Biodegradable Polymers in Biomedical Applications: A Review-Developments, Perspectives and Future Challenges.

Biodegradable polymers are materials that, thanks to their remarkable properties, are widely understood to be suitable for use in scientific fields such as tissue engineering and materials engineering. Due to the alarming increase in the number of diagnosed diseases and conditions, polymers are of great interest in biomedical applications especially. The use of biodegradable polymers in biomedicine is constantly expanding. The application of new techniques or the improvement of existing ones makes it possible to produce materials with desired properties, such as mechanical strength, controlled degradation time and rate and antibacterial and antimicrobial properties. In addition, these materials can take virtually unlimited shapes as a result of appropriate design. This is additionally desirable when it is necessary to develop new structures that support or restore the proper functioning of systems in the body.

Changes in the Mechanical Properties of Alginate-Gelatin Hydrogels with the Addition of Pygeum africanum with Potential Application in Urology.

New hydrogel materials developed to improve soft tissue healing are an alternative for medical applications, such as tissue regeneration or enhancing the biotolerance effect in the tissue-implant-body fluid system. The biggest advantages of hydrogel materials are the presence of a large amount of water and a polymeric structure that corresponds to the extracellular matrix, which allows to create healing conditions similar to physiological ones. The present work deals with the change in mechanical properties of sodium alginate mixed with gelatin containing Pygeum africanum. The work primarily concentrates on the evaluation of the mechanical properties of the hydrogel materials produced by the sol-gel method. The antimicrobial activity of the hydrogels was investigated based on the population growth dynamics of Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923, as well as the degree of degradation after contact with urine using an innovative method with a urine flow simulation stand. On the basis of mechanical tests, it was found that sodium alginate-based hydrogels with gelatin showed weaker mechanical properties than without the additive. In addition, gelatin accelerates the degradation process of the produced hydrogel materials. Antimicrobial studies have shown that the presence of African plum bark extract in the hydrogel enhances the inhibitory effect on Gram-positive and Gram-negative bacteria. The research topic was considered due to the increased demand from patients for medical devices to promote healing of urethral epithelial injuries in order to prevent the formation of urethral strictures.

Histological and morphometrical evaluation of the urethral wall after bioresorbable stent implantation in male New Zealand White Rabbits: A preliminary study.

The aim of the study was the histological and morphometrical evaluation of the urethral wall at three time points after bioresorbable stent implantation in male New Zealand White Rabbits. The research was performed on 26 male New Zealand White rabbits aged 3-4 months and weighing 2.1-3.0 kg. Two models of bioresorbable sodium alginate-based stents were developed and implanted into the urethral lumen for one (T1), three (T3), and six weeks (T6). Sections of 5 µm thickness were cut from the urethra at intervals of 2 mm. The sliced sections were stained with hematoxylin-eosin (H&E), Van Gieson's (VG), Von Kossa, and Movat-Russell modified pentachrome (MOVAT) staining methods. The study provided valuable information for future models of urethral stents. The first model of the stent failed to fit the requirements due to inadequate mechanical properties. It curled up on itself losing the ability to adhere to the animals' urethra and was bioresorbed three weeks after implantation. The more rigid no. 2 stent was effective in widening the urethral lumen but did not biodegrade during the experiment. A comprehensive assessment of the second model's properties of biosorption and biointegration requires an extended observation of at least 12 months for an in depth morphological analysis. Stent migration is not likely to be caused solely by the mechanical properties of the urethra or urinary flow but mainly by muscle contraction of the organ wall.

Evaluation of Selected Properties of Sodium Alginate-Based Hydrogel Material-Mechanical Strength, µDIC Analysis and Degradation.

The search for ideal solutions for the treatment of urethral stenosis continues. This includes developing the material, design, while maintaining its optimal and desired properties. This paper presents the results of the research conducted on sodium alginate-based hydrogel material (AHM), which may be used as a material for stents dedicated to the treatment of pathologies occurring in the genitourinary system. In order to determine the selected parameters of the AHM samples, strength and degradation tests, as well as analysis of the micro changes occurring on the surface of the material using a digital image correlation (µDIC) system, were performed. This study shows that the material possessed good mechanical strength parameters, the knowledge of which is particularly important from the point of view of the stent-tissue interaction. The degradation analysis performed showed that the AHM samples degrade in an artificial urine environment, and that the degradation time mainly depends on the chemical composition of the material. The novel µDIC method performed allowed us to characterize the homogeneity of the material structure depending on the cross-linking agent used.

