Multimaterial 3D Laser Printing of Cell-Adhesive and Cell-Repellent Hydrogels

Here, a straightforward method is reported for manufacturing 3D microstructured cell-adhesive and cell-repellent multimaterials using two-photon laser printing. Compared to existing strategies, this approach offers bottom-up molecular control, high customizability, and rapid and precise 3D fabrication. The printable cell-adhesive polyethylene glycol (PEG) based material includes an Arg-Gly-Asp (RGD) containing peptide synthesized through solid-phase peptide synthesis, allowing for precise control of the peptide design. Remarkably, minimal amounts of RGD peptide (< 0.1 wt%) suffice for imparting cell-adhesiveness, while maintaining identical mechanical properties in the 3D printed microstructures to those of the cell-repellent, PEG-based material. Fluorescent labeling of the RGD peptide facilitates visualization of its presence in cell-adhesive areas. To demonstrate the broad applicability of the system, the fabrication of cell-adhesive 2.5D and 3D structures is shown, fostering the adhesion of fibroblast cells within these architectures. Thus, this approach allows for the printing of high-resolution, true 3D structures suitable for diverse applications, including cellular studies in complex environments.

Microarchitected Compliant Scaffolds of Pyrolytic Carbon for 3D Muscle Cell Growth

The integration of additive manufacturing technologies with the pyrolysis of polymeric precursors enables the design-controlled fabrication of architected 3D pyrolytic carbon (PyC) structures with complex architectural details. Despite great promise, their use in cellular interaction remains unexplored. This study pioneers the utilization of microarchitected 3D PyC structures as biocompatible scaffolds for the colonization of muscle cells in a 3D environment. PyC scaffolds are fabricated using micro-stereolithography, followed by pyrolysis. Furthermore, an innovative design strategy using revolute joints is employed to obtain novel, compliant structures of architected PyC. The pyrolysis process results in a pyrolysis temperature- and design-geometry-dependent shrinkage of up to 73%, enabling the geometrical features of microarchitected compatible with skeletal muscle cells. The stiffness of architected PyC varies with the pyrolysis temperature, with the highest value of 29.57 ± 0.78 GPa for 900 °C. The PyC scaffolds exhibit excellent biocompatibility and yield 3D cell colonization while culturing skeletal muscle C2C12 cells. They further induce good actin fiber alignment along the compliant PyC construction. However, no conclusive myogenic differentiation is observed here. Nevertheless, these results are highly promising for architected PyC scaffolds as multifunctional tissue implants and encourage more investigations in employing compliant architected PyC structures for high-performance tissue engineering applications.

Multiple neuronal populations control the eating behavior in Hydra and are responsive to microbial signals

Although recent studies indicate the impact of microbes on the central nervous systems and behavior, it remains unclear how the relationship between the functionality of the nervous system, behavior, and the microbiota evolved. In this work, we analyzed the eating behavior of Hydra, a host that has a simple nervous system and a low-complexity microbiota. To identify the neuronal subpopulations involved, we used a subpopulation-specific cell ablation system and calcium imaging. The role of the microbiota was uncovered by manipulating the diversity of the natural microbiota. We show that different neuronal subpopulations are functioning together to control eating behavior. Animals with a drastically reduced microbiome had severe difficulties in mouth opening due to a significantly increased level of glutamate. This could be reversed by adding a full complement of the microbiota. In summary, we provide a mechanistic explanation of how Hydra's nervous system controls eating behavior and what role microbes play in this.

Tetrapodal ZnO-Based Composite Stents for Minimally Invasive Glaucoma Surgery

The glaucoma burden increases continuously and is estimated to affect more than 100 million people by 2040. As there is currently no cure to restore the optic nerve damage caused by glaucoma, the only controllable parameter is the intraocular pressure (IOP). In recent years, minimally invasive glaucoma surgery (MIGS) has emerged as an alternative to traditional treatments. It uses micro-sized drainage stents that are inserted through a small incision, minimizing the trauma to the tissue and reducing surgical and postoperative recovery time. However, a major challenge for MIGS devices is foreign body reaction and fibrosis, which can lead to a complete failure of the device. In this work, the antifibrotic potential of tetrapodal ZnO (t-ZnO) microparticles used as an additive is elucidated by using rat embryonic fibroblasts as a model. A simple, direct solvent-free process for the fabrication of stents with an outer diameter of 200-400 μm is presented, in which a high amount of t-ZnO particles (45-75 wt %) is mixed into polydimethylsiloxane (PDMS) and a highly viscous polymer/particle mixture is extruded. The fabricated stents possess increased elastic modulus compared to pure PDMS while remaining flexible to adapt to the curvature of an eye. In vitro experiments showed that the fibroblast cell viability was inhibited to 43 ± 3% when stents with 75 wt % t-ZnO were used. The results indicate that cell inhibiting properties can be attributed to an increased amount of protruding t-ZnO particles on the stent surface, leading to an increase in local contacts with cells and a disruption of the cell membrane. As a secondary mechanism, the released Zn ions could also contribute to the cell-inhibiting properties in the close vicinity of the stent surface. Overall, the fabrication method and the antifibrotic and mechanical properties of developed stents make them promising for application in MIGS.

