Residual Thermal Damage Research Articles

Solid-phase transient soldering method based on Au/Ni–W multilayer thin-film-modified copper-based structures

The copper crystal cone-shaped micro-nanostructure is used as the substrate, and the Ni–W alloy layer and Au nanolayer are plated sequentially. Instantaneous soldering with lead-free solder is realized under ultrasonic assistance at room temperature. This solves the residual stress and thermal damage caused by high melting point lead-free solder on thin chips and thermal components, and ensures the safety and reliability of electronic components. Copper-based microstructures are deposited by electrochemical methods. An amorphous Ni–W alloy layer with a thickness of 180 nm is deposited on the Cu-based microstructures by adjusting the atomic ratio of the plating solution. The Ni–W layer is further coated with a 50 nm Au layer to prevent oxidation. Solid-phase transient soldering is realized by combining the Au/Ni–W multilayer thin-film-modified Cu substructures with commercial solder (SAC305) for a holding time of 3 s at a soldering pressure of 10,000 gf (20 MPa) while ultrasonically assisted. The soldered samples are aged at 180 °C for 10 min, 30 min, and 60 min, respectively. Copper substructures with different surface modifications are subjected to destructive shear experiments with solder balls. Scanning electron microscope and X-ray fluorescence thickness gauge are used to study the microstructure, intermetallic compound (IMC) composition thickness and properties of the soldered interface and section. The cone height of the Cu-based structure is 2–4 μm, and the diameter of the bottom is 800 nm–1200 nm, which has a sharp tip and an excellent L/D ratio. The interface between the Au/Ni–W modified Cu substructure and the solder ball is almost free of holes. The average shear strength at the soldering interface is about 43.06 MPa. The fracture surface after the shear experiment basically occurs inside the solder ball matrix, which belongs to the pure toughness fracture. The interface between the Au/Ni–W-modified Cu-based structure and the solder ball is subjected to long aging treatment at 180 °C. The soldering interface showed a “bright layer”. New phases are generated on the solder side above the “bright layer”, while no new phases appear on the Cu substructure side below the “bright layer”. The copper-based microstructure is inserted into the inside of the solder ball to form an inlay and produce mechanical interlocking. Au/Ni–W alloy modification layer can effectively improve the surface hardness of copper-based structures. This creates a large hardness difference with soft solder and enables the formation of fewer holes in the insertion solder. Amorphous Ni–W alloys are prone to form dense oxide films during ultrasonication. The Au film modification prevents oxide generation and increases the average shear strength of the soldering interface. The Ni–W alloy layer retards the interdiffusion between Cu–Sn, blocks the excessive growth of Cu–Sn IMCs, and reduces the reliability problems caused by interface failure.

Experimental analysis of electro-jet machining of thin metal sheets under the application of ultrasonic vibration, continuous and pulsed direct current

Electrochemical machining is considered to be suitable for precision and micromachining without the development of residual stress, mechanical distortion and thermal damage. In this work, an in-house developed electro-jet machining system, a variant of electrochemical machining, has been used for machining in thin metal sheets, where the electrolyte is supplied in the form of a fine jet, concentrically to a wire electrode, through a nozzle. Machining performance was studied for generation of through slits of sub-millimetre range in 500 μm thick aluminium sheets, under the application of continuous and pulsed direct current (DC) power sources as well as with the application of ultrasonic vibration to the workpiece, emphasizing achieving better dimensional control with minimum overcut. A detailed investigation of the effect of applied voltage, scan speed, inter-electrode gap and electrolyte concentration has been performed in the case of continuous DC supply on quality factors, kerf-width, amount of overcut and material removal rate. Furthermore, the effects of duty cycle and pulse frequency in the case of pulsed DC supply, and the effect of vibration frequency under the application of ultrasonic vibration have been analysed on the above-mentioned output factors. Though a pulsed DC power supply with a pulse frequency of more than 1 kHz and a small duty cycle was found suitable for precision machining among all conditions, ultrasonic vibrations proved beneficial for fine feature generation with tighter size control at higher frequencies (lower vibration amplitude).

