Extrusion Force and Syringe Dimensions of
`Two Hyaluronic Acid Dermal Fillers
`
`Ake Ohrlund, Katarina Edsman, Cecilia Sturesson, Lars Nord,Anne Helander Kenne and Jacques Ncisstri:im.
`Q-Med AB, Seminariegatan 2 /, SE-752 28 Uppsa/a, Sweden.
`
`Objective
`
`Conclusions
`
`The objective of this study was to compare the extrusion force of two hyaluronic acid (HA) dennal fillers,
`and to study the effect of syringe dimensions,
`
`Introduction
`
`The force that has to be applied to the syringe when injecting a dennal filler is a fu nction of many factors,
`e .g. dimensions of the syringe and the needle as well as the viscoelastic properties of the fi ller material.
`The extrusion force is easily measured in the laboratory, not taking the resistance from the tissue into
`account.
`
`Despite the obvious simplicity of the measurements, the results are often misinterpreted, Although
`different manufacturers of hyaluronic acid dermal fillers use different syringes and needles, results from
`extrusion force measurements are still compared without taking these differences into account. In some
`cases the results are wrongly considered to be an effect of the "softness" or "smoothness" of the filler
`material rather than the mechanical dimensions of the syringe.
`
`In Figure I, the parameters affecting the extrusion force is illustrated.The required pressure P is not
`readily calculated from parameters 1-4 given in the figure, but is easily calculated from a simple extrusion
`force measurement where F is measured and A is given from the syringe inner diameter.
`
`Required pressure (P) is a function of
`
`1. Viscosity of the gel
`Injection rate (volume/time)
`2.
`3. Needle length
`4. Needle inner diameter
`
`Required
`extrusion
`force
`(F= P x A)
`
`Area (A) of syringe plunger
`(TT x (inner diameter)2/4)
`
`Figure I. Illustration of the factors affecting extrusion force
`
`Extrusion force vs syringe dimensions
`
`If the syringe inner diameter is decreased in order to decrease the extrusion force, inevitably the other
`syringe dimensions will also be affected if fill volume is to be maintained.Assume a syringe with a I ml fill
`volume and a required pressure of 6 bar to achieve the desired injection rate with the used needle size.
`Choosing a syringe inner diameter of 6.3 or 4.4 mm would give an extrusion force of 19 or 9 N respectively.
`To maintain the I ml fill volume, the length of the syringe will also have to be adjusted (Figure 2).
`
`• The difference in the extrusion fo rce between the two fillers was
`found to be mainly due to syringe dimensions.
`
`• For any given HA filler material, using syringes with a smaller inner
`diameter will give lower extrusion force, but may also have negative
`effects on the ergonomics of the syringe. Therefore the extrusion
`force and the syringe dimensions will always have to be balanced for
`optimal ergonomics.
`
`Results
`
`When compared using equal plunger speed, but each vendors syringe and needle, the difference in
`extrusion force may wrongly be interpreted as being an effect of the difference in viscosity of the HA
`filler materials (Figure 4).What should be taken into account, however; is that the difference in syringe
`inner diameter will cause a difference in the force required at a certain pressure, and that the actual
`volume/time ejection rate will be different at equal plunger speed. It should also be noted that a 30 G
`needle was used for Restylane®, while a 27 G needle was used for Juvederm, as supplied with the
`syringes.
`
`When measuring the extrusion force for Restylane after transfer into the Juvederm syringe, the extrusion
`in Figure 4.The difference
`force was notably lower (Figure 5) and at about the same level as for Juv€:derm
`in extrusion force corresponded to what should be expected from syringe dimensions alone. Also in this
`experiment, the 30 G needle was used for Restylane.
`
`RN4~• .. Re■/.,..... I~
`
`20
`18 ~-1-· ~~~,./~ ✓-"'--'-...,..,,
`z 16
`.!: 14
`.,
`~ 12
`,2 10
`C:
`8
`0
`·;;;
`2 6
`>< w
`4
`2
`0
`
`~W!Juvedrirm"~
`
`0
`
`50
`
`100
`Test duration in s
`
`150
`
`200
`
`Figure ◄. Extrusion force for two different products in syringes with different needles and syringe inner
`diameter; measured at equal plunger speed.
`
`9.1 N Ex1 force
`
`4.4 mmi.d.
`
`7.6 cm grip
`
`11 .1 cm hand to patient
`
`Figure 2. Illustration of the effect that changing only the syringe inner diameter will have on syringe length
`and extrusion force, keeping needle and injection rate equal
`
`20
`18
`z 16
`.,
`.!: 14
`~ 12
`,2 10
`C:
`8
`0
`·;;;
`f
`2 6
`><
`4
`w ~L
`
`0
`
`50
`
`100
`Te st duration in s
`
`150
`
`200
`
`Syringe dimensions vs ergonomy
`
`Figure 5. Extrusion force for Restylane in syringes with different inner diameter; using equal plunger speed
`and identical 30 G needles.
`
`The increased syringe length will cause an increased grip length, which may be less comfortable for
`doctors with smaller hands. Also the distance hand to patient will increase, which may cause loss of
`control, resulting in less precise injections (Figure 3). Due to these interdependencies, the extrusion force
`and the syringe dimensions have to be balanced for optimal ergonomics.
`
`Materials
`
`Table I. Investigated HA-filler products
`
`Product
`
`Restylane®
`juvederm® Ultra 4
`
`Lot No
`
`9686
`S30L478286
`
`Manufacturer
`
`Q-Med AB, Sweden
`Allergan, France
`
`Methods
`
`The extrusion force was measured using a Zwick BTC-FR2.STH.D09 material tester with a 100 N load cell,
`a plunger speed of IO mm/min and IO measurements/s. Two commercial HA filler products were tested,
`using the needles supplied by the vendor, a B-D, Hypoint, 30 G ½" for Restylane and a Kendall 27 G ½" for
`JuvedellTI. Since the syringe inner diameters for each product were different, 6.3 and 4.4 mm for Restylane
`and Juvederm respectively, the filler material in the 6.4 mm syringe was transferred to the 4.4 mm syringe
`for comparative measurements.
`
`Figure 3. Illustration of the effect that changing syringe dimensions will have on ergonomic factors like grip
`length and hand to patient distance
`
`8th Anti-aging Medicine World Congress (AMWq Monte-Carlo, Monaco - April 8-9- 10, 20 I 0
`
`Q-MED
`
`Exhibit 1036
`Prollenium v. Allergan
`
`