Extracting, quantifying, and comparing dynamical and biomechanical properties of living matter through single particle tracking

A panoply of new tools for tracking single particles and molecules has led to an explosion of experimental data, leading to novel insights into physical properties of living matter governing cellular development and function, health and disease. In this Perspective, we present tools to investigate the dynamics and mechanics of living systems from the molecular to cellular scale via single-particle techniques. In particular, we focus on methods to measure, interpret, and analyse complex data sets that are associated with forces, materials properties, transport, and emergent organisation phenomena within biological and soft-matter systems. Current approaches, challenges, and existing solutions in the associated fields are outlined in order to support the growing community of researchers at the interface of physics and the life sciences. Each section focuses not only on the general physical principles and the potential for understanding living matter, but also on details of practical data extraction and analysis, discussing limitations, interpretation, and comparison across different experimental realisations and theoretical frameworks. Particularly relevant results are introduced as examples. While this Perspective describes living matter from a physical perspective, highlighting experimental and theoretical physics techniques relevant for such systems, it is also meant to serve as a solid starting point for researchers in the life sciences interested in the implementation of biophysical methods.

A Co-Polymerizable Linker for the Covalent Attachment of Fibronectin Makes pHEMA Hydrogels Cell-Adhesive

Hydrogels are attractive biomaterials because their chemical and mechanical properties can be tailored to mimic those of biological tissues. However, many hydrogels do not allow cell or protein attachment. Therefore, they are post-synthetically functionalized by adding functional groups for protein binding, which then allows cell adhesion in cell culture substrates. However, the degree of functionalization and covalent binding is difficult to analyze in these cases. Moreover, the density of the functional groups and the homogeneity of their distribution is hard to control. This work introduces another strategy for the biofunctionalization of hydrogels: we synthesized a polymerizable linker that serves as a direct junction between the polymeric structure and cell adhesion proteins. This maleimide-containing, polymerizable bio-linker was copolymerized with non-functionalized monomers to produce a bioactive hydrogel based on poly(2-hydroxyethyl methacrylate) (pHEMA). Therefore, the attachment site was only controlled by the polymerization process and was thus uniformly distributed throughout the hydrogel. In this way, the bio-conjugation by a protein-binding thiol-maleimide Michael-type reaction was possible in the entire hydrogel matrix. This approach enabled a straightforward and highly effective biofunctionalization of pHEMA with the adhesion protein fibronectin. The bioactivity of the materials was demonstrated by the successful adhesion of fibroblast cells.

Cellular properties of human gingival fibroblasts on novel and conventional implant-abutment materials

OBJECTIVES

To characterize human-gingival-fibroblast-(HGFs) viability, proliferation and adhesion on polymer-infiltrated-ceramic-network-(PICN), polyetheretherketone-(PEEK), hydroxyapatite-reinforced-polyetheretherketone-(HA-PEEK), polyetherketoneketone-(PEKK), as well as conventional titanium-(Ti) and zirconia ceramic-(Zr) implant materials in-vitro.

METHODS

Six materials (n = 40/group, 240 specimens) were standardized for surface roughness, assessed employing water contact angle measurements (WCA) and loaded with HGFs. HGF viability and proliferation were assessed at 24 and 72 h. Cell adhesion strength was evaluated after 24 h exposure to lateral shear forces using a shaking-device at 320 and 560-rpm.and qualitatively tested by scanning-electron-microscopy-(SEM) at 3, 24 and 72 h.

RESULTS

PICN demonstrated the lowest mean WCA (48.2 ± 6.3º), followed by Zr (73.8 ± 5.1º), while HA-PEEK showed the highest WCA (87.2 ± 1.5º; p ≤ 0.05). After 24 h, Zr showed the highest mean HGFs-viability rate (88 ± 14%), while PEKK showed the lowest one (78 ± 7%). At 72 h, Zr continued to show the highest HGF-viability (80 ± 6%) compared to PEKK (67.5 ± 6%) and PEEK (67%±5). SEM did not reveal differences between different materials with respect to cell attachment at 3, 24 or 72 h. At 320 rpm shaking, HGFs showed to be best attached to PICN (mean%-of-detached-cells ± SD; 26 ± 11%) and worst to PEEK (54 ± 18%). At 560 rpm shaking, Zr showed the least detached cells (32 ± 4%), while HA-PEEK revealed the highest number of detached cells (58 ± 3%; ANOVA/Tukey-post-hoc-test, differences not statistically significant).

SIGNIFICANCE

Dental implant abutment materials and their wettability strongly affect HGF proliferation and adhesion properties. Although, PICN showed the best wettability properties, Zr exhibited the strongest adhesion strength at high shaking. Within the current study's limitations, Zr remains the most biocompatible abutment material.

Tunable 3D Hydrogel Microchannel Networks to Study Confined Mammalian Cell Migration

Cells adapt and move due to chemical, physical, and mechanical cues from their microenvironment. It is therefore important to create materials that mimic human tissue physiology by surface chemistry, architecture, and dimensionality to control cells in biomedical settings. The impact of the environmental architecture is particularly relevant in the context of cancer cell metastasis, where cells migrate through small constrictions in their microenvironment to invade surrounding tissues. Here, a synthetic hydrogel scaffold with an interconnected, random, 3D microchannel network is presented that is functionalized with collagen to promote cell adhesion. It is shown that cancer cells can invade such scaffolds within days, and both the microarchitecture and stiffness of the hydrogel modulate cell invasion and nuclear dynamics of the cells. Specifically, it is found that cell migration through the microchannels is a function of hydrogel stiffness. In addition to this, it is shown that the hydrogel stiffness and confinement, influence the occurrence of nuclear envelope ruptures of cells. The tunable hydrogel microarchitecture and stiffness thus provide a novel tool to investigate cancer cell invasion as a function of the 3D microenvironment. Furthermore, the material provides a promising strategy to control cell positioning, migration, and cellular function in biological applications, such as tissue engineering.