Simplified modelling of the performance of concrete tunnels during fire and post-fire damage classification

The performance of concrete tunnel structures during and after fire is not well understood. This is an obstacle to the adoption of risk-based approaches for fire safety design of tunnel structures. Upon the request of the Belgian fire safety consultancy FESG, a simplified assessment of the collapse probability and post-fire damages for a reference tunnel structure has been made. The structural system is modelled through 2D beam finite elements, where spalling rates have been assumed based on available literature data. Structural stability is verified for both the heating and cooling phases of the fire. In those cases where the structure survives up to burnout, the residual deformations and thermal damage to the tunnel structure are assessed.

Er:YAG laser brainsurgerywithvascularspecificcoagulation.

Erbium:yttrium-aluminum-garnet (Er:YAG) laser ablation can effectively resect water-bearing tissues. Application of Er:YAG resection in neurosurgery is complicated by unpredictable bleeding in surgical field. Recently, an integrated theranostic system combining a dual-wavelength laser surgery system using a thulium (Tm) fiber-laser for coagulation and Er:YAG for resection, combined with optical coherence tomography (OCT) guidance was demonstrated for the in vivo resection of tumor tissue. However, lateral thermal spread in the range of 100s of micrometers is common due to lack of vascular specificity using a Tm fiber-laser for coagulation. In this study, a vascular specific ytterbium (Yb) fiber-laser is utilized for enhanced photocoagulation during in vivo neurosurgery improving the precision of Er:YAG tissue resection with minimal lateral thermal spread. Mice underwent stereotactic laser surgery with the proposed Yb/Er:YAG dual wavelength vascular specific neurosurgery in vivo. AnOCTsystem (wavelength range 1310 ± 70 nm) and OCT derived angiography images were used to record cortical images to confirm the coagulation of blood vessels and guide subsequent Er:YAG resection steps. After the laser surgery, mice were killed, and histological analysis was carried out using hematoxylin and eosin staining and Nissl staining to compare the lateral thermal spread with our previously reported Tm/Er:YAG neurosurgery where a continuous wave Tm fiber-laser was used for coagulation. Coagulation scheme using a Yb fiber-laser allowed stoppage of blood flow in disparately sized blood vessels encountered in the mice brain. Histological analysis of murine brain slices post Yb/Er:YAG laser surgery yielded lower thermal spread compared withTm/Er:YAG laser surgery, maximizing the efficiency in both hemostasis (blood flow stoppage) and maximizing tissue ablation efficiency with minimal residual thermal damage zone. In this study, a vascular specific coagulation scheme with Yb/Er:YAG dual-wavelength surgery is presented for neurosurgery. Additionally, Yb/Er:YAG study results are compared with that of a tissue coagulation approach in Tm/Er:YAG surgery previously reported to highlight improved coagulation, reduced nonspecific thermal damage and limited lateral thermal spread. Experimental results suggest that the developed dual-wavelength laser system can effectively resect neural tissues with high localization, minimal lateral thermal spread at the micrometer level while maintaining a bloodless surgical field.

Flexible Oxide Thin-Film Transistors Fabricated at Room Temperature By Introducing Polymer Dielectric and Microwave Annealing

