Patterned co-culture of primary hepatocytes and fibroblasts using polyelectrolyte multilayer templates

This paper describes the formation of patterned cell co-cultures using the layer-by-layer deposition of synthetic ionic polymers and without the aid of adhesive proteins/ligands such as collagen or fibronectin. In this study, we used synthetic polymers, namely poly(diallyldimethylammonium chloride) (PDAC) and sulfonated polystyrene (SPS) as the polycation and polyanion, respectively, to build the multilayer films. We formed SPS patterns on polyelectrolyte multilayer (PEM) surfaces either by microcontact printing PDAC onto SPS surfaces or vice-versa. To create patterned co-cultures on PEMs, we capitalize on the preferential attachment and spreading of primary hepatocytes on SPS as opposed to PDAC surfaces. In contrast, fibroblasts readily attached to both PDAC and SPS surfaces, and as a result, we were able to obtain patterned co-cultures of fibroblast and primary hepatocytes on synthetic PEM surfaces. We characterized the morphology and hepatic-specific functions of the patterned cell co-cultures with microscopy and biochemical assays. Our results suggest an alternative approach to fabricating controlled co-cultures with specified cell-cell and cell-surface interactions; this approach provides flexibility in designing cell-specific surfaces for tissue engineering applications.     

Tunable resistive m-dPEG acid patterns on polyelectrolyte multilayers at physiological conditions: template for directed deposition of biomacromolecules

This paper describes a new class of salt-responsive poly(ethylene glycol) (PEG) self-assembled monolayers (SAMs) on top of polyelectrolyte multilayer (PEMs) films. PEM surfaces with poly(diallyldimethylammonium chloride) as the topmost layer are chemically patterned by microcontact printing (muCP) oligomeric PEG molecules with an activated carboxylic acid terminal group (m-dPEG acid). The resistive m-d-poly(ethylene glycol) (m-dPEG) acid molecules on the PEMs films were subsequently removed from the PEM surface with salt treatment, thus converting the nonadhesive surfaces into adhesive surfaces. The resistive PEG patterns facilitate the directed deposition of various macromolecules such as polymers, dyes, colloidal particles, proteins, liposomes, and nucleic acids. Further, these PEG patterns act as a universal resist for different types of cells (e.g., primary cells, cell lines), thus permitting more flexibility in attaching a wide variety of cells to material surfaces. The patterned films were characterized by optical microscopy and atomic force microscopy (AFM). The PEG patterns were removed from the PEM surface at certain salt conditions without affecting the PEM films underneath the SAMs. Removal of the PEG SAMs and the stability of the PEM films underneath it were characterized with ellipsometry and optical microscopy. Such salt- and pH-responsive surfaces could lead to significant advances in the fields of tissue engineering, targeted drug delivery, materials science, and biology.     

Superlow fouling sulfobetaine and carboxybetaine polymers on glass slides

This work describes the superlow fouling properties of glass slides grafted with zwitterionic polymers to highly resist the adsorption of proteins and the adhesion of mammalian cells. Glass slides were first silanized using 2-bromo-2-methyl-N-3-[(triethoxysilyl)propyl]propanamide (BrTMOS). Two zwitterionic polymers, poly(sulfobetaine methacrylate) (polySBMA) and poly(carboxybetaine methacrylate) (polyCBMA), were then grafted from the silanized glass substrates using the atom-transfer radical polymerization (ATRP) method. X-ray photoelectron spectroscopy (XPS) was used to analyze the surfaces of the silanized glass substrates and the substrates grafted with the polymers. An enzyme-linked immonosobrbent assay (ELISA) using polyclonal antibodies was used to measure fibrinogen adsorption on these surfaces. The surfaces with polySBMA or polyCBMA layers were shown to reduce fibrinogen adsorption to a level comparable with that of adsorption on poly(ethylene glycol)-like films. Bovine aortic endothelial cells (BAECs) were seeded on these surfaces. The attachment and spreading of the cells were observed only on unpolymerized glass surfaces. This work further demonstrates that zwitterionic polymers highly resist nonspecific protein adsorption and cell adhesion and provides an effective method to modify glass slides or other oxide surfaces to achieve superlow fouling.     

