Noncovalent cell surface engineering with cationic graft copolymers

Pd-, Cu-, and Ni-Catalyzed Reactions: A Comprehensive Review of the Efficient Approaches towards the Synthesis of Antibacterial Molecules

A strong synthetic tool for many naturally occurring chemicals, polymers, and pharmaceutical substances is transition metal-catalyzed synthesis. A serious concern to human health is the emergence of bacterial resistance to a broad spectrum of antibacterial medications. The synthesis of chemical molecules that are potential antibacterial candidates is underway. The main contributions to medicine are found to be effective in transition metal catalysis and heterocyclic chemistry. This review underlines the use of heterocycles and certain effective transition metals (Pd, Cu, and Ni) as catalysts in chemical methods for the synthesis of antibacterial compounds. Pharmaceutical chemists might opt for clinical exploration of these techniques due to their potential.

Materials for Cell Surface Engineering

Cell therapies are emerging as a promising new therapeutic modality in medicine, generating effective treatments for previously incurable diseases. Clinical success of cell therapies has energized the field of cellular engineering, spurring further exploration of novel approaches to improve their therapeutic performance. Engineering of cell surfaces using natural and synthetic materials has emerged as a valuable tool in this endeavor. This review summarizes recent advances in the development of technologies for decorating cell surfaces with various materials including nanoparticles, microparticles, and polymeric coatings, focusing on the ways in which surface decorations enhance carrier cells and therapeutic effects. Key benefits of surface-modified cells include protecting the carrier cell, reducing particle clearance, enhancing cell trafficking, masking cell-surface antigens, modulating inflammatory phenotype of carrier cells, and delivering therapeutic agents to target tissues. While most of these technologies are still in the proof-of-concept stage, the promising therapeutic efficacy of these constructs from in vitro and in vivo preclinical studies has laid a strong foundation for eventual clinical translation. Cell surface engineering with materials can imbue a diverse range of advantages for cell therapy, creating opportunities for innovative functionalities, for improved therapeutic efficacy, and transforming the fundamental and translational landscape of cell therapies.

Charge-Reversed Exosomes for Targeted Gene Delivery to Cartilage for Osteoarthritis Treatment

Gene therapy has the potential to facilitate targeted expression of therapeutic proteins to promote cartilage regeneration in osteoarthritis (OA). The dense, avascular, aggrecan-glycosaminoglycan (GAG) rich negatively charged cartilage, however, hinders their transport to reach chondrocytes in effective doses. While viral vector mediated gene delivery has shown promise, concerns over immunogenicity and tumorigenic side-effects persist. To address these issues, this study develops surface-modified cartilage-targeting exosomes as non-viral carriers for gene therapy. Charge-reversed cationic exosomes are engineered for mRNA delivery by anchoring cartilage targeting optimally charged arginine-rich cationic motifs into the anionic exosome bilayer by using buffer pH as a charge-reversal switch. Cationic exosomes penetrated through the full-thickness of early-stage arthritic human cartilage owing to weak-reversible ionic binding with GAGs and efficiently delivered the encapsulated eGFP mRNA to chondrocytes residing in tissue deep layers, while unmodified anionic exosomes do not. When intra-articularly injected into destabilized medial meniscus mice knees with early-stage OA, mRNA loaded charge-reversed exosomes overcame joint clearance and rapidly penetrated into cartilage, creating an intra-tissue depot and efficiently expressing eGFP; native exosomes remained unsuccessful. Cationic exosomes thus hold strong translational potential as a platform technology for cartilage-targeted non-viral delivery of any relevant mRNA targets for OA treatment.

Macrophage based drug delivery: Key challenges and strategies

As a natural immune cell and antigen presenting cell, macrophages have been studied and engineered to treat human diseases. Macrophages are well-suited for use as drug carriers because of their biological characteristics, such as excellent biocompatibility, long circulation, intrinsic inflammatory homing and phagocytosis. Meanwhile, macrophages' uniquely high plasticity and easy re-education polarization facilitates their use as part of efficacious therapeutics for the treatment of inflammatory diseases or tumors. Although recent studies have demonstrated promising advances in macrophage-based drug delivery, several challenges currently hinder further improvement of therapeutic effect and clinical application. This article focuses on the main challenges of utilizing macrophage-based drug delivery, from the selection of macrophage sources, drug loading, and maintenance of macrophage phenotypes, to drug migration and release at target sites. In addition, corresponding strategies and insights related to these challenges are described. Finally, we also provide perspective on shortcomings on the road to clinical translation and production.

Cell-drug conjugates

By combining living cells with therapeutics, cell-drug conjugates can potentiate the functions of both components, particularly for applications in drug delivery and therapy. The conjugates can be designed to persist in the bloodstream, undergo chemotaxis, evade surveillance by the immune system, proliferate, or maintain or transform their cellular phenotypes. In this Review, we discuss strategies for the design of cell-drug conjugates with specific functions, the techniques for their preparation, and their applications in the treatment of cancers, autoimmune diseases and other pathologies. We also discuss the translational challenges and opportunities of this class of drug-delivery systems and therapeutics.

