Influence of Rheological Properties and Needle Size on Extrusion Forces of Hyaluronic Acid Based Soft Tissue Fillers

May 2021 | Volume 20 | Issue 5 | Original Article | 498 | Copyright © May 2021


Published online April 14, 2021

Konstantin Frank MDa, Thilo L. Schenck MD PhDa, Diana Gavril MDb, Arthur Swift MDc, Steven Liew MDd, David L. Freytag a, Antonia Kaiser a, Jeremy B. Green MDe, Kate Beleznay MDf, Sebastian Cotofana MD PhDg

aDepartment for Hand, Plastic and Aesthetic Surgery, Ludwig - Maximilians University Munich, Germany
bPrivate practice, Cluj-Napoca, Romania
cWestmount Institute of Plastic Surgery, Montreal, Quebec, Canada
dShape Clinic, Sydney, Australia
eSkin Associates of South Florida, Coral Gables, FL
fDepartment of Dermatology and Skin Science, University of British Columbia, Vancouver, British Columbia, Canada
gDepartment of Clinical Anatomy, Mayo Clinic College of Medicine and Science, Rochester, MN

Abstract
Background: To date no precise data are available for extrusion forces related to the G-prime and G-double-prime of fillers in combination with different 27G and 30G needles. Therefore, the objective of this study was to analyze extrusion forces of various product-needle-combinations containing two different 27G and two different 30G needles in combination with fillers of a wide range of elastic moduli starting from 2.0 – 166.0 Pa.
Material and Methods: Four different fillers with the following elastic moduli 1.87, 11.65, 61.80, 165.50 Pa were combined with four different needles: 27G ½”, internal diameter: 0.300 μm; 27G ½”, internal diameter: 0.241 μm; 30G ½”, internal diameter: 0.241 μm and 30G ½“, internal diameter: 0.240 μm. Product-needle-combination were subjected to uni-axial mechanical testing and the respective extrusion force was measured.
Results: The results of this study revealed that the G-prime and the G-double-prime of a product are statistically significantly related to their extrusion force, with higher G-prime/G-double-prime products requiring higher extrusion forces. The results additionally revealed that whether the size of the needle was described as 27G or 30G by the respective manufacturer statistically significant differences between the measured extrusion forces were detected.
Conclusion: Injectors need to be aware that not every 27G/30G needle has the same extrusion force even though the external diameter is similar (27G or 30G); this might additionally influence the ability to withdraw blood during a pre-injection aspiration manoeuvre.

J Drugs Dermatol. 20(5):498-502. doi:10.36849/JDD.5237

INTRODUCTION

More than 1 billion US dollars were spent in 2018 on treatments with injectable agents like neuromodulators or soft tissue fillers for aesthetic purposes according to the annual statistic report released by The Aesthetic Society.1 This large number is indicative of the acceptance of these treatment options which, when compared to surgical procedures, are less invasive, less expensive, require less down time, and can be combined with energy-based devices to enhance outcomes.

Hyaluronic acid based soft tissue fillers can be injected in various facial regions and fascial layers depending on the utilized product. Differences in products can be classified according to their rheological properties which are influenced by a multitude of physico-chemical characteristics including the hyaluronic acid content per mg, the cross-linking technology and other manufacturing specifics ultimately influencing cohesivity, swelling factor and the elastic and loss modulus (ie, G-prime and G-double-prime).2–4 These factors are currently used to predict the aesthetic outcome of an injection procedure together with the targeted anatomic location and depth of injection.

The injection procedure itself however is influenced by the injector’s experience but also by the injection technique (superficial, deep, fanning), the utilized needle/cannula and by the selected product.5–7 Choosing a suitable product-needle-combination can influence the outcome due to the extrusion