Cellular micromasonry: biofabrication with single cell precision

A functional human liver tissue model: 3D bioprinted co-culture discoids

To reduce costs and delays related to developing new and effective drugs, there is a critical need for improved human liver tissue models. Here we describe an approach for 3D bioprinting functional human liver tissue models, in which we fabricate disc-shaped structures (discoids) 200 μm in thickness and 1-3 mm in diameter from mixtures of cells and collagen-1, embedded in a highly permeable support medium made from packed polyethylene glycol (PEG) microgels. We demonstrate that the method is precise, accurate, and scalable; up to 100 tissues/h can be manufactured with a variability and error in diameter of about 4 %. Histologic and immunohistochemical evaluation of printed discs reveal self-organization, cell cohesion, and key liver marker expression. Over the course of three weeks in culture, the tissues stably synthesize albumin and urea at high levels, outperforming spheroid tissue models. We find the tissues express >100 genes associated with molecular absorption, distribution, metabolism, and excretion (ADME) at levels within the range of human liver. The liver tissue models exhibit enzymatic formation of metabolites after exposure to multiple test compounds. Together, these results demonstrate the promise of 3D printed discoids for pharmacological and toxicological applications.

Progress in the mechanical properties of nanoparticles for tumor-targeting delivery

Cancer nanomedicines have attracted significant attention in the past several decades, and the physicochemical properties, such as the size, shape, composition, surface charge, hydrophobicity, and mechanical properties, of nanoparticles have been optimized for potent cancer therapy. Since publishing our 2020 tutorial review "Influence of nanomedicine mechanical properties on tumor targeting delivery" in Chemical Society Reviews, substantial advancements have been made in understanding the role of mechanical properties in cancer nanomedicine. Notably, in vivo transport processes that are dependent on the mechanical properties of nanomedicine, including long circulation, tumor accumulation, and deep penetration, have been extensively studied using various nano-drug delivery systems. These studies have demonstrated that leveraging these mechanical properties can significantly enhance the antitumor efficacy of nanomedicine. In this review, we categorize the advancements in the mechanical properties of cancer nanomedicine into three distinct themes: the interactions between nanoparticles with varied mechanical properties and cells (2002 - present), the impact of these properties on in vivo delivery processes (2007 - present), and the strategic use of mechanical properties to boost cancer therapy (2023 - present). We analyze how different mechanical properties of organic, inorganic, hybrid, and biological nanoparticles affect their delivery processes at the macroscopic level, i.e., in tissues, organs and cells. At the microscopic level, their biological and physical interactions with biological barriers, physiological structures, cell membranes, organelles, and other structures reveal the potential mechanism of nanoparticles' mechanical properties in determining their antitumor efficacy. Furthermore, we address the current challenges and future prospects in the mechanical properties of cancer nanomedicine, as well as the clinical translation potential of nanoparticles with diverse mechanical characteristics.

Controlling Cell Interactions with DNA Directed Assembly

The creation of complex cellular environments is critical to mimicking tissue environments that will play a critical role in next-generation tissue engineering, stem cell programming, and therapeutic screening. To address this growing need, techniques capable of manipulating cell-cell and cell-material interactions are required that span single-cell to 3D tissue architectures. DNA programmed assembly and placement of cells present a powerful technique for the bottom-up synthesis of living microtissues for probing key questions in cell-cell and cell-material-driven behaviors through its refined control over placement and architecture. This review examines the current state of the art in the programming of cellular interactions with DNA and its applications spanning tissue model building, fundamental cellular biology, and cell manipulation for measurements across a host of applications.

Determining Rates of Molecular Secretion from Supernatant Concentration Measurements in a 3D-Bioprinted Human Liver Tissue Model

The secretion rate of albumin is a key indicator of function in liver tissue models used for hepatotoxicity and pharmacokinetic testing. However, it is not generally clear how to determine molecular secretion rates from measurements of the molecular concentration in supernatant media. Here, we develop computational and analytical models of molecular transport in an experimental system that enable determination of albumin secretion rates based on measurements of albumin concentration in supernatant media. The experimental system is a 3D-bioprinted human liver tissue construct embedded in a 3D culture environment made from packed microgel particles swollen in liquid growth media. The mathematical models reveal that the range of albumin synthesis rates necessary to match experimentally measured albumin concentrations corresponds to reaction-limited conditions, where a steady state of albumin spatial distribution is rapidly reached between media exchanges. Our results show that temporally resolved synthesis rates can be inferred from serial concentration measurements of collected supernatant media. This link is critical to confidently assessing in vitro tissue performance in applications where critical quality attributes must be quantified, like in drug development and screening.

