Application Of Liquid Nitrogen Research Articles

Effectiveness of cryotherapy with liquid nitrogen for the treatment of cutaneous warts at Dermatology Clinic, Hue University of Medicine and Pharmacy Hospital

Background: Cryotherapy with liquid nitrogen is a cutaneous warts treatment technique that seldom results in deep damage and physicians both domestically and abroad continue to favor the application of liquid nitrogen. It is frequently used in the dermatology clinic at Hue University of Medicine and Pharmacy Hospital, however the outcomes of cutaneous wart treatments using this technique are not systematically documented. The goal of the study is to evaluate treatment outcomes of the cutaneous warts with liquid nitrogen and determine factors related to the treatment results. Materials and Method: Prospective cohort study, the patients with cutaneous warts were treated with liquid nitrogen at Hue University of Medicine and Pharmacy Hospital from 7/2019 to 7/2020. Results: 68 pateints were participated in the study. The average number of treatments was 4.9 ± 2.1 times. The cure rate was 44.1% after four weeks, 76.5% after six weeks, and 100% after eight weeks. The side effects of the treatment are transient, include: blisters (82.4%), discomfort (64.7%), subcutaneous hemorrhage (11.8%), local infection (7.4%), and scarring (6.4%). The duration of the disease, the size of cutaneous wart lesions and subtype of diseases are related to the number of treatments (p < 0.001). Conclusion: There is a high cure rate for cutaneous warts with liquid nitrogen. The side effects are transient. The duration of the disease, the size of cutaneous wart lesions and subtype of diseases are related to the number of treatments and and limited. Key words: cryotherapy with liquid nitrogen, cutaneous warts, palmar plantar wart.

Micro-CT, Mechanical, and Histological Examination of the Effect of Local Adjuvants on Porcine Cortical Bone Following Intralesional Curettage of Bone Tumors.

Curettage is the removal of a tumor from the bone while preserving the surrounding healthy cortical bone, and is associated with higher rates of local recurrence. To lower these rates, curettage should be combined with local adjuvants, although their use is associated with damage to nearby healthy bone. The purpose of this analysis is to determine the effect of local adjuvants on cortical porcine bone by using micro-computed tomography (micro-CT) along with histological and mechanical examination. Local adjuvants were applied to porcine specimens under defined conditions. To assess changes in bone mineral density (BMD), a micro-CT scan was used. The pixel gray values of the volume of interest (VOI) were evaluated per specimen and converted to BMD values. The Vickers hardness test was employed to assess bone hardness (HV). The depth of necrosis was measured histologically using hematoxylin and eosin-stained tissue sections. A noticeable change in BMD was observed on the argon beam coagulation (ABC) sample. Comparable hardness values were measured on samples following electrocautery and ABC, and lowering of bone hardness was obtained in the case of liquid nitrogen. Extensive induced depth of necrosis was registered in the specimen treated with liquid nitrogen. This study determined the effect of local adjuvants on cortical bone by using micro-CT along with histological and mechanical examination. Phenolization and liquid nitrogen application caused a decrease in bone hardness. The bone density was affected in the range of single-digit percentage values. Liquid nitrogen induced extensive depth of necrosis with a wide variance of values.

Investigation of the impact of heating and liquid nitrogen (LN2) cooling on the mechanical and acoustic emission (AE) properties of coal

