*2.7. Two-Photon Polymerization*

While single-photon polymerization requires one-photon absorption, in TPP, the molecule simultaneously absorbs two photons. By employing a focused femtosecond near-IR, TPP stereolithography, processing biocompatible synthetic or natural hydrogels or polymers, grants the ultra-fast production of 3D structures with submicron resolution [67].

#### **3. Applications of 3DP Mesoporous Material for Drug Delivery**

Doing a search on the Web of Science and on Pubmed at the beginning of June 2020, resulted that in the last decades a fair number of publications are strictly related to the specific topic covered in this review and, more in details, related to mesoporous 3D printed materials for drug delivery applications. As highlighted in Table 1, most of the results focalized on the application of these 3D porous materials for tissue engineering bone substitute realization. Their porosity, by mimicking the bone structure, allows nutrient transport, waste removal, cell migration, angiogenesis and differentiation phenomena, assisting bone regeneration in bone defects related to traumatic events or pathologies.
