A custom-built planar biaxial system for soft tissue material testing

Accurate material characterization of soft tissues is crucial for understanding the physiopathology of cardiovascular diseases. However, commercial biaxial testing systems are expensive, prompting the need for affordable custom solutions. This study aimed to develop a low-cost custom biaxial system capable of accurately characterizing the mechanical behavior of soft tissues. The biaxial system was constructed using 3D printing technology and non-captive linear actuators for precise displacement control. A real-time marker tracking system was implemented to estimate dis-placements without the need for costly hardware. The system's performance was evaluated through tests on a calibration spring and frozen porcine aorta samples. The linear actuators demonstrated excellent response to user position input after motor tuning, showing no discrepancies between commands and actual positions. The experimental testing of the calibration spring showed good agreement with the analytical solution, validating the system's ability to accurately test materials. Testing on porcine aorta samples revealed stress-strain responses consistent with existing literature, accounting for potential variations due to tissue preservation and regional material property heterogeneity. Overall, this custom biaxial system demonstrates promising performance in accurately assessing the mechanical behavior of soft tissues, providing researchers with a valuable tool for cardiovascular disease research and tissue engineering applications.

Noninfectious tissue interactions at periprosthetic interfaces

The success of hip arthroplasty is based on modern materials in addition to the continuous development of surgical techniques and clinical experience gained over six decades. The biocompatible implant materials used in hip arthroplasty can be textured or coated with biomimetic surfaces to ensure durable component ingrowth and moderate host response. Material integrity plays a critical role in the durability of the stable interface between implant components and periprosthetic tissues. Inflammation at the interfaces due to the release of degradation products from the implant materials is one of the causes of hip arthroplasty failure. This review summarizes the implant materials currently used in hip arthroplasty, their preclinical testing and the postoperative neogenesis of periprosthetic tissues, and the interactions of periprosthetic bone and the implant materials at the periprosthetic interfaces.

Experimental and numerical modeling approach for thermomechanical low cycle fatigue analysis of cyclically non-stabilized steels

The widely used fatigue life prediction models, such as the Coffin–Manson model or S–N curve related models are based on the assumption that the response of a material experiencing low cycle fatigue loading is stabilized during some period. However, for many materials such a stabilized state is hardly observed, and the activated mechanisms for cyclic hardening or softening depend on test conditions. In general, the selected test conditions (stress or strain control) should depend on the intended use of the obtained material data. If testing conditions do not correspond to the operation mode of the considered mechanical facilities, the above mentioned life prediction models will produce inaccurate results. Hence, selecting and identifying proper fatigue parameters, which would represent the state of a material during the whole fatigue life, is extremely important in reliability evaluation of structures.

In the case of non-stabilizing steels, the common challenges are:•

Selecting and performing a suitable set of experimental tests to recognize various aspects of the material behavior under low-cycle thermomechanical fatigue;

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Adjusting a proper constitutive modelling, reflecting the real physical phenomena taking place in the material microstructure;

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Effective numerical implementation and optimal parameter identification.

Needle penetration test - qualifying examination of 3D printable silicones for vascular models in surgical practice

Background

During cardiogenic shock blood circulation is minimal in the human body and does not suffice to survive. The extracorporeal life support system (ECLS) acts as a miniature heart-lung-machine that can be temporarily implanted over major vessels e.g. at the groin of the patient to bridge cardiogenic shock. To perform this procedure in an emergency, a proper training model is desirable. Therefore, a 3-dimensional-printable (3D) material must be found that mimics large vessel needle penetration properties. A suitable test bench for material comparison is desirable.

Methods

A test setup was built, which simulated the clinically relevant wall tension in specimens. The principle was derived from an existing standardized needle penetration test. After design, the setup was fabricated by means of 3D printing and mounted onto an universal testing machine. For testing the setup, a 3D printable polymer with low Shore A hardness and porcine aorta were used. The evaluation was made by comparing the curves of the penetration force to the standardized test considering the expected differences.

Results

3D printing proved to be suitable for manufacturing the test setup, which finally was able to mimic wall tension as if under blood pressure and penetration angle. The force displacement diagrams showed the expected curves and allowed a conclusion to the mechanical properties of the materials. Although the materials forces deviated between the porcine aorta and the Agilus30 polymer, the graphs showed similar but still characteristic curves.

