You can use glass and metal syringes if they are the correct diameter. The movements of the syringe head were optimized for plastic syringes so it is recommended to use caution to ensure damage does not occur to the syringe head, particularly if a nozzle blockage occurs during printing that may strain the motor due to rigid metal plungers or may result in a glass syringe breaking due to a mismatch of bioink properties with the chosen nozzle.