Microengineered Hollow Graphene Tube Systems Generate Conductive Hydrogels with Extremely Low Filler Concentration

The fabrication of electrically conductive hydrogels is challenging as the introduction of an electrically conductive filler often changes mechanical hydrogel matrix properties. Here, we present an approach for the preparation of hydrogel composites with outstanding electrical conductivity at extremely low filler loadings (0.34 S m-1, 0.16 vol %). Exfoliated graphene and polyacrylamide are microengineered to 3D composites such that conductive graphene pathways pervade the hydrogel matrix similar to an artificial nervous system. This makes it possible to combine both the exceptional conductivity of exfoliated graphene and the adaptable mechanical properties of polyacrylamide. The demonstrated approach is highly versatile regarding porosity, filler material, as well as hydrogel system. The important difference to other approaches is that we keep the original properties of the matrix, while ensuring conductivity through graphene-coated microchannels. This novel approach of generating conductive hydrogels is very promising, with particular applications in the fields of bioelectronics and biohybrid robotics.

Microfabricated bioelectrodes on self-expandable NiTi thin film devices for implants and diagnostic instruments

State of the art minimally invasive treatments and diagnostics of neurological and cardiovascular diseases demand for flexible instruments and implants that enable sensing and stimulation of bioelectric signals. Besides medical applications, implantable bioelectronic brain-computer interfaces are envisioned as the next step in communication and data transfer. Conventional microelectrode arrays used for these types of applications are based on polymer substrates that are not suitable for biostable, rigid and self-expanding devices. Here, we present fully integrated bioelectrodes on superelastic NiTi carriers fabricated by microsystem technology processes. The insulation between the metallic NiTi structure and the Pt electrode layer is realized by different oxide layers (SiO_x, TaO_x and Yttrium stabilized Zirconia YSZ). Key properties of bioelectronic implants such as dissolution in body fluids, biocompatibility, mechanical properties and bioelectrical sensing/stimulation capabilities have been investigated by in vitro methods. Particular devices with YSZ are biostable and biocompatible, enabling sensing and stimulation. The major advantage of this system is the combination of medically approved materials and novel fabrication technology that enables miniaturization and integration beyond the state-of-the-art processes. The results demonstrate that this functionalization of superelastic NiTi is an enabling technology for the development of new kinds of bioelectronic devices.

Migration of Microparticle-Containing Amoeba through Constricted Environments

In many situations, cells migrate through tiny orifices. Examples include the extravasation of immune cells from the bloodstream for fighting infections, the infiltration of cancer cells during metastasis, and the migration of human pathogens. An extremely motile and medically relevant type of human pathogen is Acanthamoeba castellanii. In the study presented here, we investigated how a combination of microparticles and microstructured interfaces controls the migration of A. castellanii trophozoites. The microinterfaces comprised well-defined micropillar arrays, and the trophozoites easily migrated through the given constrictions by adapting the shape and size of their intracellular vacuoles and by adapting intracellular motion. After feeding the trophozoite cells in microinterfaces with synthetic, stiff microparticles of various sizes and shapes, their behavior changed drastically: if the particles were smaller than the micropillar gap, migration was still possible. If the cells incorporated particles larger than the pillar gap, they could become immobilized but could also display remarkable problem-solving capabilities. For example, they turned rod-shaped microparticles such that their short axis fit through the pillar gap or they transported the particles above the structure. As migration is a crucial contribution to A. castellanii pathogenicity and is also relevant to other biological processes in microenvironments, such as cancer metastasis, our results provide an interesting strategy for controlling the migration of cells containing intracellular particles by microstructured interfaces that serve as migration-limiting environments.

Living Materials Herald a New Era in Soft Robotics

Living beings have an unsurpassed range of ways to manipulate objects and interact with them. They can make autonomous decisions and can heal themselves. So far, a conventional robot cannot mimic this complexity even remotely. Classical robots are often used to help with lifting and gripping and thus to alleviate the effects of menial tasks. Sensors can render robots responsive, and artificial intelligence aims at enabling autonomous responses. Inanimate soft robots are a step in this direction, but it will only be in combination with living systems that full complexity will be achievable. The field of biohybrid soft robotics provides entirely new concepts to address current challenges, for example the ability to self-heal, enable a soft touch, or to show situational versatility. Therefore, "living materials" are at the heart of this review. Similarly to biological taxonomy, there is a recent effort for taxonomy of biohybrid soft robotics. Here, an expansion is proposed to take into account not only function and origin of biohybrid soft robotic components, but also the materials. This materials taxonomy key demonstrates visually that materials science will drive the development of the field of soft biohybrid robotics.

