Cassie-Baxter Surfaces for Reversible, Barrier-Free Integration of Microfluidics and 3D Cell Culture.

3D cell culture and microfluidics both represent powerful tools for replicating critical components of the cell microenvironment; however, challenges involved in the integration of the two and compatibility with standard tissue culture protocols still represent a steep barrier to widespread adoption. Here we demonstrate the use of engineered surface roughness in the form of microfluidic channels to integrate 3D cell-laden hydrogels and microfluidic fluid delivery. When a liquid hydrogel precursor solution is pipetted onto a surface containing open microfluidic channels, the solid/liquid/air interface becomes pinned at sharp edges such that the hydrogel forms the "fourth wall" of the channels upon solidification. We designed Cassie-Baxter microfluidic surfaces that leverage this phenomenon, making it possible to have barrier-free diffusion between the channels and the hydrogel; in addition, sealing is robust enough to prevent leakage between the two components during fluid flow, but the sealing can also be reversed to facilitate recovery of the cell/hydrogel material after culture. This method was used to culture MDA-MB-231 cells in collagen, which remained viable and proliferated while receiving media exclusively through the microfluidic channels over the course of several days.

Hydrogel Patches on Live Cells through Surface-Mediated Polymerization.

Many naturally occurring cells possess an intrinsic ability to cross biological barriers that block conventional drug delivery, and these cells offer a possible mode of active transport across the blood-brain barrier or into the core of tumor masses. While many technologies for the formation of complete, nanoparticle-loaded coatings on cells exist, a complete coating on the cell surface would disrupt the interaction of cells with their environments. To address this issue, cell surface patches that partially cover cell surfaces might provide a superior approach for cell-mediated therapeutic delivery. The goal of this study is to establish a simplified approach to producing polymeric patches of arbitrary shapes on a live cell via surface-mediated photopolymerization. Cell surfaces were nonspecifically labeled with eosin, and polyethylene (glycol) diacrylate (PEGDA) coatings were directed to specific sites using 530 nm irradiation through a chrome-coated photomask. These coatings may entrap drug-loaded or imaging particles. The extent of nonspecific formation of PEGDA hydrogel coatings increased with irradiation time, light intensity, and initiating species; 40 mW/cm2 irradiation for 5 min delivered high-resolution patterns on the surface of A549 cells, and these cells remained viable for 48 h postpatterning with fluorescent nanoparticle-loaded coatings. This work first demonstrated the feasibility of photopatterning polymer patches directly on the surface of cells.

The Role of Surface Receptor Density in Surface-Initiated Polymerizations for Cancer Cell Isolation.

Fluid biopsies potentially offer a minimally invasive alternative to traditional tissue biopsies for the continual monitoring of metastatic cancer. Current established technologies for isolating circulating tumor cells (CTCs) suffer from poor purity and yield and require fixatives that preclude the collection of viable cells for longitudinal analyses of biological function. Antigen specific lysis (ASL) is a rapid, high-purity method of cell isolation based on targeted protective coatings on antigen-presenting cells and lysis depletion of unprotected antigen-negative cells. In ASL, photoinitiators are specifically labeled on cell surfaces that enable subsequent surface-initiated polymerization. Critically, the significant determinants of process yield have yet to be investigated for this emerging technology. In this work, we show that the labeling density of photoinitiators is strongly correlated with the yield of intact cells during ASL by flow cytometry analysis. Results suggest ASL is capable of delivering ∼25% of targeted cells after isolation using traditional antibody labeling approaches. Monomer formulations of two molecular weights of PEG-diacrylate (Mn ∼ 575 and 3500) are examined. The gelation response during ASL polymerization is also investigated via protein microarray analogues on planar glass. Finally, a density threshold of photoinitiator labeling required for protection during lysis is determined for both monomer formulations. These results indicate ASL is a promising technology for high yield CTC isolation for rare-cell function assays and fluid biopsies.

Relative Contribution of Lateral Packing Density to Albumin Adsorption on Monolayers.

