Immunofunctional photodegradable poly(ethylene glycol) hydrogel surfaces for the capture and release of rare cells

Hydrogel-based technologies in liquid biopsy for the detection of circulating clinical markers: challenges and prospects

Liquid biopsy, which promises noninvasive detection of tumor-derived material, has recently been highlighted because of its potential to lead us to an era of precision medicine. However, its development has encountered challenges owing to the extremely low frequency and low purity of circulating tumor markers, such as circulating tumor cells (CTCs), circulating exosomes, and circulating tumor nucleic acids (ctNAs). Much effort has been made to overcome this limitation over the last decade, and an increasing number of studies have shown interest in the special characteristics of hydrogels. This hydrophilic and biocompatible polymeric network, which absorbs a large amount of water, can aid in the isolation, protection, and analysis of these low-abundance and short-lived circulating biomarkers. The role of hydrogels in liquid biopsy is extensive and ranges from enrichment to encapsulation. This review provides an overview of hydrogel-based technologies to pave the way in liquid biopsy.

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.

Photoactive hydrogels for pre-concentration, labelling, and controlled release of proteins

We report a novel hydrogel for pre-concentration, fluorescent labelling, and light-triggered release of proteins for detection of low abundance biomarkers. The hydrogel was a co-polymer of acrylamide/bisacrylamide and methacrylamide attached to fluorescein isothiocyanate via a light cleavable bond and a poly(ethylene glycol) spacer arm of molecular weight of 3400 g mol-1. Unlike previous work, proteins were captured by an irreversible chemical reaction rather than by non-covalent affinity binding or physical entrapment. Because the protein-reactive group was attached to fluorescein, which in turn was coupled to the hydrogel by a photocleavable bond, on release the protein was labelled with fluorescein. Our hydrogel offered a pre-concentration factor of up to 236 for a model protein, streptavidin. Each protein molecule was labelled with 85 fluorescein molecules, and 50% of the proteins in the hydrogel were released after UV exposure for ∼100 s. The proteins released from the hydrogel were captured in biotinylated microtitre plates and detected by fluorescence, allowing measurement of at least 0.01 ppm (or ∼166 pM) of protein in sample solutions. The reported hydrogel is promising for detection of low abundance proteins while being less laborious than enzyme-linked immunosorbent assay and less affected by changes in environmental conditions than label-free biosensors.

Cell therapy biomanufacturing: integrating biomaterial and flow-based membrane technologies for production of engineered T-cells

Adoptive T-cell therapies (ATCTs) are increasingly important for the treatment of cancer, where patient immune cells are engineered to target and eradicate diseased cells. The biomanufacturing of ATCTs involves a series of time-intensive, lab-scale steps, including isolation, activation, genetic modification, and expansion of a patient's T-cells prior to achieving a final product. Innovative modular technologies are needed to produce cell therapies at improved scale and enhanced efficacy. In this work, well-defined, bioinspired soft materials were integrated within flow-based membrane devices for improving the activation and transduction of T cells. Hydrogel coated membranes (HCM) functionalized with cell-activating antibodies were produced as a tunable biomaterial for the activation of primary human T-cells. T-cell activation utilizing HCMs led to highly proliferative T-cells that expressed a memory phenotype. Further, transduction efficiency was improved by several fold over static conditions by using a tangential flow filtration (TFF) flow-cell, commonly used in the production of protein therapeutics, to transduce T-cells under flow. The combination of HCMs and TFF technology led to increased cell activation, proliferation, and transduction compared to current industrial biomanufacturing processes. The combined power of biomaterials with scalable flow-through transduction techniques provides future opportunities for improving the biomanufacturing of ATCTs.

Optimizing Immunofunctionalization and Cell Capture on Micromolded Hydrogels via Controlled Oxygen-Inhibited Photopolymerization

