Transdermal wires for improved integration in vivo.

Alternative engineering approaches have led the design of implants with controlled physical features to minimize adverse effects in biological tissues. Similar efforts have focused on optimizing the design features of percutaneous VAD drivelines with the aim to prevent infection, omitting however a thorough look on the implant-skin interactions that govern local tissue reactions. Here, we utilized an integrated approach for the biophysical modification of transdermal implants and their evaluation by chronic sheep implantation in comparison to the standard of care VAD drivelines. We developed a novel method for the transfer of breath topographical features on thin wires with modular size. We examined the impact of implant's diameter, surface topography, and chemistry on macroscopic, histological, and physical markers of inflammation, fibrosis, and mechanical adhesion. All implants demonstrated infection-free performance. The fibrotic response was enhanced by the increasing diameter of implants but not influenced by their surface properties. The implants of small diameter promoted mild inflammatory responses with improved mechanical adhesion and restricted epidermal downgrowth, in both silicone and polyurethane coated transdermal wires. On the contrary, the VAD drivelines with larger diameter triggered severe inflammatory reactions with frequent epidermal downgrowth. We validated these effects by quantifying the infiltration of macrophages and the level of vascularization in the fibrotic zone, highlighting the critical role of size reduction for the benign integration of transdermal implants with skin. This insight on how the biophysical properties of implants impact local tissue reactions could enable new solutions on the transdermal transmission of power, signal, and mass in a broad range of medical devices.

Control of hydrostatic pressure and osmotic stress in 3D cell culture for mechanobiological studies.

Hydrostatic pressure (HP) and osmotic stress (OS) play an important role in various biological processes, such as cell proliferation and differentiation. In contrast to canonical mechanical signals transmitted through the anchoring points of the cells with the extracellular matrix, the physical and molecular mechanisms that transduce HP and OS into cellular functions remain elusive. Three-dimensional cell cultures show great promise to replicate physiologically relevant signals in well-defined host bioreactors with the goal of shedding light on hidden aspects of the mechanobiology of HP and OS. This review starts by introducing prevalent mechanisms for the generation of HP and OS signals in biological tissues that are subject to pathophysiological mechanical loading. We then revisit various mechanisms in the mechanotransduction of HP and OS, and describe the current state of the art in bioreactors and biomaterials for the control of the corresponding physical signals.

Building an interdisciplinary program of cardiovascular research at the Swiss Federal Institute of Technology- the ETHeart story.

In this backstory, researchers from Swiss Federal Institute of Technology (ETH Zurich) who initiated an interdisciplinary program to generate innovative solutions for different cardiovascular diseases, such as myocardial infarction, valvular replacement, and movement-based rehabilitation therapy, discuss the benefits and challenges of interdisciplinary research.

Systems of conductive skin for power transfer in clinical applications.

The primary aim of this article is to review the clinical challenges related to the supply of power in implanted left ventricular assist devices (LVADs) by means of transcutaneous drivelines. In effect of that, we present the preventive measures and post-operative protocols that are regularly employed to address the leading problem of driveline infections. Due to the lack of reliable wireless solutions for power transfer in LVADs, the development of new driveline configurations remains at the forefront of different strategies that aim to power LVADs in a less destructive manner. To this end, skin damage and breach formation around transcutaneous LVAD drivelines represent key challenges before improving the current standard of care. For this reason, we assess recent strategies on the surface functionalization of LVAD drivelines, which aim to limit the incidence of driveline infection by directing the responses of the skin tissue. Moreover, we propose a class of power transfer systems that could leverage the ability of skin tissue to effectively heal short diameter wounds. In this direction, we employed a novel method to generate thin conductive wires of controllable surface topography with the potential to minimize skin disruption and eliminate the problem of driveline infections. Our initial results suggest the viability of the small diameter wires for the investigation of new power transfer systems for LVADs. Overall, this review uniquely compiles a diverse number of topics with the aim to instigate new research ventures on the design of power transfer systems for IMDs, and specifically LVADs.

