Thermal Damage Prediction for Collagenous Tissues Part I: A Clinically Relevant Numerical Simulation Incorporating Heating Rate Dependent Denaturation*

Expansion of Renuvion Application to Areas Beyond the Submental Region: Review and Experience

Background

Minimally invasive and consistent skin redraping following liposuction remains an elusive goal. With the application of Renuvion (Apyx Medical, Clearwater, FL), helium induced cold atmospheric plasma provides coagulation, collagen contraction, and subsequent skin tightening, making this elusive goal attainable.

Objectives

The objective of this study is to evaluate energy settings, and the safety profile of Renuvion in an effort to achieve optimal cosmesis through the improvement of skin laxity.

Methods

A retrospective review at a single site evaluated cases of Renuvion between March 2020 and May 2022. Energy settings, use of concomitant VASER (Solta Medical, Bothwell, WA) liposuction frequency, and adverse events were analyzed.

Results

In total, 180 patients were evaluated, of whom 135 (75%) underwent concomitant VASER liposuction. Renuvion was used on the abdomen (47.8%), thighs (45.6%), arms (27.2%), submental region (25%), hip rolls (21.2%), and back (19.4%). Among the entire cohort, there were a total of 24 (13.3%) complications. The complications consisted of 3 (12.5%) hematomas, 1 (4.2%) burn, 6 (25%) persistent skin laxity with 2 returned operating room (OR) treatments, 4 (16.7%) seromas, 9 (37.5%) postoperative lymphedema that self-resolved, and 1 (4.2%) self-limited neuralgia. There were no complications that required an immediate return to the OR.

Conclusions

Renuvion utilization with or without VASER has a relatively high complication rate-with minor complications as the most common-relatively safe barring proper patient selection, which can be mitigated with proper patient selection.

Level of Evidence 4

Paradoxal dyeing affinity's inversion of the connective tissue at Goldner's Masson trichrome staining as a peculiar characteristic of compressed and exsiccated cadaveric skin

The microscopic examination of a hanging cutaneous furrow, stained with Goldner's Masson trichrome staining, highlighted an abnormal dyeing inversion affinity of the connective tissue - red instead of green - located in the region of maximal cutaneous compression and exsiccation. To identify if this different stainability could be considered as an intrinsic characteristic of all biological tissues compressed and exsiccated, we have assessed different cadaveric skin samples that underwent traumatic detrimental phenomena that can produce such effects. We collected skin fragments from 24 corpses deceased because of gunshot injuries, electrocution, hanging, and heat-induced lesions, sampling the areas directly involved, as well as skin specimens to use as a control. The slides were stained with hematoxylin and eosin and two different protocols of Goldner's Masson trichrome staining (one homemade and one commercial kit). The inversion of the staining affinity of the connective tissue was observed in 83% of the cutaneous samples, using both the Goldner's Masson trichrome staining protocols. This phenomenon was not observed in any of the control cases. Therefore, the inversion of the staining affinity of the connective tissue dyed with Goldner's Masson trichrome staining may represent a histomorphological aspect that must be expected when the skin has been affected by specific detrimental modalities able of producing compression and exsiccation.

The role of laser power and pullback velocity in the endovenous laser ablation efficacy: an experimental study

Endovenous laser ablation is an effective and minimally invasive alternative to surgical removal of incompetent veins. However, many controversies concerning optimal laser parameters usage in this procedure still remain. The purpose of this experimental study was to assess the adequate parameters required for vein wall destruction and to evaluate the role of fiber pullback velocity on vessel wall degradation. Varicose vein segments were treated with 1470-nm diode laser 3 to 9.5 W in power. The fiber moved through the vein at a velocity of 0.7 or 1.5 mm/s; the applied linear endovenous energy density (LEED) was 40-95 J/cm. The temperature of the vein surface in the course of laser irradiation was controlled by IR thermography. The intact collagen in treated vein specimens was studied by differential scanning calorimetry. The increase in the surface temperature with applied energy was found to be about three times slower for the pullback velocity of 0.7 mm/s than that of 1.5 mm/s. The collagen in the tissue was totally denatured in the case of the surface temperature of about 91 °C. The critical values of LEED ensured complete degradation of vein wall were of 53 and 71.5 J/cm for velocities of 1.5 and 0.7 mm/s, respectively. Our experimental study supports the conception that it is laser power and pullback velocity rather than LEED value that determine the temperature as well the collagen framework degradation and therefore the thermal response of procedure.