Liquid nitrogen has emerged as a promising fracturing medium for unconventional natural gas extraction, particularly in the context of coalbed methane extraction, generating significant interest in recent times. In this paper, we analyze the acoustic emission (AE) characteristics of coal samples treated with liquid nitrogen under three-point bending load conditions using indoor experiments and field investigations. We investigate the impact of liquid nitrogen on coal samples by analyzing AE data. The mechanical properties of coal samples with varying initial temperatures were tested under three-point bending load conditions after treatment with liquid nitrogen. The load-displacement curve was analyzed to study the mechanical properties of the coal samples after treatment with liquid nitrogen. Through indoor three-point bending experiments, data analysis, and knowledge of mechanics, we systematically investigated the changes in mechanical properties caused by liquid nitrogen treatment under different conditions. The results demonstrate that the application of liquid nitrogen has significant impacts on the mechanical and AE characteristics of coal samples. The load-displacement curve indicated that the mechanical properties of the coal samples changed after treatment with liquid nitrogen. The AE experiment revealed regular changes in vibration and energy parameters of coal samples after liquid nitrogen treatment under different conditions. We further investigated the changes in mechanical properties and deformation characteristics of coal samples after undergoing liquid nitrogen freezing and thawing in differing environments. Graphs such as load-displacement curves, load-time curves, cumulative vibration count-energy count graphs, and RA-AF density distribution diagrams visually demonstrated the changes in mechanical properties and deformation characteristics. Through an integrated approach of indoor experiments, data analysis, and knowledge of mechanics, our study provides a better understanding of the behavior of coal samples under different conditions. This understanding can contribute to the development of safer and more efficient methods for extracting coalbed methane.

Development of a numerical cutting model for understanding the chip formation in cryogenic machining

The aim of this study is to develop a finite element model of metal cutting that includes fluid structure interaction. The proposed model is used to improve the physical comprehension of the chip formation during cryogenic assisted machining. This is performed based on the coupled-Eulerian-Lagrangian formulation. An algorithm is also developed to ensure heat exchange between the fluid and the structure. It also allows decoupling the mechanical and thermal effects induced by liquid nitrogen. The titanium alloy Ti17 is used as a work material, and uncoated tungsten carbide is used as a tool under dry and cryogenic conditions with cutting speeds of 50 m/min and 70 m/min and feeds of 0.1 mm/rev and 0.2 mm/rev. Simulation is validated by comparison with the experimental results. Standard deviations of both forces and chip thickness are low; they stay under 15% and 35% of the average value, respectively. The chip formation, the cutting force and the temperature are studied. It is shown that cryogenic machining has a significant effect on the chip formation and the temperature distribution in the cutting zone. A remarkable temperature reduction by up to 500 °C is observed at the tool rake face. However, the tool tip temperature slightly decreases with the application of liquid nitrogen when compared to dry machining.

Comparison of the Results of Patients Treated With Limb-Sparing Treatment Options in Malignant Bone Tumors: Sharing the Experience of Twelve Bicentric Patients.

Extremity-sparing surgery should be the main objective if a functional extremity is to be obtained in cases of malignant bone tumors. After extensive resection, numerous techniques have been described to reconstruct bone defects. This study aimed to compare the outcomes of patients who underwent external radiation therapy and liquid nitrogen biological reconstruction at two different facilities. The study included 12 patients who received biological reconstruction therapy for bone sarcoma and had at least two years of follow-up. Demographic data, pathological diagnosis, presence of systemic metastasis, and recurrence during follow-up were among the information logged. Patients who used liquid nitrogen were placed in group 1, and those who underwent external irradiation were placed in group 2. After being contacted for their final follow-up appointments, the outcomes were compared by recording the Musculoskeletal Tumor Society Score (MSTSS). For participants with a mean age of 10.75±3.6 (5-17), the follow-up period was 30.2±16.3 months in total. In contrast to the patients in group 1, who experienced union on average after 7.5±1.2 months, those in group 2 experienced union after 7.6±1.1 months. Patients in group 1 had an MSTSS of 75.5±11.8%, while those in group 2 had a score of 77±4.4.There was no discernible difference between the two groups' union times (p>0.05). There was no statistically significant difference between the two groups' MSTSS (p>0.05). After tumor resection, extracorporeal radiation therapyand the application of liquid nitrogen are still useful treatment options and neither of them is superior to the other.

A Circular Approach to Finished Tanned Leather: Regeneration by Cryogenic Technology.

