In vitro pyrogen test—A new test method for solid medical devices

Assessment of Pyrogenic Response of Medical Devices and Biomaterials by the Monocyte Activation Test (MAT): A Systematic Review

Pyrogens are fever-inducing substances routinely investigated in health products through tests such as the Rabbit Pyrogen Test (RPT), the Limulus Amebocyte Lysate (LAL), and the Monocyte Activation Test (MAT). However, the applications of the MAT for medical devices and biomaterials remain limited. This work aimed to overview the studies evaluating the pyrogenicity of medical devices and biomaterials using the MAT, highlighting its successes and potential challenges. An electronic search was performed by December 2023 in PubMed, Scopus, and Web of Science, identifying 321 records which resulted in ten selected studies. Data were extracted detailing the tested materials, MAT variants, interferences, and comparisons between methods. Methodological quality was assessed using the ToxRTool, and the results were synthesized descriptively. The selected studies investigated various materials, including polymers, metals, and natural compounds, employing the different biological matrices of the MAT. Results showed the MAT's versatility, with successful detection of pyrogens in most materials tested, though variability in sensitivity was noted based on the material and testing conditions. Challenges remain in optimizing protocols for different material properties, such as determining the best methods for direct contact versus eluate testing and addressing the incubation conditions. In conclusion, the MAT demonstrates significant potential as a pyrogen detection method for medical devices and biomaterials. However, continued research is essential to address existing gaps, optimize protocols, and validate the test across a broader range of materials.

Biosafety and chemical solubility studies of multiscale crystal-reinforced lithium disilicate glass-ceramics

Lithium disilicate (Li2 Si2 O5 ) glass-ceramics are currently a more widely used all-ceramic restorative material due to their good mechanical properties and excellent aesthetic properties. However, they have a series of problems such as high brittleness and low fracture toughness, which has become the main bottleneck restricting its development. Therefore, in order to compensate for these shortcomings, we propose to prepare a reinforced glass-ceramics with better mechanical properties and to test the biosafety and chemical solubility of the material. Li2 Si2 O5 whiskers were synthesized by a one-step hydrothermal method, and multi-scale crystal-enhanced Li2 Si2 O5 glass-ceramics were prepared by reaction sintering. The biosafety of multi-scale crystal-reinforced Li2 Si2 O5 glass-ceramics was investigated by in vitro cytotoxicity test, rabbit pyrogen test, mice bone marrow micronucleus test, skin sensitization test, sub-chronic systemic toxicity test, and chronic systemic toxicity test. Additionally, the chemical solubility of multi-scale crystal-reinforced Li2 Si2 O5 glass-ceramics was investigated. The test results showed that the material was non-cytotoxic, non-thermogenic, non-mutagenic, non-sensitizing, and non-systemic. The chemical solubility, determined to be 377 ± 245 μg/cm2 , complied with the ISO 6872 standard for the maximum solubility of ceramic materials. Multi-scale crystal-reinforced Li2 Si2 O5 glass-ceramics' biosafety and chemical solubility met current normative criteria, and they can move on to mechanical property measurements (such as flexural strength test, fatigue life test, friction and wear property study, etc.) and bonding property optimization, which shows promise for future clinical applications.

Advances in endotoxin analysis

The outer membrane of gram-negative bacteria is primarily composed of lipopolysaccharide (LPS). In addition to protection, LPS defines the distinct serogroups used to identify bacteria specifically. Furthermore, LPS also act as highly potent stimulators of innate immune cells, a phenomenon essential to understanding pathogen invasion in the body. The complex multi-step process of LPS binding to cells involves several binding partners, including LPS binding protein (LBP), CD14 in both membrane-bound and soluble forms, membrane protein MD-2, and toll-like receptor 4 (TLR4). Once these pathways are activated, pro-inflammatory cytokines are eventually expressed. These binding events are also affected by the presence of monomeric or aggregated LPS. Traditional techniques to detect LPS include the rabbit pyrogen test, the monocyte activation test and Limulus-based tests. Modern approaches are based on protein, antibodies or aptamer binding. Recently, novel techniques including electrochemical methods, HPLC, quartz crystal microbalance (QCM), and molecular imprinting have been developed. These approaches often use nanomaterials such as gold nanoparticles, quantum dots, nanotubes, and magnetic nanoparticles. This chapter reviews current developments in endotoxin detection with a focus on modern novel techniques that use various sensing components, ranging from natural biomolecules to synthetic materials. Highly integrated and miniaturized commercial endotoxin detection devices offer a variety of options as the scientific and technologic revolution proceeds.

