Size dependent uptake and trophic transfer of polystyrene microplastics in unicellular freshwater eukaryotes.

Microplastics (MP) have become a well-known and widely investigated environmental pollutant. Despite the huge amount of new studies investigating the potential threat posed by MP, the possible uptake and trophic transfer in lower trophic levels of freshwater ecosystems remains understudied. This study aims to investigate the internalization and potential trophic transfer of fluorescent polystyrene (PS) beads (0.5 µm, 3.6 × 108 particles/mL; 6 µm, 2.1 × 105 particles/mL) and fragments (<30 µm, 5 × 103 particles/mL) in three unicellular eukaryotes. This study focuses on the size-dependent uptake of MP by two freshwater Ciliophora, Tetrahymena pyriformis, Paramecium caudatum and one Amoebozoa, Amoeba proteus, serving also as predator for experiments on potential trophic transfer. Size-dependent uptake of MP in all three unicellular eukaryotes was shown. P. caudatum is able to take up MP fragments up to 27.7 µm, while T. pyriformis ingests particles up to 10 µm. In A. proteus, small MP (PS0.5µm and PS6µm) were taken up via pinocytosis and were detected in the cytoplasm for up to 14 days after exposure. Large PS-MP (PS<30µm) were detected in A. proteus only after predation on MP-fed Ciliophora. These results indicate that A. proteus ingests larger MP via predation on Ciliophora (PS<30µm), which would not be taken up otherwise. This study shows trophic transfer of MP at the base of the aquatic food web and serves as basis to study the impact of MP in freshwater ecosystems.

Influence of the polymer type of a microplastic challenge on the reaction of murine cells.

Due to global pollution derived from plastic waste, the research on microplastics is of increasing public interest. Until now, most studies addressing the effect of microplastic particles on vertebrate cells have primarily utilized polystyrene particles (PS). Other studies on polymer microparticles made, e.g., of polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP), or poly (ethylene terephthalate) (PET), cannot easily be directly compared to these PS studies, since the used microparticles differ widely in size and surface features. Here, effects caused by pristine microparticles of a narrow size range between 1 - 4 µm from selected conventional polymers including PS, PE, and PVC, were compared to those of particles made of polymers derived from biological sources like polylactic acid (PLA), and cellulose acetate (CA). The microparticles were used to investigate cellular uptake and assess cytotoxic effects on murine macrophages and epithelial cells. Despite differences in the particles' properties (e.g. ζ-potential and surface morphology), macrophages were able to ingest all tested particles, whereas epithelial cells ingested only the PS-based particles, which had a strong negative ζ-potential. Most importantly, none of the used model polymer particles exhibited significant short-time cytotoxicity, although the general effect of environmentally relevant microplastic particles on organisms requires further investigation.

Polystyrene microparticle distribution after ingestion by murine macrophages.

The impact of microplastic particles on organisms is currently intensely researched. Although it is well established that macrophages ingest polystyrene (PS) microparticles, little is known about the subsequent fate of the particles, such as entrapment in organelles, distribution during cell division, as well as possible mechanisms of excretion. Here, submicrometer (0.2 and 0.5 µm) and micron-sized (3 µm) particles were used to analyze particle fate upon ingestion of murine macrophages (J774A.1 and ImKC). Distribution and excretion of PS particles was investigated over cycles of cellular division. The distribution during cell division seems cell-specific upon comparing two different macrophage cell lines, and no apparent active excretion of microplastic particles could be observed. Using polarized cells, M1 polarized macrophages show higher phagocytic activity and particle uptake than M2 polarized ones or M0 cells. While particles with all tested diameters were found in the cytoplasm, submicron particles were additionally co-localized with the endoplasmic reticulum. Further, 0.5 µm particles were occasionally found in endosomes. Our results indicate that a possible reason for the previously described low cytotoxicity upon uptake of pristine PS microparticles by macrophages may be due to the preferential localization in the cytoplasm.

Role of Residual Monomers in the Manifestation of (Cyto)toxicity by Polystyrene Microplastic Model Particles.