Amorphous oxide semiconductors (AOSs) have attracted considerable attention as an active layer material for thin-film transistors (TFTs), due to their many advantages such as high field effect mobility and large area uniformity compared to amorphous Si counterparts. In particular, amorphous indium gallium zinc oxide (a-IGZO) have widely studied for high performance TFTs which require high mobility, high on/off ratio, low leakage current and room temperature fabrication. Even if, a-IGZO TFTs can be deposited at room temperature, additional thermal treatment is still required in order to obtain satisfactory electrical characteristic and stability.Organic materials can be used for dielectrics of flexible TFTs because of their flexible mechanical properties. Generally, organic dielectric films are fabricated by solution process like spin-coating. Spin coating process can be easy and cheap method, however, the quality of films is not as good as the one with vacuum process because of the residual impurities and thermal damage to the substrate during post-coating bake. Poly(chloro para-xylylene) (Parylene C) can be fabricated via pyrolysis-CVD process at room temperature, which lead to unique characteristics of pinhole-free nature. Also, electrical properties of parylene C films are quite enough to utilize as dielectric layer of TFTs. Moreover, parylene C can act as passivation layer due to their remarkable chemical resistance.In this work, microwave annealing and parylene C are adopted to IGZO TFTs to reduce overall process temperature. Microwave can selectively heat target material by conversion of electromagnetic energy to thermal energy inside of the target material. Finally, flexible IGZO TFTs were realized on PET substrate owing to low process temperature of microwave annealing and parylene C deposition.Transfer and output characteristics were measured in order to investigate the possibility of parylene C as an insulator on oxide TFTs. The device exhibit typical output characteristics with a clear pinch-off, current saturation and no current crowding. When the applied gate voltage bias was 20 V, the saturation drain current was around 230 μA at drain voltage of 20 V. From transfer curve, fully room temperature fabricated IGZO TFTs exhibit mobility, Vth, S.S and hysteresis of 12.9 cm2/Vs, 0.796 V, 0.651 V/dec and 0.62 V. Flexible IGZO TFTs were fabricated using PET substrate which shows low glass transition temperature. The device was well operated which indicate microwave annealing and parylene C deposition process is suitable for low glass transition temperature substrate. The electrical stability of the IGZO TFTs with parylene C gate dielectric under bending stress was evaluated. After bending 15,000 times, switching characteristics was still remained. Mobility and S.S were hardly deteriorated, however, Vth shows small negative shift of near -1 V. In this work, IGZO TFTs were fabricated at room temperature by introducing microwave annealing and room temperature deposited gate dielectric, parylene C. By combining microwave annealing and room temperature fabricated parylene C, the process temperature was decreased enough to utilize flexible substrate with low glass transition temperature. Fabricated flexible IGZO TFTs was shown to withstand harsh 15,000 bending test. Figure 1

Potential neurotoxic effects of polymethylmethacrylate during cranioplasty

Cranioplasty for the surgical correction of cranial defects is often performed using polymethyl methacrylate (PMMA), or bone cement. Immediately prior to PMMA application, a liquid monomer form (methylacrylate) and a benzoyl peroxide accelerator are mixed resulting in polymerization, an exothermic reaction during which monomer linking and subsequent formation of solid polymer occur. The potential side effects of residual methylacrylate monomer toxicity and thermal damage of neural tissue during PMMA hardening have been described in various in vitro, animal, and cadaveric studies; however, clinically documented in vivo neurotoxicity in humans attributed to either of the above two mechanisms during PMMA cranioplasty is lacking. We present a series of four patients operated for removal of cerebellopontine angle lesions and two operated for the excision of parieto-occipital tumors who sustained cranial neuropathies and encephalopathies with transient or permanent neurological deficits that could not be attributed to surgical manipulation. We hypothesize that these complications most likely occurred due to thermal damage and/or chemical toxicity from exposure to PMMA during cranioplasty. Our case series indicates that even small volumes of PMMA used for cranioplasty may cause severe side effects related to thermal damage or to exposure of neural tissue to methylacrylate monomer.

Experimental Research on the Thermal Damage of Concrete

In order to investigate the effect of temperature (from normal temperature to 850°C) coursed by fire on the strength damage of concrete, thermal compression tests for concrete specimens named C35 have been performed under different temperature conditions. Emphasis is laid on the relationship between temperature and thermal damage strength; and the relevant formula is proposed in this paper. The regularity and mechanism of thermal damage evolution in concrete on strength under high temperature are analyzed. Combined the result of tests with the residual strength thermal damage model, we obtain the specific damage variable value D under different temperatures. Finally, we compare the fitting formula curve to relevant reference; there are some important conclusions which can be partly applied to fire design of concrete structure.