Renal Clearable Nanodots-Engineered Erythrocytes with Enhanced Circulation and Tumor Accumulation for Photothermal Therapy of Hepatocellular Carcinoma

Living cell-mediated nanodelivery system is considered a promising candidate for targeted antitumor therapy; however, their use is restricted by the adverse interactions between carrier cells and nanocargos. Herein, a novel erythrocyte-based nanodelivery system is developed by assembling renal-clearable copper sulfide (CuS) nanodots on the outer membranes of erythrocytes via a lipid fusion approach, and demonstrate that it is an efficient photothermal platform against hepatocellular carcinoma. After intravenous injection of the nanodelivery system, CuS nanodots assembled on erythrocytes can be released from the system, accumulate in tumors in response to the high shear stress of bloodstream, and show excellent photothermal antitumor effect under the near infrared laser irradiation. Therefore, the erythrocyte-mediated nanodelivery system holds many advantages including prolonged blood circulation duration and enhanced tumor accumulation. Significantly, the elimination half-life of the nanodelivery system is 74.75 ± 8.77 h, which is much longer than that of nanodots (33.56 ± 2.36 h). Moreover, the other two kinds of nanodots can be well assembled onto erythrocytes to produce other erythrocyte-based hitchhiking platforms. Together, the findings promote not only the development of novel erythrocyte-based nanodelivery systems as potential platforms for tumor treatment but also their further clinical translation toward personalized healthcare.

Recent Developments in Layer-by-Layer Assembly for Drug Delivery and Tissue Engineering Applications

Surfaces with biological functionalities are of great interest for biomaterials, tissue engineering, biophysics, and for controlling biological processes. The layer-by-layer (LbL) assembly is a highly versatile methodology introduced 30 years ago, which consists of assembling complementary polyelectrolytes or biomolecules in a stepwise manner to form thin self-assembled films. In view of its simplicity, compatibility with biological molecules, and adaptability to any kind of supporting material carrier, this technology has undergone major developments over the past decades. Specific applications have emerged in different biomedical fields owing to the possibility to load or immobilize biomolecules with preserved bioactivity, to use an extremely broad range of biomolecules and supporting carriers, and to modify the film's mechanical properties via crosslinking. In this review, the focus is on the recent developments regarding LbL films formed as 2D or 3D objects for applications in drug delivery and tissue engineering. Possible applications in the fields of vaccinology, 3D biomimetic tissue models, as well as bone and cardiovascular tissue engineering are highlighted. In addition, the most recent technological developments in the field of film construction, such as high-content liquid handling or machine learning, which are expected to open new perspectives in the future developments of LbL, are presented.

Biohybrid Microalgae Robots: Design, Fabrication, Materials, and Applications

The integration of microorganisms and engineered artificial components has shown considerable promise for creating biohybrid microrobots. The unique features of microalgae make them attractive candidates as natural actuation materials for the design of biohybrid microrobotic systems. In this review, microalgae-based biohybrid microrobots are introduced for diverse biomedical and environmental applications. The distinct propulsion and phototaxis behaviors of green microalgae, as well as important properties from other photosynthetic microalga systems (blue-green algae and diatom) that are crucial to constructing powerful biohybrid microrobots, will be described first. Then the focus is on chemical and physical routes for functionalizing the algae surface with diverse reactive materials toward the fabrication of advanced biohybrid microalgae robots. Finally, representative applications of such algae-driven microrobots are presented, including drug delivery, imaging, and water decontamination, highlighting the distinct advantages of these active biohybrid robots, along with future prospects and challenges.

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.

Polymerization in living organisms

Vital biomacromolecules, such as RNA, DNA, polysaccharides and proteins, are synthesized inside cells via the polymerization of small biomolecules to support and multiply life. The study of polymerization reactions in living organisms is an emerging field in which the high diversity and efficiency of chemistry as well as the flexibility and ingeniousness of physiological environment are incisively and vividly embodied. Efforts have been made to design and develop in situ intra/extracellular polymerization reactions. Many important research areas, including cell surface engineering, biocompatible polymerization, cell behavior regulation, living cell imaging, targeted bacteriostasis and precise tumor therapy, have witnessed the elegant demeanour of polymerization reactions in living organisms. In this review, recent advances in polymerization in living organisms are summarized and presented according to different polymerization methods. The inspiration from biomacromolecule synthesis in nature highlights the feasibility and uniqueness of triggering living polymerization for cell-based biological applications. A series of examples of polymerization reactions in living organisms are discussed, along with their designs, mechanisms of action, and corresponding applications. The current challenges and prospects in this lifeful field are also proposed.