Polystyrene (PS) is an important model polymer for the investigation of effects of microplastic (MP) and nanoplastic (NP) particles on living systems. Aqueous dispersions of PS MP or NP contain residual monomers of styrene. In consequence, it is not clear if the effects observed in standard (cyto)toxicity studies are evoked by the polymer (MP/NP) particle or by residual monomers. We addressed that question by comparing standard PS model particle dispersions with in-house synthesized PS particle dispersions. We proposed a rapid purification method of PS particle dispersions by dialysis against mixed solvents and developed a simple method of UV-vis spectrometry to detect residual styrene in the dispersions. We found that standard PS model particle dispersions, which contain residual monomers, exerted a low but significant cytotoxicity on mammalian cells, while the in-house synthesized PS, after rigorous purification to reduce the styrene content, did not. However, the PS particles per se but not the residual styrene in both PS particle dispersions resulted in immobilization of Daphnia. Only by using freshly monomer-depleted particles, will it be possible in the future to assess the (cyto)toxicities of PS particles, avoiding an otherwise not controllable bias effect of the monomer.

Thoroughly Hydrophilized Electrospun Poly(L-Lactide)/ Poly(ε-Caprolactone) Sponges for Tissue Engineering Application.

Biodegradable electrospun sponges are of interest for various applications including tissue engineering, drug release, dental therapy, plant protection, and plant fertilization. Biodegradable electrospun poly(l-lactide)/poly(ε-caprolactone) (PLLA/PCL) blend fiber-based sponge with hierarchical pore structure is inherently hydrophobic, which is disadvantageous for application in tissue engineering, fertilization, and drug delivery. Contact angles and model studies for staining with a hydrophilic dye for untreated, plasma-treated, and surfactant-treated PLLA/PCL sponges are reported. Thorough hydrophilization of PLLA/PCL sponges is found only with surfactant-treated sponges. The MTT assay on the leachates from the sponges does not indicate any cell incompatibility. Furthermore, the cell proliferation and penetration of the hydrophilized sponges are verified by in vitro cell culture studies using MG63 and human fibroblast cells.

Cultivation of Encapsulated Primary Human B Lymphocytes: A First Step toward a Bioartificial Germinal Center.

Polyelectrolyte microcapsules based on sodium cellulose sulfate (SCS) and poly-diallyl-dimethyl-ammonium chloride (PDADMAC) have previously been proposed as a suitable ex vivo microenvironment for the cultivation and differentiation of primary human T lymphocytes. Here, the same system is investigated for the cultivation of human primary B cells derived from adult tonsillar tissue. Proliferation and differentiation into subtypes are followed and compared to suspension cultures of B cells from the same pool performed in parallel. Total cell expansion is somewhat lower in the capsules than in the suspension cultures. More importantly, however, the differentiation of the initially mainly memory B cells into various subtypes, in particular into plasma cell (PC), shows significant differences. Clearly, the microenvironment provided by the microcapsules is beneficial for an accelerated induction of a germinal center-like B cell phenotype and afterward supports the long-term survival of the PC cells. Then, varying the encapsulation conditions (i.e., presence of human serum and dedicated cytokines in the capsule core) provides a tool for finetuning the B cell response. Hence, this methodology is suggested to pave the way toward ex vivo development of human immune organoids.

The transcriptomic landscape of Magnetospirillum gryphiswaldense during magnetosome biomineralization.

BACKGROUND: One of the most complex prokaryotic organelles are magnetosomes, which are formed by magnetotactic bacteria as sensors for navigation in the Earth's magnetic field. In the alphaproteobacterium Magnetospirillum gryphiswaldense magnetosomes consist of chains of magnetite crystals (Fe3O4) that under microoxic to anoxic conditions are biomineralized within membrane vesicles. To form such an intricate structure, the transcription of > 30 specific structural genes clustered within the genomic magnetosome island (MAI) has to be coordinated with the expression of an as-yet unknown number of auxiliary genes encoding several generic metabolic functions. However, their global regulation and transcriptional organization in response to anoxic conditions most favorable for magnetite biomineralization are still unclear. RESULTS: Here, we compared transcriptional profiles of anaerobically grown magnetosome forming cells with those in which magnetosome biosynthesis has been suppressed by aerobic condition. Using whole transcriptome shotgun sequencing, we found that transcription of about 300 of the > 4300 genes was significantly enhanced during magnetosome formation. About 40 of the top upregulated genes are directly or indirectly linked to aerobic and anaerobic respiration (denitrification) or unknown functions. The mam and mms gene clusters, specifically controlling magnetosome biosynthesis, were highly transcribed, but constitutively expressed irrespective of the growth condition. By Cappable-sequencing, we show that the transcriptional complexity of both the MAI and the entire genome decreased under anaerobic conditions optimal for magnetosome formation. In addition, predominant promoter structures were highly similar to sigma factor σ70 dependent promoters in other Alphaproteobacteria. CONCLUSIONS: Our transcriptome-wide analysis revealed that magnetite biomineralization relies on a complex interplay between generic metabolic processes such as aerobic and anaerobic respiration, cellular redox control, and the biosynthesis of specific magnetosome structures. In addition, we provide insights into global regulatory features that have remained uncharacterized in the widely studied model organism M. gryphiswaldense, including a comprehensive dataset of newly annotated transcription start sites and genome-wide operon detection as a community resource (GEO Series accession number GSE197098).

