<p>A method of monitoring the formation of a tissue in a tissue construct or the viability or function of cells in a tissue comprises contacting a micromembrane probe with the tissue construct; carrying out microdialysis and/or ultrafiltration to extract a marker into the dialysate and analysing the marker in the dialysate. The methods can be used to monitor formation, viability or function of tissues in vitro or to monitor viability or function in vivo.</p>