Finished tanned leather is usually covered by a thin polymeric layer. This layer has the scope to change the morphological aspect of the last leather layer as well as improve the impermeabilization properties. Often, the finished product is refused by the final client, and tanneries must restore significant quantities of materials. Therefore, it is very important to remove this finished polymeric layer, recover the underneath tanned leather, and predispose it to a new finishing. The bonding between the polymeric film and leather is so strong that, today, only a blade shaving process can perform this separation at the expense of also removing a layer of tanned leather and consequently reducing the leather thickness. Here, a novel separation method was developed based on the significant difference in the dilation properties between the tanned hide and the polymeric film at low temperatures. The use of cryogenic fluids, in particular the direct application of liquid nitrogen, can freeze the polymeric layer below the glass transition temperature, inducing brittle behavior. The result is an easy separation without any alteration of the tanned leather layer; for a demonstration of that, some techniques were used, such as FTIR, SEM, Tensile strength evaluation, DSC, and TGA. By this last analysis, it is possible to check how a decrease of weight to 90% happened for the polymeric layer at about 400 °C against the complete blank at about 600 °C. A similar great distance of results exists in the case of tensile strength, where an average value of 34.5% is the deformation stress for blank samples, against 34.8% for processed samples. Thus, the process here developed allows the reuse of the tanned leather towards a new life in respect of the principles of the circular economy.

Sustainable High-Speed Milling of Magnesium Alloy AZ91D in Dry and Cryogenic Conditions

Magnesium alloy AZ91D is used extensively in the automotive industry because of its high strength-to-weight ratio. Typically, components produced using the alloy are required to have good surface finish and to contribute to high productivity but require long cutting times. Cryogenic cooling is an environmentally friendly technology which has been proven to improve cutting tool life and surface finish. This paper presents an investigation on the effects of dry and cryogenic cutting conditions at a high cutting speed regime for milling of magnesium alloy. This study focused on a high-speed regime due to the chips of magnesium alloy being highly combustible and an effective means of decreasing the temperature in the cutting zone was of great concern. The machining experiment was carried out using uncoated carbide end milling utilizing a full factorial design (L16) with cutting speeds of 900 m/min and 1300 m/min, feed rate of 0.02 mm/tooth and 0.05 mm/tooth, axial depth of cut at 0.2 mm and 0.3 mm, and radial depth of cut at 10 mm and 40 mm. For dry machining, the longest tool life at flank wear (VBmax) of 0.21 mm was at 30 min, which was obtained at cutting speeds of 1300 m/min, feed rate of 0.02 mm/tooth, axial depth of cut at 0.2 mm, and radial depth of cut at 40 mm. Using this cutting condition, a mirror-like surface of 0.106 µm was produced. For machining under cryogenic condition at VBmax of 0.2 mm, the maximum tool life of 1864 min was achieved at a cutting speed of 900 m/min, feed rate of 0.02 mm/tooth, axial depth of cut of 0.3 mm, and radial depth of cut of 40 mm. Under this cutting condition, a lower surface finish of 0.091 µm was obtained. It can be concluded that the application of liquid nitrogen (LN2) is very effective in enhancing the tool life and in obtaining a better-machined surface, especially at a lower cutting speed of 900 m/min. A longer tool life and high-quality machined parts will significantly improve the productivity and cost savings in the related industry.

Liquid nitrogen spraying in hard machining process of AISI H13 steel

ABSTRACT The application of liquid nitrogen is being considered nowadays because it is clean and environmentally friendly and improves product quality. The cryogenic cooling can also be useful in hard machining process where workpiece is exposed to high thermo-mechanical loads. Thermal loads are one of the factors affecting residual stresses and microstructural changes in a material. There is no study in literature to evaluate the effect of cryogenic cooling for evaluation of thermo-mechanical loads during the machining of the hardened AISI H13 steel. Therefore, in the present study, to control and investigate the thermal loads, microhardness, white layer thickness, and surface quality in hard machining of AISI H13 steel, the cryogenic cooling system was employed during the process. Results indicated that depth of cut was the most influential item on temperature enhancement of cutting zone, while high feed rates were responsible for enhancement of microhardness surface roughness. Intense and rapid cooling using the liquid nitrogen spraying was found effective strategy to reduce white layer thickness and improve surface quality at the machined surface.

