© Fraunhofer IZM

Ultra­sound: With wire­less charg­ing to per­son­al­ized medicine

In order to reduce hos­pi­tal stays and health­care costs through per­son­al­ized solu­tions, new ther­a­peu­tic approach­es have been used for sev­er­al decades. One exam­ple is so-called elec­tro­ceu­ti­cals, i.e. microim­plants equipped with elec­tron­ic solu­tions that use elec­tric­i­ty to pro­vide per­son­al­ized and local­ized treat­ment with­out trig­ger­ing side effects in the body. Researchers at Fraun­hofer IZM have now set them­selves the task of tak­ing a new approach and are using ultra­sound instead of electricity.

Ultra­sound waves are pres­sure waves that are applied from the out­side, pen­e­trate the body and thus reach the microim­plant. There are clear advan­tages com­pared to con­ven­tion­al bat­tery-charged devices: Using ultra­sound, the implants can be charged exter­nal­ly, mak­ing fre­quent inva­sive pro­ce­dures or wired charg­ing obso­lete. Above all, the extreme minia­tur­iza­tion of the sys­tems is an inno­va­tion in the field and enables the microim­plants to pre­cise­ly stim­u­late nerves that are just 20 microm­e­ters in size.

By using ultra­sound to charge the implants, the Fraun­hofer IZM team has found a solu­tion for effi­cient ener­gy trans­fer, one of the great­est tech­no­log­i­cal chal­lenges in med­ical tech­nol­o­gy. This is because built-in bat­ter­ies have so far made minia­tur­iza­tion dif­fi­cult, with ener­gy deple­tion inevitable and thus requir­ing replace­ment, i.e. fur­ther sur­gi­cal inter­ven­tion. In addi­tion, bat­tery-pow­ered implants equipped with induc­tion coils can only be insert­ed close to the skin.

In con­trast, the small­est ultra­sound trans­duc­ers make it pos­si­ble to use the microim­plants of the future even far inside the body. When high-fre­quen­cy sound hits them, they start to vibrate. These tiny move­ments are con­vert­ed into elec­tri­cal ener­gy for the microim­plant. The chal­lenge is to opti­mal­ly align the vibrat­ing microstruc­tures in order to avoid high loss­es dur­ing ener­gy trans­fer. At the same time, only extreme­ly small struc­tures can be used, as the over­all size of the implant must not exceed a few millimetres.

Ultra­son­ic trans­duc­ers, elec­trodes for record­ing neu­ronal activ­i­ty and pas­sive com­po­nents — minia­tur­iz­ing all these com­po­nents down to a few mil­lime­ters, inte­grat­ing them and assem­bling them in a durable man­ner is a major, but not insur­mount­able hur­dle. The researchers are cur­rent­ly eval­u­at­ing which mate­ri­als they can use for the pro­to­type: This is a key deci­sion, because they must be bio­com­pat­i­ble and at the same time suit­able for encap­su­la­tion and ener­gy trans­mis­sion by sound waves. In the fur­ther course, sev­er­al trans­duc­ers are also built up in groups, so that a com­bi­na­tion of the elec­tron­ic com­po­nents and thus a more con­cen­trat­ed radi­a­tion of the ultra­son­ic wave is achieved.

The Fraun­hofer Insti­tute for Reli­a­bil­i­ty and Microin­te­gra­tion IZM is one of 66 com­pa­nies involved in the EU-fund­ed Moore4Medical project. The Insti­tute is respon­si­ble for the coor­di­na­tion and imple­men­ta­tion of the work pack­age “Implantable Devices”. At the end of the project in June 2023, an open tech­nol­o­gy plat­form is to be cre­at­ed in a kind of tool­box that will enable faster, more cost-effec­tive and more effi­cient med­ical tech­nol­o­gy. Future research could fur­ther devel­op these basic build­ing blocks devel­oped in the project for spe­cial­ized appli­ca­tions in the areas of wire­less microim­plants, organ-on-chip, 3D ultra­sound, per­ma­nent mon­i­tor­ing using sen­sors, drug adher­ence through intel­li­gent deliv­ery, and X‑ray-free surgery with opti­cal detec­tion, thus advanc­ing med­ical tech­nol­o­gy in a pow­er­ful way.