dead working solution is prepared at present.

(3) The scaffolds were washed 2 times with PBS, transferred to a confocal dish, added with 1 mL Live/Dead working solution, and incubated in a 37 ℃ cell incubator for 15 min.

(4) The working solution was discarded, the scaffolds were washed 2 times with PBS, and the distribution of live cells (green fluorescence) and dead cells (red fluorescence) on the scaffolds was observed using a laser confocal microscope.

2.8.3 morphology of cells on scaffolds

(1) After plating the cells on the scaffolds as described in 2.8.1 above, culture was continued for 72 h.

(2) The supernatant was discarded, cells were fixed with 4% paraformaldehyde for 15 min and washed 3 times with PBS for 5 min each.

(3) The cytoskeleton is stained with rhodamine ‒ phalloidin for 15 min, and washed with PBS for 3 times, 5 min each time.

(4) Nuclei were stained with Hoechst 33342 for 15 min and washed 3 times with PBS for 5 min each.

(5) Observed by confocal laser microscopy and photographed.

2.8.4 detection of proliferation potency of cells on scaffolds

(1) After the cells were seeded on the scaffolds as described in 2.8.1 above, culture was continued by replacing the MEM-alpha complete medium containing 10% of exosome-free FBS.

(2) After 1 d, 3d, 5 d and 7d the scaffolds were removed, washed 3 times with PBS, and placed in new 24-well cell culture plates.

(3) 1 mL of MEM-. alpha.medium containing 10% of CCK-8 reagent (ready to use) was added to each well, and incubated in a cell incubator at 37 ℃ for 2 hours.

(4) A volume of 100. mu.L of the incubation solution was placed in a 96-well cell culture plate, and the absorbance at a wavelength of 450 nm was measured using a microplate reader.

2.9 chondrogenic and osteogenic induced differentiation of cells on scaffolds

After BMSCs were planted in scaffolds and cultured for 3d, washed 2 times with PBS, and replaced with cartilage-induced differentiation complete medium or osteogenic-induced differentiation complete medium (FBS without exosome) for induction of 7d and 14 d, respectively. The next correlation test is then performed.

2.9.1 qRT-PCR detection

And detecting the expression of the chondrogenic and chondrogenic related gene mRNA by adopting qRT-PCR. After 7d and 14 d of chondrogenic or osteogenic induction, the scaffolds were taken out and washed 2 times with PBS, placed in EP and a volume of 0.5 mL TRIzol reagent was added, sufficiently sheared, placed on ice for 30 min, shaken every 10 min, and subjected to subsequent operations, or stored at ‒ 80 ℃ for later use. See 3.2.11 for details of methods otherwise.

2.9.2 cellular immunofluorescence assay

After chondrogenic or osteogenic induced differentiation 14 d, chondrogenic and chondrogenic-related gene protein expression was detected using cellular immunofluorescence.

Third, 3D prints the experimental result of the prepared support containing exosome

3.11H NMR spectroscopy

After the synthesis of the gelatin derivative GelMA and the hyaluronic acid derivatives OHA and HA-DA, the change in the Pop of each material was analyzed by 1H NMR spectroscopy. As can be seen in FIG. 1A, GelMA gave new signals at the 5.3 and 5.5 ppm positions, indicating successful binding of acrylic acid to gelatin; the decrease in peak at 2.9 ppm and the appearance of a new signal at the 1.8 ppm position represent a combination of methyl groups, demonstrating the successful synthesis of GelMA in the present invention. As shown in figure 1B, the new signals present at 4.9 and 5.0 ppm in OHA represent binding of aldehyde groups to HA, indicating successful OHA synthesis; the new signal appearing at the 6.7 ppm position of HA-DA represents the signal of the phenyl ring, and the new signal appearing at 2.76 ppm represents the-CH 2 group adjacent to the phenyl ring, demonstrating that dopamine successfully binds HA to form HA-DA.

3.2 characterization of the acellular matrix

Collecting articular cartilage, and performing decellularization treatment to obtain a cartilage decellularized matrix DCM. Bulk observation revealed that DCM was overall thinner and brighter than normal cartilage before decellularization (fig. 2). DCM was seen to have no cell and cell debris remaining by H & E staining, while DAPI staining demonstrated that none of the nuclei in DCM disappeared (fig. 2), indicating that the decellularization process effectively removed the cellular components of cartilage. The DNA content test result shows that the DNA content in DCM is 14.2 + -1.7 ng/mg respectively (FIG. 3A), which is lower than the standard of 50 ng/mg of acellular matrix biological material. To further evaluate the effect of the decellularization process on cartilage and bone tissue components, the subject examined the content of GAG and collagen before and after decellularization of both tissues, respectively. The results showed that the GAG content in DCM was 28.7% of that in normal cartilage tissue (fig. 3B), respectively, while the collagen content in DCM was 77.7% of that in normal cartilage tissue (fig. 3C), respectively.

