Thermal stresses from large volumetric expansion during freezing of biomaterials

Causal factors concerning the texture of French fries manufactured at industrial scale

In this paper, we review the physical/chemical phenomena, contributing to the final texture of French fries, as occurs in the whole industrial production chain of frozen par-fried fries. Our discussion is organized following a multiscale hierarchy of these causal factors, where we distinguish the molecular, cellular, microstructural, and product levels. Using the same multiscale framework, we also discuss currently available theoretical knowledge, and experimental methods probing the relevant physical/chemical phenomena. We have identified knowledge gaps, and experimental methods are evaluated in terms of the effort and value of their results. With our overviews, we hope to give promising research directions such to arrive at a multiscale model, encompassing all causal factors relevant to the final texture. This multiscale model is the ultimate tool to evaluate process innovations for effects on final textural quality, which can be balanced against the impacts on sustainability and economics.

Dust formation in French fries

In this study we report on the analysis of dust formation, a quality problem arising in the industrial processing of par-fried, frozen french fries. This dust constitutes fractured pieces broken off the crust during finish frying. We claim that this dust problem has many similarities with flaking arising during the final-baking of par-baked french baguettes, i.e. the two problems are governed by the same physical principles. Inspired by the hypotheses behind flaking, we have made an experimental design, where we have perturbed the operating conditions of an industrial processing line of french fries. The measured dust during finish frying is correlated with the physical properties of the crust, measured in the different unit operations of the industrial processing line, and the operating conditions. We have shown that dust is non-linearly correlated to 1) the moisture content of the crust as influenced by drying and par-frying, and 2) the freezing rate in the industrial tunnel freezer. Remarkably, the amount of dust decrease with the increase of frozen storage time, which we have explained via viscoelastic relaxation of locked-in stress - mediated by moisture migrating from core to crust. This decay is shown to be independent of pretreatments, which only determines its starting value. With the given relations industry can in principle control the dust problem, but these measures have to be weighed against their effects on other objectives of the industry.

Computer-aided food engineering

Computer-aided food engineering (CAFE) can reduce resource use in product, process and equipment development, improve time-to-market performance, and drive high-level innovation in food safety and quality. Yet, CAFE is challenged by the complexity and variability of food composition and structure, by the transformations food undergoes during processing and the limited availability of comprehensive mechanistic frameworks describing those transformations. Here we introduce frameworks to model food processes and predict physiochemical properties that will accelerate CAFE. We review how investments in open access, such as code sharing, and capacity-building through specialized courses could facilitate the use of CAFE in the transformation already underway in digital food systems.

Impact of Processing Factors on Quality of Frozen Vegetables and Fruits

In this paper I review the production of frozen vegetables and fruits from a chain perspective. I argue that the final quality of the frozen product still can be improved via (a) optimization of the complete existing production chain towards quality, and/or (b) introduction of some promising novel processing technology. For this optimization, knowledge is required how all processing steps impact the final quality. Hence, first I review physicochemical and biochemical processes underlying the final quality, such as water holding capacity, ice crystal growth and mechanical damage. Subsequently, I review how each individual processing step impacts the final quality via these fundamental physicochemical and biochemical processes. In this review of processing steps, I also review the potential of novel processing technologies. The results of our literature review are summarized via a causal network, linking processing steps, fundamental physicochemical and biochemical processes, and their correlation with final product quality. I conclude that there is room for optimization of the current production chains via matching processing times with time scales of the fundamental physicochemical and biochemical processes. Regarding novel processing technology, it is concluded in general that they are difficult to implement in the context of existing production chains. I do see the potential for novel processing technology combined with process intensification, incorporating the blanching pretreatment—but which involves quite a change of the production chain.