The effect of functional group density on protein adsorption is systematically studied to support ongoing efforts in molecular imprinting of surfaces and bulk materials. In these applications, functional commodity chemicals are molded to complement the shape and chemistry of the target molecule. Here, we study the relationship between bovine serum albumin adsorption and ligand density for carboxylate, alcohol, and alkyl terminal groups. Control surfaces consisting of densely packed self-assembled monolayers (SAMs) are contrasted with low-density SAMs formed through thiol-yne chemistry. Direct comparison consistently yielded greater protein adsorption on low-density SAMs than conventional pure component SAMs of the same functional group. Critically, the carboxylate and alcohol low-density SAMS are more hydrophobic than their analogous dense SAMs. Mixed functional group, dense SAMs were formed with alkyl diluents to match the hydrophobicity of the low-density SAMs. Once hydrophobicity is matched, the dense carboxylate and alcohol SAMs have higher adsorption than the low-density SAMs. We conclude (1) surface charge and hydrophobicity trends dominate over surface density contributions; (2) when hydrophobicity is matched, greater adsorption occurs on dense hydrophilic groups than on lower density hydrophilic groups; (3) when hydrophobicity is matched, greater adsorption occurs on lower density hydrophobic groups than on higher density hydrophobic groups.

Toward Spatiotemporally Controlled Synthesis of Photoresponsive Polymers: Computational Design of Azobenzene-Containing Monomers for Light-Mediated ROMP.

Density functional theory calculations have been used to identify the optimum design for a novel, light-responsive ring monomer expected to allow spatial and temporal control of ring-opening metathesis polymerization (ROMP) via light-mediated changes in ring strain energy. The monomer design leverages ring-shaped molecules composed of 4,4'-diaminoazobenzene (ABn) closed by alkene-α,ω-dioic acid linkers. The atomic geometries, formation enthalpies and ring strain energies of azobenzene (AB)-containing rings with various length linkers have been calculated. The AB(2,2) monomer is identified as having optimal properties for light-mediated ROMP, including high thermodynamic stability, low ring strain energy (RSE) with cis-AB, and high RSE with trans-AB. Time-dependent DFT calculations have been used to explore the photoisomerization mechanism of isolated AB and AB-containing rings, and calculations show that trans-to-cis and cis-to-trans photoisomerization of the optimal AB(2,2) ring molecule can be achieved with monochromatic green and blue light, respectively. The AB(2,2) monomer identified here is expected to allow precise, reversible, spatial and temporal light-mediated control of ROMP through AB photoisomerization, and to have promising potential applications in the fabrication of patterned and/or responsive AB-containing polymer materials.

Photopatterning of stable, low-density, self-assembled monolayers on gold.

Photoinitiated thiol-yne chemistry is utilized as a click reaction for grafting of acid-terminated alkynes to thiol-terminated monolayers on a gold substrate to create stable, low-density monolayers. The resulting monolayers are compared with a well-packed 11-mercaptoundecanoic acid monolayer and the analogous low-density monolayers prepared through a solution phase synthetic approach. The overall structuring of the monolayer prepared by solid-phase grafting is characterized by contact angle goniometry and Fourier transform infrared spectroscopy. The results show that the product monolayer has an intermediate surface energy and a more disordered chemical structuring compared to a traditional well-packed self-assembled monolayer, showing a low-packing density of the chains at the monolayer surface. The monolayer's structure and electrochemical stability were studied by reductive desorption of the thiolates. The prepared low-density monolayers have a higher electrochemical stability than traditional well-packed monolayers, which results from the crystalline structure at the gold interface. This technique allows for simple, fast preparation of low-density monolayers of higher stability than well-packed monolayers. The use of a photomask to restrict light access to the substrate yielded these low-density monolayers in patterned regions defined by light exposure. This general thiol-yne approach is adaptable to a variety of analogous low-density monolayers with diverse chemical functionalities.

Characterization of molecular transport in ultrathin hydrogel coatings for cellular immunoprotection.

PEG hydrogels are routinely used in immunoprotection applications to hide foreign cells from a host immune system. Size-dependent transport is typically exploited in these systems to prevent access by macromolecular elements of the immune system while allowing the transport of low molecular weight nutrients. This work studies a nanoscale hydrogel coating for improved transport of beneficial low molecular weight materials across thicker hydrogel coatings while completely blocking transport of undesired larger molecular weight materials. Coatings composed of PEG diacrylate of molecular weight 575 and 3500 Da were studied by tracking the transport of fluorescently labeled dextrans across the coatings. The molecular weight of dextran at which the transport is blocked by these coatings are consistent with cutoff values in analogous bulk PEG materials. Additionally, the diffusion constants of 4 kDa dextrans across PEG 575 coatings (9.5 × 10(-10)-2.0 × 10(-9) cm(2)/s) was lower than across PEG 3500 coatings (5.9-9.8 × 10(-9) cm(2)/s), and these trends and magnitudes agree with bulk scale models. Overall, these nanoscale thin PEG diacrylate films offer the same size selective transport behavior of bulk PEG diacrylate materials, while the lower thickness translates directly to increased flux of beneficial low molecular weight materials.