The acellular matrix material biological ink can self-assemble to form jelly and maintain the shape at 37 ℃. Subsequently, the pH of the DCM bio-ink pre-gel was adjusted to neutral by the present invention on ice, and after 30 min of incubation at 37 ℃, DCM acellular matrix was observed to form a gel, which substantially maintained the morphology after inversion (fig. 4A). Subsequently, the invention adopts a rheometer to further detect the dynamic changes of the elastic modulus G 'and the viscous modulus G' of the two acellular matrix biological ink pre-gels along with the temperature change. The results show that at below 15 ℃, DCM pregel behaves more like a liquid material, with a significant increase in elastic modulus G 'starting after 15 ℃, while after incubation for a period of time at 37 ℃, the rheological behavior behaves like a cross-linked gel with an elastic modulus G' significantly higher than the viscous modulus G "(fig. 4B).

3.3 characterization of the Stent

3.3.1 microstructure of scaffolds

GelMA accounts for the main proportion in various biological ink systems, so that the biological ink has good printing performance. After the printed scaffold was freeze-dried, the effect of the decellularized matrix on the micro-morphology of the bioscaffold was observed by scanning electron microscopy (fig. 5). The surface of a Hydrogel stent line printed by three components of GelMA, HA-DA and OHA biological ink is smooth, the concave-convex wavy morphology can be seen, and after the acellular matrix is added, an obvious pore structure can be seen in the stent line. The addition of DCM can obviously improve the internal pore diameter of the stent line, and the combination of the frame big pore and the line small pore of the 3D printing stent is realized.

3.3.2 degradation Rate, swelling detection and Infrared Spectroscopy of scaffolds

As shown in FIG. 6A, 72 h of the Hydrogel scaffold and the Hydrogel-DCM Hydrogel scaffold reach the equilibrium state of water absorption, and the water absorption rates are 221.0% and 187.8% respectively, which shows that the addition of DCM can reduce the swelling rate of the Hydrogel. The degradation rates of the Hydrogel scaffold of Hydrogel and Hydrogel-DCM were 77.9% and 64.1% in 28 days, respectively (FIG. 6B), indicating that the addition of acellular matrix can delay the degradation of the scaffold. Fourier transform infrared spectroscopy was used to characterize the various components of the present invention and the printed hydrogel scaffolds (fig. 6C) to determine the chemical composition and structural changes of the scaffolds. Wherein, the peak at 1652 cm-1 represents C = O in the Amide (Amide) I interval, the peak at 1534 cm-1 represents N-H in the Amide II interval, and the peak at 1230 cm-1 represents C-N in the Amide III interval. A signal peak appears at 1735 cm < -1 > in OHA and represents the introduction of-CHO, and the signal peak disappears in Hydrogel and Hydrogel-DCM, which indicates that the-CHO and-NH 2 undergo Schiff base reaction to form a dynamic covalent bond network.

3.4 biocompatibility of the scaffold

BMSCs were seeded on Hydrogel scaffolds and Hydrogel-DCM scaffolds and after 24 h incubation Live/Dead staining was performed on each set of scaffolds (FIG. 7A). It was observed by confocal laser microscopy that the BMSCs on both scaffolds exhibited mostly live cells, and only individual dead cells were visible. The appearance of individual dead cells corresponds to the normal growth cycle of the cells. As can be seen, no significant cytotoxicity was found for either scaffold.

In order to further observe the distribution and morphological characteristics of BMSCs on the scaffold, rhodamine ‒ phalloidin and DAPI are adopted to stain cytoskeleton and cell nucleus respectively. Observation under a laser confocal microscope shows that after BMSCs are planted on the scaffold and cultured for 3d, cells on the Hydrogel-DCM scaffold containing the acellular matrix are uniformly distributed along the line of the scaffold, and the cytoskeleton presents a shape walking in a consistent direction; in the Hydrogel scaffold, cells are distributed along the scaffold and aggregated, and the cytoskeleton morphology is relatively disordered (fig. 7B). The results indicate that the acellular matrix component can obviously improve the extensibility of the cells on the scaffold and promote the uniform distribution of the cells in a three-dimensional microenvironment.

