Objective:To investigate the effect of tissue engineered bladder patch constructed by double-layer silk scaffold and adipose-derived stem cells (ADSCs) in the repair and reconstruction of bladder.Methods:This study was conducted from May 2020 to March 2021. The silk fibroin (SF) aqueous solution was obtained from silkworm cocoons, and a double-layer silk scaffold composed of silk fibroin film and silk fibroin sponge was further prepared. The rat ADSCs were isolated, cultured, and the ADSCs surface markers (CD29, CD90, CD45, CD106) were identified by flow cytometry. The ADSCs were planted on a double-layer silk scaffold to construct a tissue-engineered bladder patch. Thirty-six male SD rats were randomly divided into three groups: tissue engineered bladder patch group (SF-ADSCs group, n=15), double-layer silk scaffold group (SF group, n=15), control group ( n=6). The tissue engineered bladder patch (SF-ADSCs group) and double-layer silk scaffold (SF group) were wrapped on the omentum to promote vascularization. The vascularization was evaluated by HE and immunofluorescence staining. The wrapped tissue engineered bladder patch and double-layer silk scaffold were used to repair the defective bladder. In the control group (six rats), the incision was closed immediately after the bladder tissue fully exposed. At 4 weeks and 12 weeks after operation, the general morphology of bladder tissue and cystography were performed to evaluate the recovery of bladder morphology. After the graft was harvested, HE and Masson's trichrome staining and immunofluorescence staining were used to observe the regeneration of bladder wall tissue. Urodynamics was used to assess the recovery of bladder function at 12 weeks after operation. Results:The flow cytometry results confirmed that the isolated cells positively expressed CD29 and CD90, and there was no significant expression of CD45 and CD106. Gross observation and scanning electron microscope confirmed that the preparation of double-layer silk scaffold not only had a pore structure that was conducive to cell planting, but also had good toughness and was facilitated to surgical suture. The number (43.50±2.66) and area (0.73±0.03)% of vascular-like structures in the SF-ADSCs group after the omentum encapsulation was significantly higher than that in the SF group [(24.50±3.51), (0.55±0.05)%], and the difference was statistically significant ( P<0.05). At 4 weeks after bladder repair, the histological staining of the grafts in the SF-ADSCs and SF groups showed a large number of degraded fragments of double-layer silk scaffold. At 12 weeks, the morphology of the graft in the SF-ADSCs group showed uniform bladder morphology, which was similar to that of normal bladder tissue. Immunofluorescence staining showed that the continuous urothelial layer, abundant smooth muscle tissue, vascular structure and regenerated neurons could be observed in the SF-ADSCs group. Urodynamic test showed that the bladder maximum volume (0.74±0.03)ml and compliance (16.68±0.44)μl/cm H 2O in the SF-ADSCs group, which were better than that in the SF group [(0.47±0.05)ml, (14.89±0.37)μl/cm H 2O], but lower than that in the control group [(1.12±0.08)ml, (19.34±0.45)μl/cm H 2O], and the difference was statistically significant ( P<0.05). Conclusions:The tissue engineered bladder patch constructed with double-layer silk scaffolds and ADSCs could promote the morphological repair of bladder tissue, the regeneration of bladder wall structure and the recovery of bladder physiological function.

Objective:To prepare the whole bladder acellular matrix (BAM) using the self-designed perfusion decellularization system, and evaluate the feasibility of constructing the tissue engineering bladder with the adipose-derived stem cells (ADSCs).Methods:This study was conducted from October 2020 to April 2021. The self-designed perfusion decellularization system was used, and four different decellularization protocols (group A, group B, group C and group D) were formulated, according to the flow direction of the perfusate and the action time of different decellularization solutions. Among them, the urethral orifice of the bladder tissue was used as the outflow tract of the perfusion fluid in groups A and B. The top of the bladder was cut off and used as the outflow tract of the perfusion fluid in groups C and D. In groups A and C, 1% Triton X-100 was treated for 6 h, and 1% sodium dodecyl sulfate (SDS) was treated for 2 h. In groups B and D, 1% Triton X-100 was treated for 7 h, and 1% sodium dodecyl sulfate (SDS) was treated for 1 h. In addition, the tissue in the normal bladder group was directly obtained from the natural bladder tissue, which did not require perfusion, cryopreservation and thawing. The fast and efficient decellularization protocol was screened out through HE, DAPI, Masson trichrome and Alcian Blue staining and quantitative analyses to prepare the whole bladder scaffold. The prepared BAM was used as the scaffold material, and the ADSCs were used as the seeding cells to construct the tissue engineering bladder. HE and DAPI staining were used to observe the distribution of ADSCs on the BAM.Results:HE and DAPI staining showed that there was no obvious nuclear residue in the group C. Masson trichrome and Alcian Blue staining showed that the collagen structure and glycosaminoglycan were well preserved in the group C. There was no significant difference in bladder wall thickness between the group C and the normal bladder group [(975.44±158.62)μm vs.(1 064.49±168.52)μm, P > 0.05]. The DNA content in the group C [(43.59 ±4.59) ng/mg] was lower than that in the normal bladder group, group A, group B and group D [(532.50±26.69), (135.17±6.99), (182.49±13.69) and(84.00±4.38)ng/mg], and the difference was statistically significant ( P<0.05). The collagen content [(10.98 ± 0.29)μg/mg] and glycosaminoglycan content [(2.30±0.18)μg/mg] in group C were not significantly different with those in the normal bladder group [(11.69±0.49) and (2.36±0.09)μg/mg, P>0.05]. Scanning electron microscopy showed that a large number of pore structures could be observed on the surface of the prepared BAM in groups A-D and were facilitated to cell adhesion. The isolated and cultured ADSCs were identified by flow cytometry to confirm the positive expression of CD90 and CD29, and the negative expression of CD45 and CD106. Live/dead staining and CCK-8 detection confirmed that the prepared BAM in the group C had no cytotoxicity. HE and DAPI staining showed that a large number of ADSCs were distributed on the surface and inside of the tissue engineering bladder. Conclusions:The whole bladder shape BAM prepared by the self-designed perfusion decellularization system could be used as the scaffold material for bladder tissue engineering, and the constructed tissue engineering bladder could be used for bladder repair and reconstruction.