Thiol-yne adsorbates for stable, low-density, self-assembled monolayers on gold.

We present a novel approach toward carboxylate-terminated, low-density monolayers on gold, which provides exceptional adsorbate stability and conformational freedom of interfacial functional groups. Adsorbates are synthesized through the thiol-yne addition of two thiol-containing head groups to an alkyne-containing tail group. The resulting monolayers have two distinct phases: a highly crystalline head phase adjacent to the gold substrate, and a reduced density tail phase, which is in contact with the environment. The ellipsometric thickness of 27 Å is consistent with the proposed structure, where a densely packed decanedithiol monolayer is capped with an 11 carbon long, second layer at 50% lateral chain density. The Fourier transform infrared peak at 1710 cm(-1) supports the presence of the carbonyl group. Further, the peaks associated with asymmetric and symmetric methylene stretching are shifted toward higher wavenumbers compared to those of well-packed self-assembled monolayers (SAMs), which shows a lower average crystallinity of the thiol-yne monolayers compared to a typical monolayer. Contact angle measurements indicate an intermediate surface energy for the thiol-yne monolayer surface, owing to the contribution of exposed methylene functionality at the surface in addition to the carbonyl terminal group. The conformational freedom at the surface was demonstrated through remodeling the thiol-yne surface under an applied potential. Changes in the receding contact angle in response to an external potential support the capacity for reorientation of the surface presenting groups. Despite the low packing at the solution interface, thiol-yne monolayers are resistant to water and ion transport (R(f) ~ 10(5)), supporting the presence of a densely structured layer at the gold surface. Further, the electrochemical stability of the thiol-yne adsorbates exceeded that of well-packed SAMs, requiring a more reductive potential to desorb the thiol-yne monolayers from the gold surface. The thiol-yne monolayer approach is not limited to carboxylate functionality and is readily adapted for low-density monolayers of varied functionality.

Spontaneous Alignment of Myotubes Through Myogenic Progenitor Cell Migration.

In large-volume muscle injuries, widespread damage to muscle fibers and the surrounding connective tissue prevents myogenic progenitor cells (MPCs) from initiating repair. There is a clinical need to rapidly fabricate large muscle tissue constructs for integration at the site of large volume muscle injuries. Most strategies for myotube alignment require microfabricated structures or prolonged orientation times. We utilize the MPC's natural propensity to close gaps across an injury site to guide alignment on collagen I. When MPCs are exposed to an open boundary free of cells, they migrate unidirectionally into the cell-free region and align perpendicular to the original boundary direction. We study the utility of this phenomenon with biotin-streptavidin adhesion to position the cells on the substrate, and then demonstrate the robustness of this strategy with unmodified cells, creating a promising tool for MPC patterning without interrupting their natural function. We preposition MPCs in straight-line patterns separated with small gaps. This temporary positioning initiates the migratory nature of the MPCs to align and form myotubes across the gaps, similar to how they migrate and align with a single open boundary. There is a directional component to the MPC migration perpendicular (90°) to the original biotin-streptavidin surface patterns. The expression of myosin heavy chain, the motor protein of muscle thick filaments, is confirmed through immunocytochemistry in myotubes generated from MPCs in our patterning process, acting as a marker of skeletal muscle differentiation. The rapid and highly specific binding of biotin-streptavidin allows for quick formation of temporary patterns, with MPC alignment based on natural regenerative behavior rather than complex fabrication techniques.

Gelatin coating enhances therapeutic cell adhesion to the infarcted myocardium via ECM binding.

