Biomaterials for Bone Regeneration

Photopolymerization-based additive manufacturing 159

(Li et al ., 2013b). Due to their hydrophobic nature, they are only soluble in

organic solvents and therefore are not suitable to produce hydrogels. Water-

soluble derivatives of R1 and M2CMK have recently been introduced for

two-photon induced polymerization. Generally, initiation occurs via bimo-

lecular electron transfer process (Rumi et al ., 2008) that is generally less

ef cient compared to classical Norrish Type I cleavage processes due to the

possibility of back electron transfer and the solvent cage effect, especially in

aqueous systems (Ullrich et al ., 2005).

With the exception ...