Thermodynamic Theory and Experimental Validation of a Multiphase Isochoric Freezing Process

Freezing of the aqueous solutions that comprise biological materials, such as isotonic physiological saline, results in the formation of ice crystals and the generation of a hypertonic solution, both of which prove deleterious to biological matter. The field of modern cryopreservation, or preservation of biological matter at subfreezing temperatures, emerged from the 1948 discovery that certain chemical additives such as glycerol, known as cryoprotectants, can protect cells from freeze-related damage by depressing the freezing point of water in solution. This gave rise to a slew of important medical applications, from the preservation of sperm and blood cells to the recent preservation of an entire liver, and current cryopreservation protocols thus rely heavily on the use of additive cryoprotectants. However, high concentrations of cryoprotectants themselves prove toxic to cells, and thus there is an ongoing effort to minimize cryoprotectant usage while maintaining protection from ice-related damage. Herein, we conceive from first principles a new, purely thermodynamic method to eliminate ice formation and hypertonicity during the freezing of a physiological solution: multiphase isochoric freezing. We develop a comprehensive thermodynamic model to predict the equilibrium behaviors of multiphase isochoric systems of arbitrary composition and validate these concepts experimentally in a simple device with no moving parts, providing a baseline from which to design tailored cryopreservation protocols using the multiphase isochoric technique.

Cryoplasty for the Treatment of Femoropopliteal Arterial Disease: Extended Follow-up Results

Purpose:

To report the findings from a multicenter study of patients treated with cryoplasty who were then followed for an average of >2 years post-treatment.

Methods:

Extended clinical follow-up was obtained for 70 patients (45 men; mean age 70.5±8.8 years) who originally received cryoplasty therapy to treat symptoms of intermittent claudication as part of a multicenter investigational device exemption (IDE) study. For all subjects, cryoplasty was used to treat stenoses or occlusions ≤10 cm in the femoropopliteal arteries. The original IDE study protocol enrolled 102 patients with a primary endpoint of target lesion patency at 9 months post-treatment. This collection of additional longer term follow-up data was initiated 2.5 years after the onset of study enrollment.

Results:

Extended clinical follow-up ranged from 11 to 41 months (mean 31). The clinical patency rate (freedom from target lesion revascularization) calculated by the Kaplan-Meier method was 83.2% after the original follow-up period of 300 days. After >3 years (1253 days), the clinical patency rate was well maintained at 75.0%.

Conclusions:

Long-term data indicate that cryoplasty is a durable therapy, with relatively low long-term restenosis rates compared to other endovascular treatment approaches.

Indications and Results with Cryoplasty in the Treatment of Infrainguinal Arterial Occlusive Disease

Percutaneous transluminal angioplasty of the superficial femoral and popliteal arteries has been an accepted therapy for short focal stenosis. Elastic recoil and flow-limiting dissection have limited the durability of angioplasty, especially in long lesions and total occlusions. Cryoplasty couples cold therapy with angioplasty to induce mechanical and biologic effects to reduce elastic recoil and potentially to reduce restenosis. The mechanical and biologic mechanisms of this therapy are discussed. The results of cryoplasty for femoropopliteal lesions from a single-center series and a multicenter registry are reviewed. Cryoplasty appears to improve patency over conventional angioplasty and to reduce the need for bailout stenting in femoropopliteal stenoses and occlusions < 10 cm in length. Cryoplasty appears to be promising to treat critical limb ischemia in patients with tibial disease.

Role of cells in freezing-induced cell-fluid-matrix interactions within engineered tissues

During cryopreservation, ice forms in the extracellular space resulting in freezing-induced deformation of the tissue, which can be detrimental to the extracellular matrix (ECM) microstructure. Meanwhile, cells dehydrate through an osmotically driven process as the intracellular water is transported to the extracellular space, increasing the volume of fluid for freezing. Therefore, this study examines the effects of cellular presence on tissue deformation and investigates the significance of intracellular water transport and cell-ECM interactions in freezing-induced cell-fluid-matrix interactions. Freezing-induced deformation characteristics were examined through cell image deformetry (CID) measurements of collagenous engineered tissues embedded with different concentrations of MCF7 breast cancer cells versus microspheres as their osmotically inactive counterparts. Additionally, the development of a biophysical model relates the freezing-induced expansion of the tissue due to the cellular water transport and the extracellular freezing thermodynamics for further verification. The magnitude of the freezing-induced dilatation was found to be not affected by the cellular water transport for the cell concentrations considered; however, the deformation patterns for different cell concentrations were different suggesting that cell-matrix interactions may have an effect. It was, therefore, determined that intracellular water transport during freezing was insignificant at the current experimental cell concentrations; however, it may be significant at concentrations similar to native tissue. Finally, the cell-matrix interactions provided mechanical support on the ECM to minimize the expansion regions in the tissues during freezing.

