Mechanical manipulation of human osteoblast and chondrocyte cells with `optical tweezers´

The single beam optical gradient trap, known less formally as optical tweezers, uses a single beam of laser light to noninvasively manipulate microscopic particles. In this study, optical tweezers were used to apply force to single human bone and cartilage derived cells in vitro. Effects of various forces applied were monitored by observing intracellular calcium fluctuation during application. In all cell types, human and rat bone derived osteoblasts and human chondrocytes, an increase in fluorescent intensity of calcium indicating fluo-3 was observed within seconds in response to force applied with the optical tweezers, suggesting a rise in [Ca²⁺]i. The greatest response was observed in the human derived osteoblasts and a minimal responses recorded in the dedifferentiated chondrocytes in low density culture and rat derived osteoblasts. Force applied to different regions of cells identified variations in responses with the greatest response observed when the force was transmitted through the body of the cell. This preliminary study highlights a variation in calcium response to a force applied via optical tweezers on individual connective tissue cells. These results suggest a possible role for optical tweezers as a method for application of mechanical strain without additional fluid flow on single cells in culture. This technique will assist one in modelling the mechanical environment in vitro to enable one to identify mechanical effects in connective tissue cell types that are important when designing artificial materials for tissue repair