Numerical Analyses of Fracture Mechanism of the Pelvic Ring during Side-Impact Load.

The aim of this study is the analysis of the multiple pelvis fracture mechanism in side-impact dynamic load cases. The elaborated numerical model of a pelvis complex includes pelvic and sacral bones as well as soft tissues such as ligaments and cartilages. The bone has been modelled as a viscoelasticity material based on the Johnson-Cook model. The model parameters have been chosen based on the experimental data. The uniqueness of a presented approach refers to the selection of crack criteria for the bone. Thus, it was allowed to analyse the process of multiple fractures inside the pelvic bones. The analysis was evaluated for the model in which the deformation rate influences the bone material properties. As a result, the stress distributions inside particular bones were changed. It has been estimated that the results can vary by 50% or even more depending on the type of boundary conditions adopted. The second step of work was a numerical analysis of military vehicle subjected to an IED. An analysis of the impactor's impact on the pelvis of the Hybrid ES-2RE mannequin was conducted. It was shown that the force in the pelvis exceeds the critical value by a factor of 10. The results of the numerical analysis were then used to validate the model of a military vehicle with a soldier. It was shown that for the adopted loading conditions, the critical value of the force in the pelvis was not exceeded.

Histological and morphometric evaluation of the urethra and penis in male New Zealand White rabbits.

This stereudy aimed at performing a histological and morphometric evaluation of the urethra and penis of male rabbits. Seven male New Zealand White rabbits weighing 2.1-3 kg were used in the study. The whole urethra, from the urinary bladder to the external urethral orifice, was dissected from the rabbits, and the tissue was sliced into sections at an interval of 2 mm. The sections were stained with haematoxylin-eosin, Masson-Goldner trichrome stain, Van Gieson's stain and Movat-Russell modified pentachrome stain. A detailed evaluation of the morphology and morphometry was performed. The parameters assessed were the type and height of epithelium, thickness and composition of connective tissue, and thickness and structure of muscularis. The histological structure of the rabbit urethra was found to be similar to humans. However, although the rabbits were found to have the same type of penis as the humans, the internal structure of the corpora cavernosa, the relative thickness of the tunica albuginea and the rudimentary glands of the penis were found to differ in these animals. The results of the present study may be useful in the designing of implants, drug testing or surgical procedures on the physiological and pathological urethra.

Determination of Stent Load Conditions in New Zealand White Rabbit Urethra.

BACKGROUND: Frequency of urethral stenosis makes it necessary to develop new innovative methods of treating this disease. This pathology most often occurs in men and manifests itself in painful urination, reduced urine flow, or total urinary retention. This is a condition that requires immediate medical intervention. METHODS: Experimental tests were carried out on a rabbit in order to determine the changes of pressure in the urethra system and to estimate the velocity of urine flow. For this purpose, a measuring system was proposed to measure the pressure of a fluid-filled urethra. A fluoroscope was used to observe the deformability of the bladder and urethra canal. RESULTS: Based on these tests, the range of changes in the urethra tube diameter, the pressures inside the system, and the flow velocity during micturition were determined. CONCLUSIONS: The presented studies allowed determining the behavior of the urethra under the conditions of urinary filling. The fluid-filled bladder and urethra increased their dimensions significantly. Such large changes require that the stents used for the treatment of urethral stenosis should not have a fixed diameter but should adapt to changing urethral dimensions.

Accessory Genital Glands in the New Zealand White Rabbit: A Morphometrical and Histological Study.