Bidirectional Supramolecular Display and Signal Amplification on the Surface of Living Cells

The ability to display exogenous molecules or nanomaterials on the surface of cells holds great potential for biomedical applications such as cell imaging and delivery. Numerous methods have been well established to enhance the display of biomolecules and nanomaterials on the cell surface. However, it is challenging to remove these biomolecules or nanomaterials from the cell surface. The purpose of this study was to investigate the reversible display of supramolecular nanomaterials on the surface of living cells. The data show that DNA initiators could induce the self-assembly of DNA-alginate conjugates to form supramolecular nanomaterials and amplify the fluorescence signals on the cell surface. Complementary DNA (cDNA), DNase, and alginase could all trigger the reversal of the signals from the cell surface. However, these three molecules exhibited different triggering efficiencies in the order cDNA > alginase > DNase. The combination of cDNA and alginase led to the synergistic reversal of nanomaterials and fluorescent signals from the cell surface. Thus, this study has successfully demonstrated a method for the bidirectional display of supramolecular nanomaterials on the surface of living cells. This method may find its application in numerous fields such as intact cell imaging and separation.

Synthetic Receptor-Based Targeting Strategies to Improve Tumor Drug Delivery

Heterogeneity in tumor expression as well as expression in normal tissues of various targets limit the usefulness of current ligand-based active targeting approaches. Incorporation of synthetic receptors, which can be recognized by delivery systems engineered to present specific functional groups on the surface, is a novel approach to improve tumor targeting. Alternatively, introduction of synthetic functionalities on cellular carriers can also enhance tumor targeting. We review various strategies that have been utilized for the introduction of synthetic targets in tumor tissues. The introduction of synthetic functional groups in the tumor through improved strategies is anticipated to result in improved target specificity and reduced heterogeneity in target expression.

Modifying Cell Membranes with Anionic Polymer Amphiphiles Potentiates Intracellular Delivery of Cationic Peptides

Rapid, facile, and noncovalent cell membrane modification with alkyl-grafted anionic polymers was sought as an approach to enhance intracellular delivery and bioactivity of cationic peptides. We synthesized a library of acrylic acid-based copolymers containing varying amounts of an amine-reactive pentafluorophenyl acrylate monomer followed by postpolymerization modification with a series of alkyl amines to afford precise control over the length and density of aliphatic alkyl side chains. This synthetic strategy enabled systematic investigation of the effect of the polymer structure on membrane binding, potentiation of peptide cell uptake, pH-dependent disruption of lipid bilayers for endosome escape, and intracellular bioavailability. A subset of these polymers exhibited pK_a of ∼6.8, which facilitated stable membrane association at physiological pH and rapid, pH-dependent endosomal disruption upon endocytosis as quantified in Galectin-8-YFP reporter cells. Cationic cell penetrating peptide (CPP) uptake was enhanced up to 15-fold in vascular smooth muscle cells in vitro when peptide treatment was preceded by a 30-min pretreatment with lead candidate polymers. We also designed and implemented a new and highly sensitive assay for measuring the intracellular bioavailability of CPPs based on the NanoLuciferase (NanoLuc) technology previously developed for measuring intracellular protein-protein interactions. Using this split luciferase class of assay, polymer pretreatment enhanced intracellular delivery of the CPP-modified HiBiT peptide up to 30-fold relative to CPP-HiBiT without polymer pretreatment (p < 0.05). The overall structural analyses show that polymers containing 50:50 or 70:30 molar ratios of carboxyl groups to alkyl side chains of 6-8 carbons maximized peptide uptake, pH-dependent membrane disruption, and intracellular bioavailability and that this potentiation effect was maximized by pairing with CPPs with high cationic charge density. These results demonstrate a rapid, mild method for polymer modification of cell surfaces to potentiate intracellular delivery, endosome escape, and bioactivity of cationic peptides.

Transplantation of PEGylated islets enhances therapeutic efficacy in a diabetic nonhuman primate model

Islet cell transplantation can lead to insulin independence, reduced hypoglycemia, and amelioration of diabetes complications in patients with type 1 diabetes. The systemic delivery of anti-inflammatory agents, while considered crucial to limit the early loss of islets associated with intrahepatic infusion, increases the burden of immunosuppression. In an effort to decrease the pharmaceutical load to the patient, we modified the pancreatic islet surface with long-chain poly(ethylene glycol) (PEG) to mitigate detrimental host-implant interactions. The effect of PEGylation on islet engraftment and long-term survival was examined in a robust nonhuman primate model via three paired transplants of dosages 4300, 8300, and 10 000 islet equivalents per kg body weight. A reduced immunosuppressive regimen of anti-thymocyte globulin induction plus tacrolimus in the first posttransplant month followed by maintenance with sirolimus monotherapy was employed. To limit transplant variability, two of the three pairs were closely MHC-matched recipients and received MHC-disparate PEGylated or untreated islets isolated from the same donors. Recipients of PEGylated islets exhibited significantly improved early c-peptide levels, reduced exogenous insulin requirements, and superior glycemic control, as compared to recipients of untreated islets. These results indicate that this simple islet modification procedure may improve islet engraftment and survival in the setting of reduced immunosuppression.

