Control of cell attachment through polyDNA hybridization

Nucleic acid amphiphiles: Synthesis, properties, and applications

Nucleic acid amphiphiles, referring to nucleic acids modified with large hydrophobic groups, have been widely used in programmable bioengineering. Since nucleic acids are intrinsically hydrophilic, the hydrophobic groups endow nucleic acid amphiphiles with unique properties, such as self-assembling, interactions with artificial or biological membranes, and transmembrane transport. Importantly, the hybridization or target binding capability of oligonucleotide itself supplies nucleic acid amphiphiles with excellent programmability. As a result, this type of molecule has attracted considerable attention in academic studies and has enormous potential for further applications. For a comprehensive understanding of nucleic acid amphiphiles, we review the reported research on nucleic acid amphiphiles from their molecular design to final applications, in which we summarize the synthetic strategies for nucleic acid amphiphiles and draw much attention to their unique properties in different contexts. Finally, a summary of the applications of nucleic acid amphiphiles in drug development, bioengineering, and bioanalysis are critically discussed.

Surface modulation of extracellular vesicles with cell-penetrating peptide-conjugated lipids for improvement of intracellular delivery to endothelial cells

Exosomes (diameter 30-200 nm) are a subtype of extracellular vesicles secreted by cells containing DNA, microRNA (miRNA), and proteins. Exosomes are expected to be valuable as a means of delivering drugs or functional miRNAs in treatment of diseases. However, the delivery of exosomes is not sufficiently effective, even though exosomes have intrinsic delivery functions. Cell-penetrating peptides (CPPs) are short peptide families that facilitate cellular intake of molecules and vesicles. We previously reported that the modification of cells, and liposomes with CPP-conjugated-lipids, CPPs conjugated with poly (ethylene glycol)-conjugated phospholipids (PEG-lipid), that induce adhesion by CPPs, can be useful for cell-based assays and harvesting liposomes. In this study, we aimed to modulate the exosome surface using Tat peptide (YGRKKRRQRRR)-PEG-lipids to improve intracellular delivery to endothelial cells. We isolated and characterized exosomes from the medium of HEK 293 T cell cultures. Tat conjugated PEG-lipids with different spacer molecular weights and lipid types were incorporated into exosomes using fluorescein isothiocyanate labeling to optimize the number of Tat-PEG-lipids immobilized on the exosome surface. The exosomes modified with Tat-PEG-lipids were incubated with human umbilical vein endothelial cells (HUVECs) to study the interaction. Tat conjugated with 5 kDa PEG and C16 lipids incorporated on the exosome surface were highly detected inside HUVECs by flow cytometry. Fluorescence was negligible in HUVECs for control groups. Thus, Tat-PEG-lipids can be modified on the exosome surface, improving the intracellular delivery of exosomes.

Lipid-mediated ex vivo cell surface engineering for augmented cellular functionalities

Once administrated, intercellular adhesion to recognize and/or arrest target cells is essential for specific treatments, especially for cancer or tumor. However, immune cells administrated into the tumor-microenvironment could lose their intrinsic functionalities such as target recognition ability, resulting in an ineffective cancer immunotherapy. Various manipulation techniques for decorating functional moieties onto cell surface and enhancing target recognition have been developed. A hydrophobic interaction-mediated ex-vivo cell surface engineering using lipid-based biomaterials could be a state-of-the-art engineering technique that could achieve high-efficiency cell surface modification by a single method without disturbance of intrinsic characteristics of cells. In this regard, this review provides design principles for the development of lipid-based biomaterials with a linear structure of lipid, polyethylene glycol, and functional group, strategies for the synthesis process, and their practical applications in biomedical engineering. Especially, we provide new insights into the development of a novel surface coating techniques for natural killer (NK) cells with engineering decoration of cancer targeting moieties on their cell surfaces. Among immune cells, NK cells are interesting cell population for substituting T cells because of their excellent safety and independent anticancer efficacy. Thus, optimal strategies to select cancer-type-specific targeting moieties and present them onto the surface of immune cells (especially, NK cells) using lipid-based biomaterials could provide additional tools to capture cancer cells for developing novel immune cell therapy products. Enhanced anticancer efficacies by surface-engineered NK cells have been demonstrated both in vitro and in vivo. Therefore, it could be speculated that recent progresses in cell surface modification technology via lipid-based biomaterials could strengthen immune surveillance and immune synapses for utilization in a next-generation cancer immunotherapy, beyond currently available genetic engineering tool such as chimeric antigen receptor-mediated immune cell modulation.

Rapalog-induced cell adhesion molecule inhibits mesoderm migration in Xenopus embryos by increasing frequency of adhesion to the ectoderm

During the gastrula stage of Xenopus laevis, mesodermal cells migrate on the blastocoel roof (BCR) toward the animal pole. In this process, mesodermal cells directly adhere to the BCR via adhesion molecules, such as cadherins, which in turn trigger a repulsive reaction through factors such as Eph/ephrin. Therefore, the mesoderm and BCR repeatedly adhere to and detach from each other, and the frequency of this adhesion is thought to control mesoderm migration. Although knockdown of cadherin or Eph/ephrin causes severe gastrulation defects, these molecules have been reported to contribute not only to boundary formation but also to the internal function of each tissue. Therefore, it is possible that the defect caused by knockdown occurs due to tissue function abnormalities. To address this problem, we developed a method to specifically induce adhesion between different tissues using rapalog (an analog of rapamycin). When adhesion between the BCR and mesoderm was specifically enhanced by rapalog, mesoderm migration was strongly suppressed. Furthermore, we confirmed that rapalog significantly increased the frequency of adhesion between the two tissues. These results support the idea that the adhesion frequency controls mesoderm migration, and demonstrate that our method effectively enhances adhesion between specific tissues in vivo.