Cryogenic ultrasonic vibration assisted turning to texturize AZ31 magnesium alloy surfaces

Magnesium alloys are increasingly used in the biomedical field thanks to their biocompatibility. However, poor corrosion resistance greatly limits their applications. Coating the devices is known to represent the most efficient way to increase the corrosion performances of magnesium alloys, but it requires specific surface preparation of the metal substrate. In the present paper, a hybrid machining technology, namely cryogenic–ultrasonic-assisted turning, is applied to generate magnesium alloy texturized surfaces with enhanced surface integrity characteristics. Results showed that the application of liquid nitrogen led to a harder and more complex surface texture than in the case of ultrasonic-assisted turning under dry conditions.

Effect of Topical Liquid Nitrogen on Pain Reduction during Intradermal Platelet-Rich Plasma Therapy Scalp in Androgenic Alopecia

Objective: To compare the effect of topical liquid Nitrogen and normal saline on pain during intradermal Platelet-rich Plasma therapy in androgenic alopecia.
 Study Design: Prospective Comparative study.
 Place and Duration of Study: Tertiary Care Hospital, Gujranwala Pakistan, from Mar to Nov 2021.
 Methodology: Sixty-four patients with the clinical diagnosis of androgenic alopecia were enrolled after informed consent.After liquid Nitrogen contact application, Group- A patients opted to receive intradermal Platelet-rich Plasma on the scalp. In contrast, patients in Group-B opted to receive Platelet-rich Plasma after normal Saline topical application for improved pain tolerance.
 Results: Out of Sixty-four patients, there were 45(70.3%) males, 19(29.7%) females. Pain in intradermal Platelet-rich Plasma injection of the scalp in Group-A had a median (IQR) score of 4 (3-5), while Group-B had a median (IQR) of 5(3-7.5). Patient satisfaction score at the end of three sessions of PRP in group-A had a median (IQR) of 1.5(1-2), and in Group-B, a median (IQR) of 2(1-2).
 Conclusion: Topical liquid Nitrogen application improved pain tolerance during intradermal Platelet-rich Plasma therapy in androgenic alopecia compared to normal saline. Satisfaction of patients with Platelet-rich Plasma therapy between the two groups had no significant difference.

Preventing effect of liquid nitrogen on the thermal runaway propagation in 18650 lithium ion battery modules

Thermal runaway (TR) and its propagation in lithium ion battery (LIB) are major factors of inducing serious fire accidents, and their prevention remains a technical barrier. In this work, a novel strategy with liquid nitrogen (LN) to prevent TR propagation (TRP) was proposed and investigated experimentally. Nozzle diameter screening and blank TRP experiments of module were conducted. To comprehensively understand suppression mechanism, LN cooling strategy was analyzed by changing the mass of LN. Results show that 4 mm diameter nozzle owns the best cooling capacity due to its maximum average cooling rate. TRP of a 2 × 3 module presents three typical stages with different TRP time and heating powers. LN exhibits excellent cooling prevention and delay capacity for different stages of TRP. During LN application, the maximum cooling rate and maximum cooling power for single battery reaches 34.25 ℃/s and 1529.6 W, respectively. The critical suppression temperature, Ttr ,cs was proposed to forecast the suppression effect before LN application, and TRP could be prevented below Ttr ,cs. The internal mechanism of LN preventing TRP was discussed in three typical scenarios. This work owns important guidance for process safety assurance and fire protection design of LIB system.