Automated analysis of soft hydrogel microindentation: Impact of various indentation parameters on the measurement of Young's modulus

Measurements of Young's moduli are mostly evaluated using strong assumptions, such as sample homogeneity and isotropy. At the same time, descriptions of measurement parameters often lack detailed specifications. Many of these assumptions are, for soft hydrogels especially, not completely valid and the complexity of hydrogel microindentation demands more sophisticated experimental procedures in order to describe their elastic properties more accurately. We created an algorithm that automates indentation data analysis as a basis for the evaluation of large data sets with consideration of the influence of indentation depth on the measured Young's modulus. The algorithm automatically determines the Young's modulus in indentation regions where it becomes independent of the indentation depth and furthermore minimizes the error from fitting an elastic model to the data. This approach is independent of the chosen elastic fitting model and indentation device. With this, we are able to evaluate large amounts of indentation curves recorded on many different sample positions and can therefore apply statistical methods to overcome deviations due to sample inhomogeneities. To prove the applicability of our algorithm, we carried out a systematic analysis of how the indentation speed, indenter size and sample thickness affect the determination of Young's modulus from atomic force microscope (AFM) indentation curves on polyacrylamide (PAAm) samples. We chose the Hertz model as the elastic fitting model for this proof of principle of our algorithm and found that all of these parameters influence the measured Young's moduli to a certain extent. Hence, it is essential to clearly state the experimental parameters used in microindentation experiments to ensure reproducibility and comparability of data.

Systematically Designed Periodic Electrophoretic Deposition for Decorating 3D Carbon-Based Scaffolds with Bioactive Nanoparticles

The coating of porous scaffolds with nanoparticles is crucial in many applications, for example to generate scaffolds for catalysis or to make scaffolds bioactive. A standard and well-established method for coating surfaces with charged nanoparticles is electrophoresis, but when used on porous scaffolds, this method often leads to a blockage of the pores so that only the outermost layers of the scaffolds are coated. In this study, the electrophoretic coating process is monitored in situ and the kinetics of nanoparticle deposition are investigated. This concept can be extended to design a periodic electrophoretic deposition (PEPD) strategy, thus avoiding the typical blockage of surface pores. In the present work we demonstrate successful and homogeneous electrophoretic deposition of hydroxyapatite nanoparticles (HAn, diameter ≤200 nm) on a fibrous graphitic 3D structure (ultralightweight aerographite) using the PEPD strategy. The microfilaments of the resulting scaffold are covered with HAn both internally and on the surface. Furthermore, protein adsorption assays and cell proliferation assays were carried out and revealed that the HAn-decorated aerographite scaffolds are biocompatible. The HAn decoration of the scaffolds also significantly increases the alkaline phosphatase activity of osteoblast cells, showing that the scaffolds are able to promote their osteoblastic activity.

Biomimetic Carbon Fiber Systems Engineering: A Modular Design Strategy To Generate Biofunctional Composites from Graphene and Carbon Nanofibers

Carbon-based fibrous scaffolds are highly attractive for all biomaterial applications that require electrical conductivity. It is additionally advantageous if such materials resembled the structural and biochemical features of the natural extracellular environment. Here, we show a novel modular design strategy to engineer biomimetic carbon fiber-based scaffolds. Highly porous ceramic zinc oxide (ZnO) microstructures serve as three-dimensional (3D) sacrificial templates and are infiltrated with carbon nanotubes (CNTs) or graphene dispersions. Once the CNTs and graphene coat the ZnO template, the ZnO is either removed by hydrolysis or converted into carbon by chemical vapor deposition. The resulting 3D carbon scaffolds are both hierarchically ordered and free-standing. The properties of the microfibrous scaffolds were tailored with a high porosity (up to 93%), a high Young's modulus (ca. 0.027-22 MPa), and an electrical conductivity of ca. 0.1-330 S/m, as well as different surface compositions. Cell viability, fibroblast proliferation rate and protein adsorption rate assays have shown that the generated scaffolds are biocompatible and have a high protein adsorption capacity (up to 77.32 ± 6.95 mg/cm3) so that they are able to resemble the extracellular matrix not only structurally but also biochemically. The scaffolds also allow for the successful growth and adhesion of fibroblast cells, showing that we provide a novel, highly scalable modular design strategy to generate biocompatible carbon fiber systems that mimic the extracellular matrix with the additional feature of conductivity.

3D Hydrogels Containing Interconnected Microchannels of Subcellular Size for Capturing Human Pathogenic Acanthamoeba Castellanii

Porous hydrogel scaffolds are ideal candidates for mimicking cellular microenvironments, regarding both structural and mechanical aspects. We present a novel strategy to use uniquely designed ceramic networks as templates for generating hydrogels with a network of interconnected pores in the form of microchannels. The advantages of this new approach are the high and guaranteed interconnectivity of the microchannels, as well as the possibility to produce channels with diameters smaller than 7 μm. Neither of these assets can be ensured with other established techniques. Experiments using the polyacrylamide substrates produced with our approach have shown that the migration of human pathogenic Acanthamoeba castellanii trophozoites is manipulated by the microchannel structure in the hydrogels. The parasites can even be captured inside the microchannel network and removed from their incubation medium by the porous polyacrylamide, indicating the huge potential of our new technique for medical, pharmaceutical, and tissue engineering applications.

