An apparatus is provided for applying to a surface of mammalian tissue including soft, living tissue an initially fluent material and then activating the material by exposure to an energy source. The material may be a liquid capable of polymerization to a non-fluent state by exposure to actinic light. The device, and methods that may be practised in association with the device, enable a wide range of medical conditions to be treated including, for example, the application of a barrier to soft tissue to prevent post-surgical adhesions.