Colonization of biofilm in wastewater treatment: A review

The attachment and colonization process of microorganisms on a carrier is an interdisciplinary research field. Through a series of physical, chemical, and biological actions, the microorganisms can eventually reproduce on the carrier. This article introduces biofilm start-up and its applications, and explores the current issues to look forward to future development directions. Firstly, the mechanism of microbial film formation is analyzed from the microbial community colonization and reproduction process. Secondly, when analyzing the factors influencing microbial membrane formation, the effect of microbial properties (e.g., genes, proteins, lipids) and external conditions (i.e., carrier, operating environment, and regulation mechanism among microbial communities) were discussed in depth. Aimed at exploring the mechanisms and influencing factors of biofilm start-up, this article proposes the application measures to strengthen this process. Finally, the problems encountered and the future development direction of the technology are analyzed and prospected.

Enhancement of intercellular interaction between iPSC-derived neural progenitor cells and activated endothelial cells using cell surface modification with functional oligopeptides

Cell-based therapy has been used to treat stroke related disorders, which have no treatment options available 4.5 hours after onset. Although the administration of tissue plasminogen activator and mechanical thrombectomy are potent treatments, their clinical implementation is limited within the available time. Here, we aimed to use induced pluripotent stem cell-derived neural progenitor cells (NPCs) for stroke treatment with higher delivery efficiency in stroke areas, which will improve the therapeutic effect. E-selectin binding oligopeptide (Esbp) was conjugated with poly(ethylene glycol)-conjugated-lipid (Esbp-PEG-lipid) with different molecular weights of PEG (5 and 40 kDa) for cell surface modification. Then, we optimized the cell surface modification of NPCs by studying cell-binding ability onto the model surfaces of stroke areas, such as recombinant E-selectin-immobilized surfaces and TNF-α activated endothelium. As a result, the cell surface modification of NPCs with Esbp-PEG-lipid was found to induce specific intercellular interactions with the activated endothelium through the binding of Esbp with E-selectin. Additionally, the shorter PEG spacer was suitable for intercellular interactions. Thus, our technique shows potential for use in cell therapy with enhanced cell accumulation in infarct areas.

Artificial Taste Buds: Bioorthogonally Ligated Gustatory-Neuronal Multicellular Hybrids Enabling Intercellular Taste Signal Transmission

Heterogeneous tissue models require the assembly and co-culture of multiple types of cells. Our recent work demonstrated taste signal transmission from gustatory cells to neurons by grafting single-stranded DNA into the cell membrane to construct multicellular assemblies. However, the weak DNA linkage and low grafting density allowed the formation of large gustatory cell self-aggregates that cannot communicate with neurons efficiently. This article presents the construction of artificial taste buds exhibiting active intercellular taste signal transmission through the hybridization of gustatory-neuronal multicellular interfaces using bioorthogonal click chemistry. Hybrid cell clusters were formed by the self-assembly of neonatal gustatory cells displaying tetrazine with a precultured embryonic hippocampal neuronal network displaying trans-cyclooctene. A bitter taste signal transduction was provoked in gustatory cells using denatonium benzoate and transmitted to neurons as monitored by intracellular calcium ion sensing. In the multicellular hybrids, the average number of signal transmissions was five to six peaks per cell, and the signal transmission lasted for ∼5 min with a signal-to-signal gap time of 10-40 s. The frequent and extended intercellular signal transmission suggests that the cell surface modification by the bioorthogonal click chemistry is a promising approach to fabricating functional multicellular hybrid clusters potentially useful for cell-based biosensors, toxicity assays, and tissue regeneration.

Accessing and Assessing the Cell-Surface Glycocalyx Using DNA Origami

The cell-surface glycocalyx serves as a physiological barrier regulating cellular accessibility to macromolecules and other cells. Conventional glycocalyx characterization has largely been morphological rather than functional. Here, we demonstrated direct glycocalyx anchoring of DNA origami nanotiles and performed a comprehensive comparison with traditional origami targeting to the phospholipid bilayer (PLB) using cholesterol. While DNA nanotiles effectively accessed single-stranded DNA initiators anchored on the glycocalyx, their accessibility to the underlying PLB was only permitted by extended nanotile-to-initiator spacing or by enzymatic glycocalyx degradation using trypsin or pathogenic neuraminidase. Thus, the DNA nanotiles, being expelled by the physiologic glycocalyx, provide an effective functional measure of the glycocalyx barrier integrity and faithfully predict cell-to-cell accessibility during DNA-guided multicellular assembly. Lastly, the glycocalyx-anchoring mechanism enabled enhanced cell-surface stability and cellular uptake of nanotiles compared to PLB anchoring. This research lays the foundation for future development of DNA nanodevices to access the cell surface.