Objective:This study aimed to investigate the physical properties, biocompatibility, and 3D printing performance of a novel hybrid bioink composed of gelatin methacrylated (GelMA) and chitin nanocrystal (ChiNC).Methods:The study was conducted from May 2021 to December 2022, four different bioinks were prepared by adding varying amounts of ChiNC to GelMA bioink. The GelMA concentration in all four bioinks was 100 mg/ml, while the ChiNC concentrations were 0 mg/ml (no ChiNC added), 5 mg/ml, 10 mg/ml, and 20 mg/ml, respectively, named as GC0, GC5, GC10, and GC20 bioinks. The cross-sectional morphology of the hydrogels formed after photocuring the four bioinks was observed using scanning electron microscopy, and the porosity was calculated. Weighing the hydrogels before and after swelling, and then calculate the equilibrium swelling rate. HUVECs were seeded on the surfaces of the hydrogels prepared from the four bioinks and cultured in medium. Cell proliferation was assessed using CCK-8 assays at 1d, 3d, and 7d to compare the proliferation rates of cells on the four hydrogels. HUVECs were added to the four bioinks, and grid-like scaffolds were printed and cultured in medium. Live-Dead staining was performed at 1d and 7d to observe cell viability. Compare the printing effect of bioinks by observing its forming continuous threads properties during extrusion. Finally, tissue-engineered bladder patches simulating the mucosal layer, submucosal layer, and muscular layer anatomical structures of the bladder wall were 3D bioprinted using the optimized bioink composition, and the stability and fidelity of the printed structures were observed to further validate the feasibility of printing multi-layered complex structures with the bioink.Results:Scanning electron microscopy revealed that the porosity of the GC0, GC5, GC10, and GC20 hydrogels were (51.43±6.23)%, (51.85±6.47)%, (50.55±4.59)%, and (42.49±2.20)%, respectively. The differences in porosity between the GC0 group and the other three groups were not statistically significant ( P=0.9994, P=0.9948, P=0.1200). The equilibrium swelling ratio of the other three groups [(8.81±0.41), (7.95±0.19), (7.71±0.14)] was significantly lower than that of the GC0 group (9.37 ± 0.49), and the differences were statistically significant ( P=0.0457, P<0.01, P<0.01). CCK-8 assay showed no significant difference in absorbance value between the GC10 group (0.360±0.009) and the GC0 group (0.357±0.007), GC5 group (0.350±0.012), and GC20 group (0.345±0.018) on the first day ( P=0.9332, P=0.5464, P=0.4937). However, on the third day, the absorbance value of the GC10 group (0.755±0.012) was significantly higher than that of the GC0 group (0.634±0.010), GC5 group (0.704±0.009), and GC20 group (0.653±0.015) ( P<0.01, P=0.0033, P=0.0002). On the seventh day, the absorbance value of the GC10 group (1.001±0.031) was significantly higher than that of the GC0 group (0.846±0.026), GC5 group (0.930±0.043), and GC20 group (0.841±0.024)( P=0.0012, P=0.1390, P=0.0010). The addition of human umbilical vein endothelial cells (HUVECs) into the four groups of hydrogels enabled the printing of grid-like scaffolds, and Live-Dead staining was performed on day 1 and day 7. The cell viability of HUVECs in the four groups on day 1 was (90.13±1.63)%, (90.6±2.45)%, (92.58±2.15)%, and (91.40±3.17)%, respectively. There were no statistically significant differences between the GC0 group and the other three groups ( P=0.9869, P=0.3093, P=0.8008). On day 7, the cell viability was (89.97±3.10)%, (92.18±2.21)%, (92.05±2.25)%, and (90.12±1.97)% for the four groups, respectively. There were no statistically significant differences between the GC0 group and the other three groups ( P=0.3965, P=0.4511, P=0.9995). Bioink extrusion test showed that the GC0 hydrogel could be extruded continuously and form threads at temperatures between 24℃ and 25℃, while the GC10 hydrogel could be extruded continuously and form threads at temperatures between 24℃ and 27℃. Printing tissue engineered bladder patches simulating the anatomical structure of the bladder mucosal layer, submucosal layer, and muscular layer using GC10 bioink, and the printed patches were stable, without collapse, and had high fidelity. Conclusions:Adding ChiNC to GelMA promotes cell adhesion, proliferation, and expands the printing window of GelMA bioink. The biocompatibility of the mixed bioink prepared by adding 10 mg/ml ChiNC in GelMA is good, capable of printing tissue-engineered bladder patches that mimic the anatomical structure of natural bladder walls.

For the damage and loss of tissues and organs caused by urinary system diseases, the current clinical treatment methods have limitations. Tissue engineering provides a therapeutic method that can replace or regenerate damaged tissues and organs through the research of cells, biological scaffolds and biologically related molecules. As an emerging manufacturing technology, three-dimensional (3D) bioprinting technology can accurately control the biological materials carrying cells, which further promotes the development of tissue engineering. This article reviews the research progress and application of 3D bioprinting technology in tissue engineering of kidney, ureter, bladder, and urethra. Finally, the main current challenges and future prospects are discussed.
Bioprinting ; Regeneration ; Technology ; Tissue Engineering/methods*