Is there an optimal timing interval between hCG trigger and oocyte vitrification?

ObjectiveOocyte vitrification has been developed as a promising alternative to slow freezing; however, the clinical outcome is highly operator dependent. From the past study, we know the timing of cryoprotectant exposure and understand that the intervals between the application of liquid nitrogen and thawing solution are crucial factors in the vitrification process. However, the optimal time intervals between hCG trigger and oocyte vitrification and equilibration remain unknown. This study aimed to evaluate the optimal intervals before and during modified vitrification. Materials and methodsThis retrospective study included 66 patients undergoing vitrified-thawed oocyte cycles from June 2018 to May 2019. Oocyte in vitro maturation (IVM) is defined as the maturation in vitro of an immature oocyte collected using a standard pick up procedure. Oocytes were grouped into the following intervals: (1) human chorionic gonadotropin (hCG) trigger to oocyte vitrification (<38 h; 38–39 h; >39 h; IVM) (2) oocyte equilibration time (<10 min; 10–12 min; 12–15 min). The vitrification and warming procedures were performed following the steps as shown in the Cryotec method. ResultsA total of 390 mature oocytes were vitrified with the Cryotec method. The survival rates were not significantly different among the various intervals after the hCG trigger (97.59%; 95.54%; 100%); however, there was a trend of decreased survival rate in IVM group (66.67%). The oocyte survival rates were not significantly different among the various times of oocyte equilibration (96.77%; 97.33%; 95.42%). ConclusionsThis was the first study to demonstrate no correlation between oocyte survival rate and the time intervals between hCG trigger and oocyte vitrification. Nor did the oocyte survival rate correlate with the various equilibration times during vitrification, as long as the oocyte was mature. In the future, large, prospective, randomized controlled studies will be required to confirm the clinical outcomes.

On the trajectory and reach of fire-suppressant liquid nitrogen droplets released from a spray nozzle

Liquid nitrogen (LN2) can be used to supplement or replace currently used fire extinguishers in challenging fire situations. This environmentally-benign cryogenic fluid can be produced readily from deep refrigeration of air. This manuscript addresses the application of liquid nitrogen to fires through a nozzle. Its aim is to investigate the survivability of LN2 droplets, following breakup of the jet exiting the nozzle, and the amount of liquid that reaches a target. Numerical simulations were carried out to explore the effects of relevant parameters, such as the initial droplet size and velocity, the droplet injection angle, and the thermal radiation on the droplet flight distance and the liquid droplet mass. The results indicate that all these parameters influence the fate of the LN2 droplets. Coarse atomization, high initial velocities, short nozzle-to-target distances, and shallow jet angles maximize the amount of the cryogen delivered to the target. A small-scale experiment was performed to test the results of the calculations. The comparison of the experimental results and the theoretical calculations was deemed satisfactory. In both cases the reach of the liquid droplets was in the order of 1 m from the nozzle, for an initial droplet velocity in the neighborhood of 20 m/s as measured in the experiments.

Turning of Inconel 718 using liquid nitrogen: multi-objective optimization of cutting parameters using RSM

The objective of this research was to investigate the effectiveness of application of liquid nitrogen (LN2) in turning of Inconel 718 compared to flooded cutting and select suitable LN2 cutting parameters using response surface methodology (RSM). The results of turning experiments conducted by spraying LN2 to the cutting area of Inconel 718 bar showed that using either low or high cutting parameters, cutting performance of Inconel 718 under the cryogenic condition was generally worse than the flooded cutting. However, using the medium cutting parameters, the LN2 cutting performance was as good as that of the flooded cutting both showing a cutting force of 90 N, 60 µm of flank wear and 0.5–0.6 µm of surface roughness (Ra). These parameters were further optimized using desirability function of RSM to determine the set of parameters that provided the lowest cutting force, flank wear and Ra values and the highest material removal rate (MRR) under cryogenic cutting. Analysis of variance (ANOVA) performed on the regression models developed showed that cutting speed was the only significant factor on the cutting force. Feed rate was the most influential parameter on the flank wear. Feed rate and depth of cut were significant factors both affecting Ra. Multi-objective optimization showed that a cutting speed of 87 m/min, a feed rate of 0.06 mm/rev and a depth of cut of 0.37 mm constituted the optimum cutting parameters for achieving a cutting force of 78 N, flank wear of 58 µm, Ra of 0.49 µm and the MRR of 1.97 cm3/min under the cryogenic cutting condition.

