Mechatronic devices for the investigation of fibroblast populated collagen gel contraction and the effects of mechanical loading.

In this study mechatronic devices have been designed and developed that enable quantitative analysis of fibroblast populated collagen lattices (FPCL) to be made. The Culture Force Monitor (CFM) enables forces as low as 1 dyne (1 x 10-5N) to be made of the contraction of FPCLs whilst growing in culture. The CFM has enabled the force of contraction to be quantified over a range of cell lines and types. Each normal human dermal fibroblast can produce an average force of approximately 10-10N. The contraction process can be divided into 3 distinct phases during the initial 24 hrs. These phases are hypothesised to be due to the processes of cell attachment and spreading. This has been tested using the CFM in conjunction with a stereoscopic microscope to relate the initial phase of contraction (0-8hrs) with the morphological changes in the cells. There was a positive correlation between development of force with time and the shape and extension of cell processes. Disruption of cytoskeletal elements can either increase or decrease the measured force. Disruption of microtubules with colchicine or vinblastine elicited an immediate rise in force, whilst disruption of microfilaments with cytocholasin B caused an immediate fall in force. Based on these observations a hypothesis has been proposed for cytoskeletal function based on a 'balanced space frame' model within the cell. The tensioning-Culture Force Monitor (t-CFM) was developed from the CFM. This instrument utilises a computer controlled microdriver to apply precise loads to FPCLs, whilst simultaneously measuring the actual force applied. Mechanically loading fibroblasts by approximately 20% above the endogenous force elicited an opposite mechanical response. This may represent a form of 'tensional homeostasis' within cells in a 3D matrix or tissue. Mechanically loaded fibroblasts appear to adjust matrix tension back towards the pre loading levels. Cellular orientation and morphology is also altered by mechanical loading, leading to a hypothesis that cells become orientated with iso-strains to reduce the perceived loading