Numerical Study of Heat and Mass Transfer during Cryopreservation Process with Application of Directed Interval Arithmetic

In the present paper, numerical modelling of heat and mass transfer proceeding in a two-dimensional axially symmetrical articular cartilage sample subjected to a cryopreservation process is presented. In the model under consideration, interval parameters were assumed. The heat transfer process is described using the Fourier interval equation, while the cryoprotectant transport (DMSO) across the cell membrane is analyzed using a two-parameter model taking into account the simulation of the water volume in the chondrocytes and the change in DMSO concentration over time. The liquidus tracking (LT) protocol introduced by Pegg et al. was used to model the cryopreservation process. This procedure divides the heating and cooling phases into eight and seven steps, respectively, allowing precise regulation of temperature and cryoprotectant (CPA) concentration of bathing solutions. This protocol protects chondrocytes from ice crystal, osmotic stress, and electrolyte damage. The obtained interval concentrations of cryoprotectant in chondrocytes were compared with previous simulations obtained using the deterministic model and they are mostly in agreement with the simulation data.

High-Frequency Acoustic Imaging Using Adhesive-Free Polymer Transducer

The piezoelectric polymer PVDF and its copolymers have a long history as transducer materials for medical and biological applications. An efficient use of these polymers can potentially both lower the production cost and offer an environment-friendly alternative for medical transducers which today is dominated by piezoelectric ceramics containing lead. The main goal of the current work has been to compare the image quality of a low-cost in-house transducers made from the copolymer P(VDF-TrFE) to a commercial PVDF transducer. Several test objects were explored with the transducers used in a scanning acoustic microscope, including a human articular cartilage sample, a coin surface, and an etched metal film with fine line structures. To evaluate the image quality, C- and B-scan images were obtained from the recorded time series, and compared in terms of resolution, SNR, point-spread function, and depth imaging capability. The investigation is believed to provide useful information about both the strengths and limitations of low-cost polymer transducers.

Numerical Modeling of Heat and Mass Transfer during Cryopreservation Using Interval Analysis

In the paper, the numerical analysis of heat and mass transfer proceeding in an axially symmetrical articular cartilage sample subjected to the cryopreservation process is presented. In particular, a two-dimensional (axially symmetrical) model with imprecisely defined parameters is considered. The base of the heat transfer model is given by the interval Fourier equation and supplemented by initial boundary conditions. The phenomenon of cryoprotectant transport (Me2SO) through the extracellular matrix is described by the interval mass transfer equation. The liquidus-tracking (LT) method is used to control the temperature, which avoids the formation of ice regardless of the cooling and warming rates. In the LT process, the temperature decreases/increases gradually during addition/removal of the cryoprotectant, and the articular cartilage remains on or above the liquidus line so that no ice forms, independent of the cooling/warming rate. The discussed problem is solved using the interval finite difference method with the rules of directed interval arithmetic. Examples of numerical computations are presented in the final part of the paper. The obtained results of the numerical simulation are compared with the experimental results, realized for deterministically defined parameters.

Experimental Study on Creep Characteristics of Microdefect Articular Cartilages in the Damaged Early Stage

Traumatic joint injury is known to cause cartilage deterioration and osteoarthritis. In order to study the mechanical mechanism of damage evolution on articular cartilage, taking the fresh porcine articular cartilage as the experimental samples, the creep experiments of the intact cartilages and the cartilages with different depth defect were carried out by using the noncontact digital image correlation technology. And then, the creep constitutive equations of cartilages were established. The results showed that the creep curves of different layers changed exponentially and were not coincident for the cartilage sample. The defect affected the strain values of the creep curves. The creep behavior of cartilage was dependent on defect depth. The deeper the defect was, the larger the strain value was. The built three-parameter viscoelastic constitutive equation had a good correlation with the experimental results and could predict the creep performance of the articular cartilage. The creep values of the microdefective cartilage in the damaged early stage were different from the diseased articular cartilage. These findings pointed out that defect could accelerate the damage of cartilage. It was helpful to study the mechanical mechanism of damage evolution.

The Effect of Charge and Mechanical Loading on Antibody Diffusion Through the Articular Surface of Cartilage

Molecular transport of osteoarthritis (OA) therapeutics within articular cartilage is influenced by many factors, such as solute charge, that have yet to be fully understood. This study characterizes how solute charge influences local diffusion and convective transport of antibodies within the heterogeneous cartilage matrix. Three fluorescently tagged solutes of varying isoelectric point (pI) (4.7–5.9) were tested in either cyclic or passive cartilage loading conditions. In each case, local diffusivities were calculated based on local fluorescence in the cartilage sample, as observed by confocal microscopy. In agreement with past research, local solute diffusivities within the heterogeneous cartilage matrix were highest around 200–275 μm from the articular surface, but 3–4 times lower at the articular surface and in the deeper zones of the tissue. Transport of all 150 kDa solutes was significantly increased by the application of mechanical loading at 1 Hz, but local transport enhancement was not significantly affected by changes in solute isoelectric point. More positively charged solutes (higher pI) had significantly higher local diffusivities 200–275 μm from the tissue surface, but no other differences were observed. This implies that there are certain regions of cartilage that are more sensitive to changes in solute charge than others, which could be useful for future development of OA therapeutics.