EFFECTS OF LIQUID NITROGEN IN HARDLY IMPREGNABLE FIR WOOD

The main purpose of this study was to develop new methods to eliminate the problems encountered during the impregnation of wood material, and in this context, to improve theretention of wood materialby using liquefied nitrogen. Uludağ Fir (Abies nordmannianasubsp. Bornmulleriana) was used as wood material impregnated with Tanalith-E, Immersol aqua and borax. The effects of liquid nitrogen and the amount of retention on the mechanical properties were investigated. Application of liquid nitrogen before impregnation has increased theretention in fir wood by an average of 150-200% in all impregnation methods, compared to the groups without liquid nitrogen application. Despite this increase in retention amounts, no significant changes were observed in mechanical properties due to the application of liquid nitrogen.

Post-processing of 3D printed thermoplastic CFRP composites using cryogenic machining

Additive manufacturing (AM) or three-dimensional (3D) printing allows manufacturing of parts of complex shapes using carbon fiber reinforced polymer (CFRP) composites. However, in many cases, the parts fabricated by 3D printing suffer from poor surface quality and dimensional accuracy, requiring extensive post-processing. This research aims at improving the dimensional accuracy and surface finish of 3D printed CFRP composites by analyzing the effectiveness of three sustainable machining practices: dry, minimum quantity lubrication (MQL), and cryogenic machining, as post-processing techniques for 3D printed CFRP composites. This study specifically investigates effects of printing and machining parameters and cooling/lubricating conditions on the machining performance, i.e., burr formation, surface finish, cutting forces, and tool wear during edge and slot milling of 3D printed thermoplastic CFRP composites. Among three sustainable machining processes, cryogenic machining significantly reduced burr formation and tool wear, and improved surface finish irrespective of the fiber orientation and machining conditions. The application of MQL at the tool-workpiece interface was found to be effective in reducing tool wear, surface roughness, and burr formation to some extent compared to dry machining. However, MQL process was not able to completely eliminate burr formation for most of the machining conditions. Cryogenic machining caused the highest cutting forces due to the increased surface and sub-surface hardness of the workpiece caused by application of liquid nitrogen; however, no adverse effect of increased cutting forces was observed. This study finds that cryogenic machining is able to completely eliminate or reduce burrs by 90% and bring down the surface roughness (Rq) from >10 μm to about 1 μm, thus making it a suitable post-process technique for 3D printed CFRP composites.

Visualized study on the mechanism of temperature effect on coal during liquid nitrogen cold shock

• Analysis of temperature effect combined with temperature field and strain field. • The range and thermal stress of liquid nitrogen cold shock are obtained. • Visualize the local stress concentration caused by the temperature effect of liquid nitrogen. This study is aimed to investigate the mechanism of temperature effect on coal during cold shock resulting from anhydrous low-temperature liquid nitrogen, which is a key issue in the application of liquid nitrogen in coalbed methane exploitation engineering. In this study, the temperature and strain distributions of coal around the drill hole during liquid nitrogen cold shock (LNCS) in an open environment were analyzed by using an infrared measurement device, thermocouples and a digital image correlation (DIC) full-field strain measurement system. The following beneficial results were obtained. With respect to the temperature field, the low-temperature zone of coal around the drill hole keeps expanding in a semicircular shape at a decelerated rate. An obvious temperature gradient exists. The position closer to the drill hole corresponds to a lower temperature and a larger temperature difference under the condition of equal spacing. The strain field around the drill hole is unevenly distributed. The strain experiences two stages in turn, namely short-term frost heave and long-term frost contraction. A strain-concentrated area exists in the vicinity of the drill hole. This area is dominated by the frost contraction strain which is distributed in a circular shape. Finally, a hierarchical model for thermal stress calculation was established. Through a combination of the model and the strain field, the variations of the radial thermal stress based on temperature difference and the radial thermal stress based on strain, as well as their distribution functions at 30 min of LNCS were concluded.

