Most medical and scientific illustrations are either hand-painted digitally or rendered in 3D-software. Consequently, such images require experience and skill. Mastering the software needs time and dedication. That being said, most professional illustrators work with different software. Industry standard is the Adobe Creatives Suite with programs such as Illustrator for vector-drawings and Photoshop for pixel-drawings. The Freeware analogs are inkskape and gimp. When it comes to 3D-Software there are many good solutions such as 3Dsmax, Maya and Houdini. However, many in the field use Cinema4D by Maxon. Blender3D is the go-to opensource software here.