## 1 Introduction
SPRF has slightly different features than PRP, as its growth factor and cytokine milieu are highly natural, because PRF does not contain an extremely large number of platelets and they release their contents over a longer period of time [34], and thus the cytokine level of SPRF is also lower than that of PRP. The existing methods of SPRF production aim to squeeze out PRF exudate from the PRF clot produced in vacuum blood collection tubes. Blood is drawn into glass tubes or glass containing plastic tubes, then it is immediately centrifuged in one step, but using various centrifugation protocols [35], and whole blood gets separated into the red blood cell containing fraction and fibrin clot, which is formed during centrifugation helped by the activating effect of glass. SPRF can be squeezed out from the fibrin clot. The most common method is placing PRF on a sterile grid and pressing out PRF exudate [32]. There is a medical device, called the PFR box, for the same indication, which contains compression wells to prepare dense PRF cylinders, while the serum exudate is collected in the second level of the box. It is a user-friendly device that allows one to prepare PRF membranes in a sterile and protected environment, while the SPRF squeezed out from the clots is a secondary product [36]. Using a centrifuge or a shaker and a vortex may be another option to separate PRF exudate from PRF [37]. These methods require, besides a centrifuge, blood collection tubes and other equipment to produce sterile SPRF, including a laminar flow hood as the procedures require open handling of the PRF membrane. For clinical applications, where sterile isolation may be problematic, we developed a syringe-shaped closed system for SPRF production. The HypACT Inject Auto device was designed for orthopaedic surgeons who intend to treat knee osteoarthritis using autologous serum in a point of care therapy. During the procedure, blood is drawn from the patient and SPRF is isolated, which is then injected into the patient's knee immediately, while the sterility of the serum can be maintained. The device is a sterile single-use syringe, designed for blood drawing and SPRF isolation aseptically and simply in a closed system. The principle of SPRF production is the same as used in a stepwise isolation, but the device makes the process easier, faster and safer. It works as a syringe, which contains a glass part to promote blood coagulation and platelet activation. After blood drawing, the device gets immediately centrifuged and PRF is formed inside the syringe. The red blood cell-containing fraction gets into a waste container part and can be discarded. SPRF can be squeezed out from the fibrin matrix using the plunger part of the device, while the PRF clot becomes a flat membrane inside the device. Attaching a needle onto the end of the device allows the physician to inject the SPRF directly to the knee of the patient. Besides the device, only blood drawing needles and a swing-rotor centrifuge for 50 mL conical centrifuge vials are needed for the treatment. As medical device development is an expensive, difficult and time-consuming process, in this article we aim to demonstrate the main processes, scheduling and required mindset of medical device development, manufacturing and regulation steps on the actual steps of a Class IIa medical device development. We used this HypACT device to demonstrate the steps of medical device development. We intend to give an impression on the complexity of the processes [38], requirements and human resources that need to work together in order to achieve a medical device product. The demonstrated development was presented from a technological point of view, with the addition of the mandatory regulatory and quality management (QM)-related requirements in the realization of an actual medical device that was put on the market.