Dermal Filler Rheology & Facial Suitability Guide

Published:

October 27, 2025

Purpose

Educate clinicians on rheological concepts—G′ (elasticity), G″ (viscosity), tanδ, cohesion, viscosity, extrusion force, and crosslink density ¹ ² ³ ⁴ ⁵—and translate this science into zone-specific product selection by skin thickness, tissue support needs, and safety requirements. ⁶ ⁷

1. Core Rheology Concepts

G′ reflects elastic or ‘firmness’ behaviour under oscillation; higher G′ products resist deformation and better maintain projection in high‑mobility or load‑bearing planes (e.g., lateral zygoma, chin). ⁴ ⁵G″ and complex viscosity capture flow behaviour; fillers with higher viscosity may resist spread but can require greater injection force and may be less suitable for superficial planes prone to Tyndall effect. Tanδ (G″/G′) indicates whether a filler behaves more solid‑ or fluid‑like under stress. ⁴ ⁵ ⁶ ¹⁵

2. Hyaluronic Acid Chemistry & Crosslinking

Most contemporary HA fillers are crosslinked with BDDE to create a 3‑D gel network. Crosslink density, HA concentration, and whether the product is monophasic (homogeneous) or biphasic (particulate) determine G′, cohesivity, water uptake, and longevity. ⁶ ⁷ ⁸Greater crosslinking generally increases G′ and resistance to enzymatic degradation but may elevate extrusion force and palpability if placed too superficially. ⁶ ⁷ ¹⁵

3. Cohesivity & Tissue Integration

Cohesivity describes a gel’s tendency to resist fragmentation and maintain integrity under stress. Highly cohesive fillers can integrate as a continuous sheet—useful for superficial contouring—whereas less cohesive, high‑G′ products may perform better for deep, structural boluses. ⁶ ⁹ ¹⁰In vivo, cohesivity interacts with tissue movement and hydration; histologic studies show variable integration, with some gels interdigitating between collagen bundles while others remain more discrete. ⁸ ⁹

4. Measurement Methods & Clinical Translation

Oscillatory rheometry reports G′/G″ under controlled frequency and strain; however, injection reality adds shear, compression, and temperature effects. Thus, rheology is a guide—not an absolute rule. ⁴ ⁵ ⁶Clinically, combine rheology with anatomy, intended plane, and dynamic loading: high‑G′ for projection on bone; mid‑G′ with good cohesivity for malar shaping in deep fat; low‑G′, high‑cohesivity for fine lines and dynamic superficial planes. ⁹ ¹¹

5. Extrusion Force, Needle vs Cannula

Higher viscosity and particle size increase extrusion force, influencing ergonomics and accuracy. Match needle gauge or cannula bore to the product to maintain controlled flow and reduce bolus surges. ⁹ ¹⁵Blunt cannulas may lower intravascular injection risk in selected zones, but require tactile skill and adequate port size; needles can be precise in periosteal placement with aspiration and micro‑aliquots. Choice depends on zone, plane, and risk profile. ¹² ¹³

6. Zone‑Specific Selection (Narrative Guidance)

Temple (deep): Prefer high‑G′, low‑swelling, cohesive gels in supraperiosteal plane via cannula through posterior entry to minimise vascular injury and irregularity. ¹⁰ ¹¹ ¹⁴

Lateral zygoma/zygion on bone: High‑G′ for projection with small boluses; avoid superficial placement to prevent visibility or nodularity. ⁴ ⁵ ⁹

Medial cheek (deep fat): Mid‑to‑high G′ with balanced cohesivity; consider cannula in deep plane to avoid infraorbital vessels. ⁹ ¹⁰ ¹¹

Tear trough/superficial peri‑orbital: Very low G′, high‑cohesivity, low hydrophilicity micro‑threads in the correct sub‑orbicularis or superficially subdermal plane to mitigate Tyndall; conservative volumes. ⁸ ⁹ ¹¹

Nasolabial fold: Mid‑G′ with controlled cohesivity; linear threading in subdermal or deep periosteal contact depending on anatomy, avoiding mid‑plane artery. ¹⁰ ¹¹ ¹⁴

Lips: Low G′, high cohesivity for vermilion/body to accommodate motion; micro‑aliquots with low pressure to reduce vascular events and lumping. ⁹ ¹¹ ¹²

Chin and jawline on bone: High‑G′ for projection and mandibular definition; layered periosteal technique with small boluses; watch mental foramen and antegonial notch. ¹¹ ¹⁴

7. Longevity, Swelling & Water Binding

Longevity depends on crosslink density, HA concentration, placement depth, and mechanical loading. More crosslinked, higher‑G′ products may last longer in low‑motion, periosteal planes; superficial dynamic zones remodel faster. ⁶ ⁷ ⁹Hydrophilicity influences early swelling; select lower‑swelling gels for tear troughs and peri‑oral areas where edema visibility is high. ⁴ ⁹

8. Safety & Risk Translation

Rheology does not eliminate vascular risk; zone anatomy and technique dominate safety outcomes. Use low injection pressures, micro‑aliquots, frequent perfusion checks, and cannulas where appropriate. Maintain immediate access to hyaluronidase and an anaphylaxis kit; document lot/batch numbers for pharmacovigilance and TGA reporting when required. ¹ ¹⁵ ¹¹ ¹⁴

9. Documentation & Consent

Record product brand, HA concentration, crosslink type (if known), lot/batch and expiry, injection plane, volumes per site, and rationale linking rheology to indication. Provide AHPRA‑compliant consent and aftercare, and align with NSQHS governance for audit readiness. ¹ ² ³

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The policies and procedures contained within this document are the exclusive property of Newcastle Cosmetic Doctor and are provided for internal clinical governance and educational purposes only. These materials represent the internal operational framework, safety standards, and evidence-based protocols developed and implemented by Dr. Bart John Scanlon and the Newcastle Cosmetic Doctor team. They are designed specifically for use within Newcastle Cosmetic Doctor and reflect our clinic’s own professional standards, risk assessments, and compliance obligations under Australian law and regulatory authorities. External individuals, practitioners, or organisations must not copy, reproduce, distribute, or rely upon these materials, in whole or in part, for their own clinical, commercial, or educational use without prior written consent from Newcastle Cosmetic Doctor. These materials do not constitute medical, legal, or professional advice and are not intended to be adopted as official protocols or procedures by any other entity. Any external use or adaptation must be independently reviewed and modified to meet the relevant laws, guidelines, and standards applicable to the user’s own jurisdiction, scope of practice, and facility operations. Newcastle Cosmetic Doctor and Dr. Bart Scanlon accept no liability for any loss, injury, or damage arising from the unauthorised use, reliance upon, or misinterpretation of this material.