Photopatterned nanoporosity in polyelectrolyte multilayer films

We report on spatial control of nanoporosity in polyelectrolyte multilayer (PEM) films using photopatterning and its effects on film optical and adsorption properties. Multilayers assembled from poly(acrylic acid-ran-vinylbenzyl acrylate) (PAArVBA), a photo-cross-linking polymer, and poly(allylamine hydrochloric acid) (PAH) were patterned using ultraviolet light followed by immersion in low pH and then neutral pH solutions to induce nanoporosity in unexposed regions. Model charged small molecules rhodamine B, fluorescein, and propidium iodide and the model protein albumin exhibit increased adsorption to nanoporous regions of patterned PEM films as shown by fluorescence microscopy and radiolabeling experiments. Films assembled with alternating stacks of PAH/poly(sodium-4-styrene sulfonate) (SPS), which do not become nanoporous, and stacks of PAH/PAArVBA were patterned to create nanoporous capillary channels. Interdigitated channels demonstrated simultaneous, separate wicking of dimethyl sulfoxide-solvated fluorescein and rhodamine B. In addition, these heterostack structures exhibited patternable Bragg reflectivity of greater than 25% due to refractive index differences between the nanoporous and nonporous stacks. Finally, the PEM assembly process coupled with photo-cross-linking was used to create films with two separate stacked reflective patterns with a doubling in reflectivity where patterns overlapped. The combined adsorptive and reflective properties of these films hold promise for applications in diagnostic arrays and therapeutics delivery.     

Apparent dewetting of ultrathin multilayered polyelectrolyte films incubated in aqueous environments

We have investigated and characterized changes in film morphology and surface structure that occur when ultrathin multilayered polyelectrolyte films fabricated from linear poly(ethylene imine) (LPEI), sodium poly(styrene sulfonate) (SPS), and two hydrolytically degradable polyamines (polymers 1 and 2) are incubated in physiologically relevant environments. Characterization of the physical erosion profiles of films having the structure (LPEI/SPS)10(1/SPS)4(2/SPS)4 (approximately 80 nm thick) by atomic force microscopy (AFM), reflective optical microscopy, and scanning electron microscopy (SEM) demonstrated that these materials undergo large-scale changes in surface structure and morphology upon incubation in phosphate-buffered saline (PBS) at 37 degrees C. The patterns and structures generated during this transformation (e.g., nucleation and growth of holes, coalescence of holes, formation of cell-type structures, and the subsequent breakup of these features into droplets) are similar in many ways to those observed for the dewetting of thin films of conventional polymers, such as polystyrene, on nonwetting surfaces. The processes reported here are sufficiently slow (they occur over approximately 100 h) and occur under sufficiently mild conditions (e.g., incubation in PBS at 37 degrees C) to permit characterization and quantification of the structures and features that arise during the course of these transformations. The apparent dewetting of these ultrathin films upon exposure to aqueous environments creates future opportunities to investigate and characterize processes of mass transport in this class of ionically cross-linked assemblies.     

Arrays of lipid bilayers and liposomes on patterned polyelectrolyte templates

This paper presents novel methods to produce arrays of lipid bilayers and liposomes on patterned polyelectrolyte multilayers. We created the arrays by exposing patterns of poly(dimethyldiallylammonium chloride) (PDAC), polyethylene glycol (m-dPEG) acid, and poly(allylamine hydrochloride) (PAH) on polyelectrolyte multilayers (PEMs) to liposomes of various compositions. The resulting interfaces were characterized by total internal reflection fluorescence microscopy (TIRFM), fluorescence recovery after pattern photobleaching (FRAPP), quartz crystal microbalance (QCM), and fluorescence microscopy. Liposomes composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) and 1,2-dioleoyl-sn-glycero-3-phosphate (monosodium salt) (DOPA) were found to preferentially adsorb on PDAC and PAH surfaces. On the other hand, liposome adsorption on sulfonated poly(styrene) (SPS) surfaces was minimal, due to electrostatic repulsion between the negatively charged liposomes and the SPS-coated surface. Surfaces coated with m-dPEG acid were also found to resist liposome adsorption. We exploited these results to create arrays of lipid bilayers by exposing PDAC, PAH and m-dPEG patterned substrates to DOPA/DOPC vesicles of various compositions. The patterned substrates were created by stamping PDAC (or PAH) on SPS-topped multilayers, and m-dPEG acid on PDAC-topped multilayers, respectively. This technique can be used to produce functional biomimetic interfaces for potential applications in biosensors and biocatalysis, for creating arrays that could be used for high-throughput screening of compounds that interact with cell membranes, and for probing, and possibly controlling, interactions between living cells and synthetic membranes.     

