The present disclosure relates to core-wire joints for micro-fabricated medical devices, such as guidewires. A hybrid guidewire device includes a core (102) having a joint (105) between a proximal section (110) and a distal section (112) of the core and a tube structure (104) surrounding the joint. The proximal section of the core is made of or includes stainless steel and the distal section is made of or includes a superelastic material such as nitinol. Further, the terminal, distal portion of the proximal section of the core includes serrations (116), and a terminal, proximal portion of the distal section of the core includes complementary serrations (118) sized and shaped to interlock with serrations (116). The distal end of the proximal section mechanically interlocks with a proximal end the distal section to form the joint.