INTRODUCTION: The aim of this research was to provide a detailed description of the morphology, topography, and histometry of rabbit accessory genital glands. MATERIAL AND METHODS: Seven male New Zealand White rabbits, 3-4 months of age and weighing 2.1-3 kg were used for the study. The whole urethra from the urinary bladder to the external urethral orifice accompanied by accessory genital glands was sliced at intervals of 1 mm. The serial sections were prepared with haematoxylin-eosin (H&E) and Movat-Russell modified pentachrome stain. RESULTS: A detailed description of the morphology and morphometry was provided. The topography of the organs was explained on the basis of characteristic cross-sections on histological slides. The inconsistent nomenclature and descriptions of these glands by different authors were also discussed. CONCLUSION: The morphometric analysis indicated that some of the glands described have similar dimensions in different individuals, while others like paraprostates revealed high diversity in the number of lobes, their size, and their structure. The accessory glands are also good topographic markers which precisely define the segment of the urethra. The terms "proprostate", "prostate", and "paraprostates" as the nomenclature of the prostate complex reflect the location of these glands well and indicate their common origin and function.

Material and Structural Modeling Aspects of Brain Tissue Deformation under Dynamic Loads.

The aim of this work was to assess the numerous approaches to structural and material modeling of brain tissue under dynamic loading conditions. The current technological improvements in material modeling have led to various approaches described in the literature. However, the methods used for the determination of the brain's characteristics have not always been stated or clearly defined and material data are even more scattered. Thus, the research described in this paper explicitly underlines directions for the development of numerical brain models. An important element of this research is the development of a numerical model of the brain based on medical imaging methods. This approach allowed the authors to assess the changes in the mechanical and geometrical parameters of brain tissue caused by the impact of mechanical loads. The developed model was verified through comparison with experimental studies on post-mortem human subjects described in the literature, as well as through numerical tests. Based on the current research, the authors identified important aspects of the modeling of brain tissue that influence the assessment of the actual biomechanical response of the brain for dynamic analyses.

The influence of osteoporotic bone structures of the pelvic-hip complex on stress distribution under impact load.

PURPOSE: The aim of this study was to determine the effect of bone mineral density (BMD) on the stress distribution in pelvic-hip complex (PHC) model which included bone structures and soft tissues. Bone mass changes in osteoporosis and osteopenia were considered in this analysis. In addition, the relations between force direction and stress distribution causing PHC fractures were determined. METHODS: This paper presents the development and validation of a detailed 3D finite element model with high anatomical fidelity of the PHC and BMD changes in trabecular and cortical bones, modelled based on CT scans. 10 kN loading was induced on a model consisting of 8 ligaments, the pelvis, sacrum, femur in front and side directions. RESULTS: For validation, the results of this model were compared to physiological stress in standing position and previous results with high-energy crashes under side impact load. Analysis of side-impact indicated the influence of BMD on femoral neck fractures, acetabular cartilage and sacroiliac joint delaminations. Front-impact analysis revealed the inferior pubic ramus, femoral neck fractures and soft tissue injuries, i.e., acetabular cartilage and symphysis pubis in osteoporosis and osteopenia. CONCLUSIONS: The elaborated PHC model enables effective prediction of pelvis injuries in high-energy trauma, according to Young-Burgess classification, and the determination of the influence of BMD reduction on pelvis trauma depending on force direction. The correlation between BMD and stress distribution causing varying injuries was determined.

The process of subsidence after cervical stabilizations by cage alone, cage with plate and plate-cage. A biomechanical comparative study.

BACKGROUND AND PURPOSE: Clinical observations show that subsidence of cervical interbody implants takes place in the early postoperative period. Additional plating or use of a plate-cage is thought to be helpful to avoid excessive subsidence. We performed a biomechanical comparative study to assess the process of subsidence after the use of three different cervical stabilization methods. MATERIAL AND METHODS: Porcine cervical specimens after anterior discectomy were stabilized by a cage alone (n=6), cage with plate (n=6) and a plate-cage (n=6), and were exposed to 21 000 cycles of 20-200 N cyclic axial loads with frequency of 2.5 Hz. Size of subsidence was continually calculated by the software of the testing machine. One-way ANOVA test was applied for statistical evaluation. RESULTS: The test revealed two phases in the course of subsidence: an initial phase and a final one. In the initial phase rapid increase of subsidence occurred. Velocity and size of subsidence in this phase differed significantly between the stabilizing systems. The fastest and biggest subsidence occurred in the case of the cage alone, less subsidence was noted for the cage with plate and the least for the plate-cage. The final phase of the subsidence was markedly slower and longer. Velocity and size in this phase were the biggest for the cage alone. The differences between the cage with plate and the plate-cage in that phase were not significant. CONCLUSIONS: The study shows that subsidence occurs in two phases irrespective of the type of cervical stabilization and this finding confirms similar clinical observations. Additional plating can be helpful in controlling the course of subsidence.