A study on the effect of metabolic heat generation on biological tissue freezing

The effect of metabolic heat generation on the freezing of biological tissue has been studied. Quasi-steady approximation is used to solve the Pennes bioheat equation in tissues. Temperature profile and motion of freezing interfaces are obtained for different values of metabolic heat generation. It is observed that metabolism has a significant effect on freezing of biological tissues during cryosurgery.

Biphasic investigation of tissue mechanical response during freezing front propagation

Cryopreservation of engineered tissue (ET) has achieved limited success due to limited understanding of freezing-induced biophysical phenomena in ETs, especially fluid-matrix interaction within ETs. To further our understanding of the freezing-induced fluid-matrix interaction, we have developed a biphasic model formulation that simulates the transient heat transfer and volumetric expansion during freezing, its resulting fluid movement in the ET, elastic deformation of the solid matrix, and the corresponding pressure redistribution within. Treated as a biphasic material, the ET consists of a porous solid matrix fully saturated with interstitial fluid. Temperature-dependent material properties were employed, and phase change was included by incorporating the latent heat of phase change into an effective specific heat term. Model-predicted temperature distribution, the location of the moving freezing front, and the ET deformation rates through the time course compare reasonably well with experiments reported previously. Results from our theoretical model show that behind the marching freezing front, the ET undergoes expansion due to phase change of its fluid contents. It compresses the region preceding the freezing front leading to its fluid expulsion and reduced regional fluid volume fractions. The expelled fluid is forced forward and upward into the region further ahead of the compression zone causing a secondary expansion zone, which then compresses the region further downstream with much reduced intensity. Overall, it forms an alternating expansion-compression pattern, which moves with the marching freezing front. The present biphasic model helps us to gain insights into some facets of the freezing process and cryopreservation treatment that could not be gleaned experimentally. Its resulting understanding will ultimately be useful to design and improve cryopreservation protocols for ETs.

Primary cryoplasty therapy provides durable support for limb salvage in critical limb ischemia patients with infrapopliteal lesions: 12-month follow-up results from the BTK Chill Trial

PURPOSE

To report the 12-month follow-up data from the prospective 16-center Below-the-Knee (BTK) Chill Trial, which examined the use of primary cryoplasty for BTK occlusive disease in patients with critical limb ischemia (CLI).

METHODS

The trial included 108 patients (77 men; mean age 73 +/- 11 years, range 41-101) with CLI (Rutherford categories 4-6) involving 111 limbs with 115 target infrapopliteal lesions. Angiographic inclusion criteria were reference vessel diameter > or = 2.5 mm and < or = 5.0 mm and target lesion stenosis > or = 50%. The primary study endpoints were acute technical success (the ability to achieve < or = 50% residual stenosis and continuous inline flow to the foot) and absence of major amputation of the target limb at 6 months. Secondary endpoints were serious adverse events specifically related to use of primary cryoplasty and absence of major amputation of the target limb at 1, 3, and 12 months.

RESULTS

Acute technical success was achieved in 108 (97.3%) of treated limbs, with only 1 clinically significant dissection (> or = type C) and 2 residual stenoses >50%; stent placement was required following cryoplasty in only 3 (2.7%) procedures. At 6 months and 1 year, major amputation was avoided in 93.4% (85/91) and 85.2% (69/81) of patients, respectively. Through 1 year, 21% (17/81) of patients underwent target limb revascularization. Rates of major amputation and death at 1 year were 0% for limbs of patients with initial Rutherford category 4; 11.4% and 0%, respectively, for initial category 5; and 40.0% and 31.8% for initial category 6. One-year rates of major amputation and death were 20.4% and 8.8%, respectively, for diabetics, versus 4.0% and 10.7% for non-diabetics. At 1 year, major amputation occurred in 16.7% (2/12) of limbs that were expected to be amputated at the time of treatment.