Conclusions

The test bench provided the expected results and was able to show the differences between the two materials. To improve the setup, limitations has been discussed and changes can be implemented without complications.

Supplementary Information

The online version contains supplementary material available at 10.1186/s41205-021-00110-y.

Frontal plane roll-over analysis of prosthetic feet

In prosthetic walking mediolateral balance is compromised due to the lack of active ankle control, by moments of force, in the prosthetic limb. Active control is reduced to the hip strategy, and passive mechanical stability depends on the curvature of the prosthetic foot under load. Mediolateral roll-over curvatures of prosthetic feet are largely unknown. In this study we determined the mediolateral roll-over characteristics of various prosthetic feet and foot-shoe combinations. Characteristics were determined by means of an inverted pendulum-like apparatus. The relationship between the centre of pressure (CoP) and the shank angle was measured and converted to roll-over shape and effective radius of curvature. Further, hysteresis (i.e., lagging in CoP displacement due to material compliance or slip) at vertical shank angle was determined from the hysteresis curve. Passive mechanical stability varied widely, though all measured foot-shoe combinations were relatively compliant. Mediolateral motion of the CoP ranged between 4 mm and 40 mm, thereby remaining well within each foot's physical width. Derived roll-over radii of curvature are also small, with an average of 102 mm. Hysteresis ranges between 20% and 115% of total CoP displacement and becomes more pronounced when adding a shoe. This may be due to slipping of the foot core in its cosmetic cover, or the foot in the shoe. Slip may be disadvantageous for balance control by limiting mediolateral travel of the CoP. It may therefore be clinically relevant to eliminate mediolateral slip in prosthetic foot design.

Cytocompatibility of filling pastes by primary teeth root simulating model

Evaluate the cytocompatibility of Calen^®/ZO, Calcicur^®, Vitapex^®, Endoflas^®, and zinc oxide/eugenol-based (ZOE) root canal pastes (RCP) to human primary osteoblasts (HPO) through a simplified model for primary teeth. The model employed pipette tips filled with 0.037 g of paste, exposed to 185 µL of culture medium for 24 h (n = 6). Release of components was analysed by Proton Nuclear Magnetic Resonance Spectroscopy (¹H-NMR). HPO were exposed to conditioned media for 24 h. Cell viability was assessed by cell density and metabolic activity, and release of interleukin 6 (IL-6), vascular endothelial growth factor (VEGF) and fibroblast growth factor (bFGF) by immunological assay. Physicochemical properties and antimicrobial efficacy were also evaluated. ¹H-NMR spectra analysis showed similarity between ZOE, Endoflas^®, Calcicur^®, and Vitapex^® compared to Calen^®/ZO and positive control, which showed distinct released components. Calen^®/ZO and Calcicur^® exhibited high alkaline pH in all periods and showed similar solubility. Calen^®/ZO, ZOE, and Vitapex^® showed similar flow rate. Calen^®/ZO, Calcicur^®, and Vitapex^® did not exhibit antimicrobial efficacy. Calen^®/ZO presented cytotoxicity (p < 0.05). Pastes did not increase IL-6 release compared to control. Apart from Vitapex^®, all pastes significantly induced VEGF/bFGF release. Interactive effects among released products may affect biological response to filling pastes. Calcicur^®, ZOE, Endoflas^® and Calen^®/ZO presented good to moderate cytocompatibility, with low impact on pro-inflammatory cytokine release and induction of growth factors of interest to tissue repair. This simplified model, specific for the evaluation of the cytocompatibility of RCPs on primary teeth, suggests how these pastes might contribute to bone repair in clinical situations of apical periodontitis in children.

CAD/CAM supported production process of standardized enamel and dentin tooth discs with different thicknesses for in vitro material testing

OBJECTIVE

The production of similar specimens for material testing is very difficult and crucial. This has much influence on the results of an experiment. With CAD design and new printing technologies it is possible to create individual devices to produce specimens for different testing situations. In this study different devices were designed for the standardized production of tooth discs for testing with bonded materials.

METHODS

The different devices were designed using optimized CAD for 3D printing. After the design, the different parts of the devices were printed using a desktop SLA 3D printer with high precision. Three different tools were needed for the generation of a standardized disc. After the production, the different devices were tested on natural teeth.