Tailor-Made Protein Corona Formation on Polystyrene Microparticles and its Effect on Epithelial Cell Uptake.

Microplastic particles are pollutants in the environment with a potential impact on ecology and human health. As soon as microplastic particles get in contact with complex (biological) environments, they will be covered by an eco- and/or protein corona. In this contribution, protein corona formation was conducted under defined laboratory conditions on polystyrene (PS) microparticles to investigate the influence on surface properties, protein corona evolution, particle-cell interactions, and uptake in two murine epithelial cells. To direct protein corona formation, PS particles were preincubated with five model proteins, namely, bovine serum albumin (BSA), myoglobin, ß-lactoglobulin, lysozyme, and fibrinogen. Subsequently, the single-protein-coated particles were incubated in a cell culture medium containing a cocktail of serum proteins to analyze changes in the protein corona profile as well as in the binding kinetics of the model proteins. Therein, we could show that the precoating step has a critical impact on the final composition of the protein corona. Yet, since proteins building the primary corona were still detectable after additional incubations in a protein-containing medium, backtracking of the particle's history is possible. Interestingly, whereas the precoating history significantly disturbs particle-cell interactions (PCIs), the cellular response (i.e., metabolic activity, MTT assay) stays unaffected. Of note, lysozyme precoating revealed one of the highest rates in PCI for both epithelial cell lines. Taken together, we could show that particle history has a significant impact on protein corona formation and subsequently on the interaction of particles with murine intestinal epithelial-like cells. However, as this study was limited to one cell type, further work is needed to assess if these observations can be generalized to other cell types.

High Strength and High Toughness Electrospun Multifibrillar Yarns with Highly Aligned Hierarchy Intended as Anisotropic Extracellular Matrix.

Electrospun nanofibers can be effectively used as a surrogate for extracellular matrices (ECMs). However, in the context of cellular mechanobiology, their mechanical performances can be enhanced by using nanofibrous materials with a high level of structural organization. Herein, this work develops multifibrillar yarns with superior mechanical performance based on biocompatible polyacrylonitrile (PAN) as surrogate ECM. Nearly perfect aligned nanofibers along with the axis of the multifibrillar yarn are prepared. These highly aligned yarns exhibit high strength, high toughness, good stress relaxation behavior, and are robust enough for technical or medical applications. Further, this work analyzes the influence of the highly aligned-hierarchical topological structure of the material on cell proliferation and cell orientation using cells derived from epithelial and connective tissues. Compared to nonoriented electrospun multifibrillar yarns and flat films, the well-ordered topology in the electrospun PAN multifibrillar yarns triggers an improved proliferation of fibroblasts and epithelial cells. Fibroblasts acquire an elongated morphology analogous to their behavior in the natural ECM. Hence, this heterogeneous multifibrillar material can be used to restore or reproduce the ECM for tissue engineering applications, notably in the skeletal muscle and tendon.

Disentangling biological effects of primary nanoplastics from dispersion paints' additional compounds.

Microplastic particles (MP) and nanoplastic particles (NP) as persistent anthropogenic pollutants may impact environmental and human health. A relevant potential source of primary MP and NP is water-based dispersion paint which are commonly used in any household. Given the worldwide high application volume of dispersion paint and their diverse material composition MP and NP may enter the environment with unforeseeable consequences. In order to understand the relevance of these MP and NP from paint dispersion we investigated the components of two representative wall paints and analyzed their composition in detail. The different paint components were then investigated for their impact on the model organism Daphnia magna and on a murine cell line. Plastic NP, dissolved polymers, titanium dioxide NPs, and calcium carbonate MPs demonstrated adverse effects in both biological test systems, indicating detrimental consequences of several typical components of wall paints upon release into the environment. The outcome of this study may form the basis for the evaluation of impact on other organisms, environmental transport and impact, other related technical materials and for the development of strategies for the prevention of potential detrimental effects on organisms.

