Low-temperature synthesis of nanoparticle-assembled, transparent, and low-crystallized hydroxyapatite blocks

► Transparent blocks were assembled with low-crystallized hydroxyapatite nanoparticles. ► A crack-free nanoparticle-assembled block was fabricated by a novel casting method on flowable substrates. ► The nanoparticle-assembled transparent HAp had nanosized pores among the particles.