Bioactive Carbon-Based Hybrid 3D Scaffolds for Osteoblast Growth

Bone, nerve, and heart tissue engineering place high demands on the conductivity of three-dimensional (3D) scaffolds. Fibrous carbon-based scaffolds are excellent material candidates to fulfill these requirements. Here, we show that highly porous (up to 94%) hybrid 3D framework structures with hierarchical architecture, consisting of microfiber composites of self-entangled carbon nanotubes (CNTs) and bioactive nanoparticles are highly suitable for growing cells. The hybrid 3D structures are fabricated by infiltrating a combination of CNTs and bioactive materials into a porous (∼94%) zinc oxide (ZnO) sacrificial template, followed by the removal of the ZnO backbone via a H2 thermal reduction process. Simultaneously, the bioactive nanoparticles are sintered. In this way, conductive and mechanically stable 3D composites of free-standing CNT-based microfibers and bioactive nanoparticles are formed. The adopted strategy demonstrates great potential for implementing low-dimensional bioactive materials, such as hydroxyapatite (HA) and bioactive glass nanoparticles (BGN), into 3D carbon-based microfibrous networks. It is demonstrated that the incorporation of HA nanoparticles and BGN promotes the biomineralization ability and the protein adsorption capacity of the scaffolds significantly, as well as fibroblast and osteoblast adhesion. These results demonstrate that the developed carbon-based bioactive scaffolds are promising materials for bone tissue engineering and related applications.

High-throughput micro-nanostructuring by microdroplet inkjet printing

The production of micrometer-sized structures comprised of nanoparticles in defined patterns and densities is highly important in many fields, ranging from nano-optics to biosensor technologies and biomaterials. A well-established method to fabricate quasi-hexagonal patterns of metal nanoparticles is block copolymer micelle nanolithography, which relies on the self-assembly of metal-loaded micelles on surfaces by a dip-coating or spin-coating process. Using this method, the spacing of the nanoparticles is controlled by the size of the micelles and by the coating conditions. Whereas block copolymer micelle nanolithography is a high-throughput method for generating well-ordered nanoparticle patterns at the nanoscale, so far it has been inefficient in generating a hierarchical overlay structure at the micrometer scale. Here, we show that by combining block copolymer micelle nanolithography with inkjet printing, hierarchical patterns of gold nanoparticles in the form of microstructures can be achieved in a high-throughput process. Inkjet printing was used to generate droplets of the micelle solution on surfaces, resulting in printed circles that contain patterns of gold nanoparticles with an interparticle spacing between 25 and 42 nm. We tested this method on different silicon and nickel-titanium surfaces and the generated patterns were found to depend on the material type and surface topography. Based on the presented strategy, we were able to achieve patterning times of a few seconds and produce quasi-hexagonal micro-nanopatterns of gold nanoparticles on smooth surfaces. Hence, this method is a high-throughput method that can be used to coat surfaces with nanoparticles in a user-defined pattern at the micrometer scale. As the nanoparticles provide a chemical contrast on the surface, they can be further functionalized and are therefore highly relevant for biological applications.

Adhesion forces and mechanics in mannose-mediated acanthamoeba interactions

The human pathogenic amoeba Acanthamoeba castellanii (A. castellanii) causes severe diseases, including acanthamoeba keratitis and encephalitis. Pathogenicity arises from the killing of target-cells by an extracellular killing mechanism, where the crucial first step is the formation of a close contact between A. castellanii and the target-cell. This process is mediated by the glycocalix of the target-cell and mannose has been identified as key mediator. The aim of the present study was to carry out a detailed biophysical investigation of mannose-mediated adhesion of A. castellanii using force spectroscopy on single trophozoites. In detail, we studied the interaction of a mannose-coated cantilever with an A. castellanii trophozoite, as mannose is the decisive part of the cellular glycocalix in mediating pathogenicity. We observed a clear increase of the force to initiate cantilever detachment from the trophozoite with increasing contact time. This increase is also associated with an increase in the work of detachment. Furthermore, we also analyzed single rupture events during the detachment process and found that single rupture processes are associated with membrane tether formation, suggesting that the cytoskeleton is not involved in mannose binding events during the first few seconds of contact. Our study provides an experimental and conceptual basis for measuring interactions between pathogens and target-cells at different levels of complexity and as a function of interaction time, thus leading to new insights into the biophysical mechanisms of parasite pathogenicity.

Adhesion of living cells to abutment materials, dentin, and adhesive luting cement with different surface qualities

OBJECTIVE

We tested the adhesion properties of living gingival fibroblasts on three different implant abutment materials, adhesive resin used to bond bi-partite abutments, and human dentin.

METHODS

Discs of lithium disilicate (LS), zirconium dioxide (Zr), adhesive resin cement (AR), titanium (Ti), and human dentin (HD) were fabricated with three different levels of surface roughness (rough, machined, and polished). Ra and Rz, water contact angle, and cell detachment forces were measured. Cell detachment force was measured for single cells using single-cell force spectroscopy. Data were statistically analyzed using parametric tests (ANOVA, MANOVA, Bonferroni post-hoc tests).

