Objectives: This lecture presents the first studies to define key biomechanical properties for absorbable suspension threads. The objective is to devise specific biomechanical profiles for different types of threads that can be matched to facial anatomy and procedural objectives to achieve consistent and optimal outcomes. This novel concept of biomechanical tailoring, which parallels rheological tailoring of soft tissue fillers, empowers the use of threads alone or in combination with fillers, fat grafting or surgery to create anatomically and physiologically appropriate results in repose and animation.
Introduction: A total of 45 threads were evaluated in an independent, university-affiliated laboratory. They comprised poly-L-lactic acid-co-ε-caprolactone (PLLA-co-PCL) with 23.2cm and 12cm lengths from one source and 10cm from another source, poly-L-lactic/glycolic acid (Lac/Gly) with 27.5cm length, and polydioxanone (PDO) with 10cm length. All types of thread are CE-marked, and two are currently approved by the US FDA.
Materials / method: Stereomicroscopic examination was performed at four magnifications. Rheologic testing was performed in triplicate on multiple thread specimens using a dynamic mechanical analysis device. Tensile Strength and Rheological Creep & Recovery were measured under supra-physiological stress conditions. Statistical analysis quantified the pattern and balance of elastic and plastic behavior and assessed the threads’ capacity to withstand and adapt to cumulative forces, as they would experience from muscular contractions and gravity over their lifespan after facial implantation.
Results: Stereomicroscopy showed significant structural differences between different types of thread. PLLA-co-PCL and PDO threads had notches that created periodic, bi-directional barbs or arrow-shaped anchors respectively along their length. For PLLA-co-PCL, the barb orientation was specific to thread source. Lac/Gly threads had a series of sliding cones bounded by torus knots and separated by linear segments. Supra-physiological rheologic stress testing displayed reproducible biomechanical behavior including specific mechanical strengths, yield points, and kinetics of elastic and plastic behavior.
Conclusion: These first scientific studies of threads are of value to identify their points of distinction, define appropriate clinical indications, and avoid and manage complications such as pain, inflammation, extrusion and contour irregularities. Biomechanical tailoring can evolve the use of threads from short-lived, 2D static lifting to longer-lasting, 3D dynamic facial support.
Sundaram H. The New Science of Threads: An Evidence-Based Paradigm for Physiological Tissue Mobilisation and Reshaping. Prime Journal (2019).
Sundaram H, Delmar H. American Academy of Dermatology Annual Meeting (2019).
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