Chronic wounds are one of the many problems facing the medical community. These types of injuries are very common, but they are very difficult to diagnose. Currently, doctors assess wounds after a visual analysis. The problem with this assessment is that it varies from one doctor to another, and until after a few days it is not known if the wound is healing correctly or if on the contrary, it is becoming a chronic wound. These lesions are associated with imbalances between the degradation/regeneration processes of cell membranes derived from the activity of metalloproteases. Under normal conditions, these enzymes degrade damaged tissues so that they can be replaced by healthy ones. When their activity get out of control they begin to attack healthy and damaged tissues indistinctly, thus preventing wound healing. Therefore, the enzymatic activity of metalloproteases is the most appropriate biomarker for evaluating the state of a wound. In this work, it is proposed to measure the enzymatic activity of proteases indirectly, by determining the concentration of amino acids, derived from the degradation of membrane proteins. That is to say, the higher enzymatic activity, the higher concentration of amino acids. To carry out this measure, it has been designed a colorimetric sensory polymeric film based on ninhydrin, that changes color when getting in contact with amino acids. This change will be analyzed through the RGB parameters of a digital photo taken with a smartphone.