Although adhesive interactions between cells and nanostructured interfaces have been studied extensively1–6, there is a paucity of data on how nanostructured interfaces repel cells by directing cell migration and cell-colony organization. Here, by using multiphoton ablation lithography7 to pattern surfaces with nanoscale craters of various aspect ratios and pitches, we show that the surfaces altered the cells’ focal-adhesion size and distribution, thus affecting cell morphology, migration and ultimately localization. We also show that nanocrater pitch can disrupt the formation of mature focal adhesions to favour the migration of cells toward higher-pitched regions, which present increased planar area for the formation of stable focal adhesions. Moreover, by designing surfaces with variable pitch but constant nanocrater dimensions, we were able to create circular and striped cellular patterns. Our surface-patterning approach, which does not involve chemical treatments and can be applied to various materials, represents a simple method to control cell behaviour on surfaces.

Organ-on-a-chip systems possess a promising future as drug screening assays and as testbeds for disease modeling in the context of both single-organ systems and multi-organ-chips. Although it comprises approximately one fourth of the body weight of a healthy human, an organ frequently overlooked in this context is white adipose tissue (WAT). WAT-on-a-chip systems are required to create safety profiles of a large number of drugs due to their interactions with adipose tissue and other organs via paracrine signals, fatty acid release, and drug levels through sequestration. We report a WAT-on-a-chip system with a footprint of less than 1 mm2 consisting of a separate media channel and WAT chamber connected via small micropores. Analogous to the in vivo blood circulation, convective transport is thereby confined to the vasculature-like structures and the tissues protected from shear stresses. Numerical and analytical modeling revealed that the flow rates in the WAT chambers are less than 1/100 of the input flow rate. Using optimized injection parameters, we were able to inject pre-adipocytes, which subsequently formed adipose tissue featuring fully functional lipid metabolism. The physiologically relevant microfluidic environment of the WAT-chip supported long term culture of the functional adipose tissue for more than two weeks. Due to its physiological, highly controlled, and computationally predictable character, the system has the potential to be a powerful tool for the study of adipose tissue associated diseases such as obesity and type 2 diabetes.

Human organ-on-a-chip systems for drug screening have evolved as feasible alternatives to animal models, which are unreliable, expensive, and at times erroneous. While chips featuring single organs can be of great use for both pharmaceutical testing and basic organ-level studies, the huge potential of the organ-on-a-chip technology is revealed by connecting multiple organs on one chip to create a single integrated system for sophisticated fundamental biological studies and devising therapies for disease. Furthermore, since most organ-on-a-chip systems require special protocols with organ-specific media for the differentiation and maturation of the tissues, multi-organ systems will need to be temporally customizable and flexible in terms of the time point of connection of the individual organ units. We present a customizable Lego®-like plug & play system, μOrgano, which enables initial individual culture of single organ-on-a-chip systems and subsequent connection to create integrated multi-organ microphysiological systems. As a proof of concept, the μOrgano system was used to connect multiple heart chips in series with excellent cell viability and spontaneously physiological beat rates.

Soft lithography techniques using polydimethylsiloxane (PDMS) are a cornerstone of microfluidic microdevices and emerging technologies such as microphysiological systems (MPS). Most of these systems employ hydrophobic small molecules during either stem cell differentiation, drug screening, or organoid development. However, due to PDMS's structure and hydrophobicity, lipophilic molecules are strongly absorbed creating unpredictable concentrations of mitogens, drugs, differentiation factors, and analytes, which is a major limitation in its use for biological applications. In this study, several catechol-functionalized calix[4]arene based macrocyclic polyphenols (MPPs) are synthesized and coated on PDMS through a dip-coating or flow through process. One molecule, MPP-5 cone , synthesized from catechol and resorcinol in its cone isomer form, increases the hydrophilicity of PDMS and drastically reduces the absorption of a number of hydrophobic drug surrogates, while preserving high oxygen permeability, good cell viability and function. However, simple rules of molecular absorption based on Log P are not observed, suggesting screening barrier coatings for PDMS with single probes is not sufficient. The coating procedure is easily translated to microfluidic devices by infusion through channels with a pump, and therefore should find use in applications where molecular absorption into PDMS is a significant problem.

The musculo-skeletal system comprises a variety of both hard and soft tissue types (bone, cartilage, tendon, ligament), generative cell types (osteoblasts, chondrocytes, tenocytes, fibroblasts, all of which can derive from multipotent mesenchymal stem cell precursors), and fibrous connective-tissue proteins (chiefly collagen, types I and III) that are susceptible to varying degrees of mineralization. In the case of bone, mineralization is extensive and forms a bicontinuous composite of mineral (chiefly carbonated hydroxyapatite and precursors) and self-assembling proteins (mostly type I collagen). The important connections between tissue types are mostly hard-tissue/soft-tissue interfaces, which may involve gradients in mineralization and cell type or cell morphologies. Medical intervention in cases of orthopaedic injury-such as joint replacement, ligament replacement, or reattachment of detached tendon-invariably involves recruiting natural tissue repair processes at these interfaces, in order to affix original hard tissue (bone) to hard implants (e.g replacement femoral heads and acetabular cups for hip joint replacement, replacement condyles and tibial trays for knee joint replacement); to affix replacement soft tissue (e.g. autologous or allograft ligament or substitute autologous tendon for repair of ruptured anterior cruciate ligament in knee joints) to original hard tissue (condylar and tibial bone); or to re-affix original soft tissue (e.g. tendon) to original hard tissue (e.g. scapular bone in rotator-cuff injuries) when rupture of the original interface occurs.Electron microscopies are extending the understanding of these crucial interfaces-their microstructures and ultrastructures, their formation routes and recruitment for repair-beyond that provided by traditional light-microscope-based histology. Bone-Implant IntegrationThe most studied interface re-establishment is that between bone and an orthopaedic implant made of metal (e.g. Ti-Al-V, Co-Cr alloys) or ceramic (alumina, zirconia), usually (but not always [1]) coated with an osteoconductive coating (usually hydroxyapatite (HA) [2] deposited by plasma spraying or electrodeposition [3]). The first stage in the integration of original bone and implant is essentially the same process as occurs during bone remodeling [2], which is the formation of mineralized precursor protein ribbon-like bundles (Fig. 1a) originating from osteoblasts anchored within several micrometers of the (coated) implant surface. This initial stage of developing a mineralized extracellular matrix in the gap between bone and implant occurs within three days following implantation (at least in canine and ovine in vitro models), before widespread expression of collagen, and the crystalline mineral involved does not appear to be hydroxyapatite but a lower Ca/P ratio calcium phosphate. Only later (~10 days) does the usual (Fig. 1b) mineralization morphology of staggered hydroxyapatite platelets decorating self-assembled collagen bundles [2] characteristic of mature bone appear. Analog...