Nanotechnology Approaches to Modulate Immune Responses to Cell-based Therapies for Type 1 Diabetes

Islet transplantation is a promising curative treatment option for type 1 diabetes (T1D) as it can provide physiological blood glucose control. The widespread utilization of islet transplantation is limited due to systemic immunosuppression requirements, persisting graft immunodestruction, and poor islet engraftment. Traditional macro- and micropolymeric encapsulation strategies can alleviate the need for antirejection immunosuppression, yet the increased graft volume and diffusional distances imparted by these coatings can be detrimental to graft viability and glucose control. Additionally, systemic administration of pro-engraftment and antirejection therapeutics leaves patients vulnerable to adverse off-target side effects. Nanoscale engineering techniques can be used to immunocamouflage islets, modulate the transplant microenvironment, and provide localized pro-engraftment cues. In this review, we discuss the applications of nanotechnology to advance the clinical potential of islet transplantation, with a focus on cell surface engineering, bioactive functionalization, and use of nanoparticles in T1D cell-based treatments.

Advanced Bottom-Up Engineering of Living Architectures

Bottom-up tissue engineering is a promising approach for designing modular biomimetic structures that aim to recapitulate the intricate hierarchy and biofunctionality of native human tissues. In recent years, this field has seen exciting progress driven by an increasing knowledge of biological systems and their rational deconstruction into key core components. Relevant advances in the bottom-up assembly of unitary living blocks toward the creation of higher order bioarchitectures based on multicellular-rich structures or multicomponent cell-biomaterial synergies are described. An up-to-date critical overview of long-term existing and rapidly emerging technologies for integrative bottom-up tissue engineering is provided, including discussion of their practical challenges and required advances. It is envisioned that a combination of cell-biomaterial constructs with bioadaptable features and biospecific 3D designs will contribute to the development of more robust and functional humanized tissues for therapies and disease models, as well as tools for fundamental biological studies.

Fabrication of a Controlled in Situ Forming Polypeptide Hydrogel with a Good Biological Compatibility and Shapeable Property

A hydrogel is required to have a good biocompatibility, permeability for nutrients, and an easy construction procedure for biomedical applications. In particular, in situ forming hydrogels (ISFHs) have triggered considerable interest in their facile preparation methods. Here, an enzyme-prompted ISF, biodegradable poly(l-lysine)-graft-4-hydroxyphenylacetic acid (PLL-g-HPA) hydrogel in the conditions of horseradish peroxidase (HRP) and hydrogen peroxide (H2O2) and with a good biocompatibility was developed. The gelling time varied from a couple of seconds to several minutes depending on the amounts of catalyst, H2O2, and polymer. Due to the conveniently ISF means, the fabricated hydrogel could be applied in any form according to the need. The hydrogels display a good biological compatibility, as demonstrated in vitro cell culture and attachment experiments. Besides, the remaining NH2 groups in the hydrogel could be further functionalized for various cell research and bioapplications.

Nanotechnology in cell replacement therapies for type 1 diabetes

Islet transplantation is a promising long-term, compliance-free, complication-preventing treatment for type 1 diabetes. However, islet transplantation is currently limited to a narrow set of patients due to the shortage of donor islets and side effects from immunosuppression. Encapsulating cells in an immunoisolating membrane can allow for their transplantation without the need for immunosuppression. Alternatively, "open" systems may improve islet health and function by allowing vascular ingrowth at clinically attractive sites. Many processes that enable graft success in both approaches occur at the nanoscale level-in this review we thus consider nanotechnology in cell replacement therapies for type 1 diabetes. A variety of biomaterial-based strategies at the nanometer range have emerged to promote immune-isolation or modulation, proangiogenic, or insulinotropic effects. Additionally, coating islets with nano-thin polymer films has burgeoned as an islet protection modality. Materials approaches that utilize nanoscale features manipulate biology at the molecular scale, offering unique solutions to the enduring challenges of islet transplantation.

Biomedical Applications of Layer-by-Layer Self-Assembly for Cell Encapsulation: Current Status and Future Perspectives

Encapsulating living cells within multilayer functional shells is a crucial extension of cellular functions and a further development of cell surface engineering. In the last decade, cell encapsulation has been widely utilized in many cutting-edge biomedical fields. Compared with other techniques for cell encapsulation, layer-by-layer (LbL) self-assembly technology, due to the versatility and tunability to fabricate diverse multilayer shells with controllable compositions and structures, is considered as a promising approach for cell encapsulation. This review summarizes the state-of-the-art and potential future biomedical applications of LbL cell encapsulation. First of all, a brief introduction to the LbL self-assembly technique, including assembly mechanisms and technologies, is made. Next, different cell encapsulation strategies by LbL self-assembly techniques are explained. Then, the biomedical applications of LbL cell encapsulation in cell-based biosensors, cell transplantation, cell/molecule delivery, and tissue engineering, are highlighted. Finally, discussions on the current limitations and future perspectives of LbL cell encapsulation are also provided.

