Cyber-physical systems (CPSs) are a new class of engineered systems based on interactions between cyber and physical components, by integrating three main components: communications, control, and computing. When these systems are brought to the nanoscale, some design and implementation issues arise. A high level of complexity is due to the use of biological components in a CPS, such as engineered cells, which may play the role of sensors, actuators, or even controllers. In this paper, we study the effectiveness of control solutions implemented through the usage of molecular communications in a biological nanoscale cyber-physical system, where a biological nanomachine plays the role of actuator, that releases drug molecules, and another acts as both sensor and controller. The goal of the proposal is to control the release rate, so that target cells can receive the desired amount of drug in a given time, by limiting potential side effects. Basically, we aim to limit congestion, which can arise when large amounts of molecules are released toward a target. To this aim, we propose a simple congestion detection scheme, and compare different rate control algorithms used to throttle the molecules release rate at the transmitter upon the reception of a feedback signal sent by the receiver. We validate the proposed techniques against delivery efficiency and delivery time of molecules by means of an extensive simulation campaign
