Histological structure of the rat femurs after filling of defects in the distal metaphysis with 3d-printed implants based on polylactide and tricalcium phosphate in combination with mesenchymal stromal cells

Polylactide (PLA) frameworks printed on a 3D printer are used for filling the bone defects. The osteotropic properties of 3D-PLA can be improved by combining with tricalcium phosphate (TCP) and mesenchymal stromal cells (MSCs). Objective. Study the reconstruction in the rat femurs after implanting 3D-printed implants based on PLA and TCP (3D-I) in combination with cultured allogeneic MSCs into defects in the distal metaphysis. Methods. 48 white laboratory rats (age 5–6 months) were used, which were randomly divided into groups: Control — 3D-I; Experiment-I — 3D-I, saturated MSCs; Experiment II — 3D-I, with injection of 0.1‒0.2 ml of medium with MSCs into the area of surgical intervention 7 days after implantation. 15, 30 and 90 days after the operation, histological (with histomorphometry) studies were conducted. Results. The area of 3D-I decreased with time in all groups and connective and bone tissues formed in different ratios. 15 days after the surgery, in the Experiment-I group, the area of the connective tissue was 1.9 and 1.6 times greater (p<0.001) in comparison to the Control and Experiment II; 30 days it was greater 1.6 times (p < 0.001) and 1.4 times (p=0.001), respectively. 30 days after the surgery, the area of newly formed bone in the Experiment-I group was 2.2 times (p < 0.001) less than in the Control. On the contrary, in the Experiment-II, the area of newly formed bone was 1.5 and 3.3 times greater (p < 0.001) compared to Experiment-I and Control, respectively. Conclusions. The studied 3D-I with time after their implantation into the metaphyseal defects of the rats’ femurs are replaced by connective and bone tissues. The use of 3D-I, saturated MSCs, 15 and 30 days after the surgery, caused excessive formation of connective tissue and slower bone formation. Local injection of MSCs 7 days after the implantation of 3D-I caused to the formation of a larger area of newly bone 30th day after surgery compared to 3D-I alone and 3D-I with MSCs.