Cell surface engineering and application in cell delivery to heart diseases

Cell-based therapy has expanded its influence in cancer immunotherapy, regenerative medicine, and tissue engineering. Due to their secretory functions, differentiation capabilities, specific homing effects through chemotaxis, distinctive therapeutic potentials, and ex vivo expandability, cells have become an attractive reagent for advanced therapeutic strategies. Therefore, the ability to modify cells and manipulate their functions according to intended therapeutic designs has been the central scientific interest in the field of biomedical research. Many innovative methods have been developed with genetic modification of cells being the most advanced cell surface engineering technique. Although genetic modification is a powerful tool, it has a limited applicability due to the permanent modifications made on cells. Alternatively, many endeavors have been made to develop surface engineering techniques that can circumvent the limitations of genetic modification. In this review, current methods of non-genetic cell surface modification, including chemical conjugations, polymeric encapsulation, hydrophobic insertion, enzymatic and metabolic addition, will be introduced. Moreover, cell surface engineering plausible for cardiac remodeling and the future prospective will be discussed at the end.

Surface-Modified Macrophages Facilitate Tracking of Breast Cancer-Immune Interactions

The immune system has been found to play key roles in cancer development and progression. Macrophages are typically considered to be pro-inflammatory cells but can also facilitate pro-oncogenic activities via associations with tumors and metastases. The study of macrophages and their interactions within the context of cancer microenvironments is stymied by the lack of a system to track them. We present a cell-based strategy for studying cancer-immune cell interactions by chemically modifying the surfaces of macrophages with fluorophores. Two widely used methods are employed, affecting cell surface proteins and glycans via NHS-ester and Staudinger ligation reactions, respectively. We show that these modifications do not interfere with macrophage responses to chemoattractants and that interactions with cancer cells can be readily monitored. This work describes the development of macrophage-based imaging agents for tumor detection and assessment of interactions between immune cells and cancers.

Oncotically Driven Control over Glycocalyx Dimension for Cell Surface Engineering and Protein Binding in the Longitudinal Direction

Here we present a simple technique for re-directing reactions on the cell surface to the outermost region of the glycocalyx. Macromolecular crowding with inert polymers was utilized to reversibly alter the accessibility of glycocalyx proteoglycans toward cell-surface reactive probes allowing for reactivity control in the longitudinal direction (‘z’-direction) on the glycocalyx. Studies in HUVECs demonstrated an oncotically driven collapse of the glycocalyx brush structure in the presence of crowders as the mechanism responsible for re-directing reactivity. This phenomenon is consistent across a variety of macromolecular agents including polymers, protein markers and antibodies which all displayed enhanced binding to the outermost surface of multiple cell types. We then demonstrated the biological significance of the technique by increasing the camouflage of red blood cell surface antigens via a crowding-enhanced attachment of voluminous polymers to the exterior of the glycocalyx. The accessibility to Rhesus D (R_hD) and CD47 proteins on the cell surface was significantly decreased in crowding-assisted polymer grafting in comparison to non-crowded conditions. This strategy is expected to generate new tools for controlled glycocalyx engineering, probing the glycocalyx structure and function, and improving the development of cell based therapies.

Improving long-term subcutaneous drug delivery by regulating material-bioenvironment interaction

Subcutaneous long-acting release (LAR) formulations have been extensively developed in the clinic to increase patient compliance and reduce treatment cost. Despite preliminary success for some LAR systems, a major obstacle limiting the therapeutic effect remains on their interaction with surrounding tissues. In this review, we summarize how living bodies respond to injected or implanted materials, and highlight some typical strategies based on smart material design, which may significantly improve long-term subcutaneous drug delivery. Moreover, possible strategies to achieve ultra-long (months, years) subcutaneous drug delivery systems are proposed. Based on these discussions, we believe the well-designed subcutaneous long-acting formulations will hold great promise to improve patient quality of life in the clinic.

Engineering the Surface of Therapeutic "Living" Cells

Biological cells are complex living machines that have garnered significant attention for their potential to serve as a new generation of therapeutic and delivery agents. Because of their secretion, differentiation, and homing activities, therapeutic cells have tremendous potential to treat or even cure various diseases and injuries that have defied conventional therapeutic strategies. Therapeutic cells can be systemically or locally transplanted. In addition, with their ability to express receptors that bind specific tissue markers, cells are being studied as nano- or microsized drug carriers capable of targeted transport. Depending on the therapeutic targets, these cells may be clustered to promote intercellular adhesion. Despite some impressive results with preclinical studies, there remain several obstacles to their broader development, such as a limited ability to control their transport, engraftment, secretion and to track them in vivo. Additionally, creating a particular spatial organization of therapeutic cells remains difficult. Efforts have recently emerged to resolve these challenges by engineering cell surfaces with a myriad of bioactive molecules, nanoparticles, and microparticles that, in turn, improve the therapeutic efficacy of cells. This review article assesses the various technologies developed to engineer the cell surfaces. The review ends with future considerations that should be taken into account to further advance the quality of cell surface engineering.