Natural discoidal lipoproteins with tiny modification for tumor extracellular dissociation in antitumor chemoimmunotherapy

Appealing cancer immunotherapy requires synchronous presentation of tumor antigens and immunoadjuvant. Herein, a "one-step" modification strategy is proposed to tinily remould endogenous discoidal high density lipoprotein (dHDL) for tumor-homing and site-specific chemoimmunotherapy. For molecular targeting therapy, lipophilic immunoadjuvant CpG oligodeoxynucleotides is conjugated to facilitate HDL-surface anchoring; and GC nucleotides provide enough reservoir for completion of doxorubicin (Dox) "sandwich". After administration, the tiny size (~30 nm) of disc nanodrug can maneuver deeply into tumors for receptor binding and in situ structural collapse. The intracellular concentrated CpG-Dox induce potent immunogenic cell death from burst Dox liberation at acidic pH. In turn, the released antigens and CpG motifs are simultaneously recognized by dendritic cells for antigen presentation and antitumor T cell responses. Combination chemoimmunotherapy with discoidal nanodrugs performed highest tumor weight inhibitory of 93.2% and extend the median survival time at a safe level. Collectively, this study suggests that the minimalist revolution of natural dHDL particulates may provide a biomimicry nanoplatform for site-specific amplified chemoimmunotherapy.

Functional Immunostimulating DNA Materials: The Rising Stars for Cancer Immunotherapy

Cancer immunotherapy has risen as a promising method in clinical practice for cancer treatment and DNA-based immune intervention materials, along with DNA nanotechnology, have obtained increasing importance in this field. In this review, various immunostimulating DNA materials are introduced and the mechanisms via which they exerted an immune effect are explained. Then, representative examples in which DNA is used as the leading component for anticancer applications through immune stimulation are provided and their efficacy is evaluated. Finally, the challenges for those materials in clinical applications are discussed and suggestions for possible further research directions are also put forward.

Non-genetic cell-surface modification with a self-assembling molecular glue

This report describes the development of a non-genetic cell-surface modification method, in which a self-assembling small molecule is combined with Halo-tag proteins. Cell-surface functionalization with cancer-linked extracellular proteins led to enhanced cell motility, angiogenesis, and immune shielding of the cells, paving the way for translational opportunities for cell therapy.

Engineering reversible cell-cell interactions using enzymatically lipidated chemically self-assembled nanorings

Multicellular biology is dependent on the control of cell-cell interactions. These concepts have begun to be exploited for engineering of cell-based therapies. Herein, we detail the use of a multivalent lipidated scaffold for the rapid and reversible manipulation of cell-cell interactions. Chemically self-assembled nanorings (CSANs) are formed via the oligomerization of bivalent dihydrofolate reductase (DHFR2) fusion proteins using a chemical dimerizer, bis-methotrexate. With targeting proteins fused onto the DHFR2 monomers, the CSANs can target specific cellular antigens. Here, anti-EGFR or anti-EpCAM fibronectin-DHFR2 monomers incorporating a CAAX-box sequence were enzymatically prenylated, then assembled into the corresponding CSANs. Both farnesylated and geranylgeranylated CSANs efficiently modified the cell surface of lymphocytes and remained bound to the cell surface with a half-life of >3 days. Co-localization studies revealed a preference for the prenylated nanorings to associate with lipid rafts. The presence of antigen targeting elements in these bifunctional constructs enabled them to specifically interact with target cells while treatment with trimethoprim resulted in rapid CSAN disassembly and termination of the cell-cell interactions. Hence, we were able to determine that activated PBMCs modified with the prenylated CSANs caused irreversible selective cytotoxicity toward EGFR-expressing cells within 2 hours without direct engagement of CD3. The ability to disassemble these nanostructures in a temporally controlled manner provides a unique platform for studying cell-cell interactions and T cell-mediated cytotoxicity. Overall, antigen-targeted prenylated CSANs provide a general approach for the regulation of specific cell-cell interactions and will be valuable for a plethora of fundamental and therapeutic applications.

Potential of Cell Surface Engineering with Biocompatible Polymers for Biomedical Applications

The regulation of the cellular surface with biomaterials can contribute to the progress of biomedical applications. In particular, the cell surface is exposed to immunological surveillance and reactions in transplantation therapy, and modulation of cell surface properties might improve transplantation outcomes. The transplantation of therapeutic cells, tissue, and organs is an effective and fundamental treatment and has contributed to saving lives and improving quality of life. Because of shortages, donor cells, tissues, and organs are carefully transplanted with the goal of retaining activity and viability. However, some issues remain to be resolved in terms of reducing side effects, improving graft survival, managing innate and adaptive immune responses, and improving transplant storage and procedures. Given that the transplantation process involves multiple steps and is technically complicated, an engineering approach together with medical approaches to resolving these issues could enhance success. In particular, cell surface engineering with biocompatible polymers looks promising for improving transplantation therapy and has potential for other biomedical applications. Here we review the significance of polymer-based surface modification of cells and organs for biomedical applications, focusing on the following three topics: Cell protection: cellular protection through local immune regulation using cell surface modification with biocompatible polymers. This protection could extend to preventing attack by the host immune system, freeing recipients from taking immunosuppressive drugs, and avoiding a second transplantation. Cell attachment: cell manipulation, which is an important technique for delivery of therapeutic cells and their alignment for recellularization of decellularized tissues and organs in regenerative therapy. Cell fusion: fusion of different cells, which can lead to the formation of new functional cells that could be useful for generating, e.g., immunologically competent or metabolically active cells.