Establishing the Safety and Efficacy of Simultaneous Face Lift and Intraoperative Full Face and Neck Fractional Carbon Dioxide Resurfacing

Sir:FigureCurrent literature provides little support for combining rhytidectomy with full face carbon dioxide resurfacing, except in cases where extremely low laser settings are used in combination with deep-plane rhytidectomy.1,2 We explored the possibility of combining recently developed fractional carbon dioxide resurfacing technology with standard rhytidectomy, and established the extent of skin flap elevation and laser settings for safe resurfacing during this procedure. The formulation of this study conforms to the principles detailed by the Declaration of Helsinki. Simultaneous extended supraplatysmal rhytidectomy combined with full face and neck fractional carbon dioxide resurfacing was performed on 20 patients with an average age of 56 years (range, 46 to 72 years). Rhytidectomy was performed before resurfacing. Skin flaps were elevated to the level of the nasolabial fold and midline of the neck (Fig. 1, left). Resurfacing was performed using the Fraxel Re:Pair 10,600-nm fractional carbon dioxide laser (Solta Medical, Hayward, Calif.). Skin flaps were treated at 20 mJ with a spot density of 500 microthermal zones of ablation per square centimeter, with four alternating passes creating a uniform final density of 2000 microthermal zones of ablation per square centimeter. Nonundermined perioral, nasal, and forehead skin was resurfaced with four passes at 40 mJ and 500 microthermal zones of ablation per square centimeter (Fig. 1, left). Excess resurfaced skin was sent for histologic examination. Flexzan occlusive dressing (Bertek Pharmaceuticals, Inc., Morgantown W.Va.) was applied to the face and neck and removed 5 days postoperatively. Patients were seen at weekly follow-up for 2 months.Fig. 1: (Left) Extent of skin undermining of the face and neck. (Right) Fractional carbon dioxide resurfacing settings. X, 20 mJ and 20 percent coverage; O, 40 mJ and 40 percent coverage.There were no cases of delayed healing or other complications. Resurfaced skin reepithelialized within 7 days, and all patients were able to wear makeup 10 days postoperatively. Histologic examination of resected skin revealed cylindrical zones of ablation approximately 234 μm in width penetrating to a depth of approximately 445 μm (Table 1).Table 1: Characteristics of Skin Flap Ablation by Fractional Carbon Dioxide LaserImportant differences between traditional carbon dioxide methods and newer techniques of fractional resurfacing made this combined procedure possible without associated delayed healing or loss in flap integrity. Traditional carbon dioxide lasers ablate 100 percent of the skin surface, directly penetrating less than 20 μm but inducing horizontal sheets of residual thermal damage that reach the cutaneous microvasculature, potentially causing flap failure after only one or two passes. In contrast, microthermal zones of ablation actually penetrate deeper (400 to 650 μm) into the dermal collagen but spare approximately 80 percent of tissue, thereby preserving a functional microvasculature that helps with healing and flap survival.3 In vivo experiments demonstrate rapid reepithelialization, followed by enduring dermal remodeling.4 Fractional laser technology also enables the treating physician to overcome limitations in cosmetic outcome that have prohibited past attempts to combine rhytidectomy with resurfacing. Traditional carbon dioxide using low-energy settings during rhytidectomy results in inferior resurfacing, and higher energy treatments of isolated areas such as the perioral region induce lines of demarcation between treated and untreated skin.5 Similarly, traditional carbon dioxide is not recommended for the neck because it creates a noticeable difference in quality between the resurfaced face and untreated neck. In contrast, fractional resurfacing allows the entire face and neck to be treated during rhytidectomy, imparting a youthful quality to the entirety of facial skin while avoiding lines of demarcation (Fig. 2). The patients in this study were very satisfied with their treatment outcomes and were pleased not to have to wait to undergo a second procedure with additional weeks of healing time.Fig. 2: (Left) Preoperative photograph of a patient before extended supraplatysmal plane rhytidectomy combined with fractional carbon dioxide resurfacing of the entire face and neck. (Right) Patient's appearance 3 months after the combined procedures.S. Tyler Hollmig, M.D. Department of Dermatology, Stanford University, Stanford, Calif. Steven K. Struck, M.D. Struck Plastic Surgery, Atherton, Calif., Division of Plastic Surgery, Stanford University Medical Center, Stanford, Calif. Basil M. Hantash, M.D., Ph.D. Elixir Institute of Regenerative Medicine, San Jose, Calif. DISCLOSURE The authors have no commercial associations or financial disclosures that might pose or create a conflict of interest with the information presented in this article. PATIENT CONSENT Patients provided written consent for the use of their images.