The mechanical properties of human dentin for 3-D finite element modeling: Numerical and analytical evaluation.

BACKGROUND: The FEM is often used in investigations of dentin loading conditions; however, its anisotropy is mostly neglected. OBJECTIVES: The purpose of the study was to evaluate the anisotropy and the elastic properties of an equivalent homogenous material model of human dentin as well as to compare isotropic and anisotropic dentin FE-models. MATERIAL AND METHODS: Analytical and numerical dentin homogenization according to Luciano and Barbero was performed and E-modulus (E), Poisson's ratios (v) G-modulus (G) were calculated. The E-modulus of the dentin matrix was 28.0 GPa, Poisson's ratio (v) was 0.3; finite element models of orthotropic and isotropic dentin were created, loaded and compared using Ansys® 14.5 and CodeAster® 11.2 software. RESULTS: Anisotropy of the dentin ranged from 6.9 to 35.2%. E-modulus and G-modulus were as follows: E1 = 22.0-26.0 GPa, E2/E3 = 15.7-23.0 GPa; G12/G13 = 6.96-9.35 GPa and G23 = 6.08-8.09 GPa (highest values in the superficial layer). In FEM analysis of the displacement values were higher in the isotropic than in the orthotropic model, reaching up to 16% by shear load, 37% by compression and 23% in the case of shear with bending. Strain values were higher in the isotropic model, up to 35% for the shear load, 31% for compression and 35% in the case of shear with bending. The decrease in the volumetric fraction and diameter of tubules increased the G and E values. CONCLUSIONS: Anisotropy of the dentin applied during FEM analysis decreased the displacements and strain values. The numerical and analytical homogenization of dentin showed similar results.

Outer annulus tears have less effect than endplate fracture on stress distributions inside intervertebral discs: relevance to disc degeneration.

BACKGROUND: Annulus tears and endplate fracture are common lesions in human intervertebral discs. Both cause degenerative changes in animal models, but the time course appears to be different. The purpose of the present experiment is to compare the effects of outer annulus tears and endplate fracture on intradiscal stresses. We hypothesise that endplate fracture provides a greater stimulus for disc degeneration. METHODS: Seven cadaveric lumbar "motion segments" aged 49-70 years were compressed at 2 kN while the distribution of compressive stress was measured in each disc by pulling a 1.3 mm-diameter pressure transducer along its mid-sagittal diameter. Measurements were repeated after rim tears were simulated by 10 mm-deep scalpel cuts into the outer anterior annulus. The first cut was horizontal, 15 mm to the right of the disc midline, near the junction with the upper endplate. The second cut was vertical, 15 mm to the left of the disc midline, at mid-disc height. The third cut was horizontal, in the disc midline and at mid-disc height, so that the cut passed through the needle hole of the pressure transducer. Stress profiles were recorded in three postures and at two load levels, after each cut. Stress measurements were repeated a final time following compressive overload sufficient to fracture the endplate. FINDINGS: Outer annulus tears had negligible effect on compressive stress distributions in the annulus fibrosus more than 15 mm from the scalpel cut, and they caused nucleus pressure to fall by only 1% (SD 1.3%, NS). In contrast, endplate fracture reduced nucleus pressure by 37% (P=0.004) and increased maximum stress within the posterior annulus by 93% (P=0.033). INTERPRETATION: Outer annulus tears have less (immediate) effects on intradiscal compressive stresses than endplate fracture, supporting our hypothesis.

An analysis of the effect of impact loading on the destruction of vascular structures in the brain.

