Finite element analysis of biomechanical interactions of a subcutaneous suspension suture and human face soft-tissue: a cadaver study

Mousavi et al. BioMedical Engineering OnLine https://doi.org/10.1186/s12938-023-01144-5 RESEARCH (2023) 22:79 BioMedical Engineering OnLine Open Access Finite element analysis of biomechanical interactions of a subcutaneous suspension suture and human face soft‑tissue: a cadaver study Seyed Ali Mousavi1,2,3, Mohammad Ali Nazari1,2*, Pascal Perrier3, Masoud Shariat Panahi1, John Meadows4, Marie‑Odile Christen4, Ali Mojallal5 and Yohan Payan2 *Correspondence: 1 Biomechanics Department, School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran, Iran 2 University of Grenoble Alpes, CNRS, Grenoble-INP, TIMC-IMAG, Grenoble, France 3 University of Grenoble Alpes, CNRS, Grenoble-INP, GIPSA-LAB, Grenoble, France 4 Sinclair Pharmaceutical Ltd, Chester, UK 5 Department of Plastic and Adhesive Surgery, Croix‑Rousse Hospital, Hospices Civils de Lyon, Université Claude Bernard Lyon 1, Lyon, France Abstract In order to study the local interactions between facial soft-tissues and a Silhouette Soft® suspension suture, a CE marked medical device designed for the reposition‑ ing of soft tissues in the face and the neck, Finite element simulations were run, in which a model of the suture was embedded in a three-layer Finite Element struc‑ ture that accounts for the local mechanical organization of human facial soft tissues. A 2D axisymmetric model of the local interactions was designed in ANSYS, in which the geometry of the tissue, the boundary conditions and the applied loadings were considered to locally mimic those of human face soft tissue constrained by the suture in facial tissue repositioning. The Silhouette Soft suture is composed of a knotted thread and sliding cones that are anchored in the tissue. Hence, simulating these interactions requires special attention for an accurate modelling of contact mechan‑ ics. As tissue is modelled as a hyper-elastic material, the displacement of the facial soft tissue changes in a nonlinear way with the intensity of stress induced by the suture and the number of the cones. Our simulations show that for a 4-cone suture a dis‑ placement of 4.35 mm for a 2.0 N external loading and of 7.6 mm for 4.0 N. Increasing the number of cones led to the decrease in the equivalent local strain (around 20%) and stress (around 60%) applied to the tissue. The simulated displacements are in gen‑ eral agreement with experimental observations. Keywords: Tissue repositioning, 2D axisymmetric model, Silhouette soft suture, Facial soft tissue Introduction For many years, aesthetic clinical procedures addressing facial ptosis, which is characterized by the drooping of facial soft tissues, have typically involved invasive face lift surgery. These surgeries often require sedation under general anaesthesia and may result in tissue lesions, scars, pain, and prolonged recovery periods. (see [29] or [16]). In order to reduce the severity of the procedure and avoid these potential sequels, Sulamanidze et al. [30] © The Author(s) 2023. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the mate‑ rial. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creativecommons.org/licenses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publi cdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Mousavi et al. BioMedical Engineering OnLine (2023) 22:79 have proposed a minimally invasive tissue repositioning technique that involves the insertion of suspension threads, or sutures, in the superficial face tissues. In recent years, these minimally invasive aesthetic procedures have become increasingly popular for patients not wanting to undergo face lift surgeries. Suspension sutures are medical devices in which a series of structural elements such as barbs or cones are attached to the thread. These elements are designed to physically engage with the surrounding tissues thereby anchoring the device in place, after their implantation via needle insertion techniques into the subcutaneous fat pads. This allows the clinician to apply tension to the implanted device and to move parts of the facial tissues to a new position and fix them efficiently in their new position by anchoring a more distant part of the device into a second facial region made of less mobile tissue. Because they do not imply aggressive suspension, sutures can be employed in for correction of facial paralysis [1, 5, 8] and for aesthetic purposes to enhance the appearance of the midface [17, 20, 21, 28]. Flynn et al. [12] provided a comprehensive review of the different methods involving suture suspensions. Silhouette Soft [24] is a CE marked suspension suture, made of bioresorbable polymers, which incorporates a series of hollow cones (Fig. 1). The suture is introduced, thanks to surgical needles, inside the hypodermis layer, along a predetermined pathway which is drawn on the face before the insertion after the clinician’s assessment of the desired tissue repositioning to be achieved. The role of the hollow cones is to ensure the anchoring of the suture in the tissues. The clinical use and material properties of these sutures have been studied in the literature for example see [6, 9–11, 21]. Having a special geometrical design, the mechanical consequences of various characteristics of the suture, e.g. the type of conic part (hollow or full), or the number of conic parts (1 to 4), are important issues to be investigated. Moreover, it is desirable to assess the results obtained with this suture based on quantitative data rather than just qualitative visual comparisons. So, it is important to study the biomechanical interactions of the suture-tissue coupling numerically. Finite Element (FE) modelling has been shown to be an efficient way to investigate biomechanical problems, in the face [3, 4, 13–15] or the tongue [27]. Interactions between barbed suture and soft tissue were studied by Ingle et al. [18, 19], who considered a linear Fig. 1 Silhouette Soft sutures geometry and schematic view (from https://www.sinclairpharma.com/) Page 2 of 12 Mousavi et al. BioMedical Engineering OnLine (2023) 22:79 Page 3 of 12 soft tissue model. This linear assumption is consistent with their exper (...truncated)