Identification of Metal-Binding Peptides and Their Conjugation onto Nanoparticles of Superparamagnetic Iron Oxides and Liposomes

Metallic materials are used for clinical medical devices such as vascular stents and coils to treat both ischemic and hemorrhagic vascular diseases. An antiplatelet drug is required to avoid thromboembolic complication until metallic surface is covered with a neo-endothelial cell layer. It is important to identify endothelial cell coverage on the metallic surface. However, it is difficult since there are no selective ligands. Here, we used the phage display method to identify peptide ligands that had high affinity for the metallic surface of Ni-Ti stents, Pt-W coils, and Co-Cr stents. The binding assay using fluorescence labeling revealed that several synthetic peptides could bind onto those surfaces. We also chose some oligopeptides for the conjugation onto superparamagnetic iron oxide (SPIO) nanoparticles and liposome-encapsulating SPIO nanoparticles and studied their ability to bind to the stent and coils. By SEM and fluorophotometry, we found that those modified SPIOs and liposomes were selectively bound onto those surfaces. In addition, both treated stents and coils could be detected by magnetic resonance imaging due to the magnetic artifact through the SPIOs and liposomes that were immobilized onto the surface. Thus, we identified metal-binding peptides which may enable to stop antiplatelet therapy after vascular stenting or coiling.

Targeted Repair of Vascular Injury by Adipose-Derived Stem Cells Modified with P-Selectin Binding Peptide

Percutaneous coronary intervention for coronary artery disease treatment often results in pathological vascular injury, characterized by P-selectin overexpression. Adipose-derived stem cells (ADSCs) therapeutic efficacy remains elusive due to poor ADSCs targeting and retention in injured vessels. Here, conjugated P-selectin binding peptide (PBP) to polyethylene glycol-conjugated phospholipid derivative (DMPE-PEG) linkers (DMPE-PEG-PBP; DPP) are used to facilitate the modification of PBP onto ADSCs cell surfaces via hydrophobic interactions between DMPE-PEG and the phospholipid bilayer. DPP modification neither has influence on ADSCs proliferation nor apoptosis/paracrine factor gene expression. A total of 5 × 10^-6 m DPP-modified ADSCs (DPP-ADSCs) strongly binds to P-selectin-displaying activated platelets and endothelial cells (ECs) in vitro and to wire-injured rat femoral arteries when administered by intra-arterial injection. Targeted binding of ADSCs shields injury sites from platelet and leukocyte adhesion, thereby decreasing inflammation at injury sites. Furthermore, targeted binding of ADSCs recovers injured ECs functionality and reduces platelet-initiated vascular smooth muscle cells (VSMCs) chemotactic migration. Targeted binding of DPP-human ADSCs to balloon-injured human femoral arteries is also demonstrated in ex vivo experiments. Overall, DPP-ADSCs promote vascular repair, inhibit neointimal hyperplasia, increase endothelium functionality, and maintain normal VSMCs alignment, supporting preclinical noninvasive utilization of DPP-ADSCs for vascular injury.

Promotion of cell membrane fusion by cell-cell attachment through cell surface modification with functional peptide-PEG-lipids

Cell fusion is a fundamental event in various biological processes and has been applied to a number of biotechnologies. However, cell fusion efficiency is still low and strongly depends on cell lines and skills, though some improvements have been made. Our hypothesis is that two distinct cell membranes need to be brought together for cell membrane fusion, which is important for mimicking cell fusion in vitro. Here, we aimed to improve the homogeneous and heterogeneous cell fusion efficiency using a cell-cell attachment technique. We modified cellular membranes with two distinctive poly(ethylene glycol)-lipids (PEG-lipids) carrying oligopeptide, three repeated units of the EIAALEK and KIAALKE sequences (fuE3 and fuK3, respectively), which induce cell-cell attachment. The ratio and area of cell-cell attachment can be controlled through surface modification with fuE3-and fuK3-PEG-lipids by changing the number of each incorporated peptide. By combining this technique with the PEG-induced method, the cell fusion efficiency was significantly improved for homogeneous and heterogeneous cell fusion compared to conventional PEG-induced methods. For homogeneous CCRF-CEM cell fusion, the efficiency increased up to 64% from the 8.4% with the PEG-induced method. In addition, for heterogeneous cell fusion of myeloma cells and splenocytes, the efficiency increased up to 18% from almost zero. Thus, cell membrane fusion could be promoted effectively between closely contacted cell membranes induced by the cell-cell attachment technique.

Quantitative evaluation of the impact of artificial cell adhesion via DNA hybridization on E-cadherin-mediated cell adhesion

Programmable cell adhesion with DNA hybridization is a promising approach for fabricating various tissue architectures without sophisticated instrumentation. However, little is known about how this artificial interaction influences the binding of cell adhesion proteins, E-cadherin. In this work, we designed a planar and fluid lipid membrane displaying E-cadherin and/or single-strand DNA with well-defined densities. Visualization of cells on membranes by fluorescence and interference microscopy revealed cell adhesion to be a two-step process: artificial adhesion by DNA hybridization within a few minutes followed by biological adhesion via cadherin-cadherin binding within hours. Furthermore, we discovered that DNA hybridization can substantially facilitate E-cadherin-mediated cell adhesion. The promotive effect is probably due to the enforced binding between E-cadherin molecules in geometrical confinement between two membranes. Our in vitro model of cell adhesion can potentially be used to design functional synthetic molecules that can regulate cell adhesion via cell adhesion proteins for tissue engineering.