Subdural hematomas are one of the frequent complications of head injuries. Such hematomas result from exceeding the border strength values of bridging veins. Subdural haemorrhages are life-threatening and are a frequent cause of considerable pathologies. Traffic participants and also soldiers who participate in armed conflicts are the most vulnerable to head injuries. Although hematomas have been studied for many years the mechanism of hematoma formation has not been fully clarified as yet. In the paper, the effort of brain tissue structures due to the propagation of shock wave was analyzed. Particular attention was paid to the deformation ability and changes in the energy of bridging veins. This research was concerned with changes in mechanical properties of these veins in the frontal, parietal and occipital regions of the brain. For the present research the authors have constructed finite element models of brain tissue fragments and conducted numerical studies taking into account the boundary conditions arising from violent overloads that result from combat operations. As a result of the numerical analysis conducted, critical values of strain and stress have been obtained. The analysis showed high diversity in the properties of the different regions of the brain tissue. The studies carried out by the authors rendered it possible to assess the effort of the tissue structures of veins in connection with mechanical parameters, including geometrical parameters, in particular in relation to the likelihood of hematoma formation.

Biomechanical characteristics of the jump down of healthy subjects and patients with knee injuries.

PURPOSE: The aim of this study is to investigate the drop jump performance of male patients who underwent ACLR and a control group using combined data acquisition system. METHODS: A total of 28 male subjects aged 20 to 26 were studied: 22 did not show and were not diagnosed with any knee joint dysfunction (the control group) and six men who underwent ACLR of the left limb (group of patients). The control group was age, height and body mass matched. A data acquisition setup consisting of three independent modules including force platforms, position analysis system and electromyography was used. Subjects were jumping down from 0.1, 0.2, and 0.3 m step heights. The acquired signals were used to determine the ground reaction force, muscular activity, mass centre position, velocity and acceleration. RESULTS: Statistically significant differences were found between the groups (t-test, p < 0.05) in the maximum vertical ground reaction force in the left limb for 0.2 and 0.3 m step heights. Differences in the muscle activity between the groups were found to be statistically significant (t-test, p < 0.05) before the jump, during the landing phase, and after the jump for selected muscle groups and step heights. CONCLUSION: Combing the three independent measurement systems provided new information on drop jump biomechanics. The distribution of loads in different muscles was not uniform across the groups. Patients allocated more energy to control their motion and seemed to protect their operated limb by shifting the bodyweight to the healthy limb.

Experimental and constitutive modeling approaches for a study of biomechanical properties of human coronary arteries.

The study concerns the determination of mechanical properties of human coronary arterial walls with both experimental and constitutive modeling approaches. The research material was harvested from 18 patients (range 50-84 years). On the basis of hospital records and visual observation, each tissue sample was classified according to the stage (0, I, II, III) of atherosclerosis development (SAD). Then, strip samples considered as a membrane with the shape of rectangular parallelepiped were preconditioned and subjected to uniaxial tensile tests in longitudinal (n=27) and circumferential (n=4) direction. With experimental data obtained, the stress-strain characteristics were prepared. Furthermore, tensile strengths and related strains, stiffness coefficients and tangent modules of elasticity were computed. For a constitutive model of passive mechanical behavior of coronary arteries, values of material parameters were computed. The studies led to the following conclusions. Most importantly, the atherosclerotic changes affect all the mechanical properties of arterial walls. A progress of arteriosclerosis contributes to an increase of vascular stiffness. The highest values of the stiffness coefficients are obtained for the tissues in the advanced stage of the disease. We were also able to observe that gradual calcification, progression of atherosclerosis and degradation of collagen in the tissue caused a decrease of tensile strengths and related strains. Finally, a comparison made for the tissues with the advanced SAD showed that the tensile strengths and strains were much higher in the case of the samples with the circumferential orientation rather than those with the longitudinal one.

[Effect of a compression load on intradiscal pressure of the cervical spine: in vitro investigation]. / Wplyw obciazenia sciskajacego na zmiany cisnienia wewnatrz krazków miedzykregowych odcinka szyjnego kregoslupa -- badania in vitro.

