Designing Inherently Photodegradable Cell-Adhesive Hydrogels for 3D Cell Culture

A Thermo-responsive collapse system for controlling heterogeneous cell localization, ratio and interaction for three-dimensional solid tumor modeling

Cancer immunotherapy using engineered cytotoxic effector cells has demonstrated significant potential. The limited spatial complexity of existing in vitro models, however, poses a challenge to mechanistic studies attempting to approve existing approaches of effector cell-mediated cytotoxicity within a three-dimensional, solid tumor-like environment. To gain additional experimental control, we developed an approach for constructing three-dimensional (3D) culture models using smart polymers that form temperature responsive hydrogels. By embedding cells in these hydrogels, we constructed 3D models to organize multiple cell populations at specified ratios on-demand and gently position them by exploiting the hydrogel phase transition. These systems were amenable to imaging at low- and high-resolution to evaluate cell-to-cell interactions, as well as to dissociation to allow for single cell analyses. We have called this approach "thermal collapse of strata" (TheCOS) and demonstrated its use in creating complex cell assemblies on demand in both layers and spheroids. As an application, we utilized TheCOS to evaluate the impact of directionality of degranulation of natural killer (NK) cell lytic granules. Blocking lytic granule convergence and polarization by inhibiting dynein has been shown to induce bystander killing in single cell suspensions. Using TheCOS we showed that lytic granule dispersion induced by dynein inhibition can be sustained in 3D and results in a multi-directional killing including that of non-triggering bystander cells. By imaging TheCOS experiments, we were able to map a "kill zone" associated with multi-directional degranulation in simulated solid tumor environments. TheCOS should allow for the testing of approaches to alter the mechanics of cytotoxicity as well as to generate a wide-array of human tumor microenvironments to assist in the acceleration of tumor immunotherapy.

Photoresponsive Hydrogels for Tissue Engineering

Hydrophilic and biocompatible hydrogels are widely applied as ideal scaffolds in tissue engineering. The "smart" gelation material can alter its structural, physiochemical, and functional features in answer to various endo/exogenous stimuli to better biomimic the endogenous extracellular matrix for the engineering of cells and tissues. Light irradiation owns a high spatial-temporal resolution, complete biorthogonal reactivity, and fine-tunability and can thus induce physiochemical reactions within the matrix of photoresponsive hydrogels with good precision, efficiency, and safety. Both gel structure (e.g., geometry, porosity, and dimension) and performance (like conductivity and thermogenic or mechanical properties) can hence be programmed on-demand to yield the biochemical and biophysical signals regulating the morphology, growth, motility, and phenotype of engineered cells and tissues. Here we summarize the strategies and mechanisms for encoding light-reactivity into a hydrogel and demonstrate how fantastically such responsive gels change their structure and properties with light irradiation as desired and thus improve their applications in tissue engineering including cargo delivery, dynamic three-dimensional cell culture, and tissue repair and regeneration, aiming to provide a basis for more and better translation of photoresponsive hydrogels in the clinic.

Evaluation of gelatin-based hydrogels for colon and pancreas studies using 3D in vitro cell culture

Biomimetic 3D models emerged some decades ago to address 2D cell culture limitations in the field of replicating biological phenomena, structures or functions found in nature. The fabrication of hydrogels for cancer disease research enables the study of cell processes including growth, proliferation and migration and their 3D design is based on the encapsulation of tumoral cells within a tunable matrix. In this work, a platform of gelatin methacrylamide (GelMA)-based photocrosslinked scaffolds with embedded colorectal (HCT-116) or pancreatic (MIA PaCa-2) cancer cells is presented. Prior to cell culture, the mechanical characterization of hydrogels was assessed in terms of stiffness and swelling behavior. Modifications of the UV curing time enabled a fine tuning of the mechanical properties, which at the same time, showed susceptibility to the chemical composition and crosslinking mechanism. All scaffolds displayed excellent cytocompatibility with both tumoral cells while eliciting various cell responses depending on the microenvironment features. Individual and collective cell migration were observed for HCT-116 and MIA PaCa-2 cell lines, highlighting the ability of the colorectal cancer cells to cluster into aggregates of different sizes governed by the surrounding matrix. Additionally, metabolic activity results pointed out to the development of a more proliferative phenotype within stiffer networks. These findings confirm the suitability of the presented platform of GelMA-based hydrogels to conduct 3D cell culture experiments and explore biological processes associated with colorectal and pancreatic cancer.

Photo-Controllable Smart Hydrogels for Biomedical Application: A Review

Nowadays, smart hydrogels are being widely studied by researchers because of their advantages such as simple preparation, stable performance, response to external stimuli, and easy control of response behavior. Photo-controllable smart hydrogels (PCHs) are a class of responsive hydrogels whose physical and chemical properties can be changed when stimulated by light at specific wavelengths. Since the light source is safe, clean, simple to operate, and easy to control, PCHs have broad application prospects in the biomedical field. Therefore, this review timely summarizes the latest progress in the PCHs field, with an emphasis on the design principles of typical PCHs and their multiple biomedical applications in tissue regeneration, tumor therapy, antibacterial therapy, diseases diagnosis and monitoring, etc. Meanwhile, the challenges and perspectives of widespread practical implementation of PCHs are presented in biomedical applications. This study hopes that PCHs will flourish in the biomedical field and this review will provide useful information for interested researchers.

