Application of layered poly (L-lactic acid) cell free scaffold in a rabbit rotator cuff defect model

Abstract

Background: This study evaluated the application of a layered cell free poly (L-lactic acid) (PLLA) scaffold to regenerate an infraspinatus tendon defect in a rabbit model. We hypothesized that PLLA scaffold without cultivated cells would lead to regeneration of tissue with mechanical properties similar to reattached infraspinatus without tendon defects.

Methods: Layered PLLA fabric with a smooth surface on one side and a pile-finished surface on the other side was used. Novel form of layered PLLA scaffold was created by superimposing 2 PLLA fabrics. Defects of the infraspinatus tendon were created in 32 rabbits and the PLLA scaffolds were transplanted, four rabbits were used as normal control. Contralateral infraspinatus tendons were reattached to humeral head without scaffold implantation. Histological and mechanical evaluations were performed at 4, 8, and 16 weeks after operation.

Results: At 4 weeks postoperatively, cell migration was observed in the interstice of the PLLA fibers. Regenerated tissue was directly connected to the bone composed mainly of type III collagen, at 16 weeks postoperatively. The ultimate failure load increased in a time-dependent manner and no statistical difference was seen between normal infraspinatus tendon and scaffold group at 8 and 16 weeks postoperatively. There were no differences between scaffold group and reattach group at each time of point. The stiffness did not improve significantly in both groups.

Conclusions: A novel form of layered PLLA scaffold has the potential to induce cell migration into the scaffold and to bridge the tendon defect with mechanical properties similar to reattached infraspinatus tendon model.

Figure 1

Layered PLLA scaffold. (a) SEM of the rough side of the pile-finished PLLA fabric. Scale bar represents 50 μm. (b) Schema of PLLA scaffold; two fabrics were superimposed in double layers with the smooth surface outside and rough surface inside, and both edges of the double layered fabric were bonded by thermocompression.

Figure 2

A schematic drawing of the repair of the rotator cuff defect using PLLA scaffold in a rabbit model. Defects in the infraspinatus tendons were created at their insertions and PLLA scaffolds were transplanted and both edges were fixed to tendon or bone by 4-0 nylon suture.

Figure 3

HE staining of layered scaffold after implantation in rotator cuff defect in rabbit. (a) scaffold midsubstance at 4 weeks after scaffold implantation. (b) scaffold midsubstance at 8 weeks after scaffold implantation. (c) scaffold midsubstance at 16 weeks after scaffold implantation. (d) scaffold bone interface at 4 weeks after implantation. (e) scaffold bone interface at 8 weeks after implantation. (f) scaffold bone interface at 16 weeks after implantation: Scale bar represents 100 μm.

Figure 4

Immunostaining of scaffold at 16 weeks postoperatively. (a) type I collagen (b) type III collagen: type III collagen was mainly detected at the regenerated tissue in the scaffold. Scale bar represents 500 μm.

Figure 5

Result of mechanical evaluation. (a) Ultimate failure load of tendon humeral head complex. (Error bars indicate standard deviation) The ultimate failure load of scaffold group increased time dependently. It was significantly weaker at 4 weeks postoperatively than normal infraspinatus tendon; however statistical significant difference was not seen between 8 and 16 postoperative group and normal infraspinatus tendon. There was no significant difference between scaffold group and the reattach group at each time point. (b) Siffness of tendon humeral head complex. (Error bars indicate standard deviation) The stiffness of the scaffold group increased time dependently, however it remained significantly less stiff than that of normal infraspinatus tendon at each time point. Significant difference of stiffness was not seen between the scaffold group and the reattach group at each time point.