BACKGROUND AND PURPOSE: The aim of this paper was to investigate the effects of intervertebral fusion (Cloward and Robinson-Smith techniques) on the intradiscal pressure at the adjacent levels exposed to compression loads. MATERIAL AND METHODS: A biomechanical study was performed using cadaveric cervical spine. 12 cervical spines exposed to a compression load were analyzed. Intact spines and spines after internal stabilisation using bone grafts and metal plates were already studied. All biomechanical testing was performed on the material testing machine (MTS 858 MiniBionix Test System). RESULTS: The results of investigation confirmed a linear distribution of pressure related to the applied compression loads. This study showed that intradiscal pressure was always inferior in the disc above the stabilisation segment as compared to the disc underneath (even by 49%), regardless of the investigated system (intact spine or spine with a fixator). Intradiscal pressure in the spine with a bone graft, using Cloward technique or Robinson-Smith techniques, did not show significant differences between the two methods of stabilisation. Additionally, stabilisation (in the form of a fixator plate) did not show an essential influence of the fixator on changes of the intradiscal pressure. CONCLUSION: Clinical studies have reported increased rates of disc degeneration at levels adjacent to fusion. The results presented in this paper have not shown a significant increase of the intradiscal pressure at the adjacent levels after stabilisation.

Biomechanical characteristics of the porcine denticulate ligament in different vertebral levels of the cervical spine-preliminary results of an experimental study.

BACKGROUND: Few studies exist on the mechanical properties of denticulate ligaments and none report the variation in these properties at different levels of the spine. The aim of this study was to perform an experimental determination of load-extension and stress-strain characteristics of the denticulate ligament and to establish if their properties change at different vertebral levels of the cervical spine. METHOD: The study was carried out on a total of 98 porcine denticulate ligament samples dissected from seven fresh porcine cervical spinal cord specimens. All of the samples were subjected to an uniaxial tensile test at a speed of 2mm/min, during which the load-extension characteristics were registered. RESULTS: The analysis revealed a decrease of the failure force in the caudal orientation indicated by significant differences between the C1 (1.04±0.41N) and C7 (0.55±0.12N) vertebral levels (P=0.037). The average ultimate force that broke the denticulate ligaments was 0.88N. The mean value of Young׳s modulus was 2.06MPa with a minimum of 1.31MPa for C7 and maximum of 2.46MPa for C5. CONCLUSIONS: The values of the denticulate ligament failure force in samples from different cervical vertebrae levels differ significantly. The presented data should be taken into consideration during numerical modelling of the human cervical spinal cord.

Finite element modelling of the cervical spinal cord injury -- clinical assessment.

The aim of the study was to evaluate the efficiency of Finite Element Method (FEM) modelling of the clinical cases of traumatic cervical spinal cord injury (SCI). The study population consisted of 28 patients suffering from traumatic cervical spine injury with (study group) and without (control) neurological deficits. A numerical simulation of the trauma event was performed, based on validated 3D FEM model. All the results obtained underwent statistical analysis. Statistically significant differences between both groups were found in severity of bony and neural structure damage as well as in stress and strain ratios. The highest values of tensile stress and deformation were noted in the sagittal (Y) axis. The maximum stress and strain were found in anterior spinothalamic, lateral spinothalamic and dorsal columns. It was also found that stress and strain in each segment and axis of the spinal cord model were positively correlated with the severity of the cervical spine injury (R-Spearman 0.39 to 0.64) and neurological symptoms of SCI (R-Spearman: 0.43 to 0.82). It is possible to create a clinical numerical model of the SCI with the use of FEM. The correlations between the mechanical force and neurological deficits show tendencies which require further studies based on an improved model and a greater number of patients.

Mechanical properties of cervical dura mater.

The aim of the study was to determine experimentally the stress as strain function as well as the orthotropy and heterogeneity of porcine dura mater of the cervical spinal cord. Material was divided into groups based on the place of collection, considering the dorsal side and ventral side, specifying the number of cervical vertebra, and the direction of tension of the sample - longitudinal or circumferential. Experimental studies were conducted with the MTS Synergie 100 testing machine. The tensile test was performed for each sample at a speed of 2 mm/min until the sample's break. There were determined the characteristics of stress as a function of strain in particular samples. Distribution maps of the stress and strain values at the characteristic points were then drawn (the beginning and the end of the linear range of the stress-strain characteristic and the point corresponding to the complete sample damage) for each set of samples, taking account of their collection place and direction of tension. The results confirmed the orthotropy of mechanical properties of dura mater. Stress and strain differed also in the value at the height of each vertebra and exhibited diversification on the ventral side compared to dorsal one.