CONCLUSION

Cryoplasty therapy is a safe and effective method of treating infrapopliteal disease, providing excellent results and a high rate of limb salvage in patients with CLI. Study outcomes through 1 year support the use of cryoplasty as a primary treatment option for patients with CLI secondary to BTK occlusive disease.

Minimally invasive probe system capable of performing both cryosurgery and hyperthermia treatment on target tumor in deep tissues

Cryosurgery is a clinical therapy aiming at the destruction of diseased target tissues through a controlled deep freezing and subsequent rewarming. It has recently been realized that freezing immediately followed by a rapid and strong heating of the target tissues would significantly improve the treatment effect. However, most of the currently available cryoprobe systems are only capable of performing a single freezing function. To accommodate to the rapid growth of the combined freezing and heating therapy of tumor treatment, we have developed a new cryoprobe system with a powerful heating feature, which can be conveniently applied to destroy the tumor in deep tissue using a minimally invasive approach. Its operation performance will be characterized through a series of experimental tests in air, water, phantom gel, <I>in vitro</I> tissues and rabbits under anaesthesia. This system is perhaps the first one aiming at performing both cryosurgery and hyperthermia on target tumors. Therefore, it provides the clinicians with more choices and algorithms on treating a specific diseased tissue. Further, strain sensors and thermocouples were applied to simultaneously record the transient temperature and the thermal stress fields over the tissues subjected to freezing and strong heating. It was observed that a sudden change in the transient thermal stress was often induced when phase change occurs, which may imply that an evident thermal stress occurs at the liquid-solid interface. This modifies the commonly accepted viewpoint that no stress should exist at the liquid-like phase change interface. Further, implementations of this new system in clinical cryosurgery or hyperthermia are discussed. In addition to the applications in tumor treatment, the present system can also be very useful in fundamental research such as revealing the thermal stress mechanisms in tissues due to quick freezing and heating, which is hard to do otherwise. One interesting result presented in this paper is the experimental discovery of shock rings induced in the biomaterials around the probe, due to alternant freezing and heating by the present system.

Cryoplasty therapy for limb salvage in patients with critical limb ischemia

PURPOSE

To report the 6-month outcomes from a prospective multicenter study investigating the use of cryoplasty (cold balloon angioplasty) to treat below-knee occlusive disease in patients with critical limb ischemia (CLI).

METHODS

Between August 2004 and October 2005, 108 patients (77 men; mean age 73+/-12 years, range 41-101) with CLI involving 111 limbs were enrolled in a prospective multicenter trial (Below-the-Knee Chill Study), which was conducted at 16 institutions. The primary study endpoints were acute technical success, defined as the ability to achieve < or =50% residual stenosis and continuous inline flow to the foot, and absence of major (above or below-knee) amputation of the target limb 180 days post procedure.

RESULTS

Acute technical success was achieved in 108 (97.3%) of the 111 limbs treated, with only 1 (0.9%) clinically significant dissection (> or =type C) and 2 residual stenoses >50%. During the 180-day follow-up, 15 (13.9%) of the initial 108 patients either withdrew or were lost to follow-up. Five (4.6%) deaths occurred, leaving 88 (81.5%) patients with 91 (82.0%) treated limbs available for 180-day assessment. The rate of freedom from major amputation at 180 days was 93.4%. Amputation-free survival was 89.3% at 180 days (5 deaths, 6 major amputations). Stratifying data by diabetics (n=71) versus non-diabetics (n=34), the 180-day death and amputation rates were 4.9% and 10.0%, respectively, for diabetics versus 6.7% and 0.0%, respectively, for non-diabetics.