Matrix degradation and cell proliferation are coupled to promote invasion and escape from an engineered human breast microtumor.

Metastasis, the leading cause of mortality in cancer patients, depends upon the ability of cancer cells to invade into the extracellular matrix that surrounds the primary tumor and to escape into the vasculature. To investigate the features of the microenvironment that regulate invasion and escape, we generated solid microtumors of MDA-MB-231 human breast carcinoma cells within gels of type I collagen. The microtumors were formed at defined distances adjacent to an empty cavity, which served as an artificial vessel into which the constituent tumor cells could escape. To define the relative contributions of matrix degradation and cell proliferation on invasion and escape, we used pharmacological approaches to block the activity of matrix metalloproteinases (MMPs) or to arrest the cell cycle. We found that blocking MMP activity prevents both invasion and escape of the breast cancer cells. Surprisingly, blocking proliferation increases the rate of invasion but has no effect on that of escape. We found that arresting the cell cycle increases the expression of MMPs, consistent with the increased rate of invasion. To gain additional insight into the role of cell proliferation in the invasion process, we generated microtumors from cells that express the fluorescent ubiquitination-based cell cycle indicator. We found that the cells that initiate invasions are preferentially quiescent, whereas cell proliferation is associated with the extension of invasions. These data suggest that matrix degradation and cell proliferation are coupled during the invasion and escape of human breast cancer cells and highlight the critical role of matrix proteolysis in governing tumor phenotype.

Integration of Hydrogel Microparticles With Three-Dimensional Liver Progenitor Cell Spheroids.

The study of the liver progenitor cell microenvironment has demonstrated the important roles of both biochemical and biomechanical signals in regulating the progenitor cell functions that underlie liver morphogenesis and regeneration. While controllable two-dimensional in vitro culture systems have provided key insights into the effects of growth factors and extracellular matrix composition and mechanics on liver differentiation, it remains unclear how microenvironmental signals may differentially affect liver progenitor cell responses in a three-dimensional (3D) culture context. In addition, there have only been limited efforts to engineer 3D culture models of liver progenitor cells through the tunable presentation of microenvironmental stimuli. We present an in vitro model of 3D liver progenitor spheroidal cultures with integrated polyethylene glycol hydrogel microparticles for the internal presentation of modular microenvironmental cues and the examination of the combinatorial effects with an exogenous soluble factor. In particular, treatment with the growth factor TGFß1 directs differentiation of the spheroidal liver progenitor cells toward a biliary phenotype, a behavior which is further enhanced in the presence of hydrogel microparticles. We further demonstrate that surface modification of the hydrogel microparticles with heparin influences the behavior of liver progenitor cells toward biliary differentiation. Taken together, this liver progenitor cell culture system represents an approach for controlling the presentation of microenvironmental cues internalized within 3D spheroidal aggregate cultures. Overall, this strategy could be applied toward the engineering of instructive microenvironments that control stem and progenitor cell differentiation within a 3D context for studies in tissue engineering, drug testing, and cellular metabolism.

Modeling branching morphogenesis using materials with programmable mechanical instabilities.

The architectural features of branching morphogenesis demonstrate exquisite reproducibility among various organs and species despite the unique functionality and biochemical differences of their microenvironment. The regulatory networks that drive branching morphogenesis employ cell-generated and passive mechanical forces, which integrate extracellular signals from the microenvironment into morphogenetic movements. Cell-generated forces function locally to remodel the extracellular matrix (ECM) and control interactions among neighboring cells. Passive mechanical forces are the product of in situ mechanical instabilities that trigger out-of-plane buckling and clefting deformations of adjacent tissues. Many of the molecular and physical signals that underlie buckling and clefting morphogenesis remain unclear and require new experimental strategies to be uncovered. Here, we highlight soft material systems that have been engineered to display programmable buckles and creases. Using synthetic materials to model physicochemical and spatiotemporal features of buckling and clefting morphogenesis might facilitate our understanding of the physical mechanisms that drive branching morphogenesis across different organs and species.

