Filling semi-solids in disposable syringes

Dosing syringes are an important option for the precise and clean application of pharmaceutical substances. However, the thin cylindrical cavities quickly become a challenge, especially when filling disposable syringes with highly viscous materials or semi-solids. Nevertheless, absolute precision filling of the syringe is a must. Conventional filling technologies in the pharmaceutical industry often reach their limits when it comes to semi-solid products.

ViscoTec has set itself the task of being able to fill a wide variety of products with just one dosing system. From watery to highly viscous, shear sensitive, abrasive, aggressive or toxic. This includes all viscous pharmaceutical or medical technology products and so-called semi-solids with or without highly effective substances: i.e. dermal fillers such as hyaluronic acid or depot medication drugs made of liposomes, filled with abrasive solids such as hydroxyapatite or shear-sensitive active ingredient crystals. 

Flexible but high-precision filling of syringes
The ViscoTec endless piston principle enables a precise, gentle, and pulsation-free product flow. The dispensers have a flow rate of 0.2ml/min to 700ml/min and are flexible to fill Luer Lock or Luer Slip syringes, for example, from 0.2ml to 50ml with a filling accuracy of ±1%. The net dosing time can be less than one second per syringe. A possible overfilling, but also underfilling, especially with self-medication of standard syringes, is therefore eliminated.

Even filling of small and very small batches with frequent product changes are possible thanks to the easy cleanability of the GMP-compliant Hygienic Dispensers. Cleaning is performed either by COP (Cleaning out of Place) or CIP (Cleaning in Place). Components in contact with the product can be autoclaved.

The special design of the filling pumps enables a programmable suck-back, which in turn ensures a defined thread break and therefore prevents unwanted dripping or thread pulling. This is done by the change of rotation direction in the dispenser, whereby the material is sucked-back into the dosing needle in a defined manner. The suck-back function can also be used for materials with difficult thread breakage. Dosing quantity, speed and acceleration can be individually adjusted according to the requirements of the product. The viscosity does not affect the dosing performance.

Another advantage of the volumetric filling pump is the absolute gentle handling of shear-sensitive or abrasive materials. There is no compression of the conveyed product during the filling process.

Changes to the fill quantity, due to a change in the container size, can be made without mechanical modification. This is ensured by the linear relationship between the quantity dosed and the servo revolution. Thanks to the compact design of the Hygienic Dispensers, they can be easily integrated into existing or newly designed fully automatic packaging systems. There are no limits as to the alignment of the dispensers. And in semi-automatic processes, the simple handling for the operator is a positive aspect - ideal for small batches or clinical trials.

Different filling processes depending on the application
The filling process can be performed either via the stopper or via the syringe cone. When filling via the stopper, this is done by means of a Z-movement of the container or the filling needle in order to ensure a mirror filling. To avoid air pockets, the syringe can be placed under vacuum during filling. In this way, additional so-called "head spaces" can be avoided, which are known from conventional filling.

If the filling process is implemented via the syringe cone, a special needle or Luer connection is used for connection. This is possible thanks to the high-pressure stability of ViscoTec dosing systems. An advantage of this type of filling is that the "piston" can already be mounted in the syringe. During filling, this is then pushed backwards by the inflowing fluid. Subsequent placing of the piston under vacuum is no longer necessary.

Syringe filling application example
For one customer, for example, syringes had to be filled to meet GMP conditions: Each 1 ml ointment with a dynamic viscosity of 160,000mPas. In addition, it was also a requirement to implement this without air bubbles and with a tolerance of ±1%. Due to the good preliminary results of dosing tests at the in-house technical center, the customer decided to use a ViscoTec Hygienic Dispenser 3VPHD8. The syringe is filled through the cone. Due to the viscosity of the material and the small opening, high dosing pressures occur here, which – as already mentioned - can be handled well due to the pressure stability of the endless piston technology. At the end of the filling process, the material is withdrawn from the syringe cone to keep it clean. During the first tests for the application, exceptionally good repeatability of 99.7% was achieved in addition to dosing tolerances of less than ±0.5%. This accuracy was also confirmed later during production.