Tuning intercellular adhesion with membrane-anchored oligonucleotides

Adhesive interactions between cells play an integral role in development, differentiation and regeneration. Existing methods for controlling cell-cell cohesion and adhesion by manipulating protein expression are constrained by biological interdependencies, e.g. coupling of cadherins to actomyosin force-feedback mechanisms. We use oligonucleotides conjugated to PEGylated lipid anchors (ssDNAPEGDPPE) to introduce artificial cell-cell adhesion that is largely decoupled from the internal cytoskeleton. We describe cell-cell doublets with a mechanical model based on isotropic, elastic deformation of spheres to estimate the adhesion at the cell-cell interface. Physical manipulation of adhesion by modulating the PEG-lipid to ssDNAPEGDPPE ratio, and conversely treating with actin-depolymerizing cytochalasin D, resulted in decreases and increases in doublet contact area, respectively. Our data are relevant to the ongoing discussion over mechanisms of tissue surface tension and in agreement with models based on opposing cortical and cohesive forces. PEG-lipid modulation of doublet geometries resulted in a well-defined curve indicating continuity, enabling prescriptive calibration for controlling doublet geometry. Our study demonstrates tuning of basic doublet adhesion, laying the foundation for more complex multicellular adhesion control independent of protein expression.

Multifunctionalization of Cells with a Self-Assembling Molecule to Enhance Cell Engraftment

Cell-based therapy is a promising approach to restoring lost functions to compromised organs. However, the issue of inefficient cell engraftment remains to be resolved. Herein, we take a chemical approach to facilitate cell engraftment by using self-assembling molecules which modify two cellular traits: cell survival and invasiveness. In this system, the self-assembling molecule induces syndecan-4 clusters on the cellular surface, leading to enhanced cell viability. Further integration with Halo-tag technology provided this self-assembly structure with matrix metalloproteinase-2 to functionalize cells with cell-invasion activity. In vivo experiments showed that the pretreated cells were able to survive injection and then penetrate and engraft into the host tissue, demonstrating that the system enhances cell engraftment. Therefore, cell-surface modification via an alliance between self-assembling molecules and ligation technologies may prove to be a promising method for cell engraftment.

DNA-mediated self-assembly of taste cells and neurons for taste signal transmission

Cells can communicate with one another through physical connections and chemical signaling, activating various signaling pathways that can affect cellular functions and behaviors. In taste buds, taste cells transmit taste information to neurons via paracrine signaling. However, no previous studies have reported the in vitro co-culture of taste and neuronal cells, which allows us to monitor intercellular communications and better understand the mechanism of taste perception. Here, we introduce the first investigation on the proximate assembly and co-culture of taste cells and neurons to monitor the intercellular transmission of taste signals. Taste cells and neurons are placed closely using a pair of single-stranded oligonucleotides conjugated with polyethylene glycol and a phospholipid. Complementary oligonucleotide conjugates are anchored into the cellular membrane of neonatal taste cells and embryonic hippocampal neuronal cells, respectively, and then the cells are self-assembled into a functional multicellular unit for taste perception. Treatment of the assembled cells with a bitter tastant generates the sequential influx of calcium ions into the cytoplasm in taste cells and then in neuronal cells. Our work demonstrates that the cellular self-assembly is critical for efficient taste signal transduction, which can be used as a promising platform to construct cell-based biosensors for taste sensing.

Asymmetric surface modification of yeast cells for living self-assembly

Electrostatic embedding of yeast cells in voids with similar size has been realized, which makes the bottom surface of the cells shielded. The free top surface of the cells was further decorated to afford asymmetric surface-modified living cells. Various self-assembled architectures of the cells were then constructed by changing the ratio of different cells with or without modification.

Influence of cell adhesive molecules attached onto PEG-lipid-modified fluid surfaces on cell adhesion

The involvement of intercellular interactions in various biological events indicates the importance of studying cell-cell interactions using fluid model surfaces. Here, we propose a fluid surface composed of a self-assembled monolayer (SAM) and poly(ethylene glycol)-conjugated phospholipid (PEG-lipid) derivatives, which can be an alternative to supported lipid membranes. The modification of SAM surfaces with PEG-lipids carrying functional peptides resulted in the formation of the fluid surfaces with different mobility, which was quantitatively determined by quartz crystal microbalance with dissipation (QCM-D) and fluorescence recovery after photobleaching (FRAP). Different types of fluid surfaces with calculated diffusion coefficients between 0.9 ± 0.25 and 0.16 ± 0.03 μm²/sec for PEG-lipids derivatives were fabricated, onto which arginylglycylaspartate (RGD) peptides were immobilized for cell adhesion, and compared to solid surfaces with the same surface density of RGD peptides. The fluid surfaces revealed that cell adhesions of epithelial cells (MCF-10 A) and human umbilical vein endothelial cells (HUVEC) could not be established on the surfaces with higher fluidity, while cells could adhere onto surfaces with lower fluidity, where the lateral diffusion of PEG-lipids was approximately 20 times lower, and solid surfaces. Interestingly, cells that adhered onto the surface with lower fluidity proliferated at a normal rate while maintaining their round morphology, which was a different shape from that observed on solid surfaces. Thus, the scaffold fluidity greatly influenced cell adhesion behaviors, demonstrating that it is an important parameter for designing novel biomimetic scaffolds for biomedical applications.