RESULTS

Surface roughness significantly influenced the water contact angle for all materials (P≤0.05). Overall, HD showed the lowest contact angle, followed by LS, Ti, Zr, and AR (P≤0.05). Comparison of cell detachment forces between materials with rough and machined surfaces revealed no significant differences (P>0.05), with the exception of Zr compared to HD with rough surfaces (P=0.006). For polished surfaces, HD showed the highest detachment force (P≤0.0001), followed by Ti, AR, and Zr, which did not significantly differ from each other (P>0.05) and LS; Ti/AR was significantly different from LS (P≤0.05). Except for HD, where polished surfaces exhibited the highest cell detachment force (P≤0.002), most machined surfaces showed higher cell detachment forces than polished or rough surfaces.

SIGNIFICANCE

Implant abutments should ideally be provided with a machined like surface roughness for best cell adhesion.

A Tunable Scaffold of Microtubular Graphite for 3D Cell Growth

Aerographite (AG) is a novel carbon-based material that exists as a self-supportive 3D network of interconnected hollow microtubules. It can be synthesized in a variety of architectures tailored by the growth conditions. This flexibility in creating structures presents interesting bioengineering possibilities such as the generation of an artificial extracellular matrix. Here we have explored the feasibility and potential of AG as a scaffold for 3D cell growth employing cyclic RGD (cRGD) peptides coupled to poly(ethylene glycol) (PEG) conjugated phospholipids for surface functionalization to promote specific adhesion of fibroblast cells. Successful growth and invasion of the bulk material was followed over a period of 4 days.

Rapid Reversible Photoswitching of Integrin-Mediated Adhesion at the Single-Cell Level

Rapid and reversible photoswitching of cell adhesion is achieved by c(RGDfK)-azobenzenes embedded in a poly(ethylene glycol) background on surfaces. The light-induced cis-trans-isomerization of the azobenzene enables switching of cell adhesion on the surface. Reversibility of switching over several consecutive switching cycles is demonstrated by single-cell force spectroscopy.

Cell adhesion on NiTi thin film sputter-deposited meshes

Scaffolds for tissue engineering enable the possibility to fabricate and form biomedical implants in vitro, which fulfill special functionality in vivo. In this study, free-standing Nickel–Titanium(NiTi) thin film mesheswere produced by means of magnetron sputter deposition.Meshes contained precisely defined rhombic holes in the size of 440 to 1309 μm2 and a strut width ranging from 5.3 to 9.2 μm. The effective mechanical properties of the microstructured superelastic NiTi thin film were examined by tensile testing. These results will be adapted for the design of the holes in the film. The influence of hole and strut dimensions on the adhesion of sheep autologous cells (CD133+) was studied after 24 h and after seven days of incubation. Optical analysis using fluorescence microscopy and scanning electron microscopy showed that cell adhesion depends on the structural parameters of the mesh. After 7 days in cell culture a large part of the mesh was covered with aligned fibrous material. Cell adhesion is particularly facilitated on meshes with small rhombic holes of 440 μm2 and a strut width of 5.3 μm. Our results demonstrate that free-standing NiTi thin film meshes have a promising potential for applicationsin cardiovascular tissue engineering, particularly for the fabrication of heart valves.

Handheld imaging photonic crystal biosensor for multiplexed, label-free protein detection

We present a handheld biosensor system for the label-free and specific multiplexed detection of several biomarkers employing a spectrometer-free imaging measurement system. A photonic crystal surface functionalized with multiple specific ligands forms the optical transducer. The photonic crystal slab is fabricated on a glass substrate by replicating a periodic grating master stamp with a period of 370 nm into a photoresist via nanoimprint lithography and deposition of a 70-nm titanium dioxide layer. Capture molecules are coupled covalently and drop-wise to the photonic crystal surface. With a simple camera and imaging optics the surface-normal transmission is detected. In the transmission spectrum guided-mode resonances are observed that shift due to protein binding. This shift is observed as an intensity change in the green color channel of the camera. Non-functionalized image sections are used for continuous elimination of background drift. In a first experiment we demonstrate the specific and time-resolved detection of 90.0 nm CD40 ligand antibody, 90.0 nM EGF antibody, and 500 nM streptavidin in parallel on one sensor chip. In a second experiment, aptamers with two different spacer lengths are used as receptor. The binding kinetics with association and dissociation of 250 nM thrombin and regeneration of the sensor surface with acidic tris-HCl-buffer (pH 5.0) is presented for two measurement cycles.

Cardiomyocyte behavior on biodegradable polyurethane/gold nanocomposite scaffolds under electrical stimulation

Following a myocardial infarction (MI), cardiomyocytes are replaced by scar tissue, which decreases ventricular contractile function. Tissue engineering is a promising approach to regenerate such damaged cardiomyocyte tissue. Engineered cardiac patches can be fabricated by seeding a high density of cardiac cells onto a synthetic or natural porous polymer. In this study, nanocomposite scaffolds made of gold nanotubes/nanowires incorporated into biodegradable castor oil-based polyurethane were employed to make micro-porous scaffolds. H9C2 cardiomyocyte cells were cultured on the scaffolds for one day, and electrical stimulation was applied to improve cell communication and interaction in neighboring pores. Cells on scaffolds were examined by fluorescence microscopy and scanning electron microscopy, revealing that the combination of scaffold design and electrical stimulation significantly increased cell confluency of H9C2 cells on the scaffolds. Furthermore, we showed that the gene expression levels of Nkx2.5, atrial natriuretic peptide (ANF) and natriuretic peptide precursor B (NPPB), which are functional genes of the myocardium, were up-regulated by the incorporation of gold nanotubes/nanowires into the polyurethane scaffolds, in particular after electrical stimulation.

