Kevlar body armor is fantastic against blunt trauma like small arms fire, but not so good against piercing damage from knives or sharapnel. Solution? Treat the body armor with shear thickening fluid: ( link)
The liquid - called shear thickening fluid is actually a mixture of hard nanoparticles and nonevaporating liquid. It flows normally under low-energy conditions, but when agitated or hit with an impact it stiffens and behaves like a solid. This temporary stiffening occurs less than a millisecond after impact, and is caused by the nanoparticles forming tiny clusters inside the fluid. "The particles jam up forming a log jam structure that prevents things from penetrating through them," Wagner explains.