Maintenance of Cartilaginous Gene Expression of Serially Subcultured Chondrocytes on Poly(2‐Methoxyethyl Acrylate) Analogous Polymers

Chondrocytes are important for cartilage tissue engineering. However, dedifferentiation during chondrocyte subculture prevents the application of cartilage tissue engineering. Therefore, prevention of this dedifferentiation is required. Here, the possibility of poly(2‐methoxyethyl acrylate) (PMEA) and its analogous polymers, poly(tetrahydrofurfuryl acrylate) (PTHFA) and poly(2‐(2‐methoxyethoxy) ethyl acrylate‐co‐butyl acrylate) (PMe2A), for chondrocyte subculture without dedifferentiation is examined. Chondrocytes spread on PTHFA and polyethylene terephthalate (PET), whereas their spreading is delayed on PMEA and PMe2A. When primary chondrocytes are subcultured on these polymers, the expression levels of cartilaginous genes are higher on PMEA and PMe2A than on PET and PTHFA. Integrin contribution to the initial cell adhesion is lower on PMEA and PMe2A than on PTHFA and PET. This low level of integrin contribution to cell adhesion may cause a delay in cell spreading and the maintenance of cartilaginous gene expression. These results indicate that PMEA and PMe2A may be favorable substrates for chondrocyte subculture and cartilage tissue engineering.     

Polyelectrolyte multilayers with a tunable Young's modulus: influence of film stiffness on cell adhesion

Mechanical properties of model and natural gels have recently been demonstrated to play an important role in various cellular processes such as adhesion, proliferation, and differentiation, besides events triggered by chemical ligands. Understanding the biomaterial/cell interface is particularly important in many tissue engineering applications and in implant surgery. One of the final goals would be to control cellular processes precisely at the biomaterial surface and to guide tissue regeneration. In this work, we investigate the substrate mechanical effect on cell adhesion for thin polyelectrolyte multilayer (PEM) films, which can be easily deposited on any type of material. The films were cross linked by means of a water-soluble carbodiimide (EDC), and the film elastic modulus was determined using the AFM nanoindentation technique with a colloidal probe. The Young's modulus could be varied over 2 orders of magnitude (from 3 to 400 kPa) for wet poly(L-lysine)/hyaluronan (PLL/HA) films by changing the EDC concentration. The chemical changes upon cross linking were characterized by means of Fourier transform infrared spectroscopy (FTIR). We demonstrated that the adhesion and spreading of human chondrosarcoma cells directly depend on the Young's modulus. These data indicate that, besides the chemical properties of the polyelectrolytes, the substrate mechanics of PEM films is an important parameter influencing cell adhesion and that PEM offer a new way to prepare thin films of tunable mechanical properties with large potential biomedical applications including drug release.     

Biogenic Polyelectrolyte Multilayers on Poly(L-lactide) Films for Control of Osteoblast Adhesion

Cell adhesion and spreading are important events during cell-biomaterial interaction, which control survival, growth and differentiation of cells. Layer-by-layer technique was used to generate multilayer coatings for regulating adhesion of primary osteoblasts on biomaterials. Polyelectrolyte multilayers (PEM) were based on poly (ethylene imine) as primary polycation layer. PEM were then prepared from chitosan (CHI) as polycation and heparin (HEP), or sulfated HA (sHA) as polyanions. It was observed that attachment and spreading of primary osteoblasts (pOB) was highly dependent on the composition of multilayers, as well as pH values of polyelectrolyte solutions. Results presented in this paper may pave the way for application of PEM surface coatings for bone-contacting implant materials.     