Immune lipoprotein nanostructures inspired relay drug delivery for amplifying antitumor efficiency

Chemo-immunotherapy represents an appealing approach to improving cancer treatment. Simultaneously administrating chemotherapeutics with immunoadjuvants can elicit potent tumor death and immune responses. Herein, high density lipoprotein (HDL) inspired immune lipoprotein was proposed for relay drug delivery and amplifying antitumor therapy. Lipophilic AS1411 aptamer-immunoadjuvant CpG fused sequences (Apt-CpG-DSPE) were conjugated to facilitate decoration onto HDLs; and doxorubicin (Dox) was successively intercalated into the consecutive base pairs of Apt-CpG to complete immune HDL nanodrug imHDL/Apt-CpG-Dox. For relay drug delivery, imHDL/Apt-CpG-Dox underwent site-specific structure collapse in tumor intercellular substances inspired from HDL biofunctions (sequential module I); subsequently, dissociated Apt-CpG-Dox was endocytosed into tumor cells mediated by the recognition of AS1411 and nucleolin (sequential module II), translocating Dox to nucleus and enabling tumor ablation and antigens release. The liberated CpG motif further evoked antigen recognition, induced vast secretion of pro-inflammatory cytokines and potentiated host antitumor immunity. Our studies demonstrated that HDL biomimetic platform based relay drug delivery strategy outperformed the monotherapy counterparts in malignant tumor models, eventually generating an augmented antitumor efficacy.

Nanoencapsulation of individual mammalian cells with cytoprotective polymer shell

Nanoencapsulation of individual mammalian cells has great potential in biomedical, biotechnological and bioelectronic applications. However, existing techniques for cell nanoencapsulation generally yield short sustaining period and loose structure of encapsulation shell, which fails to meet the long-term cytoprotection and immunosuppression requirements. Here, we report a mild method to realize the nanoencapsulation of individual mammalian cells by layer-by-layer (LbL) assembly of gelatin inner layer and cross-linking of poly(ethylene glycol) (PEG) outer layer through thiol-click chemistry. With the present method, the encapsulated individual HeLa cells showed a high viability, long persistence period and effective resistance against macro external entities and high physical stress. Moreover, on-demand cell release could also be achieved by selective cleavage of succinimide thioether linkage in the outer PEG layer. The approach presented here may provide a new and versatile method for the cleavable nanoencapsulation of individual mammalian cells.

Dissecting the stem cell niche with organoid models: an engineering-based approach

For many tissues, single resident stem cells grown in vitro under appropriate three-dimensional conditions can produce outgrowths known as organoids. These tissues recapitulate much of the cell composition and architecture of the in vivo organ from which they derive, including the formation of a stem cell niche. This has facilitated the systematic experimental manipulation and single-cell, high-throughput imaging of stem cells within their respective niches. Furthermore, emerging technologies now make it possible to engineer organoids from purified cellular and extracellular components to directly model and test stem cell-niche interactions. In this Review, we discuss how organoids have been used to identify and characterize stem cell-niche interactions and uncover new niche components, focusing on three adult-derived organoid systems. We also describe new approaches to reconstitute organoids from purified cellular components, and discuss how this technology can help to address fundamental questions about the adult stem cell niche.

Cell Adhesion Induced Using Surface Modification with Cell-Penetrating Peptide-Conjugated Poly(ethylene glycol)-Lipid: A New Cell Glue for 3D Cell-Based Structures

We synthesized a novel material, cell-penetrating peptide-conjugated poly(ethylene glycol)-lipid (CPP-PEG-lipid), that can induce the adhesion of floating cells. Firm cell adhesion with spreading could be induced by cell surface modification with the CPP-PEG-lipids. Cell adhesion was induced by CPPs but not by any other cationic short peptides we tested. Here, we demonstrated adherence using the floating cell line CCRF-CEM as well as primary human T cells, B cells, erythrocytes, and hepatocytes. As compared to cells grown in suspension, adherent cells were more rapidly induced to attach to substrates with the cell-surface modification. The critical factor for attachment was localization of CPPs at the cell membrane by PEG-lipids with PEG > 20 kDa. These cationic CPPs on PEG chains were able to interact with substrate surfaces such as polystyrene (PS) surfaces, glass surfaces, and PS microfibers that are negatively charged, inducing firm cell adhesion and cell spreading. Also, as opposed to normal cationic peptides that interact strongly with cell membranes, CPPs were less interactive with the cell surfaces because of their cell-penetrating property, making them more available for adhering cells to the substrate surface. No effects on cell viability or cell proliferation were observed after the induction of cell adhesion. With this technique, cells could be easily immobilized onto PS microfibers, an important step in fabricating 3D cell-based structures. Cells immobilized onto 3D PS microfibers were alive, and human hepatocytes showed normal production of urea and albumin on the microfibers. This method is novel in inducing firm cell adhesion via a one-step treatment.

Hyperbranched polyglycerols: recent advances in synthesis, biocompatibility and biomedical applications

Hyperbranched polyglycerol is one of the most widely studied biocompatible dendritic polymer and showed promising applications. Here, we summarized the recent advancements in the field.