RESULTS

It is possible to generate very precise tools for the creation of round tooth discs. 40 tooth discs divided into 4 groups with a thickness of 2.0 mm, 2.5 mm, 3.0 mm and 3.5 mm and a constant diameter of 5 mm were produced. For all groups the median of the diameter and thickness was under +/-0.05 mm and the lower and the upper quartile were all under +/-0.06 mm.

SIGNIFICANCE

With this new approach the creation of very precise and uniform tooth discs is possible. The whole process for the creation of the tooth discs was standardized.

The effect of intracanal medicaments used in Endodontics on the dislocation resistance of two calcium silicate-based filling materials

Background

Intracanal medicaments can be used in various endodontic conditions including multiple visit endodontics after trauma or in regenerative endodontics. These medicaments should be removed from the root canal before the placement of the filling or repair material. The aim of the present study was to evaluate the effect of prior calcium hydroxide (Ca(OH)₂) and modified triple antibiotic paste (mTAP) placement on the push-out bond strength of TotalFill BC fast set putty (BC fast set putty) to root dentin when compared to mineral trioxide aggregate (MTA).

Methods

The root canals of 45 extracted mandibular premolars were prepared to a standardized internal diameter (1.5 mm). The specimens were randomly assigned to 3 groups according to the intracanal medicament used: mTAP (a mixture of metronidazole, ciprofloxacin, and cefaclor), Ca(OH)₂, and no intracanal medicament. After 1 week, the medicaments were removed, and the middle third of the roots were cut into two transverse sections (2.0 ± 0.05) (n = 90 slices). Thereafter, the specimens were divided into two subgroups (n = 45 each): MTA or BC putty. After 1 week, the push-out test was performed and failure mode was evaluated. The data were statistically analyzed using two-way ANOVA and Tukey’s post hoc.

Results

The application of the intracanal medicament did not significantly affect the bond strength of BC putty (p > .05). For MTA, the prior application of Ca(OH)₂ or mTAP significantly decreased the dislocation resistance (p < .05). Specimens in the MTA subgroups showed an almost equal number of cohesive and mixed types of failure while the majority of the specimens in the BC putty subgroups revealed the cohesive type.

Conclusions

Ca(OH)₂ and mTAP promoted lower bond strength of MTA to root dentin compared to the control group. However, the BC fast set putty bond strength to dentin was not affected by prior medication with Ca(OH)₂ or mTAP.

Human pulp response to conventional and resin-modified glass ionomer cements applied in very deep cavities

OBJECTIVES

This study assessed the human pulp response after adhesive restoration of cavities by indirect pulp capping with a conventional or a resin-modified glass ionomer cement.

MATERIALS AND METHODS

Deep cavities prepared in 26 human premolars were lined with Riva Light Cure (Riva LC), Riva Self Cure (Riva SC), or Dycal, and then restored with composite resin. Four teeth were used as intact control. After time intervals of 7 or 30 days, the teeth were extracted, processed for histological evaluation of the pulp, and the remaining dentin thickness (RDT) between the cavity floor and the pulp was measured.

RESULTS

At 7 days, a slight pulp inflammation associated with discrete tissue disorganization was observed in most of t the teeth lined with Riva LC and Riva SC. Moderate pulp inflammation occurred in one tooth lined with Riva LC. Bacteria were identified in one specimen of the same group that exhibited no pulp damage. At 30 days, slight pulp inflammation and discrete tissue disorganization persisted in two specimens treated with Riva LC, in which a thin layer of tertiary dentin was deposited. Mean RDTs ranged from 383.0 to 447.8 μm.

CONCLUSIONS

Riva LC produced more damage to the pulp than Riva SC. However, the initial pulp damage decreased over time and after 30 days both GICs were labeled as biocompatible.

CLINICAL RELEVANCE

In this study conducted with human teeth, the conventional and the resin-modified glass ionomer cements investigated were shown not to cause post-operative sensitivity or persistent pulp damage when applied as liners in very deep cavities, thereby indicating their biocompatibility.

Assessment of early onset surface damage from accelerated disinfection protocol

Background

The objective of this study was to evaluate the extent and potential mechanisms of early onset surface damage from simulated wiping typical of six-months of routine disinfection and to assess the subsequent microbial risk of surfaces damaged by disinfectants.