Pristine and artificially-aged polystyrene microplastic particles differ in regard to cellular response.

Microplastic particles (MP), arising from the gradual decomposition of plastics in the environment, have been identified as a global problem. Most investigations of MP cytotoxicity use pristine spherical particles available from commercial sources when evaluating their impact on mammalian cells, while only limited data is available for the more relevant "weathered microplastic". In this study, we exposed murine macrophages to polystyrene MP either after up to 130 days of accelerated ageing or in pristine condition. Weathered and pristine MP were physicochemically characterized, and their cytotoxicity was investigated using biological assays, transcriptome analysis, and metabolic pathways prediction. Whereas the response to pristine MP is mainly dominated by a TNF-α release, sharp-edged weathered MP induce broader adverse cellular reactions. This study stresses the importance of including more realistic test particles (e.g., weathered particles) in combination with a broad range of biological assays when evaluating the potential risk of microplastic exposure.

In vitro cultivation of primary intestinal cells from Eisenia fetida as basis for ecotoxicological studies.

The earthworm Eisenia fetida is a commonly used model organism for unspecific soil feeders in ecotoxicological studies. Its intestinal cells are the first to encounter possible pollutants co-ingested by the earthworm, which makes them prime candidates for studies of toxic effects of environmental pollutants on the cellular as compared to the organismic level. In this context, the aim of this study was to demonstrate the suitability of preparations of primary intestinal E. fetida cells for in vitro ecotoxicological studies. For this purpose, a suitable isolation and cultivation protocol was established. Cells were isolated directly from the intestine, maintaining >85% viability during subsequent cultivations (up to 144 h). Exposure to established pollutants and soil elutriates comprising silver nanoparticles and metal ions (Cu2+, Cd2+) induced a significant decrease in the metabolic activity of the cells. In case of microplastic particles (MP particles), namely 0.2, 0.5, 2.0, and 3.0 µm diameter polystyrene (PS) beads as well as 0.5 and 2.0 µm diameter polylactic acid (PLA) beads, no active uptake was observed. Slight positive as well as negative dose and size dependent effects on the metabolism were seen, which to some extent might correlate with effects on the organismic level.

Noxic effects of polystyrene microparticles on murine macrophages and epithelial cells.

Microplastic (MP) contamination has been identified as an ecological problem with an increasing impact on everyday life. Yet, possible effects of MP at the cellular level are still poorly understood. Here, the interaction of murine macrophages (J774A.1, ImKC) and epithelial cells (STC-1, BNL CL.2) with well-characterized poly(styrene) MP particles (MPP) of varying sizes (0.2-6.0 µm) was studied. Macrophages are expected to actively engulf particles which could be confirmed in this study, while epithelial cells are found in tissues with direct contact with ingested or inhaled MPP. Here, the epithelial cells from both investigated cell lines did not ingest MPP in significant numbers. Concomitantly, no cytotoxic effects nor any influence on cellular proliferation were observed. Cells from the two macrophage cell lines showed high ingestion of MPP of all sizes, but cytotoxic effects were observed only for one of them (ImKC) and only at MPP concentrations above 250 µg/mL. Indications of cellular stress as well as effects on cell proliferation were observed for cell populations with high particle cell interactions.

Generation of Recombinant Primary Human B Lymphocytes Using Non-Viral Vectors.

Although the development of gene delivery systems based on non-viral vectors is advancing, it remains a challenge to deliver plasmid DNA into human blood cells. The current "gold standard", namely linear polyethyleneimine (l-PEI 25 kDa), in particular, is unable to produce transgene expression levels >5% in primary human B lymphocytes. Here, it is demonstrated that a well-defined 24-armed poly(2-dimethylamino) ethyl methacrylate (PDMAEMA, 755 kDa) nano-star is able to reproducibly elicit high transgene expression (40%) at sufficient residual viability (69%) in primary human B cells derived from tonsillar tissue. Moreover, our results indicate that the length of the mitogenic stimulation prior to transfection is an important parameter that must be established during the development of the transfection protocol. In our hands, four days of stimulation with rhCD40L post-thawing led to the best transfection results in terms of TE and cell survival. Most importantly, our data argue for an impact of the B cell subsets on the transfection outcomes, underlining that the complexity and heterogeneity of a given B cell population pre- and post-transfection is a critical parameter to consider in the multiparametric approach required for the implementation of the transfection protocol.