Cell surface engineering to control cellular interactions

Cell surface composition determines all interactions of the cell with is environment, thus cell functions such as adhesion, migration and cell-cell interactions are likely to be controlled by engineering and manipulating cell membrane. Cell membranes present a rich repertoire of molecules, therefore a versatile ground for modification. However the complex and dynamic nature of the cell surface is also a major challenge for cell surface engineering that should also involve strategies compatible with cell viability. Cell surface engineering by selective chemical reactions or by the introduction of exogenous targeting ligands can be powerful tools for engineering novel interactions and control cell function. In addition to chemical conjugation and modification of functional groups, ligands of interest to modify the surface of cells include recombinant proteins, liposomes or nanoparticles. Here, we review recent efforts to perform changes to cell surface composition. We focus on the engineering of the cell surface with biological, chemical or physical methods to modulate cell functions and control cell-cell and cell-microenvironment interactions. Potential applications of cell surface engineering are also stated.

A hybrid of cells and pancreatic islets toward a new bioartificial pancreas

Cell surface engineering using single-stranded DNA-poly(ethylene glycol)-conjugated phospholipid (ssDNA-PEG-lipid) is useful for inducing cell-cell attachment two and three dimensionally. In this review, we summarize our recent techniques for cell surface engineering and their applications to islet transplantation. Because any DNA sequence can be immobilized onto the cell surface by hydrophobic interactions between ssDNA-PEG-lipid and the cellular membrane without impairing cell function, a cell-cell hybrid can be formed through the DNA hybridization. With this technique, it would be possible to create three-dimensional hybrid structures of pancreatic islets coated with various accessory cells, such as patients' own cells, mesenchymal and adipose-derived stem cells, endothelial progenitor cells, neural crest stem cells or regulatory T cells, which might significantly improve the outcome of islet transplantation in diabetic patients.

Minireview: Directed Differentiation and Encapsulation of Islet β-Cells-Recent Advances and Future Considerations

Diabetes mellitus has rapidly become a 21st century epidemic with the promise to create vast economic and health burdens, if left unchecked. The 2 major forms of diabetes arise from unique causes, with outcomes being an absolute (type 1) or relative (type 2) loss of functional pancreatic islet β-cell mass. Currently, patients rely on exogenous insulin and/or other pharmacologies that restore glucose homeostasis. Although these therapies have prolonged countless lives over the decades, the striking increases in both type 1 and type 2 diabetic diagnoses worldwide suggest a need for improved treatments. To this end, islet biologists are developing cell-based therapies by which a patient's lost insulin-producing β-cell mass is replenished. Pancreatic or islet transplantation from cadaveric donors into diabetic patients has been successful, yet the functional islet demand far surpasses supply. Thus, the field has been striving toward transplantation of renewable in vitro-derived β-cells that can restore euglycemia. Challenges have been numerous, but progress over the past decade has generated much excitement. In this review we will summarize recent findings that have placed us closer than ever to β-cell replacement therapies. With the promise of cell-based diabetes therapies on the horizon, we will also provide an overview of cellular encapsulation technologies that will deliver critical protection of newly implanted cells.

Programmed synthesis of three-dimensional tissues

Reconstituting tissues from their cellular building blocks facilitates the modeling of morphogenesis, homeostasis and disease in vitro. Here we describe DNA-programmed assembly of cells (DPAC), a method to reconstitute the multicellular organization of organoid-like tissues having programmed size, shape, composition and spatial heterogeneity. DPAC uses dissociated cells that are chemically functionalized with degradable oligonucleotide 'Velcro', allowing rapid, specific and reversible cell adhesion to other surfaces coated with complementary DNA sequences. DNA-patterned substrates function as removable and adhesive templates, and layer-by-layer DNA-programmed assembly builds arrays of tissues into the third dimension above the template. DNase releases completed arrays of organoid-like microtissues from the template concomitant with full embedding in a variety of extracellular matrix (ECM) gels. DPAC positions subpopulations of cells with single-cell spatial resolution and generates cultures several centimeters long. We used DPAC to explore the impact of ECM composition, heterotypic cell-cell interactions and patterns of signaling heterogeneity on collective cell behaviors.

A DNA hybridization system for labeling of neural stem cells with SPIO nanoparticles for MRI monitoring post-transplantation

Neural stem cells (NSCs) demonstrate encouraging results in cell replacement therapy for neurodegenerative disorders and traumatic injury in the central nervous system. Monitor the survival and migration of transplanted cells would provide us important information concerning the performance and integration of the graft during the therapy time course. Magnetic resonance imaging (MRI) allow us to monitor the transplanted cells in a non-invasive way. The only requirement is to use an appropriate contrast agent to label the transplanted cells. Superparamagnetic iron oxide (SPIO) nanoparticles are one of the most commonly used contrast agent for MRI detection of transplanted cells. SPIO nanoparticles demonstrated to be suitable for labeling several types of cells including NSCs. However, the current methods for SPIO labeling are non-specific, depending mostly on electrostatic interactions, demanding relatively high SPIO concentration, and long incubation time, which can affect the viability of cells. In this study, we propose a specific and relatively fast method to label NSCs with SPIO nanoparticles via DNA hybridization. Two short single stranded DNAs (ssDNAs), oligo[dT]20 and oligo[dA]20 were conjugated with a lipid molecule and SPIO nanoparticle respectively. The labeling process comprises two simple steps; first the cells are modified to present oligo[dT]20 ssDNA on the cell surface, then the oligo[dA]20 ssDNA conjugated with SPIO nanoparticles are presented to the modified cells to allow the oligo[dT]20-oligo[dA]20 hybridization. The method showed to be non-toxic at concentrations up to 50 μg/mL oligo[dA]20-SPIO nanoparticles. Presence of SPIO nanoparticles at cell surface and cell cytoplasm was verified by transmission electron microscopy (TEM). SPIO labeling via DNA hybridization demonstrated to not interfere on NSCs proliferation, aggregates formation, and differentiation. NSCs labeled with SPIO nanoparticles via DNA hybridization system were successfully detected by MRI in vitro as well in vivo. Cells transplanted into the rat brain striatum could be detected by MRI scanning up to 1 month post-transplantation.