Marker-Free Tracking of Facet Capsule Motion Using Polarization-Sensitive Optical Coherence Tomography

We proposed and tested a method by which surface strains of biological tissues can be captured without the use of fiducial markers by instead, utilizing the inherent structure of the tissue. We used polarization-sensitive optical coherence tomography (PS OCT) to obtain volumetric data through the thickness and across a partial surface of the lumbar facet capsular ligament during three cases of static bending. Reflectivity and phase retardance were calculated from two polarization channels, and a power spectrum analysis was performed on each a-line to extract the dominant banding frequency (a measure of degree of fiber alignment) through the maximum value of the power spectrum (maximum power). Maximum powers of all a-lines for each case were used to create 2D visualizations, which were subsequently tracked via digital image correlation. In-plane strains were calculated from measured 2D deformations and converted to 3D surface strains by including out-of-plane motion obtained from the PS OCT image. In-plane strains correlated with 3D strains (R(2) ≥ 0.95). Using PS OCT for marker-free motion tracking of biological tissues is a promising new technique because it relies on the structural characteristics of the tissue to monitor displacement instead of external fiducial markers.

Energetic soft-tissue treatment technologies: an overview of procedural fundamentals and safety factors

BACKGROUND

Energy administered during soft-tissue treatments may cauterize, coagulate, seal, or otherwise affect underlying structures. A general overview of the functionality, procedural outcomes, and associated risks of these treatments, however, is not yet generally available. In addition, literature is sometimes inconsistent with regards to terminology. Along with the rapid expansion of available energetic instruments, particularly in the field of endoscopic surgery, these factors may complicate the ability to step back, review available treatment options, and identify critical parameters for appropriate use.

METHODS

Online databases of PubMed, Web of Science, and Google Scholar were used to collect literature on popular energetic treatments, such as electrosurgery, plasma surgery, ultrasonic surgery, and laser surgery. The main results include review and comparison studies on the working mechanisms, pathological outcomes, and procedural hazards.

RESULTS

The tissue response to energetic treatments can be largely explained by known mechanical and thermal interactions. Application parameters, such as the interaction time and power density, were found to be of major influence. By breaking down treatments to this interaction level, it is possible to differentiate the available options and reveal their strengths and weaknesses. Exact measures of damage and alike quantifications of interaction are, although valuable to the surgeon, often either simply unknown due to the high impact of tissue and application-dependent parameters or badly documented in previous studies. In addition, inconsistencies in literature regarding the terminology of used techniques were observed and discussed. They may complicate the formulation of cause and effect relations and lead to misconceptions regarding the treatment performance.

CONCLUSIONS

Some basic knowledge on used energetic treatments and settings and a proper use of terminology may enhance the practitioner's insight in allowable actions to take, improve the interpretation and diagnosis of histological and mechanical tissue changes, and decrease the probability of iatrogenic mishaps.

Mathematical models of laser-induced tissue thermal damage

Laser sources are under increasing study for in vivo tumour ablation. Photo-thermal ablation in tissues varies tremendously in governing physical phenomena, depending on wavelength, owing to wide variation in the optical properties of tissues, specifically the dominant chromophore and degree and type of scattering. Once converted into local tissue heating, however, the governing thermodynamic principles remain the same. Observed irreversible thermal alterations range from substantial structural disruption due to steam evolution in high temperature short-term activations to low temperature rise, longer-term initiation of the complex protein cascades that result in apoptosis and/or necroptosis. The usual mathematical model in hyperthermia studies, the thermal isoeffect dose, arising from the relative reaction rate formulation, is not an effective description of the higher temperature effects because multiple processes occur in parallel. The Arrhenius formulation based on the theory of absolute reaction rates is much more useful and descriptive in laser heating since the multiple thermodynamically independent processes may be studied separately.

