Marine mussels attach to substrates using adhesive proteins.It has been suggested that complex coacervation (liquid-liquid phase separation via concentration) might be involved in the highly condensed and non-water dispersed adhesion process of mussel adhesive proteins (MAPs).However,as purified natural MAPs are difficult to obtain,it has not been possible to experimentally validate the coacervation model.In the present work,we demonstrate complex coacervation in a system including recombinant MAPs and hyaluronic acid (HA).Our recombinant hybrid MAPs,fp-151 and fp-131,can be produced in large quantifies,and are readily purified.We observed successful complex coacervation using cationic fp-151 or fp-131,and an anionic HA partner.Importantly,we found that highly condensed complex coacervates significantly increased the bulk adhesive strength of MAPs in both dry and wet environments.In addition,oil droplets were successfully engulfed using a MAP-based interfacial coacervation process,to form microencapsulated particles.Collectively,our results indicate that a complex coacervation system based on MAPs shows superior adhesive properties,combined with additional valuable features including liquid/liquid phase separation and appropriate viscoelasticity.Our microencapsulation system could be useful in the development of new adhesive biomaterials,including self-adhesive microencapsulated drug carriers,for use in biotechnological and biomedical applications.