胆固醇-聚(D,L-乳酸)的制备及软骨细胞相容性研究

依据胆固醇对细胞膜良好的热力学亲和力及可以调节细胞膜磷脂双分子层的结构和动态行为的生理学的特点,采用本体聚合的方法制备了胆固醇-聚(D,L-乳酸),经GPC,1H-NMR分析证明产物分子量与理论分子量有较好的一致性,证明了聚合物的分子量可以通过调节D,L-丙交酯和胆固醇的量来控制.软骨细胞粘附率、增殖率以及3-(4,5-二甲基噻唑)-2,5-二苯基四氮唑溴盐(MTT)细胞活性的观测结果表明相比纯聚乳酸,胆固醇-聚乳酸明显促进了细胞的粘附与生长.通过激光共聚焦显微镜观察细胞形貌结果显示相比胆固醇-聚乳酸表面,纯聚乳酸表面的细胞数量较少且大多团聚没有正常铺展,而胆固醇-聚乳酸表面的软骨细胞则分布均匀,铺展充分.以上结果证明了胆固醇的存在有利于软骨细胞的生长和粘附,预示着胆固醇-聚乳酸在软骨组织工程以及其他相关的生物医疗领域有着广阔的应用前景.     

Modulation of hemocompatibility of polysulfone by polyelectrolyte multilayer films

Polyelectrolyte multilayer (PEM) films have been recently applied to surface modification of biomaterials. Cellular interactions with PEM films consisted of weak polyelectrolytes are greatly affected by the conditions of polyelectrolyte deposition, such as pH of polyelectrolyte solution. Previous studies indicated that the adhesion of several types of mammalian cells to PAH/PAA multilayer films was hindered by low pH and high layer numbers. The objective of this study is to evaluate whether the hemocompatibility of polysulfone can be modulated by deposition of poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA) multilayer films. PAH/PAA multilayer films with different layer numbers were assembled onto polysulfone at either pH 2.0 or pH 6.5. The number of platelet adhesion and the morphology of adherent platelets were determined to evaluate hemocompatibility of modified substrates. Compared to non-treat polysulfone, the PEM films developed at pH 2.0 decreased platelet adhesion, while those built at pH 6.5 enhanced platelet deposition. Platelet adhesion was found positively correlated to polyclonal antibodies binding to surface-bound fibrinogen. The extent of platelet spreading was increased with layer numbers of PEM films, suggesting that the adherent platelets on thick PEM films were prone to activation. In conclusion, PAH/PAA films with few layers developed at pH 2.0 possessed better hemocompatibility compared to other substrates.     

Ultra-thin films of conjugated polymers for opto-electronic applications

Ultra-thin films of precursor polymers for poly(benzimidazole) (PBI), poly(benzoxazole) (PBO), or poly(benzthiazole) (PBT) were formed at air/water interface by spreading monomers and then polymerizing on the water surface. These thin films could be deposited onto appropriate substrates such as quartz by using the Langmuir-Blodgett (LB) method of horizontal lifting. Moreover, the heat treatment of the built-up films of the precursor polymers transformed the films into corresponding PBI, PBO, or PBT, which were high-temperature polymers. The resulting films had uniform and controllable thickness. Electronic and opto-electronic properties of these thin films were evaluated in terms of electric conductivities and nonlinear optical properties.     

Selective depositions on polyelectrolyte multilayers: self-assembled monolayers of m-dPEG acid as molecular template

This paper describes the fabrication of self-assembled monolayer (SAM) patterns of m-d-poly(ethylene glycol) (m-dPEG) acid molecules onto polyelectrolyte multilayers (PEMs). The patterned SAMs on PEMs were created by ionic interactions using microcontact printing (microCP) technique. The created m-dPEG acid monolayer patterns on PEMs act as resistive templates, and thus further depositions of consecutive poly(anion)/poly(cation) pairs of charged particles result in the formation of three-dimensional (3-D) patterned PEM films or selective particle depositions atop the original multilayer thin films. In this study, we illustrate nonlithographic methods of patterning and controlling 3-D PEM architectures and selective particle depositions. We investigated the effect of variables--the choice of solvent, concentration, pH, substrate pretreatment, and stamp contact times--on microcontact printing of m-dPEG acid molecules onto PEM films to determine the optimal conditions for these parameters to achieve efficient transfer of m-dPEG acid patterns onto PEMs. Among the variables, the pH of the m-dPEG acid ink solution played the most important role in the transfer efficiency of the patterns onto the multilayer films. The patterned films were characterized by optical microscopy and atomic force microscopy (AFM).     