Design approaches for 3D cell culture and 3D bioprinting platforms

The natural habitat of most cells consists of complex and disordered 3D microenvironments with spatiotemporally dynamic material properties. However, prevalent methods of in vitro culture study cells under poorly biomimetic 2D confinement or homogeneous conditions that often neglect critical topographical cues and mechanical stimuli. It has also become increasingly apparent that cells in a 3D conformation exhibit dramatically altered morphological and phenotypical states. In response, efforts toward designing biomaterial platforms for 3D cell culture have taken centerstage over the past few decades. Herein, we present a broad overview of biomaterials for 3D cell culture and 3D bioprinting, spanning both monolithic and granular systems. We first critically evaluate conventional monolithic hydrogel networks, with an emphasis on specific experimental requirements. Building on this, we document the recent emergence of microgel-based 3D growth media as a promising biomaterial platform enabling interrogation of cells within porous and granular scaffolds. We also explore how jammed microgel systems have been leveraged to spatially design and manipulate cellular structures using 3D bioprinting. The advent of these techniques heralds an unprecedented ability to experimentally model complex physiological niches, with important implications for tissue bioengineering and biomedical applications.

Towards single-cell bioprinting: micropatterning tools for organ-on-chip development

Organs-on-chips (OoCs) hold promise to engineer progressively more human-relevant in vitro models for pharmaceutical purposes. Recent developments have delivered increasingly sophisticated designs, yet OoCs still lack in reproducing the inner tissue physiology required to fully resemble the native human body. This review emphasizes the need to include microarchitectural and microstructural features, and discusses promising avenues to incorporate well-defined microarchitectures down to the single-cell level. We highlight how their integration will significantly contribute to the advancement of the field towards highly organized structural and hierarchical tissues-on-chip. We discuss the combination of state-of-the-art micropatterning technologies to achieve OoCs resembling human-intrinsic complexity. It is anticipated that these innovations will yield significant advances in realization of the next generation of OoC models.

Direct Fabrication of Glycoengineered Cells via Photoresponsive Thiol-ene Reaction

Three-dimensional printing of cell constructs with high-cell density, shape fidelity, and heterogeneous cell populations is an important tool for investigating cell sociology in living tissues but remains challenging. Herein, we propose an artificial intercellular adhesion method using a photoresponsive chemical cue between a thiol-bearing polymer and a methacrylate-bearing cell membrane. This process provided cell fabrication containing 108 cells/mL, embedded multiple cell populations in one structure, and enabled millimeter-sized scaleup. Our approach allows for the artificial cell construction of complex structures and is a promising bioprinting strategy for engineering tissues that are structurally and physiologically relevant.

Microelectronic Morphogenesis: Smart Materials with Electronics Assembling into Artificial Organisms

Microelectronic morphogenesis is the creation and maintenance of complex functional structures by microelectronic information within shape-changing materials. Only recently has in-built information technology begun to be used to reshape materials and their functions in three dimensions to form smart microdevices and microrobots. Electronic information that controls morphology is inheritable like its biological counterpart, genetic information, and is set to open new vistas of technology leading to artificial organisms when coupled with modular design and self-assembly that can make reversible microscopic electrical connections. Three core capabilities of cells in organisms, self-maintenance (homeostatic metabolism utilizing free energy), self-containment (distinguishing self from nonself), and self-reproduction (cell division with inherited properties), once well out of reach for technology, are now within the grasp of information-directed materials. Construction-aware electronics can be used to proof-read and initiate game-changing error correction in microelectronic self-assembly. Furthermore, noncontact communication and electronically supported learning enable one to implement guided self-assembly and enhance functionality. Here, the fundamental breakthroughs that have opened the pathway to this prospective path are reviewed, the extent and way in which the core properties of life can be addressed are analyzed, and the potential and indeed necessity of such technology for sustainable high technology in society is discussed.