Early Immune Response in Foreign Body Reaction Is Implant/Material Specific

The design of novel biomaterials should directly influence the host-immune system and steer it towards high biocompatibility. To date, new implants/materials have been tested for biocompatibility in vitro in cell cultures and in vivo in animal models. The current methods do not reflect reality (cell cultures) or are very time-consuming and deliver results only after weeks (animal model). In this proof-of-concept study, the suitability of a Whole Blood Stimulation Assay (WBSA) in combination with a Protein Profiler Array (PPA), as a readily available and cost-effective screening tool, was investigated. Three different biomaterials based on poly(lactic-co-glycolic acid (PLGA), calcium sulphate/-carbonate (CS) and poly(methyl methacrylate) (PMMA) were exposed to native whole blood from three volunteers and subsequently screened with a PPA. Individual reproducible protein profiles could be detected for all three materials after 24 h of incubation. The most intense reaction resulted from the use of PLGA, followed by CS. If even marginal differences in implants can be reflected in protein profiles, the combination of WBSA and PPA could serve as an early biocompatibility screening tool in the development of novel biomaterials. This may also lead to a reduction in costs and the amount of animal testing required.

Inter-Subunit Dynamics Controls Tunnel Formation During the Oxygenation Process in Hemocyanin Hexamers

Hemocyanin from horseshoe crab in its active form is a homo-hexameric protein. It exists in open and closed conformations when transitioning between deoxygenated and oxygenated states. Here, we present a detailed dynamic atomistic investigation of the oxygenated and deoxygenated states of the hexameric hemocyanin using explicit solvent molecular dynamics simulations. We focus on the variation in solvent cavities and the formation of tunnels in the two conformational states. By employing principal component analysis and CVAE-based deep learning, we are able to differentiate between the dynamics of the deoxy- and oxygenated states of hemocyanin. Finally, our results identify the deoxygenated open conformation, which adopts a stable, closed conformation after the oxygenation process.

More than 70 Years of Pyrogen Detection: Current State and Future Perspectives

In the quality assurance of medical products, tests for sterility are essential. For parenteral pharmaceuticals, avoiding the presence of pyrogens is crucial. These fever-inducing substances (endotoxins and non-endotoxins) are not eliminated by standard sterilisation processes, and are biologically active once in the bloodstream, causing risks to human health, ranging from mild reactions (e.g. fever) to septic shock and death. Therefore, for injectable formulations, pyrogen testing is mandatory. Over the years, various pyrogen testing methods have been introduced, namely: in the 1940s, the rabbit pyrogen test, which is an in vivo test that measures the fever reaction as an endpoint; in the 1970s, the Limulus Amoebocyte Lysate (LAL) test, which is an in vitro test (with the haemolymph of the horseshoe crab) that specifically detects endotoxin; and in 2010, the Monocyte-Activation Test (MAT), which is a non-animal based in vitro pyrogen test that represents a full replacement of the rabbit test. Due to the ubiquity and biological significance of pyrogens, we are currently further developing the MAT so that it can be used for other applications. More specifically, our focus is on the detection of pyrogenic contamination on medical devices, as well as on the measurement of air quality. In addition, further improvements to permit the use of cryopreserved blood in the MAT, to overcome the limitations in the availability of freshly-drawn blood from human donors, are ongoing.

Highly sensitive pyrogen detection on medical devices by the monocyte activation test

Pyrogens are components of microorganisms, like bacteria, viruses or fungi, which can induce a complex inflammatory response in the human body. Pyrogen contamination on medical devices prior operation is still critical and associated with severe complications for the patients. The aim of our study was to develop a reliable test, which allows detection of pyrogen contamination on the surface of medical devices. After in vitro pyrogen contamination of different medical devices and incubation in a rotation model, the human whole blood monocyte activation test (MAT), which is based on an IL-1β-specific ELISA, was employed. Our results show that when combining a modified MAT protocol and a dynamic incubation system, even smallest amounts of pyrogens can be directly detected on the surface of medical devices. Therefore, screening of medical devices prior clinical application using our novel assay, has the potential to significantly reduce complications associated with pyrogen-contaminated medical devices.

Analysis of IL-1 β release from cryopreserved pooled lymphocytes in response to lipopolysaccharide and lipoteichoic acid

Pyrogens are heterogeneous group of fever-inducing substances derived from Gram-positive and Gram-negative bacteria, fungi, and viruses. They incite immune response by producing endogenous pyrogens such as prostaglandins and other proinflammatory cytokines like IL-1β, IL-6, and TNF-α. The present study was to analyze the influence of cryopreservation in IL-1β release, a marker for inflammatory response from human lymphocytes, in response to exogenous pyrogenic stimulants. Lymphocytes isolated from pooled blood of multiple healthy individuals were cryopreserved in DMSO and glycerol for periods of 7, 14, 30, and 60 days and were challenged with LPS and LTA in vitro. The inflammatory cytokine, IL-1β release, was measured by ELISA method. It was observed that the release of IL-1β increases instantaneously after the initiation of incubation and reaches a maximum at 3 to 5 hours and then gradually decreases and gets stabilized for both pyrogens. Moreover it was also observed that the effect of cryoprotectants, DMSO (10%) and glycerol (10%), showed almost similar results for short-term storage, but DMSO-preserved lymphocytes yielded a better viability for long-term storage. Thus, the isolated cryopreserved lymphocytes system can be a promising approach for the total replacement/alteration to animal experimentation for pyrogenicity evaluation.