Amphiphilic Graft Copolymers Capable of Mixed-Mode Interaction as Alternative Nonviral Transfection Agents.

Nonviral gene delivery vectors are attractive candidates compared to viral ones due to their lower cytotoxicity and immunogenicity. However, their efficacy still requires improvement. Major challenges are the effective complexation and protection of the DNA cargo and the intracellular dissociation of the polyplexes at the site of action. It is commonly accepted that polymer architecture and chemistry influence polyplex characteristics and have an impact on the transfection mechanism. We developed a library of biocompatible copolymers based on methoxy poly(ethylene glycol) and a hydrophobic block of poly(ε-caprolactone-co-propargyl carbonate) grafted with a predetermined number of poly(2-(dimethylamino)ethyl methacrylate) segments. Such copolymers could efficiently deliver their cargo even in the presence of serum proteins and to various "difficult to transfect" cells, thereby outperforming the current gold standard 25 kDa linear poly(ethylenimine). Statistical correlation analysis shows that an optimization of the transfection in the case of copolymers combining several interactive functions benefits from treatment as a multiparameter problem.

Towards standardized purification of bacterial magnetic nanoparticles for future in vivo applications.

Bacterial magnetosomes (MS) are well-defined membrane-enveloped single-domain iron oxide (magnetite) nanoparticles, which are susceptible to genetic and chemical engineering. Additionally, the possibility to manipulate these particles by external magnetic fields facilitates their application in biomedicine and biotechnology, e.g. as magnetic resonance imaging probes or for drug delivery purposes. However, current purification protocols are poorly characterized, thereby hampering standardized and reproducible magnetosome production and thus, reliable testing for in vivo applications. In that context, the establishment of reproducible particle isolation procedures as well as the identification of high quality control parameters and the evaluation of potential cytotoxic effects of purified particles are of major importance. In this study, we characterize a multi-step purification protocol for MS with regard to purity, iron content, size and polydispersity of magnetite particles. In addition, we address potential cytotoxic effects of isolated MS when incubated with mammalian cells. Overall, we provide a detailed overview of the process-structure relationship during the isolation of MS and thus, identify prerequisites for high-yield MS production and their future application in the biomedical and biotechnological field. STATEMENT OF SIGNIFICANCE: Magnetic nanoparticles are of increasing interest for a variety of biomedical and biotechnological applications. Due to their unprecedented material characteristics, bacterial magnetosomes represent a promising alternative to chemically synthesized iron oxide nanoparticles. As applications require well-defined, highly purified and fully characterized nanoparticles, reliable protocols are necessary for efficient and reproducible magnetosome isolation. In our study, we evaluate an improved magnetosome extraction procedure and monitor quality parameters such as particle size distribution, membrane integrity and purity of the suspension by a combination of physicochemical and biochemical methods. Furthermore, the cytotoxicity of the isolated magnetosomes is assessed using different cell lines. In summary, our study helps to establish prerequisites for many real-world applications of magnetosomes in the field of biotechnology and biomedicine.

An automated oxystat fermentation regime for microoxic cultivation of Magnetospirillum gryphiswaldense.

BACKGROUND: Magnetosomes produced by magnetotactic bacteria represent magnetic nanoparticles with unprecedented characteristics. However, their use in many biotechnological applications has so far been hampered by their challenging bioproduction at larger scales. RESULTS: Here, we developed an oxystat batch fermentation regime for microoxic cultivation of Magnetospirillum gryphiswaldense in a 3 L bioreactor. An automated cascade regulation enabled highly reproducible growth over a wide range of precisely controlled oxygen concentrations (1-95% of air saturation). In addition, consumption of lactate as the carbon source and nitrate as alternative electron acceptor were monitored during cultivation. While nitrate became growth limiting during anaerobic growth, lactate was the growth limiting factor during microoxic cultivation. Analysis of microoxic magnetosome biomineralization by cellular iron content, magnetic response, transmission electron microscopy and small-angle X-ray scattering revealed magnetosomal magnetite crystals were highly uniform in size and shape. CONCLUSION: The fermentation regime established in this study facilitates stable oxygen control during culturing of Magnetospirillum gryphiswaldense. Further scale-up seems feasible by combining the stable oxygen control with feeding strategies employed in previous studies. Results of this study will facilitate the highly reproducible laboratory-scale bioproduction of magnetosomes for a diverse range of future applications in the fields of biotechnology and biomedicine.