The Impact of Organic Liquid Nitrogen Fertilizer Application on Growth and Productivity of Barley (Hordeum vulgare L.) Varieties

Barley is a cereal used extensively in animal nutrition in the world. Nowadays, Organic practices have an important place in healthy nutrition of people and animals and protection of agricultural lands. This study was conducted to determine the effect of organic applications such as organic liquid nitrogen and barn manure on yield and quality values of barley during 2018-2019 and 2019-2020 growing seasons according to the randomized complete block design with split plot arrangements. This two-year study inferred the impact of organic liquid nitrogen fertilizer application at different growth stages on growth and productivity of barley. Organic liquid nitrogen fertilizer was applied at different phenological periods (control, tillering, beginning of booting, end of booting and heading) of spring barley varieties, Akhisar and Samyeli. Parameters such as Plant height (cm), number of heading (number m-2), hectoliter weight (kg hl-1), 1000 grain weight (g), grain yield (kg ha-1), chlorophyll content (SPAD values) and protein ratio (%) were determined in the study. All parameters investigated were significantly different (P≤0.01) between the years. Compared to the first year, higher temperature and drier weather conditions during the second year increased protein ratio in seed, while decreased starch ratio; thus, yield and yield components were lower. Yield and yield parameters of barley varieties had a negative correlation between protein ratios, while had a positive correlation with chlorophyll content. The results concluded organic liquid nitrogen application at the end of booting phenological period of Akhisar variety resulted in higher yield and improved the related traits. It has been concluded that the organic liquid fertilizer to be applied in this phenological period will increase both yield and quality in barley plants. Another result of this study was that as a result of organic applications, the yield and quality levels obtained from barley was close to conventional agriculture.

Enhanced Surface Integrity of a Biomedical Grade Polyetheretherketone through Cryogenic Machining

Polyetheretherketone (PEEK) belongs to a group of thermoplastic polymers widely used in bioengineering applications such as trauma, orthopedic and spine implants, whose mechanical and geometrical characteristics, when put in service, must be the highest possible. However, machining operations, usually carried out for their manufacturing, can assure these characteristics uniquely when they are performed in a restricted temperature window because of the PEEK mechanical behavior change nearby its glass transition temperature.To this aim, the present paper investigates the feasibility of using cryogenic machining to enhance the surface integrity of a biomedical grade PEEK. Turning trials were carried out under dry and cryogenic machining conditions at varying feed and cutting speed. The temperature reached during the process was measured by means of a thermocouple embedded in the cutting tool, whereas the surface integrity assessed in terms of surface defects, surface roughness and hardness. Additionally, the degree of crystallinity was evaluated via Differential Scanning Calorimetry (DSC). To correlate machinability results with the PEEK mechanical behavior, tensile tests were performed in the temperatures range between -100°C and 50°C.The obtained results showed that the application of liquid nitrogen always made possible achieve an enhanced surface integrity compared to the corresponding dry condition, which represent the currently used strategy for the manufacture of biomedical polymer implants. A proper temperature control during machining assured indeed the formation of lower amounts of defects as well as reduced surface roughness, by increasing the PEEK degree of crystallinity.

Особенности применения жидкого азота в технологии быстрого замораживания свиной крови

Особенности применения жидкого азота в технологии быстрого замораживания свиной крови