Acute myocardial infarction (AMI) results in weakening of the heart muscle and an increased risk for chronic heart failure. Therapeutic stem cells have been shown to reduce inflammatory signaling and scar tissue expansion, despite most of these studies being limited by poor retention of cells. Gelatin methacrylate (GelMA) coatings have been shown to increase the retention of these therapeutic cells near the infarct. In this work, we evaluate two different potential binding partners for GelMA-coated bone marrow cells (BMCs) and myocardial tissue: the extracellular matrix (ECM) and interstitial non-cardiomyocytes. While cells containing ß1 integrins mediate cell-ECM adhesion in vivo, these cells do not promote binding to our collagen-degraded, GelMA coating. Specifically, microscopic imagining shows that even with high integrin expression, GelMA-coated BMCs do not bind to cells within the myocardium. Alternatively, BMC incubation with decellularized heart tissue results in higher adhesion of coated cells versus uncoated cells supporting our GelMA-ECM binding mode. To further evaluate the ECM binding mode, cells were incubated on slides modified with one of three different major heart ECM components: collagen, laminin, or fibronectin. While all three components promoted higher adhesion than unmodified glass, collagen-coated slides resulted in a significantly higher adhesion of GelMA-coated BMCs over laminin and fibronectin. Incubation with unmodified BMCs confirmed that without a GelMA coating minimal adhesion of BMCs occurred. We conclude that GelMA cellular coatings significantly increase the binding of cells to collagen within the ECM. Our results provide progress towards a biocompatible and easily translatable method to enhance the retention of transplanted cells in human studies.

Glucose oxidase-mediated polymerization as a platform for dual-mode signal amplification and biodetection.

We report the first use of a polymerization-based ELISA substrate solution employing enzymatically mediated radical polymerization as a dual-mode amplification strategy. Enzymes are selectively coupled to surfaces to generate radicals that subsequently lead to polymerization-based amplification (PBA) and biodetection. Sensitivity and amplification of the polymerization-based detection system were optimized in a microwell strip format using a biotinylated microwell surface with a glucose oxidase (GOx)-avidin conjugate. The immobilized GOx is used to initiate polymerization, enabling the detection of the biorecognition event visually or through the use of a plate reader. Assay response is compared to that of an enzymatic substrate utilizing nitroblue tetrazolium in a simplified assay using biotinylated wells. The polymerization substrate exhibits equivalent sensitivity (2 µg/mL of GOx-avidin) and over three times greater signal amplification than this traditional enzymatic substrate since each radical that is enzymatically generated leads to a large number of polymerization events. Enzyme-mediated polymerization proceeds in an ambient atmosphere without the need for external energy sources, which is an improvement upon previous PBA platforms. Substrate formulations are highly sensitive to both glucose and iron concentrations at the lowest enzyme concentrations. Increases in amplification time correspond to higher assay sensitivities with no increase in non-specific signal. Finally, the polymerization substrate generated a signal to noise ratio of 14 at the detection limit (156 ng/mL) in an assay of transforming growth factor-beta.

Increased yield of gelatin coated therapeutic cells through cholesterol insertion.

Gelatin coatings are effective in increasing the retention of MSCs injected into the heart and minimizing the damage from acute myocardial infarction (AMI), but early studies suffered from low fractions of the MSCs coated with gelatin. Biotinylation of the MSC surface is a critical first step in the gelatin coating process, and in this study, we evaluated the use of biotinylated cholesterol "lipid insertion" anchors as a substitute for the covalent NHS-biotin anchors to the cell surface. Streptavidin-eosin molecules, where eosin is our photoinitiator, can then be bound to the cell surface through biotin-streptavidin affinity. The use of cholesterol anchors increased streptavidin density on the surface of MSCs further driving polymerization and allowing for an increased fraction of MSCs coated with gelatin (83%) when compared to NHS-biotin (52%). Additionally, the cholesterol anchors increased the uniformity of the coating on the MSC surface and supported greater numbers of coated MSCs even when the streptavidin density was slightly lower than that of an NHS-biotin anchoring strategy. Critically, this improvement in gelatin coating efficiency did not impact cytokine secretion and other critical MSC functions. Proper selection of the cholesterol anchor and the biotinylation conditions supports cellular function and densities of streptavidin on the MSC surface of up to ~105 streptavidin molecules/µm2 . In all, these cholesterol anchors offer an effective path towards the formation of conformal coatings on the majority of MSCs to improve the retention of MSCs in the heart following AMI.

Increased Retention of Cardiac Cells to a Glass Substrate through Streptavidin-Biotin Affinity.