Polyelectrolyte Multilayer Films Containing Ferrocene: Effects of Polyelectrolyte Type and Ferrocene Contents in the Film on the Redox Properties

Electrochemical properties of Fc‐PEM films have been studied by changing the chemical structure of the polymer chains and the content of Fc moiety in the film systematically. We have prepared a series of PEM films by a layer‐by‐layer deposition of polycations, Fc‐modified poly(allylamine) (Fc‐PAA) and poly(ethyleneimine) (Fc‐PEI), and polyanionic poly(vinyl sulfate) (PVS) on the surface of a gold electrode. The redox properties of the Fc‐PAA/PVS and Fc‐PEI/PVS films depended significantly on the content of Fc moiety in the polymer chains and on the polymer type. Fc‐ PAA and Fc‐PEI polymer chains can penetrate 3 or 4 PAA/PVS bilayers inserted between the redox polymers and electrode. The Fc‐PAA film‐modified electrode can be used for electrocatalytic oxidation of ascorbic acid.     

RGD改性聚醚氨酯及其内皮细胞相容性的研究

利用氢键稳定的溶液互穿技术对聚醚氨酯(PEU)进行改性.用ATR-FTIR对十八烷基-聚氧乙烯-4,4'-二苯甲烷二异氰酸酯-聚氧乙烯-十八烷基(MSPEO)与PEU共混膜表面进行研究,结果表明,MS-PEO中的氨基甲酸酯链段与PEU基材之间发生了氢键缔合的作用.通过水化处理PEO及十八烷基自发地富集在基材表面.根据氢键缔合和表面自迁移原理,设计了两种RGD改性聚醚氨酯的方法:(1)将含RGD端基的聚氧乙烯-4,4'-二苯甲烷二异氰酸酯-聚氧乙烯偶联物(MPEO-RGD)与PEU进行共混改性,利用RGD端基及PEO的自迁移特性获得RGD富集的表面;(2)将含甲磺酸酯端基的聚氧乙烯-4,4'-二苯甲烷二异氰酸酯-聚氧乙烯偶联物(MPEO-mesyl)与PEU共混成膜,并对膜片进行水化处理,使甲磺酸酯端基富集在PEU表面,浸泡于RGD的PBS溶液中,在膜片表面成功地原位接枝了RGD.对两种RGD改性方法获得的表面进行了内皮细胞的培养,结果表明,两种改性方法均大大提高了PEU的细胞相容性,其中方法(1)共混改性的表面细胞相容性略优于方法(2)的接枝改性表面.     

功能化聚乳酸微球改性聚乳酸膜片表面及其细胞相容性

以两亲三嵌段共聚物PEO PPO PEO及其氨基酸、多肽RGD衍生物作为微球制备过程中的表面稳定剂 ,低分子量的聚乳酸作为成核材料 ,采用o w乳液溶剂挥发法制备得到表面含不同氨基酸的聚乳酸微球 ,荧光标记手段证明了氨基酸存在于微球的表面 ;利用溶胀嵌入固定法将微球固定到具有生物惰性聚乳酸膜片表面 ,制备得到了具有良好稳定性的微球改性聚乳酸生物惰性膜片 ;成骨细胞相容性测试表明 ,氨基酸尤其是多肽RGD在生物惰性聚乳酸表面的引入能较大程度地提高聚乳酸生物惰性表面的细胞相容性 ,能较好地诱导细胞行为如细胞粘附、增殖等过程的发生 ,为实现对细胞行为的诱导控制提供了一种新途径 .     

Modulation of the functions of osteoblast-like cells on poly(allylamine hydrochloride) and poly(acrylic acid) multilayer films

Deposition of layer-by-layer polyelectrolyte multilayer (PEM) films has been a widely applied surface modification technique to improve the biocompatibility of biomaterials. The objective of this study was to investigate the impact of the deposition of poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) multilayer films on adhesion, growth and differentiation of osteoblasts-like MG63 cells. PAH and PAA were deposited sequentially onto tissue culture polystyrene at either pH 2.0 or pH 6.5 with 4-21 layers. While the MG63 cells attached poorly on the PAH/PAA multilayer films deposited at pH 2.0, while the cells adhered to the PEM films deposited at pH 6.5, depending on layer numbers. Cell adhesion, proliferation and osteogenic activities (alkaline phosphatase activity, expression of osteogenic marker genes and mineralization) were highest on the 4-layer PAH/PAA film and decreased with increasing layer numbers. On the other hand, the behavior of MG63 cells did not show any difference on the adjacent even and odd layers, except PEM4 and PEM5, i.e. the surface charges of the PAH/PAA multilayer films with over ten layers seem indifferent to osteoblastic functions. The results in this study suggested that the mechanical properties of PEM films may play a critical role in modulating the behavior of osteoblasts, providing guidance for application of PEM films to osteopaedic implants.     