Temporary Single-Cell Coating for Bioprocessing with a Cationic Polymer

Temporary single-cell coating is a useful tool for cell processing, allowing manipulation of cells to prevent cell attachment and agglomeration, before re-establishing normal cell function. In this work, a speckled coating method using a known polycation [poly(l-lysine), PLL] is described to induce cell surface electrostatic charges on three different cell types, namely, two bone cancer cell lines and fibroblasts. The morphology of the PLL speckled coating on the cell surface, internalization and metabolization of the polymer, and prevention of cellular aggregations are reported. Polymer concentration was found to be the key parameter controlling both capsule morphology and cell health. This approach allows a temporary cell coating over the course of 1-2 h, with cells exhibiting phenotypically normal behavior after ingesting and metabolizing the polymer. The process offers a fast and efficient alternative to aid single-cell manipulation for bioprocessing applications. Preliminary work on the application of PLL speckled cell coating in enabling reliable bioprinting is also presented.

The impact of cell surface PEGylation and short-course immunotherapy on islet graft survival in an allogeneic murine model

Islet transplantation is a promising therapy for Type 1 diabetes mellitus; however, host inflammatory and immune responses lead to islet dysfunction and destruction, despite potent systemic immunosuppression. Grafting of poly(ethylene glycol) (PEG) to the periphery of cells or tissues can mitigate inflammation and immune recognition via generation of a steric barrier. Herein, we sought to evaluate the complementary impact of islet PEGylation with a short-course immunotherapy on the survival of fully-MHC mismatched islet allografts (DBA/2 islets into diabetic C57BL/6J recipients). Anti-Lymphocyte Function-associated Antigen 1 (LFA-1) antibody was selected as a complementary, transient, systemic immune monotherapy. Islets were PEGylated via an optimized protocol, with resulting islets exhibiting robust cell viability and function. Following transplantation, a significant subset of diabetic animals receiving PEGylated islets (60%) or anti-LFA-1 antibody (50%) exhibited long-term (>100d) normoglycemia. The combinatorial approach proved synergistic, with 78% of the grafts exhibiting euglycemia long-term. Additional studies examining graft cellular infiltrates at early time points characterized the local impact of the transplant protocol on graft survival. Results illustrate the capacity of a simple polymer grafting approach to impart significant immunoprotective effects via modulation of the local transplant environment, while short-term immunotherapy serves to complement this effect.

STATEMENT OF SIGNIFICANCE

We believe this study is important and of interest to the biomaterials and transplant community for several reasons: 1) it provides an optimized protocol for the PEGylation of islets, with minimal impact on the coated islets, which can be easily translated for clinical applications; 2) this optimized protocol demonstrates the benefits of islet PEGylation in providing modest immunosuppression in a murine model; 3) this work demonstrates the combinatory impact of PEGylation with short-course immunotherapy (via LFA-1 blockage), illustrating the capacity of PEGylation to complement existing immunotherapy; and 4) it suggests macrophage phenotype shifting as the potential mechanism for this observed benefit.

Engineering live cell surfaces with functional polymers via cytocompatible controlled radical polymerization

The capability to graft synthetic polymers onto the surfaces of live cells offers the potential to manipulate and control their phenotype and underlying cellular processes. Conventional grafting-to strategies for conjugating preformed polymers to cell surfaces are limited by low polymer grafting efficiency. Here we report an alternative grafting-from strategy for directly engineering the surfaces of live yeast and mammalian cells through cell surface-initiated controlled radical polymerization. By developing cytocompatible PET-RAFT (photoinduced electron transfer-reversible addition-fragmentation chain-transfer polymerization), synthetic polymers with narrow polydispersity (M_w/M_n < 1.3) could be obtained at room temperature in 5 minutes. This polymerization strategy enables chain growth to be initiated directly from chain-transfer agents anchored on the surface of live cells using either covalent attachment or non-covalent insertion, while maintaining high cell viability. Compared with conventional grafting-to approaches, these methods significantly improve the efficiency of grafting polymer chains and enable the active manipulation of cellular phenotypes.

Parallel Control over Surface Charge and Wettability Using Polyelectrolyte Architecture: Effect on Protein Adsorption and Cell Adhesion

Surface charge and wettability, the two prominent physical factors governing protein adsorption and cell adhesion, have been extensively investigated in the literature. However, a comparison between these driving forces in terms of their independent and cooperative effects in affecting adhesion is rarely explored on a systematic and quantitative level. Herein, we formulate a protocol that features two-dimensional control over both surface charge and wettability with limited cross-parameter influence. This strategy is implemented by controlling both the polyion charge density in the layer-by-layer (LbL) assembly process and the polyion side-chain chemical structures. The 2D property matrix spans surface isoelectric points ranging from 5 to 9 and water contact angles from 35 to 70°, with other interferential factors (e.g., roughness) eliminated. The interplay between these two surface variables influences protein (bovine serum albumin, lysozyme) adsorption and 3T3 fibroblast cell adhesion. For proteins, we observe the presence of thresholds for surface wettability and electrostatic driving forces necessary to affect adhesion. Beyond these thresholds, the individual effects of electrostatic forces and wettability are observed. For fibroblast, both surface charge and wettability have an effect on its adhesion. The combined effects of positive charge and hydrophilicity lead to the highest cell adhesion, whereas negative charge and hydrophobicity lead to the lowest cell adhesion. Our design strategy can potentially form the basis for studying the distinct behaviors of electrostatic force or wettability driven interfacial phenomena and serve as a reference in future studies assessing protein adsorption and cell adhesion to surfaces with known charge and wettability within the property range studied here.

