Biocompatibility of single-walled carbon nanotube composites for bone regeneration

Abstract

Objectives: The purpose of this study was to evaluate in vivo biocompatibility of novel single-walled carbon nanotubes (SWCNT)/poly(lactic-co-glycolic acid) (PLAGA) composites for applications in bone and tissue regeneration.

Methods: A total of 60 Sprague-Dawley rats (125 g to 149 g) were implanted subcutaneously with SWCNT/PLAGA composites (10 mg SWCNT and 1gm PLAGA 12 mm diameter two-dimensional disks), and at two, four, eight and 12 weeks post-implantation were compared with control (Sham) and PLAGA (five rats per group/point in time). Rats were observed for signs of morbidity, overt toxicity, weight gain and food consumption, while haematology, urinalysis and histopathology were completed when the animals were killed.

Results: No mortality and clinical signs were observed. All groups showed consistent weight gain, and the rate of gain for each group was similar. All groups exhibited a similar pattern for food consumption. No difference in urinalysis, haematology, and absolute and relative organ weight was observed. A mild to moderate increase in the summary toxicity (sumtox) score was observed for PLAGA and SWCNT/PLAGA implanted animals, whereas the control animals did not show any response. Both PLAGA and SWCNT/PLAGA showed a significantly higher sumtox score compared with the control group at all time intervals. However, there was no significant difference between PLAGA and SWCNT/PLAGA groups.

Conclusions: Our results demonstrate that SWCNT/PLAGA composites exhibited in vivo biocompatibility similar to the Food and Drug Administration approved biocompatible polymer, PLAGA, over a period of 12 weeks. These results showed potential of SWCNT/PLAGA composites for bone regeneration as the low percentage of SWCNT did not elicit a localised or general overt toxicity. Following the 12-week exposure, the material was considered to have an acceptable biocompatibility to warrant further long-term and more invasive in vivo studies. Cite this article: Bone Joint Res 2015;4:70-7.

Keywords: Biocompatibility; Bone regeneration; Bone tissue engineering; Carbon nanotubes; SWCNT/PLAGA composites.

Fig. 1

Schematic representation of the surgical procedure involved in subcutaneous implantation of sham, poly(lactic-co-glycolic acid) (PLAGA) and single-walled carbon nanotubes (SWCNT)/PLAGA composites in the rat.

Fig. 2

Graph showing the changes in body weight in rats implanted with Sham, poly (lactic-co-glycolic acid) (PLAGA) and single-walled carbon nanotubes (SWCNT)/PLAGA composites. Data represent mean with standard error of the mean, and p < 0.05 was considered significant.

Fig. 3

Graph showing the food consumption in rats implanted with Sham, poly (lactic-co-glycolic acid) (PLAGA) and single-walled carbon nanotubes (SWCNT)/PLAGA composites at 12 weeks post-implantation. Data represent mean with standard error of the mean and p < 0.05 was considered significant.

Fig. 4

Graphs showing white blood cell differential count of rats implanted with Sham, poly(lactic-co-glycolic acid) (PLAGA) and single-walled carbon nanotubes (SWCNT)/PLAGA composites. The parameters include segmented neutrophils, immature neutrophils, lymphocyte, monocyte, eosinophil and basophil. Data represent mean with standard error of the mean and p < 0.05 was considered significant (PLAGA was significantly different from Sham).

Fig. 5

Gross pathological images of subcutaneous tissue surrounding the implants (Sham, poly (lactic-co-glycolic acid) (PLAGA) and single-walled carbon nanotubes; SWCNT/PLAGA) at eight and 12 weeks post-implantation. All incision sites were healed and the tissue surrounding the implants appeared grossly normal, with no overt evidence of inflammation.

Fig. 6

Graphs showing the relative organ weight in rats implanted with Sham, poly(lactic-co-glycolic acid) (PLAGA) and single-walled carbon nanotubes (SWCNT)/PLAGA composites. The parameters include adrenal glands, lungs, spleen, heart, liver and kidneys. Data represent mean with standard error of the mean and p < 0.05 was considered significant.

Fig. 7

Micrograph of subcutaneous skin tissues of rats implanted with Sham, poly (lactic-co-glycolic acid) (PLAGA) and single-walled carbon nanotubes (SWCNT)/PLAGA at two, four, eight and 12 weeks post-implantation stained with haematoxylin and eosin (×20 magnification). C, composite (PLAGA or SWCNT/PLAGA) implant site; M, muscular tissue; N, polymorphonuclear neutrophils; Fp, fibroplasia; Fb, fibrosis.

Fig. 8

Graph showing the histopathological changes to Sham, poly(lactic-co-glycolic acid) (PLAGA) and single-walled carbon nanotubes (SWCNT)/PLAGA in rat subcutaneous tissue as a function of the summary toxicity score on a scale of 0 to 44 over a period of 12 weeks post-implantation. Data represent mean with standard error of the mean and p < 0.05 was considered significant. PLAGA and SWCNT/PLAGA were significantly different from Sham; both PLAGA and SWCNT/PLAGA showed significant decrease from week two to week four.