3.5 identification of human ADSCs

In order to verify whether the ADSCs derived from the human infrapatellar fat pad extracted by the method are MSCs or not, the method performs a three-line induced differentiation test and flow cytometry. As shown in fig. 8, positive staining of oil red O, alizarin red, and alisnew blue indicates that the ADSCs have adipogenic, osteogenic, and chondrogenic differentiation abilities, respectively, suggesting that the MSCs have multipotentiality. Detecting cell surface markers by flow cytometry, wherein the positive rates of CD34, CD45 and HLA-DR are respectively 2.3%, 2.1% and 1.8%, and the positive rates are negative expressions; and the positive rates of CD29, CD73, CD90 and CD105 are respectively 99.9%, 100%, 99.8% and 99.9%, and the expression is strong positive (figure 9). The above results demonstrate that the ADSCs derived from human infrapatellar fat pads extracted by the present invention meet MSCs characteristics.

3.6 identification of exosomes derived from human ADSCs

Collecting cell culture supernatant of the human ADSCs, and separating by a differential centrifugation method to obtain exosomes. Transmission electron microscopy revealed a "cup-like" or "disc-like" structure typical of exosomes (fig. 10A). The nanometer particle size analysis and detection shows that the diameters of the extracted exosomes are mainly distributed below 160 nm, the average diameter is 140.3 nm (figure 10B), and the result of the Western blotting experiment shows that the isolated human ADSCs exosomes highly express the exosome-specific protein markers CD81, TSG101 and ALIX, while the expression level of the endoplasmic reticulum-specific protein marker Calnexin is very low (figure 10C).

3.7 distribution and sustained Release of exosomes in acellular matrix scaffolds

Subsequently, the present invention adds exosomes of human ADSCs to the bio-ink containing the acellular matrix, aiming to further enhance the biological function of the scaffold containing the acellular matrix by the exosomes. It was observed by confocal laser microscopy that exosomes labeled with PKH67 fluorescent dye were evenly distributed along the scaffold lines, and the black pores between the lines indirectly demonstrate the observed fluorescence emitted by the scaffold lines for exosomes (fig. 11A and 11B). As can be seen from the sustained release curve, both the Hydrogel-DCM-Exos and Hydrogel-DCM-Exos exosome scaffolds can stably release exosomes for more than 24 days (FIG. 11C).

3.8 Effect of exosome acellular matrix scaffolds on BMSCs viability

BMSCs were planted on scaffolds for 1, 3,5, and 7 days, and then CCK-8 was used to examine the effect of each group of scaffolds on cell viability, with day 1 cell viability as a reference. The results showed that no cytotoxicity was observed in all the groups of scaffolds. On day 7, the cell viability of BMSCs on the Hydrogel-DCM scaffolds with added acellular matrix was significantly higher than that of the Hydrogel group (P < 0.01), while the cell viability of BMSCs on the exosome-containing Hydrogel-DCM-Exos scaffolds was significantly higher than that of the other groups (P < 0.001) (FIG. 12). The addition of acellular matrix and exosome proves that a synergistic effect is generated, and the biocompatibility of the scaffold is increased.

3.9 in vitro induced differentiation of BMSCs on different scaffolds

3.9.1 chondrogenic differentiation of BMSCs on scaffolds

In order to evaluate the effect of three scaffolds, namely Hydrogel, Hydrogel-DCM and Hydrogel-DCM-Exos, in promoting chondrogenic differentiation of BMSCs in vitro, BMSCs were seeded on scaffolds and cultured for 3 days, and chondrogenic-induced differentiation was performed. The expression of mRNA of cartilage-related genes in various scaffolds was examined by qRT-PCR (FIG. 13A, FIG. 13B, FIG. 13C, and FIG. 13D). After 7 days of induction, ACAN, COL II and SOX9 expression in the Hydrogel-DCM-Exos group was highest in all three groups, but only the difference from the Hydrogel group was statistically significant (P < 0.01). After 14 days of induction, the expression of ACAN, COL II and SOX9 was further increased in three groups, and the expression was significantly higher in the Hydrogel-DCM-Exos group and the Hydrogel-DCM group than in the Hydrogel group, and the difference between the three groups was statistically significant. For the hypertrophic chondrocyte marker COL X, the expression was significantly lower in both the Hydrogel-DCM-Exos group and the Hydrogel-DCM group (P < 0.01) after 14 days of induction (FIG. 13D). The cellular immunofluorescence results showed that the expression of COL II protein was highest in the Hydrogel-DCM-Exos group and second in the Hydrogel-DCM group 14 days after induction, while the expression of the mRNA was consistent with the expression of the protein in the Hydrogel group (FIG. 13E). For SOX9, although no significant expression difference was observed between the Hydrogel-DCM-Exos group and the Hydrogel-DCM group, the expression was higher than that of SOX9 in the Hydrogel group (FIG. 13E). The results show that the effect of the Hydrogel-DCM scaffold added with the cartilage acellular matrix is better than that of a Hydrogel scaffold in the aspect of chondrogenic induced differentiation of MSCs, and the function of promoting cartilage regeneration of the scaffold is further improved by adding exosomes.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.