Experimental investigation of turning AISI 1045 steel using cryogenic carbon dioxide as the cutting fluid

The intensive temperatures in high speed machining not only limit the tool life but also impair the machined surface by inducing tensile residual stresses, microcracks and thermal damage. This problem can be handled largely by reducing the cutting temperature. When the conventional coolant is applied to the cutting zone, it fails to remove the extent of the heat effectively. Hence, a cryogenic coolant is highly recommended for this purpose. In this paper, an attempt has been made to use cryogenic carbon dioxide (CO 2) as the cutting fluid. Experimental investigations are carried out by turning AISI 1045 steel in which the efficiency of cryogenic CO 2 is compared to that of dry and wet machining with respect to cutting temperature, cutting forces, chip disposal and surface roughness. The experimental results show that the application of cryogenic CO 2 as the cutting fluid is an efficient coolant for the turning operation as it reduced the cutting temperature by 5%–22% when compared with conventional machining. It is also observed that the surface finish is improved to an appreciable amount in the finished work piece on the application of cryogenic CO 2. The surface finish is improved by 5%–25% in the cryogenic condition compared with wet machining.

Depth of tissue ablation and residual thermal damage caused by a pixilated 2,940 nm laser in a swine skin model

The purpose of this study was to assess the effects of fluence, pulse stacking, and multiple passes on the depth of injury caused by a fractionated Er:YAG laser in an in vivo farm pig model. DESIGN/MATERIAL/METHODS: A fractionated 2,940 nm Er:YAG laser (Pixel, Alma Lasers, Caesarea, Israel) was applied to the flank skin of a Yorkshire cross pig. The 11 mmx11 mm handpiece was comprised of either 49 or 81 microbeams (200 microm diameter), depending on the tip configuration. There were six different parameter sets divided according to total energy per pulse (150, 285, and 500 mJ) and tip type (81 or 49 microbeams per 11 mmx11 mm macrospot). Each of these six groups was subdivided according to number of stacked pulses (1, 3, and 6) and number of passes (1, 3, and 6). This resulted in a total of 36 treatment parameters. With the 49 microbeam configuration, a single pulse resulted in partial epidermal ablation at 150 mJ, complete epidermal ablation at 285 mJ and partial dermal ablation at 500 mJ to a depth of 90 microm. Stacking the pulses resulted in a significant increase in ablation with each fluence with the maximal depth of ablation measured at 140 microm after six stacked pulses at 500 mJ. Increasing the number of passes did not result in a significant increase in ablative depth, but did create a larger surface area of ablation. Residual thermal damage (RTD) was minimal and remained between 10 and 20 microm. The fractionated Er:YAG laser exhibited some of the same tissue interactions as its fully ablative counterparts. An increase in fluence resulted in an increase in ablative depth with minimal RTD. Additionally, RTD was unaffected by pulse stacking or by additional passes. Differences were that pulse stacking appeared to yield a more rapid decrease in ablation efficiency and additional passes did not seem to increase the depth of ablation.