Sequence-specific nuclease-mediated release of cells tethered by oligonucleotide phospholipids

Single-stranded oligonucleotide-conjugated lipids (ssDNA-PEG-lipids) that associate with the cell membrane confer to the cell an artificial adhesive capability via sequence-specific hybridization to complementary oligonucleotides, forming bonds of double stranded oligonucleotides (dsDNA). Such artificial tethers permit surface patterning of cells or controlled formation of cellular aggregates. However, the hybridization responsible for tethering cells to surfaces or to other cells is not trivially reversed under physiological conditions. In this study, we approach the unbinding of tethered cells by cleaving dsDNA bonds with restriction endonuclease BamHI or digesting bonds with the nonspecific nuclease Benzonase. The procedure was applied to CCRF-CEM cells bearing dsDNA suspended in isolation, cells tethered to glass substrates, and cells aggregated heterotypically with other ssDNA-bearing cells. Cells liberated from surfaces with BamHI could be flushed from flow chambers and viably recovered while the majority of cells not bearing enzyme recognition sequences were retained on the surface, and DNA-tethered cells could be nonspecifically recovered viably from surfaces after Benzonase treatment. Heterotypic aggregates of cells joined by recognition sequence DNA could be dispersed with 10 min exposure to BamHI while undispersed cells heterotypically aggregated with a control sequence remained. Likewise, 10 min exposure to Benzonase was sufficient to disperse aggregates independently of sequence. The potential to undo artificially engineered DNA-mediated adhesion offers new possibilities in the controlled arrangement of cells relative to other cells and in the study of membrane biophysics.

Cell surface modification with ssDNA-PEG-lipid for analysing intercellular interactions between different cells

Intercellular interactions are important in the development, immune responses, and functions of tissues and organs. Few methods are currently available for experimentally inducing and analysing cell-cell interaction in vitro. Here I propose a method to induce cell-cell attachment by cell surface modification with single-stranded DNA (ssDNA) and poly(ethylene glycol)-conjugated phospholipid (PEG-lipid) derivatives. The incorporation of an ssDNA pair (polyA20 and polyT20) into the cell membranes of two different cells was utilized to attach distinct cells through DNA hybridization. This technique enabled induction of cell-cell attachment between the same cell lines or different cell lines by controlling the contact area of two cells. Using this method, I investigated intercellular interactions, including the cell-in-cell invasion process, without impairing the interaction. I found that the normal cells MCF-10A were internalized into the cancer cells MCF-7, and that the intercellular interactions between them mainly involved the interaction of E-cadherin.

Cell Surface Engineering for Regulation of Immune Reactions in Cell Therapy

Transplantation of the pancreatic islets of Langerhans (islets) is a promising cell therapy for treating insulin-dependent type 1 diabetes mellitus. Islet transplantation is a minimally-invasive technique involving relatively simple surgery. However, after intraportal transplantation, the transplanted islets are attacked by the recipient's immune system, because they activate a number of systems, including coagulation, complement response, inflammation, immune rejection, and recurrence of autoimmune disease. We have developed a surface modification and microencapsulation technique that protects cells and islets with biomaterials and bioactive substances, which may be useful in clinical settings. This approach employs amphiphilic polymers, which can interact with lipid bilayer membranes, without increasing cell volume. Molecules attached to these polymers can protect transplanted cells and islets from attack by the host immune system. We expect that this surface modification technique will improve graft survival in clinical islet transplantation.

Multicellular assembly and light-regulation of cell-cell communication by conjugated polymer materials

Using cell-surface modification and biotin-streptavidin interactions, immune cells and target tumor cells are made to form multicellular assemblies. A polythiophene derivative can undergo cellular uptake, allowing the sensitization of oxygen under light irradiation. The subsequent generation of reactive oxygen species (ROS) regulates cell-cell communication in time and space.

Directing the assembly of spatially organized multicomponent tissues from the bottom up

The complexity of the human body derives from numerous modular building blocks assembled hierarchically across multiple length scales. These building blocks, spanning sizes ranging from single cells to organs, interact to regulate development and normal organismal function but become disorganized during disease. Here, we review methods for the bottom-up and directed assembly of modular, multicellular, and tissue-like constructs in vitro. These engineered tissues will help refine our understanding of the relationship between form and function in the human body, provide new models for the breakdown in tissue architecture that accompanies disease, and serve as building blocks for the field of regenerative medicine.