Histological and Anthropometric Changes in the Aging Nose

Background Rhinoplasty in the elderly requires different surgical approaches due to the morphological and structural changes affecting the nose over time. Objectives In this study, the authors aimed to evaluate the age-related cellular and architectural changes of nasal cartilages and soft tissue attachments. Methods This prospective study included 80 patients who underwent rhinoplasty. Patients were divided into 2 groups according to age. Group I included 40 patients ranging in age from 19 to 39 years. Group II included 40 patients aged at least 40 years. Samples from nasal cartilages (upper lateral, lower lateral, and septum) and nasal attachments (interdomal, inter-cartilaginous, and septo-crural) were taken. All specimens were evaluated histologically to detect age-related changes. A modified version of the Mankin grading scale was used to score each nasal cartilage sample. All attachment samples were examined by image analysis for quantitative assessment. The results were correlated to preoperative anthropometric measurements of nasolabial angle and nasal projection. Results Histologically, in group II, the cartilage matrix showed fibrinoid degeneration with a significant decrease in the number of chondrocytes and increased perichondrial fibrosis compared with group I. Attachments in group II showed a lower number of blood vessels and decreased percentage of collagen bundles. Modified Mankin scores were significantly higher in group II, indicating weak cartilages compared with group I. There was negative correlation and significance between projection, nasolabial angle, cartilages, and attachments in study groups. The linear regression model revealed that the lower lateral cartilage is the cartilage that is most affected by the aging process. Conclusions These findings not only enhance our current understanding of the natural changes that occur in the nose during aging but may also affect surgical decision-making when grafting or suturing are considered during rhinoplasty. Level of Evidence: 2

Comparative study on identification of healthy and osteoarthritic articular cartilages by fourier transform infrared imaging and chemometrics methods

Two discriminant methods, partial least squares-discriminant analysis (PLS-DA) and Fisher’s discriminant analysis (FDA), were combined with Fourier transform infrared imaging (FTIRI) to differentiate healthy and osteoarthritic articular cartilage in a canine model. Osteoarthritic cartilage had been developed for up to two years after the anterior cruciate ligament (ACL) transection in one knee. Cartilage specimens were sectioned into 10 [Formula: see text]m thickness for FTIRI. A PLS-DA model was developed after spectral pre-processing. All IR spectra extracted from FTIR images were calculated by PLS-DA with the discriminant accuracy of 90%. Prior to FDA, principal component analysis (PCA) was performed to decompose the IR spectral matrix into informative principal component matrices. Based on the different discriminant mechanism, the discriminant accuracy (96%) of PCA-FDA with high convenience was higher than that of PLS-DA. No healthy cartilage sample was mis-assigned by these two methods. The above mentioned suggested that both integrated technologies of FTIRI-PLS-DA and, especially, FTIRI-PCA-FDA could become a promising tool for the discrimination of healthy and osteoarthritic cartilage specimen as well as the diagnosis of cartilage lesion at microscopic level. The results of the study would be helpful for better understanding the pathology of osteoarthritics.

Development of a highly sensitive spectral camera for cartilage monitoring using fluorescence spectroscopy

The Ulm University Medical Center and the Ulm University of Applied Sciences are developing a bioreactor to grow facial cartilage using the methods of tissue engineering. To ensure a sufficient quality of the cartilage prior to implantation, the cartilage growth has to be monitored continuously. Current cartilage analysis methods are destructive so that analysed cartilage sample is no longer suitable for implantation. Alternatively, it seems feasible to analyse cartilage during the cultivation process and before implantation using fluorescence spectroscopy after UV light excitation. This approach is non-invasive and allows an evaluation of the cartilage in terms of composition and quality. Cultured cartilage implants can reach sizes of several square centimetres and therefore it is necessary to examine it over its entire area. For recording fluorescence spectra of different spots of the cartilage sample, a highly sensitive spectral camera is being developed in two steps. The first step is a one-dimensional spectral camera that is able to record fluorescence spectra along a sample line. The second step enables the detection of spectra over the required two-dimensional sample area. This approach is based on computed tomography imaging spectrometry (CTIS) and allows non-invasive distinguishing of the most important cartilage compounds collagen I and collagen II.

Synchronized Heterogeneous Indentation and Stress Relaxation Behavior of Articular Cartilage Upon Macroscopic Compression: A Preliminary Study

By using a newly-developed experimental technique that is enabled by a polymer-based microfluidic device for detecting distributed normal loads, a preliminary study is presented on the synchronized heterogeneous indentation and stress relaxation behavior of articular cartilage upon macroscopic compression. In a measurement, a rigid cylinder probe is employed to exert macroscopic indentation or step input to a cartilage sample on the device. Consequently, the synchronized heterogeneous viscoelastic behavior of the sample translates to distributed normal loads acting on the device and is captured by the device. While the macroscopic load acting on a sample is recorded by a load cell, the deflections of a sample along its length are captured by the device. Thus, the measured results essentially are the load-deflection relations of a sample along its length. Full-thickness lapine and bovine articular cartilage samples are prepared and measured. A thorough data analysis is implemented on the recorded data for extracting their instant and relaxed indentation modulus, as well as Young’s relaxation modulus.

Effect of Enzymatic Degeneration on the Frictonal Property of Articular Cartilage

Articular cartilage is consisted of the chondrocyte, collagen fibers and proteoglycan, and interstitial fluid. Basalo et al reported that the coefficient of friction of bovine articular cartilage on a glass surface measured in unconfined compression fashion was increased by the degeneration of proteoglycan [1]. In their friction test, it was difficult to test a small cartilage sample having undulation while the loaded area in cartilage specimen was almost unchanged during friction. For the assessment of frictional properties of enzymatically degenerated cartilage in more physiological condition, we developed a friction tester that allows for performing friction tests of articular cartilage surface against a spherical indenter. With the tester, the loaded area in cartilage specimen translated along with frictional motion while the compressive stress exceeded more than 1 MPa. In the present study, the effect of enzymatic degeneration of proteoglycan and collagen fiber on property of articular cartilage using the friction tester.