With circulating tumor cells (CTCs) playing a critical role in cancer metastasis, the quantitation and characterization of CTCs promise to provide precise diagnostic and prognostic information in service of personalized therapies. However, as CTCs are extremely rare, high yield, high purity strategies are required to target and isolate CTCs from patient samples. Recently, we demonstrated the selective capture of CTCs upon antibody-functionalized polyethylene glycol diacrylate (PEGDA) hydrogels photopolymerized within polydimethylsiloxane (PDMS) microfluidic molds. Isolated CTC purity was subsequently enriched by selectively releasing desired cells from photodegradable hydrogel capture surfaces. However, the fabrication of these acrylate-based hydrogels by photopolymerization is subject to oxygen inhibition, which dramatically affects the physical and chemical properties of hydrogel interfaces formed in proximity to PDMS boundaries. To evaluate how antibody conjugation density and cell capture is impacted by fabrication parameters affected by oxygen inhibition, PEGDA hydrogel features were polymerized within PDMS micromolds under different UV exposure conditions and linker (acrylate-PEG-biotin) concentrations. Predictions of acrylate conversion throughout the hydrogel feature were performed using a 1D reaction-diffusion model that describes oxygen-inhibited photopolymerization. The functional consequences of photopolymerization parameters and solution stoichiometry on CTC capture were experimentally quantified and evaluated. Results show that hydrogel surfaces polymerized under shorter exposure times and with higher linker concentrations display superior functionalization and higher CTC capture efficiency. Conversely, highly cross-linked hydrogel surfaces polymerized under longer exposure times are insensitive to functionalization and display poor capture, regardless of linker concentration. By highlighting the importance of oxygen-inhibited photopolymerization, these findings provide guidelines to design micromolded hydrogels with controlled ligand expression. In addition to enhancing the selective cell capture capacity of immunofunctional hydrogels, the ability to quantifiably design hydrogel interfaces described here will improve the sensitivity of hydrogel biosensors, provide a platform to finely screen cell-matrix interactions, and generally enhance the fidelity of micromolded hydrogel features.

Microfluidics for the Isolation and Detection of Circulating Tumor Cells

Nowadays, liquid biopsy represents one of the most promising techniques for early diagnosis, monitoring, and therapy screening of cancer. This novel methodology includes, among other techniques, the isolation, capture, and analysis of circulating tumor cells (CTCs). Nonetheless, the identification of CTC from whole blood is challenging due to their extremely low concentration (1-100 per ml of whole blood), and traditional methods result insufficient in terms of purity, recovery, throughput and/or viability of the processed sample. In this context, the development of microfluidic devices for detecting and isolating CTCs offers a wide range of new opportunities due to their excellent properties for cell manipulation and the advantages to integrate and bring different laboratory processes into the microscale improving the sensitivity, portability, reducing cost and time. This chapter explores current and recent microfluidic approaches that have been developed for the analysis and detection of CTCs, which involve cell capture methods based on affinity binding and label-free methods and detection based on electrical, chemical, and optical sensors. All the exposed technologies seek to overcome the limitations of commercial systems for the analysis and isolation of CTCs, as well as to provide extended analysis that will allow the development of novel and more efficient diagnostic tools.

Polymer Surface Dissection for Correlated Microscopic and Compositional Analysis of Bacterial Aggregates during Membrane Biofouling

Multispecies biofilms are a common limitation in membrane bioreactors, causing membrane clogging, degradation, and failure. There is a poor understanding of biological fouling mechanisms in these systems due to the limited number of experimental techniques useful for probing microbial interactions at the membrane interface. Here, we develop a new experimental method, termed polymer surface dissection (PSD), to investigate multispecies assembly processes over membrane surfaces. The PSD method uses photodegradable polyethylene glycol hydrogels functionalized with bioaffinity ligands to bind and detach microscale, microbial aggregates from the membrane for microscopic observation. Subsequent exposure of the hydrogel to high resolution, patterned UV light allows for controlled release of any selected aggregate of desired size at high purity for DNA extraction. Follow-up 16S community analysis reveals aggregate composition, correlating microscopic images with the bacterial community structure. The optimized approach can isolate aggregates with microscale spatial precision and yields genomic DNA at sufficient quantity and quality for sequencing from aggregates with areas as low as 2000 μm², without the need of culturing for sample enrichment. To demonstrate the value of the approach, PSD was used to reveal the composition of microscale aggregates of different sizes during early-stage biofouling of aerobic wastewater communities over PVDF membranes. Larger aggregates exhibited lower diversity of bacterial communities, and a shift in the community structure was found as aggregate size increased to areas between 25,000 and 45,000 μm², below which aggregates were more enriched in Bacteroidetes and above which aggregates were more enriched with Proteobacteria. The findings demonstrate that community succession can be observed within microscale aggregates and that the PSD method is useful for identification and characterization of early colonizing bacteria that drive biofouling on membrane surfaces.

