Cell Surface Engineering Tools for Programming Living Assemblies

Breakthroughs in precision cell surface engineering tools are supporting the rapid development of programmable living assemblies with valuable features for tackling complex biological problems. Herein, the authors overview the most recent technological advances in chemically- and biologically-driven toolboxes for engineering mammalian cell surfaces and triggering their assembly into living architectures. A particular focus is given to surface engineering technologies for enabling biomimetic cell-cell social interactions and multicellular cell-sorting events. Further advancements in cell surface modification technologies may expand the currently available bioengineering toolset and unlock a new generation of personalized cell therapeutics with clinically relevant biofunctionalities. The combination of state-of-the-art cell surface modifications with advanced biofabrication technologies is envisioned to contribute toward generating living materials with increasing tissue/organ-mimetic bioactivities and therapeutic potential.

Advancing cell surface modification in mammalian cells with synthetic molecules

Biological cells, being the fundamental entities of life, are widely acknowledged as intricate living machines. The manipulation of cell surfaces has emerged as a progressively significant domain of investigation and advancement in recent times. Particularly, the alteration of cell surfaces using meticulously crafted and thoroughly characterized synthesized molecules has proven to be an efficacious means of introducing innovative functionalities or manipulating cells. Within this realm, a diverse array of elegant and robust strategies have been recently devised, including the bioorthogonal strategy, which enables selective modification. This review offers a comprehensive survey of recent advancements in the modification of mammalian cell surfaces through the use of synthetic molecules. It explores a range of strategies, encompassing chemical covalent modifications, physical alterations, and bioorthogonal approaches. The review concludes by addressing the present challenges and potential future opportunities in this rapidly expanding field.

Double network laminarin-boronic/alginate dynamic bioink for 3D bioprinting cell-laden constructs

The design of dynamically crosslinked hydrogel bioinks for three-dimensional (3D) bioprinting is emerging as a valuable strategy to advance the fabrication of mechanically tuneable cell-laden constructs for 3Din vitrodisease modelling and tissue engineering applications. Herein, a dynamic bioink comprising boronic acid-functionalised laminarin and alginate is explored for bioprinting 3D constructs under physiologically relevant conditions. The formulated bioink takes advantage of a double crosslinked network that combines covalent but reversible boronate ester bonds and ionic gelation via divalent cations. Moreover, it exhibits suitable rheological properties and improved mechanical features owing to its modular crosslinking chemistry, yielding stable constructs with user-programmable architecture. We explored such dynamic bioink as a supporting matrix for different cell classes, namely osteoblast precursors, fibroblasts and breast cancer cells. The resulting cell-laden bioprinted hydrogels display a homogeneous cell distribution post-printing and exceptional cell viability (>90%) that can be maintained for prolonged time periods in culture (14 days) for all cell lines. This simple and chemically versatile approach is envisaged to accelerate the development of multifunctional bioinks and contribute towards the fabrication of biomimetic 3D scaffolds with applicability in a wide range of predictive or exploratory biomedical platforms.

Nongenetic Bioconjugation Strategies for Modifying Cell Membranes and Membrane Proteins: A Review

The cell membrane possesses an extensive library of proteins, carbohydrates, and lipids that control a significant portion of inter- and intracellular functions, including signaling, proliferation, migration, and adhesion, among others. Augmenting the cell surface composition would open possibilities for advances in therapy, tissue engineering, and probing fundamental cell processes. While genetic engineering has proven effective for many in vitro applications, these techniques result in irreversible changes to cells and are difficult to apply in vivo. Another approach is to instead attach exogenous functional groups to the cell membrane without changing the genetic nature of the cell. This review focuses on more recent approaches of nongenetic methods of cell surface modification through metabolic pathways, anchorage by hydrophobic interactions, and chemical conjugation. Benefits and drawbacks of each approach are considered, followed by a discussion of potential applications for nongenetic cell surface modification and an outlook on the future of the field.

Cell membrane engineering with synthetic materials: Applications in cell spheroids, cellular glues and microtissue formation

Biologically inspired materials with tunable bio- and physicochemical properties provide an essential framework to actively control and support cellular behavior. Cell membrane remodeling approaches benefit from the advances in polymer science and bioconjugation methods, which allow for the installation of un-/natural molecules and particles on the cells' surface. Synthetically remodeled cells have superior properties and are under intense investigation in various therapeutic scenarios as cell delivery systems, bio-sensing platforms, injectable biomaterials and bioinks for 3D bioprinting applications. In this review article, recent advances in the field of cell surface remodeling via bio-chemical means and the potential biomedical applications of these emerging cell hybrids are discussed. STATEMENT OF SIGNIFICANCE: Recent advances in bioconjugation methods, controlled/living polymerizations, microfabrication techniques and 3D printing technologies have enabled researchers to probe specific cellular functions and cues for therapeutic and research purposes through the formation of cell spheroids and polymer-cell chimeras. This review article highlights recent non-genetic cell membrane engineering strategies towards the fabrication of cellular ensembles and microtissues with interest in 3D in vitro modeling, cell therapeutics and tissue engineering. From a wider perspective, these approaches may provide a roadmap for future advances in cell therapies which will expedite the clinical use of cells, thereby improving the quality and accessibility of disease treatments.