Correlation of histological findings of single session Er:YAG skin fractional resurfacing with various passes and energies and the possible clinical implications

Ablative fractional resurfacing shows promise for skin resurfacing and tightening and also to improve treatment of epidermal and dermal pigmentary disorders. This study aimed at determining any correlation between epidermal ablation and effects on the dermis when using an Er:YAG laser in ablative fractional resurfacing mode. Ten female subjects participated in the study, mean age 52 years, Skin phototypes: 1 Fitzpatrick type II; 8 type III and 1 type IV. The degree of wrinkles (Glogau scale II or III) was similar in all cases. The laser used was the Pixel Er:YAG system (Alma Lasertrade mark, Israel) which delivers the laser beam via a hand-piece equipped with a beam splitter to divide the 2,940 nm beam into various microbeams of 850 microm in diameter in an 11 mmx11 mm treatment area. Using a constant energy of 1,400 mJ/cm(2), on a test area of 4 cmx2 cm. Two, 4, 6, and 8 passes on the preauricular area of the face were evaluated immediately after treatment. In all cases, the handpiece was kept in the same position, and rotated slightly around its perpendicular axis between passes, then moved on to the next spot. Biopsies were performed and tissue samples were routinely processed and stained with hematoxylin and eosin (H&E). No patient reported any noticeable discomfort, even at 8 passes. The histological findings revealed that, independent of the degree of the wrinkles, more laser passes produced more ablative removal of the epidermis. Residual thermal damage (RTD) with 2 laser passes was not observed but with 4 and 6 passes increased thermal effects and vacuole formation in the epidermal cells were noticed. With 8 laser passes, total epidermal removal was seen together with frank RTD-related changes in the upper part of the papillary dermis. In this study, we have demonstrated that high density fractional Er:YAG laser energy in a single session with multiple passes targeted not only the skin surface with elimination of the epidermis, but could also achieve heat deposition in the upper dermis. When performing ablative fractional resurfacing with an Er:YAG laser, treatment of varying degrees of damage could be achieved by varying the number of passes.

Facial resurfacing: An overview

Facial resurfacing is a broad topic referring to procedures that change the texture and appearance of skin. Resurfacing procedures are broadly classified as ablative or nonablative. Ablative procedures are considered the first line treatment for the most common indications for facial resurfacing, which are photoaging and acne scarring. The goal of this review is to provide an overview of the factors that optimize the clinical efficacy of an ablative procedure, including careful patient selection, preoperative skin preparation, correct operative technique, and vigilant postoperative care, as well as review both the traditional and some of the latest technologies that effectively resurface facial skin.

Aesthetic surgery – pertinent papers 2002–2003: A personal view

Aesthetic surgery – pertinent papers 2002–2003: A personal view

Estudo morfométrico e morfológico da cicatrização após uso do laser erbium: YAG em tecidos cutâneos de ratos

Este trabalho analisa o efeito da reparação cutânea do laser erbium:yttrium aluminunn garnet (YAG) (Er:YAG) em pele de ratos através de estudo histológico e morfométrico. Tatuaram-se duas figuras no dorso de cada animal (n = 35), denominadas controle e experimento. Na figura experimento, aplicaram-se três passadas de laser Er:YAG com parâmetros padronizados. Cinco animais foram eutanasiados nos dias 0, 7, 14, 28, 56, 84 e 112 de pós-operatório. O estudo histológico demonstrou no dia 0 dano de ablação médio de 215,24 micrômetros (mm), sendo homogêneo com vaporização da epiderme e porções superficiais da derme. O dano térmico residual foi pequeno (média de 41,45mm), observando-se áreas onde estava praticamente ausente. A fibroplasia cicatricial já estava presente no dia 7 (média de 55,58mm), aumentando rapidamente até o dia 28 (média de 209,49mm), quando atingiu um platô e se manteve até o dia 112. Não houve sinais de processo inflamatório agudo no dia 7 e a reepitelização já estava completa. Concluiu-se que a aplicação de laser na pele de ratos induz reparação cutânea ao longo de 112 dias nas condições do experimento.