Laser-induced modification of the patellar ligament tissue: comparative study of structural and optical changes

The effects of non-ablative infrared (IR) laser treatment of collagenous tissue have been commonly interpreted in terms of collagen denaturation spread over the laser-heated tissue area. In this work, the existing model is refined to account for the recently reported laser-treated tissue heterogeneity and complex collagen degradation pattern using comprehensive optical imaging and calorimetry toolkits. Patella ligament (PL) provided a simple model of type I collagen tissue containing its full structural content from triple-helix molecules to gross architecture. PL ex vivo was subjected to IR laser treatments (laser spot, 1.6 mm) of equal dose, where the tissue temperature reached the collagen denaturation temperature of 60 ± 2°C at the laser spot epicenterin the first regime, and was limited to 67 ± 2°C in the second regime. The collagen network was analyzed versus distance from the epicenter. Experimental characterization of the collagenous tissue at all structural levels included cross-polarization optical coherence tomography, nonlinear optical microscopy, light microscopy/histology, and differential scanning calorimetry. Regressive rearrangement of the PL collagen network was found to spread well outside the laser spot epicenter (>2 mm) and was accompanied by multilevel hierarchical reorganization of collagen. Four zones of distinct optical and morphological properties were identified, all elliptical in shape, and elongated in the direction perpendicular to the PL long axis. Although the collagen transformation into a random-coil molecular structure was occasionally observed, it was mechanical integrity of the supramolecular structures that was primarily compromised. We found that the structural rearrangement of the collagen network related primarily to the heat-induced thermo-mechanical effects rather than molecular unfolding. The current body of evidence supports the notion that the supramolecular collagen structure suffered degradation of various degrees, which gave rise to the observed zonal character of the laser-treated lesion.

Acute Recovery of Patellar Tendon From Heat-Induced Shrinkage and Its Inhibition by Cross-Linking

There are two important factors that accompany heat-induced shrinkage of collagenous tissues: mechanical property degradation and partial recovery from the shrunken length (elongation) upon returning to room temperature (defined here as acute recovery). These undesirable factors reduce the efficacy of thermal therapies. We applied chemical cross-linking adjuvant to thermal treatment on New Zealand White rabbit patellar tendon complexes to explore the feasibility of reducing the impact of these undesirable side-effects. Our results have shown that with exposure to 0.5% w/v glutaraldehyde solution during heating, the recovery response of the patellar tendon tissue was decreased, and the mechanical properties of the tissue were significantly improved.

Thermal conduction, compression, and electrical current--an evaluation of major parameters of electrosurgical vessel sealing in a porcine in vitro model

Bipolar vessel sealing is pivotal in laparoscopic hemostasis. However, major coaptive desiccation parameters have yet to be investigated in detail. The current investigation aims to study the impact of compressive pressure, thermal conduction, and electrical current effects on seal quality in a randomized, controlled experimental trial in an in vitro porcine model of vessel sealing. A total of 106 porcine vessels were sealed with either bipolar current or thermal conduction. Compressive pressure on the sealing site and maximum temperature were varied and monitored. Additionally, the longitudinal vessel tension was measured. The burst pressure of the resulting seal was determined as an indicator of seal quality. In bipolar coaptation, seal quality depends on the compressive pressure applied to the coagulation site in both arteries and veins. The optimal pressure interval was around 270 mN/mm2 for arteries and 200 mN/mm2 for veins. Deviation from these optimal pressures towards low and high extremes led to significantly fewer successful seals. We also found that both maximum coaptation temperature and vessel shrinking correlated with the seal quality. This correlation was reciprocal in arteries and veins. Thermal conduction alone was less successful than sealing by bipolar current. Therefore, compressive pressure during coaptation determines the seal quality. Upper and lower pressure boundaries for safe coaptation exist for both arteries and veins. Vessel sealing by thermal conduction without electrical current effects is possible but represents a less effective method for coaptation. These findings have implications for the rational design of new electrosurgical instruments.

IR Laser and Heat-induced Changes in Annulus Fibrosus Collagen Structure

The purpose of this study was to characterize essential changes in the structure of annulus fibrosus (AF) after hydrothermal and infrared (IR) laser treatment and to correlate these results with alterations in tissue state. Polarization-sensitive optical coherence tomography imaging was used to measure collagen birefringence in AF. Differential scanning calorimetry was used as a complementary technique, providing detailed information on thermodynamic processes in the tissue. Birefringence, peak of the denaturation endotherm, and the enthalpy of denaturation (DeltaHm) were determined before and after hydrothermal heat treatment (85 degrees C for 15 min) and non-ablative Er:glass fiber laser exposures on AF in the whole disk (vertebrae-disk-vertebrae complex). Our data have demonstrated quantitative differences between results of laser and hydrothermal heating. Birefringence did not disappear and DeltaHm did not change after treatment in the water bath, but loss of birefringence and a decrease in the enthalpy did occur after laser exposure. These results could be explained by the photomechanical effect of laser irradiation. We suggest that thermo-mechanical stress played a dominant role in the disruption of the collagen network of AF under non-homogeneous laser heating.