In vitro analysis of primary isolated adult cardiomyocyte physiological processes often involves optical imaging of dye-loaded cells on a glass substrate. However, when exposed to rapid solution changes, primary cardiomyocytes often move to compromise quantitative measures. Improved immobilization of cells to glass would permit higher throughput assays. Here, we engineer the peripheral membrane of cardiomyocytes with biotin to anchor cardiomyocytes to borosilicate glass coverslips functionalized with streptavidin. We use a rat cardiac myoblast cell line to determine general relationships between processing conditions, ligand density on the cell and the glass substrate, cellular function, and cell retention under shear flow. Use of the streptavidin-biotin system allows for more than 80% retention of cardiac myoblasts under conventional rinsing procedures, while unmodified cells are largely rinsed away. The adhesion system enables the in-field retention of cardiac cells during rapid fluid changes using traditional pipetting or a modern microfluidic system at a flow rate of 160 mL/min. Under fluid flow, the surface-engineered primary adult cardiomyocytes are retained in the field of view of the microscope, while unmodified cells are rinsed away. Importantly, the engineered cardiomyocytes are functional following adhesion to the glass substrate, where contractions are readily observed. When applying this adhesion system to cardiomyocyte functional analysis, we measure calcium release transients by caffeine induction at an 80% success rate compared to 20% without surface engineering.

Polymer Cell Surface Coating Enhances Mesenchymal Stem Cell Retention and Cardiac Protection.

Mesenchymal stem cell (MSC) therapy has been widely tested in clinical trials to promote healing post-myocardial infarction. However, low cell retention and the need for a large donor cell number in human studies remain a key challenge for clinical translation. Natural biomaterials such as gelatin are ideally suited as scaffolds to deliver and enhance cell engraftment after transplantation. A potential drawback of MSC encapsulation in the hydrogel is that the bulky matrix may limit their biological function and interaction with the surrounding tissue microenvironment that conveys important injury signals. To overcome this limitation, we adopted a gelatin methacrylate (gelMA) cell-coating technique that photocross-links gelatin on the individual cell surface at the nanoscale. The present study investigated the cardiac protection of gelMA coated, hypoxia preconditioned MSCs (gelMA-MSCs) in a murine myocardial infarction (MI) model. We demonstrate that the direct injection of gelMA-MSC results in significantly higher myocardial engraftment 7 days after MI compared to uncoated MSCs. GelMA-MSC further amplified MSC benefits resulting in enhanced cardioprotection as measured by cardiac function, scar size, and angiogenesis. Improved MSC cardiac retention also led to a greater cardiac immunomodulatory function after injury. Taken together, this study demonstrated the efficacy of gelMA-MSCs in treating cardiac injury with a promising potential to reduce the need for donor MSCs through enhanced myocardial engraftment.

Adhesive stem cell coatings for enhanced retention in the heart tissue.

Injection into the heart tissue is a direct route for optimally placing mesenchymal stem cells (MSC) to regulate local inflammation following a heart attack. The retention of MSCs at the injection site is severely limited by the fluid flows that rapidly wash cells away and minimize their capacity to modulate cardiac inflammation. To prevent this loss of MSCs and their function, antibody coatings were designed for the surface of MSCs to enhance their adhesion to the inflamed tissue. MSCs were biotinylated, and biotinylated antibodies against intercellular cell adhesion molecules were conjugated to the cell surface through an intermediate layer of streptavidin. MSC surfaces were modified with ~7,000 biotin/µm2 and ~23 antibodies/µm2. The heart tissue injection of antibody-coated MSCs offered a 3-fold increase of cell retention in an infarcted heart over the injection of uncoated MSCs. We supported the mechanism of adhesion through analysis of MSC adhesion to inflamed endothelial cells and also surfaces of purified adhesion molecules on glass under microfluidic shear flow.

Cell Death Persists in Rapid Extrusion of Lysis-Resistant Coated Cardiac Myoblasts.

As the demand for organ transplants continues to grow faster than the supply of available donor organs, a new source of functional organs is needed. High resolution high throughput 3D bioprinting is one approach towards generating functional organs for transplantation. For high throughput printing, the need for increased print resolutions (by decreasing printing nozzle diameter) has a consequence: it increases the forces that cause cell damage during the printing process. Here, a novel cell encapsulation method provides mechanical protection from complete lysis of individual living cells during extrusion-based bioprinting. Cells coated in polymers possessing the mechanical properties finely-tuned to maintain size and shape following extrusion, and these encapsulated cells are protected from mechanical lysis. However, the shear forces imposed on the cells during extrusion still cause sufficient damage to compromise the cell membrane integrity and adversely impact normal cellular function. Cellular damage occurred during the extrusion process independent of the rapid depressurization.

Surface-initiated growth of ionomer films from pt-modified gold electrodes.