Resurfacing of pitted facial acne scars using Er:YAG laser with ablation and coagulation mode.

Although the conventional, short-pulsed erbium: yttrium-aluminum-garnet (Er:YAG) laser provides substantial clinical improvement for pitted, facial acne scars, it shows less effective hemostasis and limited residual thermal effect in the dermis. Recently, dual-mode Er:YAG laser systems with both ablation and coagulation modes have been developed. The purpose of this study was to evaluate the clinical and histologic effects of resurfacing pitted, facial acne scars with a dual-mode Er:YAG laser. Twenty patients with pitted facial acne scars underwent laser resurfacing using a computerized-scanning, dual-mode Er:YAG laser. All patients had Fitzpatrick skin types ranging III-V. Initially, the epidermis was removed in two passes using the ablative settings. This step was followed by two passes in a mixed ablation and coagulation mode, to produce further ablation and controlled, residual thermal damage. A final pass in a ablation mode was used to remove necrotic tissue. Laser overlapping was approximately 30%. The results of laser treatment were evaluated for the degree of clinical improvement, duration of erythema, pigmentary change, and any adverse events at two weeks, one month, and three months. In two patients, skin biopsies were obtained at the following intervals: immediately and two weeks postoperatively for histologic examination. There was a 75% average clinical improvement observed in pitted, facial acne scars after laser treatment. Complete wound healing occurred between six and eight days. On histologic examination, complete re-epithelialization was observed at two weeks. Erythema occurred in all patients after laser treatment and lasted longer than three months in 10 patients (50%). Postinflammatory hyperpigmentation occurred in 12 patients (60%) two to four weeks after laser treatment and lasted longer than three months in one patient (5%). One patient (5%) experienced mild hypopigmention. Mild to moderate, postoperative acne flare-up occurred in seven patients (35%). No other adverse effects were observed. In conclusion, resurfacing with a dual-mode Er:YAG laser is a safe and effective treatment modality for pitted, facial acne scars.

Recent Trends and Developments in Excimer Laser Ablation for Medical Applications.

The ArF excimer laser ablates the cornea and other tissue with micrometer-size precision and minimal residual thermal damage. However, there is still no clear picture regarding the mechanisms for the excimer laser ablation (ELA) giving rise to this favorable and characteristic removal of hydrated tissue. In order to gain obvious insight into the role of water in the ELA mechanism of the cornea, we have macroscopically investigated the ablation behavior of gels in the swelled states. The ELA of the hydrated collagen and polyacrylamide gel using ArF laser were scrutinized using time-resolved photography, atomic force microscopy (AFM), and FT-IR attenuated total reflectance spectroscopy (FTIR-ATR). The observed results led us to the conclusion that the control of the water content in and/or on the gel matrix during ELA would reduce any thermal and mechanical damage to the soft tissue.

Use of a novel erbium laser in a Yucatan minipig: A study of residual thermal damage, ablation, and wound healing as a function of pulse duration†This article is a US Government work and, as such, is in the public domain in the United States of America.

Background and Objective Theoretical models show that varying pulse duration influences residual thermal damage in erbium YAG skin resurfacing. Accordingly, our objective was to compare residual thermal damage, ablation, tissue shrinkage, and wound healing between a variable pulsewidth erbium YAG laser and a popular CO2 resurfacing laser. Study Design/Materials and Methods The erbium laser delivered a typical ablative pulse (250 microseconds), followed by a heating pulse of variable duration. Pulse durations for specific coagulation depths were selected based on existing heat transfer models. The bilateral flanks of one Yucatan pig were irradiated. Eight sites were treated per group. Biopsies were performed just after treatment and 1, 3, 7, 21, and 60 days postoperatively. Results Just after irradiation, gross examination of “cold” (without a coagulation pulse) erbium sites showed a reddish papillary dermis consistent with conventional erbium laser ablation. Two and three pass CO2 sites showed uniform surface yellowing. The longer pulsewidth (“hot”) erbium groups showed only slight surface yellowing. Biopsies showed immediate thermal damage that increased with erbium pulse duration; however, actual residual thermal damage (RTD) was sometimes less than that predicted by the laser control panel. All wounds healed uneventfully by 14 days. Conclusions An erbium laser with a variable macropulse pulsewidth was capable of achieving RTD of up to 80 μm. Even greater RTD depths may be obtainable with future manipulations of fluence and pulse duration. Lasers Surg. Med. 30:93–100, 2002. © 2002 Wiley-Liss, Inc.