A High-throughput Cell Microarray Platform for Correlative Analysis of Cell Differentiation and Traction Forces.

Microfabricated cellular microarrays, which consist of contact-printed combinations of biomolecules on an elastic hydrogel surface, provide a tightly controlled, high-throughput engineered system for measuring the impact of arrayed biochemical signals on cell differentiation. Recent efforts using cell microarrays have demonstrated their utility for combinatorial studies in which many microenvironmental factors are presented in parallel. However, these efforts have focused primarily on investigating the effects of biochemical cues on cell responses. Here, we present a cell microarray platform with tunable material properties for evaluating both cell differentiation by immunofluorescence and biomechanical cell-substrate interactions by traction force microscopy. To do so, we have developed two different formats utilizing polyacrylamide hydrogels of varying Young's modulus fabricated on either microscope slides or glass-bottom Petri dishes. We provide best practices and troubleshooting for the fabrication of microarrays on these hydrogel substrates, the subsequent cell culture on microarrays, and the acquisition of data. This platform is well-suited for use in investigations of biological processes for which both biochemical (e.g., extracellular matrix composition) and biophysical (e.g., substrate stiffness) cues may play significant, intersecting roles.

Substrate stiffness and matrix composition coordinately control the differentiation of liver progenitor cells.

Recent approaches have utilized microfabricated platforms to examine combinations of microenvironmental signals that regulate stem and progenitor cell differentiation. However, the majority of these efforts have focused on the biochemical properties of extracellular matrix (ECM) or soluble factors without simultaneously exploring the biomechanical effects of cell-substrate interactions. To address this need, we combined a high-throughput approach for the analysis of combinatorial ECM cues with substrates of modular stiffness and traction force microscopy. This integrated approach enabled the characterization of cell-generated traction stress and phenotypic expression in response to ECM cues. We investigated the impact of substrate stiffness and ECM composition on the differentiation of bipotential mouse embryonic liver (BMEL) progenitor cells. We observed that hepatocyte differentiation was primarily regulated by ECM composition, and cholangiocyte differentiation was cooperatively influenced by ECM proteins and stiffness properties. In particular, stiffness-mediated cholangiocyte differentiation was observed for cells cultured on fibronectin, while collagen IV promoted differentiation independent of substrate stiffness. We demonstrated the influence of cell contractility and traction stress in early cholangiocyte specification and further uncovered the roles of ERK and ROCK in this differentiation process. Overall, these findings illustrate the involvement of biomechanical signals in liver progenitor differentiation. Further, this approach could enable investigations for a broad range of cell types and ECM proteins, providing an integrated platform for evaluating the combinatorial effects of biochemical and biophysical signals in cell differentiation.

Cell adhesion mechanisms on laterally mobile polymer films.

In contrast with the majority of substrates used to study cell adhesion, the natural extracellular matrix (ECM) is dynamic and remodeled over time. Here we use amphiphilic block copolymers to create self-assembled supported films with tunable lateral mobility. These films are intended to serve as partial mimics of the ECM in order to better understand cell adhesion responses, specifically in the context of dynamic substrates. Block copolymers are end-labeled with RGD peptide ligands to allow for integrin-mediated cell adhesion, and the addition of a trace hydrophobic homopolymer is used to control the film lateral mobility. We find that NIH 3T3 fibroblasts cultured on these biomimetic films exhibit non-linear spreading behavior in response to substrate mobility. In the absence of RGD ligands, however, fibroblasts do not spread. Employing quantitative analysis of focal adhesions (FA) and integrin ligation, we discover the presence of FA-dependent and FA-independent mechanisms responsible for the biphasic cell spreading behavior. The use of designed biomimetic platforms therefore yields insight into ECM mechanosensing by revealing that cells can engage distinct mechanisms to promote adhesion onto substrates with different time-dependent properties.