Controlled Self-Assembly of Hexagonal Nanoparticle Patterns on Nanotopographies

Diblock copolymer micelle nanolithography (BCML) is a versatile and efficient method to cover large surface areas with hexagonally ordered arrays of metal nanoparticles, in which the nanoparticles are equally spaced. However, this method falls short of providing a controlled allocation of such regular nanoparticle arrays with specific spacing into micropatterns. We present here a quick and high-throughput method to generate quasi-hexagonal nanoparticle structures with well-defined interparticle spacing on segments of nanotopographic Si substrates. The topographic height of these segments plays a dominant role in dictating the spacing between the gold nanoparticles, as the nanoparticle arrangement is controlled by immersion forces and by their self-assembly within the segments. Our novel strategy of employing a single-step BCML routine is a highly promising method for the fabrication of regular gold nanopatterns in micropatterns for a wide range of applications.

Superdiffusion dominates intracellular particle motion in the supercrowded cytoplasm of pathogenic Acanthamoeba castellanii

Acanthamoebae are free-living protists and human pathogens, whose cellular functions and pathogenicity strongly depend on the transport of intracellular vesicles and granules through the cytosol. Using high-speed live cell imaging in combination with single-particle tracking analysis, we show here that the motion of endogenous intracellular particles in the size range from a few hundred nanometers to several micrometers in Acanthamoeba castellanii is strongly superdiffusive and influenced by cell locomotion, cytoskeletal elements, and myosin II. We demonstrate that cell locomotion significantly contributes to intracellular particle motion, but is clearly not the only origin of superdiffusivity. By analyzing the contribution of microtubules, actin, and myosin II motors we show that myosin II is a major driving force of intracellular motion in A. castellanii. The cytoplasm of A. castellanii is supercrowded with intracellular vesicles and granules, such that significant intracellular motion can only be achieved by actively driven motion, while purely thermally driven diffusion is negligible.

Influence of the PDMS substrate stiffness on the adhesion of Acanthamoeba castellanii

BACKGROUND

Mechanosensing of cells, particularly the cellular response to substrates with different elastic properties, has been discovered in recent years, but almost exclusively in mammalian cells. Much less attention has been paid to mechanosensing in other cell systems, such as in eukaryotic human pathogens.

RESULTS

We report here on the influence of substrate stiffness on the adhesion of the human pathogen Acanthamoebae castellanii (A. castellanii). By comparing the cell adhesion area of A. castellanii trophozoites on polydimethylsiloxane (PDMS) substrates with different Young's moduli (4 kPa, 29 kPa, and 128 kPa), we find significant differences in cell adhesion area as a function of substrate stiffness. In particular, the cell adhesion area of A. castellanii increases with a decreasing Young's modulus of the substrate.

CONCLUSION

The dependence of A. castellanii adhesion on the elastic properties of the substrate is the first study suggesting a mechanosensory effect for a eukaryotic human pathogen. Interestingly, the main targets of A. castellanii infections in the human body are the eye and the brain, i.e., very soft environments. Thus, our study provides first hints towards the relevance of mechanical aspects for the pathogenicity of eukaryotic parasites.

In vitro adhesion of Acanthamoeba castellanii to soft contact lenses depends on water content and disinfection procedure

PURPOSE

To compare the potential of different soft contact lenses to be contaminated with Acanthamoeba castellanii as a function of material parameters and cleaning procedures.

METHODS

Different unworn soft hydrogel and silicone hydrogel contact lenses were incubated with human pathogenic A. castellanii. The adhesion of the acanthamoebae was investigated on the contact lenses and put into relation to their material parameters. The efficacy of a recommended contact lens cleaning procedure in reducing A. castellanii adhesion was investigated.

RESULTS

We found that material parameters such as elastic modulus, silicone content, ionic properties and swelling do not influence the adhesion of acanthamoebae to soft contact lenses. A material parameter that influenced adhesion significantly was the water content of the lens. With increasing water content, the adhesion of acanthamoebae increased. By following the cleaning instructions of the manufacturer the contamination of the lenses with A. castellanii could be reduced to a minimum, as shown both on contact lenses and in control experiments.

CONCLUSION

With this study we show that for the tested lenses, the adhesion of A. castellanii to contact lenses is independent of the silicone content of the lens, but depends nonlinearly on the water content of the lens. Furthermore, we demonstrate that applying proper lens cleaning procedures minimizes the risk of acanthamoebae adhesion to contact lenses.

Photonic crystal slabs for surface contrast enhancement in microscopy of transparent objects

In optical microscopy the contrast of transparent objects achieved with conventional methods is often not satisfactory, for example for the automated recognition of cells. In this paper we present a nano-optical label-free approach for contrast enhancement based on photonic crystal slabs (PCS) as the specimen holder. Quasi-guided modes inside these structures cause an intrinsic color of the PCS, which strongly depends on the wavelength and the quality factor of the optical mode. Objects on the surface of the PCS experience a significant color and intensity contrast enhancement, as they change properties of the optical modes.

