High elastic modulus nanoparticles: a novel tool for subfailure connective tissue matrix damage.

Subfailure matrix injuries such as sprains and strains account for a considerable portion of ligament and tendon pathologies. In addition to the lack of a robust biological healing response, these types of injuries are often characterized by seriously diminished matrix biomechanics. Recent work has shown nanosized particles, such as nanocarbons and nanocellulose, to be effective in modulating cell and biological matrix responses for biomedical applications. In this article, we investigate the feasibility and effect of using high stiffness nanostructures of varying size and shape as nanofillers to mechanically reinforce damaged soft tissue matrices. To this end, nanoparticles (NPs) were characterized using atomic force microscopy and dynamic light scattering techniques. Next, we used a uniaxial tensile injury model to test connective tissue (porcine skin and tendon) biomechanical response to NP injections. After injection into damaged skin and tendon specimens, the NPs, more notably nanocarbons in skin, led to an increase in elastic moduli and yield strength. Furthermore, rat primary patella tendon fibroblast cell activity evaluated using the metabolic water soluble tetrazolium salt assay showed no cytotoxicity of the NPs studied, instead after 21 days nanocellulose-treated tenocytes exhibited significantly higher cell activity when compared with nontreated control tenocytes. Dispersion of nanocarbons injected by solution into tendon tissue was investigated through histologic studies, revealing effective dispersion and infiltration in the treated region. Such results suggest that these high modulus NPs could be used as a tool for damaged connective tissue repair.