Progress and challenges of the bioartificial pancreas

Pancreatic islet transplantation has been validated as a treatment for type 1 diabetes since it maintains consistent and sustained type 1 diabetes reversal. However, one of the major challenges in pancreatic islet transplantation is the body's natural immune response to the implanted islets. Immunosuppressive drug treatment is the most popular immunomodulatory approach for islet graft survival. However, administration of immunosuppressive drugs gives rise to negative side effects, and long-term effects are not clearly understood. A bioartificial pancreas is a therapeutic approach to enable pancreatic islet transplantation without or with minimal immune suppression. The bioartificial pancreas encapsulates the pancreatic islets in a semi-permeable environment which protects islets from the body's immune responses, while allowing the permeation of insulin, oxygen, nutrients, and waste. Many groups have developed various types of the bioartificial pancreas and tested their efficacy in animal models. However, the clinical application of the bioartificial pancreas still requires further investigation. In this review, we discuss several types of bioartificial pancreases and address their advantages and limitations. We also discuss recent advances in bioartificial pancreas applications with microfluidic or micropatterning technology.

Contribution of polymeric materials to progress in xenotransplantation of microencapsulated cells: a review

Cell microencapsulation and subsequent transplantation of the microencapsulated cells require multidisciplinary approaches. Physical, chemical, biological, engineering, and medical expertise has to be combined. Several natural and synthetic polymeric materials and different technologies have been reported for the preparation of hydrogels, which are suitable to protect cells by microencapsulation. However, owing to the frequent lack of adequate characterization of the hydrogels and their components as well as incomplete description of the technology, many results of in vitro and in vivo studies appear contradictory or cannot reliably be reproduced. This review addresses the state of the art in cell microencapsulation with special focus on microencapsulated cells intended for xenotransplantation cell therapies. The choice of materials, the design and fabrication of the microspheres, as well as the conditions to be met during the cell microencapsulation process, are summarized and discussed prior to presenting research results of in vitro and in vivo studies. Overall, this review will serve to sensitize medically educated specialists for materials and technological aspects of cell microencapsulation.

Coating Strategies Using Layer-by-layer Deposition for Cell Encapsulation

The layer-by-layer (LbL) deposition technique is widely used to develop multilayered films based on the directed assembly of complementary materials. In the last decade, thin multilayers prepared by LbL deposition have been applied in biological fields, namely, for cellular encapsulation, due to their versatile processing and tunable properties. Their use was suggested as an alternative approach to overcome the drawbacks of bulk hydrogels, for endocrine cells transplantation or tissue engineering approaches, as effective cytoprotective agents, or as a way to control cell division. Nanostructured multilayered materials are currently used in the nanomodification of the surfaces of single cells and cell aggregates, and are also suitable as coatings for cell-laden hydrogels or other biomaterials, which may later be transformed to highly permeable hollow capsules. In this Focus Review, we discuss the applications of LbL cell encapsulation in distinct fields, including cell therapy, regenerative medicine, and biotechnological applications. Insights regarding practical aspects required to employ LbL for cell encapsulation are also provided.

Synthetic polycations with controlled charge density and molecular weight as building blocks for biomaterials

A series of polycations prepared by RAFT copolymerization of N-(3-aminopropyl)methacrylamide hydrochloride (APM) and N-(2-hydroxypropyl)methacrylamide, with molecular weights of 15 and 40 kDa, and APM content of 10-75 mol%, were tested as building blocks for electrostatically assembled hydrogels such as those used for cell encapsulation. Complexation and distribution of these copolymers within anionic calcium alginate gels, as well as cytotoxicity, cell attachment, and cell proliferation on surfaces grafted with the copolymers were found to depend on composition and molecular weight. Copolymers with lower cationic charge density and lower molecular weight showed less cytotoxicity and cell adhesion, and were more mobile within alginate gels. These findings aid in designing improved polyelectrolyte complexes for use as biomaterials.

Cell and Protein Recognition at a Supported Bilayer Interface via In Situ Cavitand-Mediated Functional Polymer Growth

Water-soluble deep cavitands embedded in a supported lipid bilayer are capable of anchoring ATRP initiator molecules for the in situ synthesis of primary amine-containing polymethacrylate patches at the water:membrane interface. These polymers can be derivatized in situ to incorporate fluorescent reporters, allow selective protein recognition, and can be applied to the immobilization of nonadherent cells at the bilayer interface.