Arachidonic acid randomizes endothelial cell motion and regulates adhesion and migration

Cell adhesion and migration are essential for the evolution, organization, and repair of living organisms. An example of a combination of these processes is the formation of new blood vessels (angiogenesis), which is mediated by a directed migration and adhesion of endothelial cells (ECs). Angiogenesis is an essential part of wound healing and a prerequisite of cancerous tumor growth. We investigated the effect of the amphiphilic compound arachidonic acid (AA) on EC adhesion and migration by combining live cell imaging with biophysical analysis methods. AA significantly influenced both EC adhesion and migration, in either a stimulating or inhibiting fashion depending on AA concentration. The temporal evolution of cell adhesion area was well described by a two-phase model. In the first phase, the spreading dynamics were independent of AA concentration. In the latter phase, the spreading dynamics increased at low AA concentrations and decreased at high AA concentrations. AA also affected EC migration; though the instantaneous speed of individual cells remained independent of AA concentration, the individual cells lost their sense of direction upon addition of AA, thus giving rise to an overall decrease in the collective motion of a confluent EC monolayer into vacant space. Addition of AA also caused ECs to become more elongated, this possibly being related to incorporation of AA in the EC membrane thus mediating a change in the viscosity of the membrane. Hence, AA is a promising non-receptor specific regulator of wound healing and angiogenesis.

Impact of local versus global ligand density on cellular adhesion

α(v)β(3) integrin-mediated cell adhesion is crucially influenced by how far ligands are spaced apart. To evaluate the impact of local ligand density versus global ligand density of a given surface, we used synthetic micronanostructured cell environments with user-defined ligand spacing and patterns to investigate cellular adhesion. The development of stable focal adhesions, their number, and size as well as the cellular adhesion strength proved to be influenced by local more than global ligand density.

In vivo anomalous diffusion and weak ergodicity breaking of lipid granules

Combining extensive single particle tracking microscopy data of endogenous lipid granules in living fission yeast cells with analytical results we show evidence for anomalous diffusion and weak ergodicity breaking. Namely we demonstrate that at short times the granules perform subdiffusion according to the laws of continuous time random walk theory. The associated violation of ergodicity leads to a characteristic turnover between two scaling regimes of the time averaged mean squared displacement. At longer times the granule motion is consistent with fractional Brownian motion.

Measuring cell adhesion forces: theory and principles

Cell adhesion is an essential prerequisite for survival, communication, and navigation of cells in organisms. It is maintained by the organized binding of molecules from the cell membrane to the extracellular space. This chapter focuses on direct measurements of cellular binding strength at the level of single adhesion molecules. Using atomic force microscopy-based force measurements, adhesion strength can be monitored as a function of adhesion time and environmental conditions. In this way, cellular adhesion strategies like changes in affinity and avidity of adhesion molecules (e.g., integrins) are characterized as well as the molecular arrangement of adhesion molecules in the cell membrane (e.g., molecular clusters, focal adhesion spots, and linkage to the cytoskeleton or tether). Some prominent values for the data evaluation are presented as well as constraints and preparative techniques for successful cell adhesion force experiments.

Quantitative analysis of single particle trajectories: mean maximal excursion method

An increasing number of experimental studies employ single particle tracking to probe the physical environment in complex systems. We here propose and discuss what we believe are new methods to analyze the time series of the particle traces, in particular, for subdiffusion phenomena. We discuss the statistical properties of mean maximal excursions (MMEs), i.e., the maximal distance covered by a test particle up to time t. Compared to traditional methods focusing on the mean-squared displacement we show that the MME analysis performs better in the determination of the anomalous diffusion exponent. We also demonstrate that combination of regular moments with moments of the MME method provides additional criteria to determine the exact physical nature of the underlying stochastic subdiffusion processes. We put the methods to test using experimental data as well as simulated time series from different models for normal and anomalous dynamics such as diffusion on fractals, continuous time random walks, and fractional Brownian motion.

Cell adhesion strength is controlled by intermolecular spacing of adhesion receptors

Spatial patterning of biochemical cues on the micro- and nanometer scale controls numerous cellular processes such as spreading, adhesion, migration, and proliferation. Using force microscopy we show that the lateral spacing of individual integrin receptor-ligand bonds determines the strength of cell adhesion. For spacings > or = 90 nm, focal contact formation was inhibited and the detachment forces as well as the stiffness of the cell body were significantly decreased compared to spacings < or = 50 nm. Analyzing cell detachment at the subcellular level revealed that rupture forces of focal contacts increase with loading rate as predicted by a theoretical model for adhesion clusters. Furthermore, we show that the weak link between the intra- and extracellular space is at the intracellular side of a focal contact. Our results show that cells can amplify small differences in adhesive cues to large differences in cell adhesion strength.

Quantitative optical trapping of single gold nanorods

We report a quantitative analysis of the forces acting on optically trapped single gold nanorods. Individual nanorods with diameters between 8 and 44 nm and aspect ratios between 1.7 and 5.6 were stably trapped in three dimensions using a laser wavelength exceeding their plasmon resonance wavelengths. The interaction between the electromagnetic field of an optical trap and a single gold nanorod correlated with particle polarizability, which is a function of both particle volume and aspect ratio.