CONCLUSION

Cryoplasty therapy is a safe and effective method of treating infrapopliteal disease, providing excellent acute outcomes and a high rate of limb salvage in patients with CLI. Study outcomes support the use of cryoplasty therapy as a primary treatment option for patients with CLI secondary to below- knee disease.

Effect of blood flow and metabolism on multidimensional heat transfer during cryosurgery

Cryosurgery has been recently accepted as a treatment option for eradicating undesirable tissues, especially tumor tissues, due to its minimally invasive nature and low hospitalization needs. A multidimensional, finite element analysis (FEA) for the cooling, holding and rewarming processes of biological tissues during cryosurgery is presented. The tissues were treated as non-ideal materials with temperature dependent thermophysical properties. The enthalpy method has been applied to solve the non-linear problem. The influence of heating effect due to blood flow and metabolism was studied, and furthermore, the effect of pre-injecting solutions with particular thermal properties into the target tissues was also numerically studied. It was found that the heat source term due to blood flow and metabolism in the bioheat transfer equation has a significant influence on the thermal and thermal gradient histories of the target tissues, and that the method of injection of solutions with particular thermal properties into the target tissues before cryosurgery may be a possible way to optimize the treatment process. However, in vitro experiments have not fully supported this viewpoint.

Experimental study on fracture mechanics properties of frozen rabbit aorta

To more scientifically discuss fracture problems associated with cryopreservation of aorta, the effects of temperature, cooling rate and cryo-protective agent on the fracture mechanics properties of frozen rabbit aorta have been investigated with Dynamical Mechanics Analyser (DMA), and the test method for crack criterion of frozen rabbit aorta was also explored. The results show that: As temperature decreasing, the fracture modes of frozen rabbit aorta are from typical ductile fracture to typical brittle fracture, and its resist-fracture ability weakens remarkably from -20 centigrade to -80 centigrade. The cooling rates have no effects on the fracture modes when cooled to -50 centigrade, but the resist-fracture ability of frozen rabbit aorta will be stronger when the sample treated by a higher cooling rate. Due to the hydration action of dimethyl sulphoxide (DMSO), the rabbit aorta permeated by 10% (V/V) DMSO presents typical ductile fracture when it was cooled to -50 centigrade, so its resist-fracture ability is enhanced obviously. Compared to the axial sample, the peripheral sample's resist-fracture ability is larger than that of the former.

Analysis of thermal stress in cryosurgery of kidneys

In this study, the thermal stress distribution in cryosurgery of kidney was investigated using a multiphysics finite element model developed in ANSYS (V8.1). The thermal portion of the model was verified using experimental data and the mechanics portion of the model (elastic) was verified using classic analytical solutions. Temperature dependent thermal and mechanical properties were used in the model. Moreover, the model accounts for thermal expansion due to both thermal expansion in single phase and volumetric expansion associated with phase change of tissue water to ice. For a clinical cylindrical cryoprobe inserted into the renal cortex from the top-middle renal capsule, it was found that the thermal stress distributions along the radial position are very different at different depths from the top renal capsule. The thermal stress is much higher at both ends than in the middle of the cryoprobe surface. It was found that there might be more tissue next to the top renal capsule than other region undergoing microcrack formation or plastic deformation. Furthermore, it was found that macrocrack formation is more likely to occur in tissue adjacent to the cryoprobe surface (especially on the sharp point tip) and during the thawing phase of cryosurgery. It was further found that the volumetric expansion associated with phase change induced much higher thermal stress than thermal expansion in a single phase and might therefore be the main cause of the frequently observed crack formation shortly after initiation of thawing in cryosurgery. Because the thermal stress adjacent to the cryoprobe is much higher than the yield stress of frozen renal tissue, a plastic stress model is required for better modeling of the thermal stress distribution in cryosurgery of kidney in future. However the computational effort will then be drastically increased due to the strong nonlinear nature of the plastic model and more experimental studies are indispensable for better understanding of the mechanical behavior of frozen tissue in cryosurgery.