Stimuli-Responsive Hydrogels: The Dynamic Smart Biomaterials of Tomorrow

In the past decade, stimuli-responsive hydrogels are increasingly studied as biomaterials for tissue engineering and regenerative medicine purposes. Smart hydrogels can not only replicate the physicochemical properties of the extracellular matrix but also mimic dynamic processes that are crucial for the regulation of cell behavior. Dynamic changes can be influenced by the hydrogel itself (isotropic vs anisotropic) or guided by applying localized triggers. The resulting swelling-shrinking, shape-morphing, as well as patterns have been shown to influence cell function in a spatiotemporally controlled manner. Furthermore, the use of stimuli-responsive hydrogels as bioinks in 4D bioprinting is very promising as they allow the biofabrication of complex microstructures. This perspective discusses recent cutting-edge advances as well as current challenges in the field of smart biomaterials for tissue engineering. Additionally, emerging trends and potential future directions are addressed.

Recent advances in defined hydrogels in organoid research

Organoids are in vitro model systems that mimic the complexity of organs with multicellular structures and functions, which provide great potential for biomedical and tissue engineering. However, their current formation heavily relies on using complex animal-derived extracellular matrices (ECM), such as Matrigel. These matrices are often poorly defined in chemical components and exhibit limited tunability and reproducibility. Recently, the biochemical and biophysical properties of defined hydrogels can be precisely tuned, offering broader opportunities to support the development and maturation of organoids. In this review, the fundamental properties of ECM in vivo and critical strategies to design matrices for organoid culture are summarized. Two typically defined hydrogels derived from natural and synthetic polymers for their applicability to improve organoids formation are presented. The representative applications of incorporating organoids into defined hydrogels are highlighted. Finally, some challenges and future perspectives are also discussed in developing defined hydrogels and advanced technologies toward supporting organoid research.

High-Throughput Synthesis and Machine Learning Assisted Design of Photodegradable Hydrogels

Due to the large chemical space, the design of functional and responsive soft materials poses many challenges but also offers a wide range of opportunities in terms of the scope of possible properties. Herein, an experimental workflow for miniaturized combinatorial high-throughput screening of functional hydrogel libraries is reported. The data created from the analysis of the photodegradation process of more than 900 different types of hydrogel pads are used to train a machine learning model for automated decision making. Through iterative model optimization based on Bayesian optimization, a substantial improvement in response properties is achieved and thus expanded the scope of material properties obtainable within the chemical space of hydrogels in the study. It is therefore demonstrated that the potential of combining miniaturized high-throughput experiments with smart optimization algorithms for cost and time efficient optimization of materials properties.

Drug Sensitivity Testing for Cancer Therapy, Key Areas

AIMS

Cancer is a high-mortality disease (9.6 million deaths in 2018 worldwide). Given various anticancer drugs, drug selection plays a key role in patient survival in clinical trials.

METHODS

Drug Sensitivity Testing (DST), one of the leading drug selective systems, was widely practiced for therapeutic promotion in the clinic. Notably, DSTs assist in drug selection that benefits drug responses against cancer from 20-22% to 30-35% over the past two decades. The relationship between drug resistance in vitro and drug treatment benefits was associated with different tumor origins and subtypes. Medical theory and underlying DST mechanisms remain poorly understood until now. The study of the clinical scenario, sustainability and financial support for mechanism and technical promotions is indispensable.

RESULTS

Despite the great technical advance, therapeutic prediction and drug selection by DST needs to be miniature, versatility and cost-effective in the clinic. Multi-parameters and automation of DST should be a future trend. Advanced biomedical knowledge and clinical approaches to translating oncologic profiles into drug selection were the main focuses of DST developments. With a great technical stride, the clinical architecture of the DST platform was entering higher levels (drug response testing at any stage of cancer patients and miniaturization of tumor samples).

DISCUSSION

The cancer biology and pharmacology for drug selection mutually benefit the clinic. New proposals to reveal more therapeutic information and drug response prediction at genetic, molecular and omics levels should be estimated overall.

CONCLUSION

By upholding this goal of non-invasive, versatility and automation, DST could save the life of several thousand annually worldwide. In this article, new insights into DST novelty and development are highlighted.

How to build a tumor: An industry perspective

During the past 15 years, a plethora of innovative 3D in vitro systems has been developed. They offer the possibility of identifying crucial cellular and molecular contributors to the disease by permitting manipulation of each in isolation. However, improvements are needed particularly with respect to the predictivity and validity of those models. The major challenge now is to identify which assay and readout combination(s) best suits the current scientific question(s). A deep understanding of the different platforms along with their pros and cons is a prerequisite to make this decision. This review aims to give an overview of the most prominent systems with a focus on applications, translational relevance and adoption drivers from an industry perspective.

Integrins, cadherins and channels in cartilage mechanotransduction: perspectives for future regeneration strategies

Articular cartilage consists of hyaline cartilage, is a major constituent of the human musculoskeletal system and has critical functions in frictionless joint movement and articular homoeostasis. Osteoarthritis (OA) is an inflammatory disease of articular cartilage, which promotes joint degeneration. Although it affects millions of people, there are no satisfying therapies that address this disease at the molecular level. Therefore, tissue regeneration approaches aim at modifying chondrocyte biology to mitigate the consequences of OA. This requires appropriate biochemical and biophysical stimulation of cells. Regarding the latter, mechanotransduction of chondrocytes and their precursor cells has become increasingly important over the last few decades. Mechanotransduction is the transformation of external biophysical stimuli into intracellular biochemical signals, involving sensor molecules at the cell surface and intracellular signalling molecules, so-called mechano-sensors and -transducers. These signalling events determine cell behaviour. Mechanotransducing ion channels and gap junctions additionally govern chondrocyte physiology. It is of great scientific and medical interest to induce a specific cell behaviour by controlling these mechanotransduction pathways and to translate this knowledge into regenerative clinical therapies. This review therefore focuses on the mechanotransduction properties of integrins, cadherins and ion channels in cartilaginous tissues to provide perspectives for cartilage regeneration.