A syringe's mechanism relies on a simple yet effective principle: creating a pressure difference to draw in and expel fluid. This is achieved through the interaction of its key components: the barrel, plunger, and needle (or other delivery mechanism).
Syringe Components and Their Roles
- Barrel: A cylindrical tube, typically made of plastic or glass, that holds the fluid. Its markings indicate the volume of fluid.
- Plunger: A tightly fitting, usually plastic, component that slides within the barrel. It either has a rubber tip to create a seal (three-part syringes) or a design that achieves a perfect fit with the barrel (two-part syringes) [Reference: A three-part syringe contains a plastic plunger/piston with a rubber tip to create a seal between the piston and the barrel, where a two-part syringe is manufactured to create a perfect fit between the plastic plunger and the barrel to create the seal without the need for a separate synthetic rubber piston.].
- Needle (or other delivery mechanism): A hollow needle or cannula, attached to the tip of the syringe, that allows for the controlled delivery of fluid. Different designs exist, such as Luer lock and Luer slip connections [Reference: Luer Lock—engages the hub of the needle with a threaded locking mechanism. · Luer Slip—secures a needle using friction after the needle hub slides or “slips”...]. Some syringes incorporate safety mechanisms to prevent needle-stick injuries [Reference: A safety syringe is a syringe with a built-in safety mechanism to reduce the risk of needlestick injuries to healthcare workers and others.].
How the Mechanism Works
- Drawing Fluid: Pulling the plunger backward creates a vacuum within the barrel. Atmospheric pressure then pushes the fluid into the barrel through the needle.
- Expelling Fluid: Pushing the plunger forward increases the pressure inside the barrel, forcing the fluid out through the needle.
Variations in Syringe Mechanisms
Syringe mechanisms are not limited to simple hand-operated devices. More complex systems exist, such as:
- Syringe pumps: These use a motor to precisely control the plunger's movement, allowing for highly accurate and controlled fluid delivery at various rates [Reference: Superior drive mechanism for unmatched smooth flow, accuracy and precision • From picoliter to 216 ml/min flow rates...].
- Syringe-like injection mechanisms in biological systems: Certain bacteria use syringe-like structures to inject toxins into host cells. These mechanisms are significantly more complex, involving multiple components and a multi-step process [References: The TcA component of Photorhabdus luminescens ABC-type toxin complexes forms a transmembrane pore and injects TcC, the functional component...; We show that shell opening is a heterogeneous process with transition times ranging from 60 ms to 1.6 s and resolve three sequential intermediate states.]. These biological systems often involve complex interactions and multiple steps, significantly different from the simple mechanical operation of a medical syringe.
Applications Beyond Medical Use
Syringes find applications beyond medical injections:
- 3D food printing: Exchangeable syringe-pump mechanisms are used in food 3D printers to deliver different food materials [Reference: Present study aimed to develop an exchangeable syringe-pump mechanism (SPM) to demonstrate transformation of conventional 3D printer from polymer to food...].
- Industrial applications: Syringes and syringe pumps are used for precise dispensing of various liquids and materials in various industrial processes.