Stimuli-responsive destructible polymeric hydrogels based on irreversible covalent bond dissociation

Covalently crosslinked stimuli-destructible hydrogels with the ability of irreversible bond dissociation have attracted great attentions due to their biodegradability, stability against hydrolysis, and controlled solubility upon insertion of desired triggers.

Photodegradable avidin-biotinylated polymer conjugate hydrogels for cell manipulation

Protein-synthetic polymer hybrid hydrogels crosslinked via protein-ligand binding are promising materials for the three-dimensional culture of various cells, while photo-responsive hydrogels have been widely used for the spatio-temporal control of cell functions and patterning. Photo-responsive protein-polymer hybrid hydrogels are therefore attractive candidates for use in cell and artificial tissue fabrication; however, no examples combining these properties have been reported to date. Herein, a photodegradable hydrogel consisting of avidin and biotinylated polyethylene glycol (PEG) was developed as a multi-functional matrix for cell culture and sorting. A four-branched PEG with a biotinylated photocleavable group at the end of each chain was crosslinked with avidin to produce a photodegradable hydrogel. A cytokine-dependent immunocyte was successfully cultured in the hydrogel by supplying cytokine from a medium layered on the hydrogel. Additionally, the adhesion and survival of fibroblasts could be controlled by decorating the hydrogel with a biotinylated cell-adhesive peptide. Cells embedded in the hydrogels could be recovered without cell damage as a result of light-induced hydrogel degradation. Moreover, model target cells expressing red fluorescent protein were selectively liberated from a hydrogel containing cells of different colors by irradiating with a targeted light. Owing to both the selective biotin-binding ability of avidin and the photocleavable properties of the synthetic polymer, the hydrogels were easy to prepare and decorate with functional molecules; they provided an internal structure suitable for cell culture, and allowed light-guided cell manipulation. The hydrogels are therefore expected to contribute to various cell fabrication processes as useful cell engineering and sorting tools.

System Modularity Chip for Analysis of Rare Targets (SMART-Chip): Liquid Biopsy Samples

Liquid biopsies are becoming popular for managing a variety of diseases due to the minimally invasive nature of their acquisition, thus potentially providing better outcomes for patients. Circulating tumor cells (CTCs) are among the many different biomarkers secured from a liquid biopsy, and a number of efficient platforms for their isolation and enrichment from blood have been reported. However, many of these platforms require manual sample handling, which can generate difficulties when translating CTC assays into the clinic due to potential sample loss, contamination, and the need for highly specialized operators. We report a system modularity chip for the analysis of rare targets (SMART-Chip) composed of three task-specific modules that can fully automate processing of CTCs. The modules were used for affinity selection of the CTCs from peripheral blood with subsequent photorelease, simultaneous counting, and viability determinations of the CTCs and staining/imaging of the CTCs for immunophenotyping. The modules were interconnected to a fluidic motherboard populated with valves, interconnects, pneumatic control channels, and a fluidic network. The SMART-Chip components were made from thermoplastics via microreplication, which lowers the cost of production making it amenable to clinical implementation. The utility of the SMART-Chip was demonstrated by processing blood samples secured from colorectal cancer (CRC) and pancreatic ductal adenocarcinoma (PDAC) patients. We were able to affinity-select EpCAM expressing CTCs with high purity (0-3 white blood cells/mL of blood), enumerate the selected cells, determine their viability, and immunophenotype the cells. The assay could be completed in <4 h, while manual processing required >8 h.

Spatiotemporal patterning of photoresponsive DNA-based hydrogels to tune local cell responses

Understanding the spatiotemporal effects of surface topographies and modulated stiffness and anisotropic stresses of hydrogels on cell growth remains a biophysical challenge. Here we introduce the photolithographic patterning or two-photon laser scanning confocal microscopy patterning of a series of o-nitrobenzylphosphate ester nucleic acid-based polyacrylamide hydrogel films generating periodically-spaced circular patterned domains surrounded by continuous hydrogel matrices. The patterning processes lead to guided modulated stiffness differences between the patterned domains and the surrounding hydrogel matrices, and to the selective functionalization of sub-regions of the films with nucleic acid anchoring tethers. HeLa cells are deposited on the circularly-shaped domains functionalized with the MUC-1 aptamers. Initiation of the hybridization chain reaction by nucleic acid tethers associated with the continuous hydrogel matrix results in stress-induced ordered orthogonal shape-changes on the patterned domains, leading to ordered shapes of cell aggregates bound to the patterns.

