DOI: 10.1002/adhm. 201400256 doses.[12] For example, Retisert implants are small polymeric tubes designed to release fluocinolone acetonide, a corticosteroid for treating PU, over 3 years. Despite improving visual acuity of the patients, these implants show some side effects such as increased intraocular pressure and cataract progression.[13] The I-vation (SurModics, Eden Prairie, MN) implant consists of a titanium helical coil coated with erodible films filled with triamcinolone acetonide to target diabetic macular edema (DME).[14] The main disadvantages of both implants include the initial surgery, as well as the removal surgery in case of adverse response or rejection of the implanted body.[15] Other implants such as Iluvien (pSivida) overcome the inconvenience of initial surgery. This implant is a small non-erodible polyimide tube that also contains fluocinolone acetonide.[16] Despite being sutureless injectable, once the tube is inserted, it is difficult to position precisely in the eye, and, in case of adverse reaction, surgery may be unavoidable. Microrobots are proposed as implantable devices that can be controlled wirelessly and may, in the future, perform tasks such as targeted drug delivery, remote diagnostics, and minimally invasive surgery.[17–19] They can be operated in areas of the body that are currently difficult to access and precisely controlled beyond the limits of human dexterity. Development of these devices requires a co-ordination between diverse disciplines such as control systems, biomaterials, and microsystems. Due to the unfavorable scaling of energy sources at the microscale, power transmission to microrobots is one of the primary challenges.[20] The most favorable strategy would be to design these robots to harvest energy from their surroundings. Magnetic manipulation has emerged as a promising method in this regard because magnetic fields are capable of penetrating most materials with minimal interaction, and are nearly harmless to human beings. Magnetic fields have been successfully used to wirelessly manipulate microdevices of various sizes and shapes.[21, 22]

In this paper, we present an implantable magnetic tubular microrobot for use in targeted drug delivery and minimally invasive surgery at the posterior segment of the eye. The tubular shape is preferred because it maximizes the volume of magnetic material that can fit into a 23-gauge needle and enables sutureless injections into the eye. Fabrication of tubular microstructures has been extensively investigated for several applications such as drug delivery, biosensing, microfluidics, and 3D cell microreactors.[23] Fabrication methods include rolling-up processes,[24] template-assisted atomic layer deposition,[25] spin forming,[26] or water-jet cutting.[27] However, these methods are either time consuming or do not produce the desired geometries of required dimensions. In contrast,