Biostable scaffolds of polyacrylate polymers implanted in the articular cartilage induce hyaline-like cartilage regeneration in rabbits

Abstract

Purpose: To study the influence of scaffold properties on the organization of in vivo cartilage regeneration. Our hypothesis was that stress transmission to the cells seeded inside the pores of the scaffold or surrounding it, which is highly dependent on the scaffold properties, determines the differentiation of both mesenchymal cells and dedifferentiated autologous chondrocytes.

Methods: 4 series of porous scaffolds made of different polyacrylate polymers, previously seeded with cultured rabbit chondrocytes or without cells, were implanted in cartilage defects in rabbits. Subchondral bone was injured during the surgery to allow blood to reach the implantation site and fill the scaffold pores.

Results: At 3 months after implantation, excellent tissue regeneration was obtained, with a well-organized layer of hyaline-like cartilage at the condylar surface in most cases of the hydrophobic or slightly hydrophilic series. The most hydrophilic material induced the poorest regeneration. However, no statistically significant difference was observed between preseeded and non-preseeded scaffolds. All of the materials used were biocompatible, biostable polymers, so, in contrast to some other studies, our results were not perturbed by possible effects attributable to material degradation products or to the loss of scaffold mechanical properties over time due to degradation.

Conclusions: Cartilage regeneration depends mainly on the properties of the scaffold, such as stiffness and hydrophilicity, whereas little difference was observed between preseeded and non-preseeded scaffolds.

Fig. 1

Scanning electron microscopy (SEM) of the scaffolds. (A) SEM cross-sectional image of P(EA-co-HEA) 50/50 (series III) scaffold. SEM pore structure images for all series: (B) series I, P(EA-co-MAAc) 90/10; (C) series II, P(EA-co-HEA) 90/10; (D) series III, P(EA-co-HEA) 50/50; and (E) series IV, PEA 100. Scale bars represent 500 μm (A) or 200 μm (B-E).

Fig. 2

Representative macroscopic views of the articular surface of the different series, 3 months after scaffold implantation. Arrows show the injury zone of non-preseeded (A-D) or preseeded (E-H) series I to IV, respectively.

Fig. 3

Representative microscopic panoramic views of implanted scaffolds of non-preseeded (A-D) or preseeded (E-H) series I to IV, respectively, 3 months after implantation. Series I, II, and IV biomaterials were not stained and thus appeared as white spaces, while series III material appeared slightly stained gray (C, G). Sections were stained with Masson's trichrome (A, F, H), Alcian blue (B), or hematoxylin-eosin (C, D, E, G). Arrowheads show fibrous tissue. AC = articular cartilage; B = subchondral bone; S = scaffold. Scale bars represent 500 μm.

Fig. 4

Different tissue responses to the implanted scaffolds, 3 months after implantation. (A) Non-preseeded scaffold series I contacts with the articular cavity. (B) Hyaline-like neocartilage grown on the surface of non-preseeded scaffold series II in continuity with native cartilage. (C) Good continuity between neocartilage grown within scaffold pores and surrounding superficial cartilage in preseeded series II. (D) Blood vessels (arrows) emerging from spongy bone tissue as well as good continuity between neotissue and subchondral bone in preseeded scaffold series II. (E) Abundant fibrous tissue (arrowheads) with numerous giant multinuclear phagocytic cells (star) inside and around the implanted preseeded scaffold series III, where the biomaterial is stained gray (S). (F) Synovial-like tissue (asterisk) over the implanted scaffold in non-preseeded series IV. Sections were stained with Masson's trichrome (A, D, E), Alcian blue (B), or hematoxylin-eosin (C, F). AC = articular cartilage; B = subchondral bone; S = scaffold. Scale bars represent 100 μm.

Fig. 5

Linear regression between Young's modulus and scaffold distance from articular surface in the series studied. A high negative correlation coefficient (R²) was observed.

Fig. 6

Control samples. Representative macroscopic view of the articular surfaces (A) and microscopic views (B, inset C), 3 months after surgery. Sections were stained with Masson's trichrome (B, C). Arrow shows the injury zone and arrowhead fibrous tissue. AC = articular cartilage; B = subchondral bone. Scale bars represent 500 μm (B) or 100 μm (C).