Fabrication and hemocompatibility of cell outer membrane mimetic surfaces on chitosan by layer by layer assembly with polyanion bearing phosphorylcholine groups

Three random copolymers poly(2-methacryloyloxyethyl phosphorylcholine-co-methacrylic acid) (PMAs) were synthesized by free radical polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) and methacrylic acid (MA) with different monomer ratios under monomer-starved conditions. The synthesized PMA polyanions were assembled on chitosan (CS) film surfaces via electrostatic interactions. Using layer by layer (LbL) assembly with PMA polyanion and chitosan polycation, PMA/CS multilayer thin films with phosphorylcholine groups on the outer surfaces were fabricated. The modified surfaces were characterized by dynamic contact angle (DCA), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). Hemocompatibility of the surfaces was estimated by protein adsorption and platelet adhesion measurements. The results indicated that cell outer membrane mimetic structures were formed on the modified surfaces with PMA as the outermost layer, and the hemocompatibility of the modified surfaces was significantly improved. This facile method of fabricating cell outer membrane mimetic surfaces may have potential applications in the fields of hemocompatible coatings, drug delivery, and tissue engineering.     

Structure/property relationships in erodible multilayered films: influence of polycation structure on erosion profiles and the release of anionic polyelectrolytes

We have investigated the influence of polymer structure on the erosion profiles of multilayered polyelectrolyte assemblies fabricated from sodium poly(styrene sulfonate) (SPS) and three different hydrolytically degradable polyamines. We synthesized three structurally related poly(beta-amino ester)s (polymers 1-3) having systematic variations in both charge density and hydrophobicity. These changes in structure did not influence film thickness significantly, but polymer structure was found to play an important role in defining the rates at which multilayered assemblies fabricated from these materials eroded in physiologically relevant media. Films 60 nm thick fabricated from polymer 1 and SPS eroded completely in 50 h when incubated in PBS buffer at 37 degrees C, as determined by ellipsometry. Analogous films fabricated from polymers 2 and 3 eroded and released SPS into solution over significantly longer time periods ranging from approximately 150 h (ca. 6 days) to 370 h (ca. 15 days), respectively. These differences are consistent with a systematic increase in the hydrophobicity of polymers 1-3 as well as the relative rates at which these polymers degrade hydrolytically. This work demonstrates that it is possible to tailor the rates at which thin, multilayered polyelectrolyte assemblies release incorporated anionic polyelectrolytes over a large range of time periods simply by changing the structure of the degradable polyamine used to fabricate a film. The principles reported here may therefore contribute to the design of multilayered assemblies that permit a broad range of spatial and temporal control over the release of therapeutic agents from coated surfaces.     

Cell surface engineering with polyelectrolyte multilayer thin films

Layer-by-layer assembly of polyelectrolyte multilayer (PEM) films represents a bottom-up approach for re-engineering the molecular landscape of cell surfaces with spatially continuous and molecularly uniform ultrathin films. However, fabricating PEMs on viable cells has proven challenging owing to the high cytotoxicity of polycations. Here, we report the rational engineering of a new class of PEMs with modular biological functionality and tunable physicochemical properties which have been engineered to abrogate cytotoxicity. Specifically, we have discovered a subset of cationic copolymers that undergoes a conformational change, which mitigates membrane disruption and facilitates the deposition of PEMs on cell surfaces that are tailorable in composition, reactivity, thickness, and mechanical properties. Furthermore, we demonstrate the first successful in vivo application of PEM-engineered cells, which maintained viability and function upon transplantation and were used as carriers for in vivo delivery of PEMs containing biomolecular payloads. This new class of polymeric film and the design strategies developed herein establish an enabling technology for cell transplantation and other therapies based on engineered cells.