Methods

Eight common material surfaces were exposed to three disinfectants and a neutral cleaner (neutral cleaner, quaternary ammonium, hydrogen peroxide, sodium hypochlorite) in accelerated aging tests to simulate a long-term disinfection routine. Materials were also immersed in dilute and concentrated chemical solutions to induce surface damage. Surfaces were chemically and physically characterized to determine extent of surface damage. Bactericidal efficacy testing was performed on the Quat-based disinfectant using a modified version of EPA standard operating procedure MB-25-02.

Results

The wiping protocol increased surface roughness for some material surfaces due to mechanical abrasion of the wiping cloth. The increased roughness did not correlate with changes in bactericidal efficacy. Chemical damage was observed for some surface-disinfectant combinations. The greatest observed effects from disinfectant exposure was in changes in wettability or water contact angle.

Conclusions

Early onset surface damage was observed in chemical and physical characterization methods. These high-throughput material measurement methods were effective at assessing nanoscale disinfectant-surface compatibility which may go undetected though routine macroscale testing.

Characterization of thick titanium plasma spray coatings on PEEK materials used for medical implants and the influence on the mechanical properties

Coating poly-ether-ether-ketone (PEEK) with rough and porous titanium plasma spray (TPS) coatings is a technique which is commonly used to enhance the osseointegrative properties of medical implants. However, the influence of the TPS coating on the PEEK mechanical properties has not been sufficiently evaluated to date. In this study, PEEK samples were coated with a thick TPS layer with grains of 90µm and 180µm diameter. The coating characteristics and the adhesive strength of the coatings on the samples were determined and compared to coatings on titanium samples. The influence of the coating process on the mechanical and chemical-physical properties of PEEK was also evaluated. All TPS coatings on PEEK and titanium fulfilled the manufacturer's requirements for thickness (200 ± 50µm), porosity (30 ± 10%) and roughness (90µm grain diameter coating: 25 ± 5µm and 180µm grain diameter coating: 45 ± 15µm) and were able to meet the demands required for adhesive strength (> 22MPa) and shear strength (> 20MPa). However, the mechanical properties i.e. yield stress, fracture strain, flexural modulus and flexural stress, of the PEEK samples were influenced by the coating process, while the chemical-physical properties were not altered.

How does tissue preparation affect skeletal muscle transverse isotropy?

The passive tensile properties of skeletal muscle play a key role in its physiological function. Previous research has identified conflicting reports of muscle transverse isotropy, with some data suggesting the longitudinal direction is stiffest, while others show the transverse direction is stiffest. Accurate constitutive models of skeletal muscle must be employed to provide correct recommendations for and observations of clinical methods. The goal of this work was to identify transversely isotropic tensile muscle properties as a function of post mortem handling. Six pairs of tibialis anterior muscles were harvested from Giant Flemish rabbits and split into two groups: fresh testing (within four hours post mortem), and non-fresh testing (subject to delayed testing and a freeze/thaw cycle). Longitudinal and transverse samples were removed from each muscle and tested to identify tensile modulus and relaxation behavior. Longitudinal non-fresh samples exhibited a higher initial modulus value and faster relaxation than longitudinal fresh, transverse fresh, and transverse rigor samples (p<0.05), while longitudinal fresh samples were less stiff at lower strain levels than longitudinal non-fresh, transverse fresh, and transverse non-fresh samples (p<0.05), but exhibited more nonlinear behavior. While fresh skeletal muscle exhibits a higher transverse modulus than longitudinal modulus, discrepancies in previously published data may be the result of a number of differences in experimental protocol. Constitutive modeling of fresh muscle should reflect these data by identifying the material as truly transversely isotropic and not as an isotropic matrix reinforced with fibers.

Characterising the material properties at the interface between skin and a skin vaccination microprojection device

The rapid emergence of micro-devices for biomedical applications over the past two decades has introduced new challenges for the materials used in the devices. Devices like microneedles and the Nanopatch, require sufficient strength to puncture skin often with sharp-slender micro-scale profiles, while maintaining mechanical integrity. For these technologies we sought to address two important questions: 1) On the scale at which the device operates, what forces are required to puncture the skin? And 2) What loads can the projections/microneedles withstand prior to failure. First, we used custom fabricated nanoindentation micro-probes to puncture skin at the micrometre scale, and show that puncture forces are ∼0.25-1.75mN for fresh mouse skin, in agreement with finite element simulations for our device. Then, we used two methods to perform strength tests of Nanopatch projections with varied aspect ratios. The first method used a nanoindenter to apply a force directly on the top or on the side of individual silicon projections (110μm in length, 10μm base radius), to measure the force of fracture. Our second method used an Instron to fracture full rows of projections and characterise a range of projection designs (with the method verified against previous nanoindentation experiments). Finally, we used Cryo-Scanning Electron Microscopy to visualise projections in situ in the skin to confirm the behaviour we quantified, qualitatively.