Convection-driven microfabricated hydrogels for rapid biosensing

A microscale biosensing platform using rehydration-mediated swelling of bio-functionalized hydrogel structures and rapid target analyte capture is described. Induced convective flow mitigates diffusion limited incubation times, enabling model assays to be completed in under three minutes. Assay design parameters have been evaluated, revealing fabrication criteria required to tune detection sensitivity.

Photodegradable Hydrogels for Rapid Screening, Isolation, and Genetic Characterization of Bacteria with Rare Phenotypes

Screening mutant libraries (MLs) of bacteria for strains with specific phenotypes is often a slow and laborious process that requires assessment of tens of thousands of individual cell colonies after plating and culturing on solid media. In this report, we develop a three-dimensional, photodegradable hydrogel interface designed to dramatically improve the throughput of ML screening by combining high-density cell culture with precision extraction and the recovery of individual, microscale colonies for follow-up genetic and phenotypic characterization. ML populations are first added to a hydrogel precursor solution consisting of polyethylene glycol (PEG) o-nitrobenzyl diacrylate and PEG-tetrathiol macromers, where they become encapsulated into 13 μm thick hydrogel layers at a density of 90 cells/mm², enabling parallel monitoring of 2.8 × 10⁴ mutants per hydrogel. Encapsulated cells remain confined within the elastic matrix during culture, allowing one to track individual cells that grow into small, stable microcolonies (45 ± 4 μm in diameter) over the course of 72 h. Colonies with rare growth profiles can then be identified, extracted, and recovered from the hydrogel in a sequential manner and with minimal damage using a high-resolution, 365 nm patterned light source. The light pattern can be varied to release motile cells, cellular aggregates, or microcolonies encapsulated in protective PEG coatings. To access the benefits of this approach for ML screening, an Agrobacterium tumefaciens C58 transposon ML was screened for rare, resistant mutants able to grow in the presence of cell free culture media from Rhizobium rhizogenes K84, a well-known inhibitor of C58 cell growth. Subsequent genomic analysis of rare cells (9/28,000) that developed into microcolonies identified that seven of the resistant strains had mutations in the acc locus of the Ti plasmid. These observations are consistent with past research demonstrating that the disruption of this locus confers resistance to agrocin 84, an inhibitory molecule produced by K84. The high-throughput nature of the screen allows the A. tumefaciens genome (approximately 5.6 Mbps) to be screened to saturation in a single experimental trial, compared to hundreds of platings required by conventional plating approaches. As a miniaturized version of the gold-standard plating assay, this materials-based approach offers a simple, inexpensive, and highly translational screening technique that does not require microfluidic devices or complex liquid handling steps. The approach is readily adaptable to other applications that require isolation and study of rare or phenotypically pure cell populations.

Photolabile Linkers: Exploiting Labile Bond Chemistry to Control Mode and Rate of Hydrogel Degradation and Protein Release

Photolabile moieties have been utilized in applications ranging from peptide synthesis and controlled protein activation to tunable and dynamic materials. The photochromic properties of nitrobenzyl (NB) based linkers are readily tuned to respond to cytocompatible light doses and are widely utilized in cell culture and other biological applications. While widely utilized, little is known about how the microenvironment, particularly confined aqueous environments (e.g., hydrogels), affects both the mode and rate of cleavage of NB moieties, leading to unpredictable limitations in control over system properties (e.g., rapid hydrolysis or slow photolysis). To address these challenges, we synthesized and characterized the photolysis and hydrolysis of NB moieties containing different labile bonds (i.e., ester, amide, carbonate, or carbamate) that served as labile crosslinks within step-growth hydrogels. We observed that NB ester bond exhibited significant rates of both photolysis and hydrolysis, whereas, importantly, the NB carbamate bond had superior light responsiveness and resistance to hydrolysis within the hydrogel microenvironment. Exploiting this synergy and orthogonality of photolytic and hydrolytic degradation, we designed concentric cylinder hydrogels loaded with different cargoes (e.g., model protein with different fluorophores) for either combinatorial or sequential release, respectively. Overall, this work provides new facile chemical approaches for tuning the degradability of NB linkers and an innovative strategy for the construction of multimodal degradable hydrogels, which can be utilized to guide the design of not only tunable materials platforms but also controlled synthetic protocols or surface modification strategies.