Transient Destabilization of Biological Membranes Contributes to the Superior Performance of Star-Shaped PDMAEMA in Delivering pDNA.

Nonviral DNA vectors are promising alternatives to viral ones. Their use in DNA medicine is limited by an inability to transfect, for example, nondividing or suspension cells. In recent years, star-shaped synthetic polycationic vectors, so called "Nanostars", have shown some promise in this regard, at least when compared to the "gold standard" in nonviral vectors, namely, linear poly(ethyleneimine) (l-PEI). It has been hypothesized that an ability to transiently destabilize cellular membranes is partially responsible for the phenomenon. This hypothesis is investigated here, taking human leukemia suspension cells (Jurkat cells) as an example. Contrary to l-PEI, the Nanostars promote the cellular uptake of small, normally membrane-impermeant molecules (trypan blue and propidium iodide) as well as that of fluorescent polystyrene beads (average diameter 100 nm). Since Nanostars, but not l-PEI, are apparently able to deliver DNA to nuclei of nondividing cells, nuclear uptake is, in addition, investigated with isolated cell nuclei. Our results provide evidence that Nanostars are more efficient than l-PEI in increasing the nuclear membrane association/permeability, allowing accumulation of their cargo on/in the nucleus.

Perfusion Cultivation of Artificial Liver Extracellular Matrix in Fibrous Polymer Sponges Biomimicking Scaffolds for Tissue Engineering.

A major challenge in tissue engineering and artificial scaffolding is to combine easily tunable scaffolds biomimicking the extracellular matrix of native organs with delivery-controlled cell culturing to create fully cellularized, large artificial 3D scaffolds. Aiming at bioartificial liver construction, we present our research using galactose-functionalized, ultraporous polylactide 3D nanofiber sponges fabricated out of electrospun fibers. Sponge biomodification by blend galactosylation and in-solution coating is performed, respectively, using a polylactide-galactose carrier-copolymer that promotes cell delivery and features a pronounced autofluorescence. It allows us to verify the galactosylation success, evaluate its quality, and record dye-free, high-resolution images of the sponge network using confocal laser scanning microscopy. The galactose carrier and its impact on scaffold cellularization is validated in benchmark to several reference systems. Verification of the human hepatic cell asialoglycoprotein receptor presence and galactose interaction in culture is performed by Cu2+ receptor-blocking experiments. The culture results are extensively investigated in and ex situ to trace and quantify the cell culture progress, cell activity, and viability at different culture stages. Bioreactor cultivation of sponges reveals that the galactose carrier does not only facilitate cell adhesion but also enhances cellular distribution throughout the scaffold. The promising 3D culture results allow us to move forward to create mature in vitro liver model research systems. The elaboration into ex vivo testing platforms could help judging native cell material interactions with drugs or therapeutics, without the need of direct human or animal testing.

Bacterial Magnetosomes as Novel Platform for the Presentation of Immunostimulatory, Membrane-Bound Ligands in Cellular Biotechnology.

Cell-cell interactions involving specific membrane proteins are critical triggers in cellular development. Ex vivo strategies to mimic these effects currently use soluble proteins or (recombinant) presenter cells, albeit with mixed results. A promising alternative are bacterial magnetosomes, which can be selectively transformed into cell-free membrane-protein presenters by genetic engineering. In this study, the human CD40 Ligand (CD40L), a key ligand for B cell activation, is expressed on the particle surface. Functionality is demonstrated on sensor cells expressing the human CD40 receptor. Binding of CD40L magnetosomes to these cells triggers a signaling cascade leading to the secretion of embryonic alkaline phosphatase. Concomitantly, the CD40-CD40L interaction is strong enough to allow cell recovery by magnetic sorting. Overall, this study demonstrates the potential of magnetosomes as promising cell-free tools for cellular biotechnology, based on the display of membrane-bound target molecules, thereby creating a biomimetic interaction.