Surface contamination of dental implants assessed by gene expression analysis in a whole-blood in vitro assay: a preliminary study

AIM

We aimed at evaluating pyrogen contamination of dental implants made of titanium and zirconia by using gene expression analysis in a whole-blood in vitro assay.

MATERIAL AND METHODS

Titanium and zirconia implants (five each) were incubated in human whole blood. Samples were assayed for gene expression levels of toll-like receptor 4 (TLR4), TLR9, interleukin (IL)-1β, nuclear factor 'kappa-light-chain-enhancer' of activated B-cells (NF-kB), tumour necrosis factor (TNF)-α, and Fas-associated protein with death domain (FADD) as indicators of surface contamination resulting in lipopolysaccharides (LPS)-stimulated TLR- or TNF-mediated immune responses. Gene expression was assayed using real-time quantitative polymerase chain reaction (RT-qPCR). Non-stimulated blood from the same donor served as a negative control, and blood stimulated with LPS served as a positive control. After dry-heat treatment with dry heat, all implants were re-analysed as described above.

RESULTS

Both implant systems contained surface contaminants evoking a pro-inflammatory response similar to that induced by LPS. After dry-heat treatment, gene expression was significantly decreased to levels similar to those of negative control samples.

CONCLUSIONS

The results demonstrated LPS-like surface-bound contaminants in both tested implant systems. Depyrogenation with dry heat seems to be an effective means of reducing such contamination in dental implants.

Investigation of interleukin-1β release from cryopreserved blood stimulated with endotoxin

The feasibility of an indigenously developed ELISA method to determine cytokine response to wide spectrum of pyrogenic stimuli utilizing fresh human whole blood is limited by the availability of healthy donors. The possibility of using cryopreservation of pooled human blood for detection of cytokine response to lipopolysaccharide is explored in this study. The effect of cryopreservation on blood parameters, cellular morphology and cytokine response were compared with that of the pooled fresh blood and cryopreserved blood from single and multiple donors. In vitro pyrogenic stimulation with 0.5 and 5 EU of LPS was monitored on fresh and cryopreserved pooled blood from single and multiple donors. The release of IL-1β was quantitated by Sandwich ELISA (1, 10, 25, 45 and 75 days) after storage. The results indicated that the cryopreserved blood displayed enhanced IL-1β release on stimulation with LPS, when compared to fresh blood. The maximum release of IL-1β level was observed at 2h when 5 EU of LPS was treated with pooled fresh blood which is similar to that of fresh blood. After 75 days storage of pooled cryopreserved blood the IL-1β release was maximum at 9 and 15 h when treated with 5 and 0.5 EU of LPS. Observations of the study suggest that cryopreserved pooled blood is an economically and experimentally viable alternative to fresh blood. This investigative study promises short term storage and regular supply of non-allergic, pathogen free human blood for the detection of interleukin-1β for the evaluation of in vitro pyrogenicity.

Surface endotoxin contamination and hemocompatibility evaluation of materials

To evaluate the blood compatibility of new materials, a clear distinction between properties of the materials and effects due to surface contamination by adsorbed endotoxins is essential. This study compares direct contact approaches and elution methods with water, organic solvents, nonionic, and zwitterionic detergents for determination of surface-adsorbed endotoxin by the limulus amoebocyte lysate (LAL) test and determines the blood compatibility of various surfaces with controlled endotoxin contamination in vitro. The LAL test in direct contact with an endotoxin-contaminated surface was concluded to be not practicable for most devices and its sensitivity showed a high dependence on surface characteristics. Among the elution methods, 0.2% Tween-20 showed most stable elution characteristics and appears therefore preferable. Biological reactions at in vitro blood exposure were found to be only minimally influenced by adsorbed endotoxin during the time window of 2 h, allowing for a straightforward discrimination between materials and endotoxin-dependent reactions.

Removal of immune-stimulatory components from surfaces by plasma discharges

Immune-stimulating microbiological components like lipopolysaccharide (LPS), lipoteichoic acid (LTA) and zymosan bound onto surfaces lead to severe problems when brought in contact with the organism via surgical instruments or implants. We have shown, in recent studies, that it is possible to detect different immune-stimulating components directly on the surface, via an indirect detection method, using human whole-blood and the monocyte reaction to measure the inflammatory mediator release (IL-1β) by ELISA. With regard to the inactivation of pyrogenic substances, we present a method based on the application of a low-pressure microwave plasma discharge working at low temperatures. We found a fast (10 s to a few minutes) removal rate of the immune-stimulating competence for LPS, LTA and zymosan. To mimic the bacterial cell-wall, LPS in combination with muramyl dipeptide was employed and the decreasing rate of the inflammatory signal did not differ from pure LPS.