Programming Cell-Cell Interactions through Non-genetic Membrane Engineering

The ability to direct targeted intercellular interactions has the potential to enable and expand the use of cell-based therapies for regenerative medicine, tissue engineering, and immunotherapy. While genetic engineering approaches have proven effective, these techniques are not amenable to all cell types and often yield permanent modifications with potentially long-lasting adverse effects, restricting their application. To circumvent these limitations, there is intense interest in developing non-genetic methods to modify cell membranes with functional groups that will enable the recognition of target cells. While many such techniques have been developed, relatively few have been applied to directing specific cell-cell interactions. This review details these non-genetic membrane engineering approaches-namely, hydrophobic membrane insertion, chemical modification, liposome fusion, metabolic engineering, and enzymatic remodeling-and summarizes their major applications. Based on this analysis, perspective is provided on the ideal features of these systems with an emphasis on the potential for clinical translation.

Rapid and Versatile Cell Aggregate Formation Using Lipid-Conjugated Heparin

Cell aggregates hold significant therapeutic promise for in vitro cell analysis, ex vivo tissue models, and in vivo cell therapy and tissue engineering. Traditional methods of making cell aggregates require long incubation times and can only produce three-dimensional-spheroid-shaped aggregates. We propose a novel method of making cell aggregates of diverse sizes and shapes using lipid-conjugated heparin. Shaking the cell suspension containing a small amount of lipid-conjugated heparin for approximately 30 min produced cell aggregates. This approach can be applied to any cell type, including stem cells, fibroblast cells, and T lymphocytes. The shape of biocompatible templates could modulate the shape of cell aggregates. In addition to layered, multicompartmental cell aggregates on template, template-free, tube-shaped cell aggregates could also be made. The cell aggregates formed were alive and maintained biological activities.

Engineering Reversible Cell-Cell Interactions with Lipid Anchored Prosthetic Receptors

Membrane-engineered cells displaying antigen-targeting ligands are useful as both scientific tools and clinical therapeutics. While genetically encoded artificial receptors have proven efficacious, their scope remains limited, as this approach is not amenable to all cell types and the modification is often permanent. Our group has developed a nongenetic method to rapidly, stably, and reversibly modify any cell membrane with a chemically self-assembled nanoring (CSAN) that can function as a prosthetic receptor. Bifunctional CSANs displaying epithelial cell adhesion molecule (EpCAM)-targeted fibronectin domains were installed on the cell membrane through hydrophobic insertion and remained stably bound for ≥72 h in vitro. These CSAN-labeled cells were capable of recognizing EpCAM-expressing target cells, forming intercellular interactions that were subsequently reversed by disassembling the nanoring with the FDA-approved antibiotic, trimethoprim. This study demonstrates the use of this system to engineer cell surfaces with prosthetic receptors capable of directing specific and reversible cell-cell interactions.

Transiently malleable multi-healable hydrogel nanocomposites based on responsive boronic acid copolymers

Dynamic multi-responsive gel nanocomposites with rapid self-healing and cell encapsulation properties are presented.

Bioreducible Polymer Nanocarrier Based on Multivalent Choline Phosphate for Enhanced Cellular Uptake and Intracellular Delivery of Doxorubicin

Limited cellular uptake and inefficient intracellular drug release severely hamper the landscape of polymer drug nanocarriers in cancer chemotherapy. Herein, to address these urgent challenges in tumor treatment simultaneously, we integrated the multivalent choline phosphate (CP) and bioreducible linker into a single polymer chain, designed and synthesized a neoteric bioreducible polymer nanocarrier. The excellent hydrophility of these zwitterionic CP groups endowed high drug loading content and drug loading efficiency of doxorubicin to this drug delivery system (∼22.1 wt %, ∼95.9%). Meanwhile, we found that the multivalent choline phosphate can effectively enhance the internalization efficiency of this drug-loaded nanocarrier over few seconds, and the degree of improvement depended on the CP density in a single polymer chain. In addition, after these nanocarriers entered into the tumor cells, the accelerated cleavage of bioreducible linker made it possible for more cargo escape from the delivery system to cytoplasm to exert their cytostatic effects more efficiently. The enhanced therapeutic efficacy in various cell lines indicated the great potential of this system in anticancer drug delivery applications.

Rapid Formation of Cell Aggregates and Spheroids Induced by a "Smart" Boronic Acid Copolymer

Cell surface engineering has emerged as a powerful approach to forming cell aggregates/spheroids and cell-biomaterial ensembles with significant uses in tissue engineering and cell therapeutics. Herein, we demonstrate that cell membrane remodeling with a thermoresponsive boronic acid copolymer induces the rapid formation of spheroids using either cancer or cardiac cell lines under conventional cell culture conditions at minute concentrations. It is shown that the formation of well-defined spheroids is accelerated by at least 24 h compared to non-polymer-treated controls, and, more importantly, the polymer allows for fine control of the aggregation kinetics owing to its stimulus response to temperature and glucose content. On the basis of its simplicity and effectiveness to promote cellular aggregation, this platform holds promise in three-dimensional tissue/tumor modeling and tissue engineering applications.