# A Brief Review on Challenges in Design and Development of Nanorobots for Medical Applications
## 1 Introduction  
Nanotechnology involves the process of designing, fabricating, and manipulating materials at the nanoscale [1]. The study of robots at the nanoscale is defined as nanorobotics, and incorporated technology is known as nanotechnology. Nanorobots are devices capable of sensing, actuating, signalling, processing information, intelligence, or exhibiting swarm behaviour at the nanoscale [2]. They are comprised of various components that carry out specific tasks; the components are constructed at the nanoscale size and can range from 1-100 nanometers [3, 4]. Nanobots (A.K.A. nanorobots), which are currently the focus of an emerging field of research, are also referred to as nanites, nanoids, nanomachines, or nano-mites [1, 4]; however, in general, nanobot consists of two words--'nano' and 'bot'. 'Nano' refers to very small or minute, and 'bot' refers to a device that can be controlled by a program, i.e. a short term for a robot [1]. Nanorobots have several potential applications in the medical field including cancer treatment [5, 6], surgery, precision medicine [7], diabetes monitoring, dentistry, blood monitoring and drug delivery [1, 4, 5]. Currently, mobile phones are proving to be a useful feedback device in accomplishing data transmission for communication, control, and energy supply inside the body. In addition, the emergence of new materials and their application in fabricating sensors and actuators has resulted in devices in the nanoscale range [6, 7, 8, 9]. Due to the potential for nanorobots to work individually or in swarms in a wide variety of applications, ranging from medicine, environmental surveillance and monitoring, armed forces, and many more emerging applications, it is essential to conduct a review on the existing state-of-the-art nanorobotic systems [1, 10, 11]. Nanomedicine is the method of diagnosing, treating, preventing disease and traumatic injury, alleviating pain, and maintaining and enhancing human health using nanotechnology and nanorobots [4, 12]. Nanomedical robots can be used for many applications, such as targeting and early diagnosis of cancer, drug delivery, tissue engineering, gene delivery systems, cardiology, analysis of body vitals, monitoring of diabetes, minimally invasive brain surgery, and imaging and detection capabilities [3, 13]. In all of these applications, themost important requirement is nanorobots to deliver the required drug to the target sites. Drug delivery is one of the key aspects in operations such as repairing tissues, cleaning blood vessels and airways, and transporting and delivering drugs to infected cells [8]. Additionally, nanorobots have aided dentists in carrying out complicated operations at a microscopic level with enhanced precision [14; 15]. With advancements in various applications, the utilization of nanorobots in medicine could elicit a paradigm shift from treatment to prevention [16]. However, nanorobots face some limitations, including high design and development costs, high complexity, and difficulties with the interface. Due to the viscous nature of blood at the nanoscale, it is nearly impossible for the drug-carrying nanorobots to pass through blood vessels. The Brownian movement of the molecules causes collisions between molecules, and therefore the behaviour of the nanorob becomes unpredictable and uncontrollable [8]. This instability has been one major limitation and a critical challenge that researchers are attempting to overcome. The other main challenge is to develop appropriate feedback sensors to facilitate autonomous control at a deeper scale [17; 18]. The concepts of micro and nanorobots are often interchangeable. The information regarding microrobots that appears in this study is applicable to nanorobots as well. Nanorobots must be highly effective, controllable, economical in mass production, and fully operational with minimal monitoring [8].