“…Whereas mass is added in the bulk material during volumetric growth [9,13,25] (e.g., in soft tumorous and arterial tissues), it accretes on to the free surface of the body during surface growth [8,12,27] (e.g., in hard horn and bone tissues). On the other hand, mass addition can also happen at a material or a non-material interface within the body [7,11,33], as is the case with ring formation in trees, healing of cutaneous animal wounds, growth of animal nails, etc. In fact, interfacial growth models can also provide a viable framework for studying problems in surface growth, e.g., by considering the external source to be the bulk body on one side of the interface [12] or by assuming the interface to be between a bulk substrate and a growing two-dimensional film [16,22].…”