STATEMENT OF SIGNIFICANCE

Micro-device development has proliferated in the past decade, including devices that interact with tissues for biomedical outcomes. The field of microneedles for vaccine delivery to skin has opened new material challenges both in understanding tissue material properties and device material. In this work we characterise both the biomaterial properties of skin and the material properties of our microprojection vaccine delivery device. This study directly measures the micro-scale puncture properties of skin, whilst demonstrating clearly how these relate to device design. This will be of strong interest to those in the field of biomedical microdevices. This includes work in the field of wearable and semi-implantable devices, which will require clear understanding of tissue behaviour and material characterisation.

Compatibility of medications during multi-infusion therapy: A controlled in vitro study on a multilumen infusion device

OBJECTIVE

Drug incompatibilities can jeopardize the safety and effectiveness of intravenous drug therapies, especially in the field of anaesthesia and intensive care. Patients receive many drugs simultaneously through limited venous accesses. This study was designed to confirm the impact of a multilumen infusion device on the occurrence of known physical drug incompatibilities.

STUDY DESIGN

In vitro laboratory work.

METHODS

Two infusion devices were studied: a standard single-lumen set and a multilumen infusion access device (Edelvaiss Multiline-8, Doran International). Up to six drugs were infused simultaneously: three acidic solutions of midazolam, amiodarone and dobutamine, and three alkaline solutions of furosemide, pantoprazole and amoxicillin/clavulanate. Saline, Ringer' solution and 5% dextrose were used as hydration vehicles with an infusion rate initially set at 100 mL/h and with stepwise decreases of 10 mL/h until precipitation. Two methods were used to highlight physical drug compatibility according to the European Pharmacopoeia: visual inspection of the extension set and an obscured-light sub-visible particle count test of infusions. The lowest infusion rate value for vehicle infusion to satisfy the two tests in all trials is reported for each infusion device.

RESULTS

The standard set did not satisfy the test in 82% of the assessed drug combinations. The Edelvaiss Multiline-8 was able to prevent the occurrence of drug incompatibilities in 49% of the drug combinations tested. This device is therefore advantageous, especially when simultaneously infusing two or four incompatible drugs.

CONCLUSIONS

Infusion device characteristics have an impact on physical drug incompatibilities. Our results confirm that the Edelvaiss Multiline-8 device prevents physical drug incompatibilities under specified conditions.

Impact of noradrenaline infusion set on mean arterial pressure: a retrospective clinical study

OBJECTIVES

Noradrenaline (NA) can be infused through various systems including single or double syringe pumps. The aim of this study was to define the best and most efficient infusion system in an emergency context.

STUDY DESIGN

This was a retrospective clinical study based on the analysis of patients' hemodynamic data.

PATIENTS AND METHOD

Three infusion lines used presently in our postoperative ICU were compared through a retrospective clinical study: an NA syringe pump at 2mL/h and a saline carrier solution syringe pump at 8mL/h (infusion system 1- IS1) or 5mL/h (IS2), both connected to a very low dead-space volume set (V=0.046mL); IS3 with the same NA syringe at 2mL/h directly connected to the central venous catheter. Mean arterial pressure (MAP) was obtained from retrospective data analysis of ICU patients with postoperative septic shock criteria. Infusion systems were compared according to the time required to reach an MAP greater than 65mmHg after the onset of infusion.

RESULTS

Data from 37 patients was analysed. The MAP objective was attained in 14:00 minutes (9:20 - 26:10, n=15) with IS1, in 19:10 minutes (12:20 - 27:20, n=13) with IS2 and in 34:10 minutes (23:10 - 62:30, n=9) with IS3 (P=0.00032).

CONCLUSION

The use of a double syringe pump system associated with a very low dead-space volume infusion set appears to be the most appropriate system for NA infusion.