Inner Surface Design of Functional Microchannels for Microscale Flow Control

Fluidic flow behaviors in microfluidics are dominated by the interfaces created between the fluids and the inner surface walls of microchannels. Microchannel inner surface designs, including the surface chemical modification, and the construction of micro-/nanostructures, are good examples of manipulating those interfaces between liquids and surfaces through tuning the chemical and physical properties of the inner walls of the microchannel. Therefore, the microchannel inner surface design plays critical roles in regulating microflows to enhance the capabilities of microfluidic systems for various applications. Most recently, the rapid progresses in micro-/nanofabrication technologies and fundamental materials have also made it possible to integrate increasingly complex chemical and physical surface modification strategies with the preparation of microchannels in microfluidics. Besides, a wave of researches focusing on the ideas of using liquids as dynamic surface materials is identified, and the unique characteristics endowed with liquid-liquid interfaces have revealed that the interesting phenomena can extend the scope of interfacial interactions determining microflow behaviors. This review extensively discusses the microchannel inner surface designs for microflow control, especially evaluates them from the perspectives of the interfaces resulting from the inner surface designs. In addition, prospective opportunities for the development of surface designs of microchannels, and their applications are provided with the potential to attract scientific interest in areas related to the rapid development and applications of various microchannel systems.

Affinity-Enhanced CTC-Capturing Hydrogel Microparticles Fabricated by Degassed Mold Lithography

Technologies for the detection and isolation of circulating tumor cells (CTCs) are essential in liquid biopsy, a minimally invasive technique for early diagnosis and medical intervention in cancer patients. A promising method for CTC capture, using an affinity-based approach, is the use of functionalized hydrogel microparticles (MP), which have the advantages of water-like reactivity, biologically compatible materials, and synergy with various analysis platforms. In this paper, we demonstrate the feasibility of CTC capture by hydrogel particles synthesized using a novel method called degassed mold lithography (DML). This technique increases the porosity and functionality of the MPs for effective conjugation with antibodies. Qualitative fluorescence analysis demonstrates that DML produces superior uniformity, integrity, and functionality of the MPs, as compared to conventional stop flow lithography (SFL). Analysis of the fluorescence intensity from porosity-controlled MPs by each reaction step of antibody conjugation elucidates that more antibodies are loaded when the particles are more porous. The feasibility of selective cell capture is demonstrated using breast cancer cell lines. In conclusion, using DML for the synthesis of porous MPs offers a powerful method for improving the cell affinity of the antibody-conjugated MPs.

Light-inducible activation of cell cycle progression in Xenopus egg extracts under microfluidic confinement

Cell-free Xenopus egg extract is a widely used and biochemically tractable model system that allows recapitulation and elucidation of fundamental cellular processes. Recently, the introduction of microfluidic extract manipulation has enabled compartmentalization of bulk extract and a newfound ability to study organelles on length scales that recapitulate key features of cellular morphology. While the microfluidic confinement of extracts has produced a compelling platform for the in vitro study of cell processes at physiologically-relevant length scales, it also imposes experimental limitations by restricting dynamic control over extract properties. Here, we introduce photodegradable polyethylene glycol (PEG) hydrogels as a vehicle to passively and selectively manipulate extract composition through the release of proteins encapsulated within the hydrogel matrix. Photopatterned PEG hydrogels, passive to both extract and encapsulated proteins, serve as protein depots within microfluidic channels, which are subsequently flooded with extract. Illumination by ultraviolet light (UV) degrades the hydrogel structures and releases encapsulated protein. We show that an engineered fluorescent protein with a nuclear localization signal (GST-GFP-NLS) retains its ability to localize within nearby nuclei following UV-induced release from hydrogel structures. When diffusion is considered, the kinetics of nuclear accumulation are similar to those in experiments utilizing conventional, bulk fluid handling. Similarly, the release of recombinant cyclin B Δ90, a mutant form of the master cell cycle regulator cyclin B which lacks the canonical destruction box, was able to induce the expected cell cycle transition from interphase to mitosis. This transition was confirmed by the observation of nuclear envelope breakdown (NEBD), a phenomenological hallmark of mitosis, and the induction of mitosis-specific biochemical markers. This approach to extract manipulation presents a versatile and customizable route to regulating the spatial and temporal dynamics of cellular events in microfluidically confined cell-free extracts.