Improving cell-based therapies by nanomodification

Cell-based therapies are emerging as a promising approach for various diseases. Their therapeutic efficacy depends on rational control and regulation of the functions and behaviors of cells during their treatments. Different from conventional regulatory strategy by chemical adjuvants or genetic engineering, which is restricted by limited synergistic regulatory efficiency or uncertain safety problems, a novel approach based on nanoscale artificial materials can be applied to modify living cells to endow them with novel functions and unique properties. Inspired by natural "nano shell" and "nano compass" structures, cell nanomodification can be developed through both external and internal pathways. In this review, some novel cell surface engineering and intracellular nanoconjugation strategies are summarized. Their potential applications are also discussed, including cell protection, cell labeling, targeted delivery and in situ regulation. It is believed that these novel cell-material complexes can have great potentials for biomedical applications.

Photophysical properties and synthesis of new dye-cyclooctyne conjugates for multicolor and advanced microscopy

Cyclooctyne conjugates with fluorophores are often used for bioorthogonal labeling in cells and tissues. However, no comprehensive library of one cyclooctyne core structure with different fluorescent dyes spanning the whole visible spectrum up to the NIR had been described so far. Hence, we synthesized and evaluated one cyclooctyne core structure which is easily accessible for the attachment of different dyes for multicolor imaging, FRET analysis, and study of metabolism in vivo. For these reasons we developed an easy one step synthesis starting from a known cyclooctyne. In combination with NHS-activated dyes, the cyclooctyne reacted to the dye DAB-MFCO conjugates within only 1-2 h at room temperature with high yields. We created conjugates with dyes that have high brightness and are bleaching stable with wavelengths from green to NIR. The ability to label glycans on cell surfaces was tested. All dye DAB-MFCO conjugates undergo click reactions on azide functionalized glycan structures with satisfactory photophysical properties. In total, seven different dye DAB-MFCO conjugates were synthesized; their photophysical properties and suitability for click labeling in biological applications were evaluated, making them suitable for single molecule and high resolution measurements.

Silk macromolecules with amino acid-poly(ethylene glycol) grafts for controlling layer-by-layer encapsulation and aggregation of recombinant bacterial cells

This study introduces double-brush designs of functionalized silk polyelectrolytes based upon regenerated silk fibroin (SF), which is modified with poly-L-lysine (SF-PLL), poly-L-glutamic acid (SF-PGA), and poly(ethylene glycol) (PEG) side chains with different grafting architecture and variable amino acid-PEG graft composition for cell encapsulation. The molecular weight of poly amino acids (length of side chains), molecular weight and degree of PEG grafting (D) were varied in order to assess the formation of cytocompatible and robust layer-by-layer (LbL) shells on two types of bacterial cells (Gram-negative and Gram-positive bacteria). We observed that shells assembled with charged polycationic amino acids adversely effected the properties of microbial cells while promoting the formation of large cell aggregates. In contrast, hydrogen-bonded shells with high PEG grafting density were the most cytocompatible, while promoting formation of stable colloidal suspensions of individual cell encapsulates. The stability to degradation of silk shells (under standard cell incubation procedure) was related to the intrinsic properties of thermodynamic bonding forces, with shells based on electrostatic interactions having stronger resistance to deterioration compared to pure hydrogen-bonded silk shells. By optimizing the charge density of silk polyelectrolytes brushes, as well as the length and the degree of PEG side grafts, robust and cytocompatible cell coatings were engineered that can control aggregation of cells for biosensor devices and other potential biomedical applications.

Optimum design of amphiphilic polymers bearing hydrophobic groups for both cell surface ligand presentation and intercellular cross-linking

Amphiphilic polymers bearing hydrophobic alkyl groups are expected to be applicable for both ligand presentation on the cell surface and intercellular crosslinking. To explore the optimum design for each application, we synthesized eight different acyl-modified dextrans with varying molecular weight, alkyl length, and alkyl modification degree. We found that the behenate-modified polymers retained on the cell surface longer than the palmitate-modified ones. Since the polymers were also modified with biotin, streptavidin can be presented on the cell surface through biotin-streptavidin recognition. The duration of streptavidin on the cell surface is longer in the behenate-modified polymer than the palmitate-modified one. As for the intercellular crosslinking, the palmitate-modified polymers were more efficient than the behenate-modified polymers. The findings in this research will be helpful to design the acyl-modified polymers for the cell surface engineering.

Molecular assembly of alkyl chain-grafted poly(l-lysine) tuned by backbone chain length and grafted alkyl chain

Alkyl chain-grafted poly(l-lysine) vesicles with tunable molecular assembly were prepared by varying the polypeptide chain length and grafted alkyl chains.

Assembly of bioactive multilayered nanocoatings on pancreatic islet cells: incorporation of α1-antitrypsin into the coatings

A novel multilayer deposition approach to the delivery of therapeutic proteins onto the surface of pancreatic islets, using a heparin polyaldehyde and glycol chitosan alternating layering scheme, has been developed for addressing the blood-mediated inflammatory reaction against islet cells.