The ability to chemically wire ionomer films to electrode surfaces can promote transport near interfaces and impact a host of energy-related applications. Here, we demonstrate proof-of-concept principles for the surface-initiated ring-opening metathesis polymerization (SI-ROMP) of norbornene (NB), 5-butylnorbornene (NBH4), and 5-perfluorobutylnorbornene (NBF4) from Pt-modified gold substrates and the subsequent sulfonation of olefins along the polymer backbones to produce ultrathin sulfonated polymer films. Prior to sulfonation, the films are hydrophobic and exhibit large barriers against ion transport, but sulfonation dramatically reduces the resistance of the films by providing pathways for proton diffusion. Sulfonated films derived from NBF4 and NBH4 yield more anodic potentials for oxygen reduction than those derived from NB or unfunctionalized electrodes. These improvements are consistent with hydrophobic structuring by the fluorocarbon or hydrocarbon side groups to minimize interfacial flooding and generate pathways for enhanced O(2) permeation near the interface. Importantly, we demonstrate that the sulfonated polymer chains remain anchored to the surface during voltammetry for oxygen reduction whereas short-chain thiolates that do not tether polymer are removed from the substrate. This approach, which we extend to unmodified gold electrodes at neutral pH, presents a method of cleaning the ionomer/electrode interface to remove molecular components that may hamper the performance of the electrode.

Coatings on mammalian cells: interfacing cells with their environment.

The research community is intent on harnessing increasingly complex biological building blocks. At present, cells represent a highly functional component for integration into higher order systems. In this review, we discuss the current application space for cellular coating technologies and emphasize the relationship between the target application and coating design. We also discuss how the cell and the coating interact in common analytical techniques, and where caution must be exercised in the interpretation of results. Finally, we look ahead at emerging application areas that are ideal for innovation in cellular coatings. In all, cellular coatings leverage the machinery unique to specific cell types, and the opportunities derived from these hybrid assemblies have yet to be fully realized.

Gelatin Based Polymer Cell Coating Improves Bone Marrow-Derived Cell Retention in the Heart after Myocardial Infarction.

BACKGROUND: Acute myocardial infarction (AMI) and the ensuing ischemic heart disease are approaching an epidemic state. Limited stem cell retention following intracoronary administration has reduced the clinical efficacy of this novel therapy. Polymer based cell coating is biocompatible and has been shown to be safe. Here, we assessed the therapeutic utility of gelatin-based biodegradable cell coatings on bone marrow derived cell retention in ischemic heart. METHODS: Gelatin based cell coatings were formed from the surface-mediated photopolymerization of 3% gelatin methacrylamide and 1% PEG diacrylate. Cell coating was confirmed using a multimodality approach including flow cytometry, imaging flow cytometry (ImageStream System) and immunohistochemistry. Biocompatibility of cell coating, metabolic activity of coated cells, and the effect of cell coating on the susceptibility of cells for engulfment were assessed using in vitro models. Following myocardial infarction and GFP+ BM-derived mesenchymal stem cell transplantation, flow cytometric and immunohistochemical assessment of retained cells was performed. RESULTS: Coated cells are viable and metabolically active with coating degrading within 72 h in vitro. Importantly, cell coating does not predispose bone marrow cells to aggregation or increase their susceptibility to phagocytosis. In vitro and in vivo studies demonstrated no evidence of heightened immune response or increased phagocytosis of coated cells. Cell transplantation studies following myocardial infarction proved the improved retention of coated bone marrow cells compared to uncoated cells. CONCLUSION: Gelation based polymer cell coating is biologically safe and biodegradable. Therapies employing these strategies may represent an attractive target for improving outcomes of cardiac regenerative therapies in human studies.

Comparison of eosin and fluorescein conjugates for the photoinitiation of cell-compatible polymer coatings.

Targeted photopolymerization is the basis for multiple diagnostic and cell encapsulation technologies. While eosin is used in conjunction with tertiary amines as a water-soluble photoinitiation system, eosin is not widely sold as a conjugate with antibodies and other targeting biomolecules. Here we evaluate the utility of fluorescein-labeled bioconjugates to photopolymerize targeted coatings on live cells. We show that although fluorescein conjugates absorb approximately 50% less light energy than eosin in matched photopolymerization experiments using a 530 nm LED lamp, appreciable polymer thicknesses can still be formed in cell compatible environments with fluorescein photosensitization. At low photoinitiator density, eosin allows more sensitive initiation of gelation. However at higher functionalization densities, the thickness of fluorescein polymer films begins to rival that of eosin. Commercial fluorescein-conjugated antibodies are also capable of generating conformal, protective coatings on mammalian cells with similar viability and encapsulation efficiency as eosin systems.