Potential applications of the erbium:YAG laser in endourology.

The holmium:YAG laser has become the laser of choice in endourology because of its multiple applications in the fragmentation of kidney stones, incision of strictures, and coagulation of tumors. This paper describes the potential use of a new laser, the erbium:YAG laser, for applications in endourology. Recent studies suggest that the Er:YAG laser may be superior to the Ho:YAG laser for precise ablation of strictures with minimal peripheral thermal damage and for more efficient laser lithotripsy. The Er:YAG laser cuts urethral and ureteral tissues more precisely than does the Ho:YAG laser, leaving a residual peripheral thermal damage zone of 30 +/- 10 microm compared with 290 +/- 30 microm for the Ho:YAG laser. This result may be important in the treatment of strictures, where residual thermal damage may induce scarring and result in stricture recurrence. The Er:YAG laser may represent an alternative to the cold knife and Ho:YAG laser in applications where minimal mechanical and thermal insult to tissue is required.

Er:YAG laser resurfacing using combined ablation and coagulation modes.

The two main laser types used in resurfacing, the CO2 and the Er:YAG lasers, have their supporters and detractors, and each system has clear advantages and disadvantages. The Er:YAG laser can be used in the usual efficient ablative mode, followed by reprogramming to achieve nonablative deeper dermal coagulation associated with the CO2 laser, thereby achieving the main advantages of both laser types. Twenty-three female patients, ages 42-72 yrs, skin types I-IV, were treated. The epidermis was first removed in the ablative settings in a single pass with 50% overlap. The Er:YAG laser was reprogrammed for the subablative mode, and several passes produced controlled residual thermal damage (RTD) without further ablation. At 2 months postresurfacing the results were assessed. Thirteen patients were rated "very good," eight as "good," and two as "fair." The dual mode Er:YAG laser can first be used in the ablative mode to remove the epidermis with minimal RTD, following which, in the subablative mode, the same laser induces a controlled layer of dermal RTD, stimulating the dermis to achieve collagenesis and collagen remodeling and giving good long-term results.

Er: YAG Laser Resurfacing Using Combined Ablation and Coagulation Modes

BACKGROUND The two main laser types used in resurfacing, the CO2 and the Er:YAG lasers, have their supporters and detractors, and each system has clear advantages and disadvantages. OBJECTIVE The Er:YAG laser can be used in the usual efficient ablative mode, followed by reprogramming to achieve nonablative deeper dermal coagulation associated with the CO2 laser, thereby achieving the main advantages of both laser types. PATIENTS AND METHODS Twenty-three female patients, ages 42–72 yrs, skin types I–IV, were treated. The epidermis was first removed in the ablative settings in a single pass with 50% overlap. The Er:YAG laser was reprogrammed for the subablative mode, and several passes produced controlled residual thermal damage (RTD) without further ablation. RESULTS At 2 months postresurfacing the results were assessed. Thirteen patients were rated “very good,” eight as “good,” and two as “fair.” CONCLUSION The dual mode Er:YAG laser can first be used in the ablative mode to remove the epidermis with minimal RTD, following which, in the subablative mode, the same laser induces a controlled layer of dermal RTD, stimulating the dermis to achieve collagenesis and collagen remodeling and giving good long-term results.