Enhancement of surface graft density of MPEG on alginate/chitosan hydrogel microcapsules for protein repellency

Alginate/chitosan/alginate (ACA) hydrogel microcapsules were modified with methoxy poly(ethylene glycol) (MPEG) to improve protein repellency and biocompatibility. Increased MPEG surface graft density (n(S)) on hydrogel microcapsules was achieved by controlling the grafting parameters including the buffer layer substrate, membrane thickness, and grafting method. X-ray photoelectron spectroscopy (XPS) model was employed to quantitatively analyze n(S) on this three-dimensional (3D) hydrogel network structure. Our results indicated that neutralizing with alginate, increasing membrane thickness, and in situ covalent grafting could increase n(S) effectively. ACAC(PEG) was more promising than ACC(PEG) in protein repellency because alginate supplied more -COO(-) negative binding sites and prevented MPEG from diffusing. The n(S) increased with membrane thickness, showing better protein repellency. Moreover, the in situ covalent grafting provided an effective way to enhance n(S), and 1.00 ± 0.03 chains/nm(2) was achieved, exhibiting almost complete immunity to protein adsorption. This antifouling hydrogel biomaterial is expected to be useful in transplantation in vivo.

Sustained local delivery of bioactive nerve growth factor in the central nervous system via tunable diblock copolypeptide hydrogel depots

Biomaterial vehicles that can provide sustained, site-specific molecular delivery in the central nervous system (CNS) have potential for therapeutic and investigative applications. Here, we present in vitro and in vivo proof of principle tests of diblock copolypeptide hydrogels (DCH) to serve as depots for sustained local release of protein effector molecules. We tested two DCH, K(180)L(20) and E(180)L(20), previously shown to self-assemble into biocompatible, biodegradable deposits that persist four to eight weeks after injection into mouse forebrain. In vitro tests demonstrated sustained release from dialysis cassettes of the representative protein, lysozyme, dissolved in K(180)L(20) or E(180)L(20) hydrogels. Release time in vitro varied in relation to DCH charge and mechanical properties, and ionic strength of the media. To evaluate bioactive protein delivery in vivo, we used nerve growth factor (NGF) and measured the size of mouse forebrain cholinergic neurons, which respond to NGF with cellular hypertrophy. For in vivo tests, the storage modulus of DCH depots was tuned to just below that of CNS tissue. In comparison with NGF injected in buffer, depots of NGF dissolved in either K(180)L(20) or E(180)L(20) provided significantly longer delivery of NGF bioactivity, maintaining hypertrophy of local forebrain cholinergic neurons for at least 4 weeks and inducing hypertrophy a further distance away (up to 5 mm) from injection sites. These findings show that depots of DCH injected into CNS can provide sustained delivery within the blood-brain barrier of a bioactive protein growth factor that exerts a predicted, quantifiable effect on local cells over a prolonged subacute time.

Macroporous hydrogel micropillars for quantifying Met kinase activity in cancer cell lysates

Overactive and overexpressed kinases have been implicated in the cause and progression of many cancers. Kinase inhibitors offer a targeted approach for treating cancers associated with increased or deregulated kinase activity. Often, however, cancer cells exhibit initial resistance to these inhibitors or evolve to develop resistance during treatment. Additionally, cancers of any one tissue type are typically heterogeneous in their oncogenesis mechanisms, and thus diagnosis of a particular type of cancer does not necessarily provide insight into what kinase therapies may be effective. For example, while some lung cancer cells that overexpress the epidermal growth factor receptor (EFGR) respond to treatment with EGFR kinase inhibitors, overexpression or hyperactivity of Met kinase correlates with resistance to EGFR kinase inhibitors. Here we describe a microfluidic-based assay for quantifying Met kinase activity in cancer cell lysates with the eventual goals of predicting cancer cell responsiveness to kinase inhibitors and monitoring development of resistance to these inhibitors. In this assay, we immobilized a phosphorylation substrate for Met kinase into macroporous hydrogel micropillars. We then exposed the micropillars to a cancer cell lysate and detected substrate phosphorylation using a fluorescently conjugated antibody. This assay is able to quantify Met kinase activity in whole cell lysate from as few as 150 cancer cells. It can also detect cells expressing overactive Met kinase in a background of up to 75% non-cancerous cells. Additionally, the assay can quantify kinase inhibition by the Met-specific kinase inhibitors SU11274 and PHA665752, suggesting predictive capability for cellular response to kinase inhibitors.

Investigating the role of substrate stiffness in the persistence of valvular interstitial cell activation

During heart valve remodeling and in many disease states, valvular interstitial cells (VICs) shift to an activated myofibroblast phenotype characterized by enhanced synthetic and contractile activity. Pronounced alpha smooth muscle actin (αSMA)-positive stress fibers, the hallmark of activated myofibroblasts, are also observed in VICs cultured on stiff substrates especially in the presence of transforming growth factor-beta1 (TGF-β1), however, the detailed relationship between stiffness and VIC phenotype has not been explored. The goal of this study was to characterize VIC activation as a function of substrate stiffness over a wide range of stiffness levels including that of diseased valves (stiff), normal valves (compliant), and hydrogels for heart valve tissue engineering (very soft). VICs obtained from porcine aortic valves were cultured on stiff tissue culture plastic to activate them, then, cultured on collagen-coated polyacrylamide substrates of predefined stiffness in a high-throughput culture system to assess the persistence of activation. Metrics extracted from regression analysis demonstrate that relative to a compliant substrate, stiff substrates result in higher cell numbers, more pronounced expression of αSMA-positive stress fibers, and larger spread area which is in qualitative agreement with previous studies. Our data also indicate that VICs require a much lower substrate stiffness level to "deactivate" them than previously thought. The high sensitivity of VICs to substrate stiffness demonstrates the importance of the mechanical properties of materials used for valve repair or for engineering valve tissue.

Gelatin methacrylate as a promising hydrogel for 3D microscale organization and proliferation of dielectrophoretically patterned cells

Establishing the 3D microscale organization of cells has numerous practical applications, such as in determining cell fate (e.g., proliferation, migration, differentiation, and apoptosis) and in making functional tissue constructs. One approach to spatially pattern cells is by dielectrophoresis (DEP). DEP has characteristics that are important for cell manipulation, such as high accuracy, speed, scalability, and the ability to handle both adherent and non-adherent cells. However, widespread application of this method is largely restricted because there is a limited number of suitable hydrogels for cell encapsulation. To date, polyethylene glycol-diacrylate (PEG-DA) and agarose have been used extensively for dielectric patterning of cells. In this study, we propose gelatin methacrylate (GelMA) as a promising hydrogel for use in cell dielectropatterning because of its biocompatibility and low viscosity. Compared to PEG hydrogels, GelMA hydrogels showed superior performance when making cell patterns for myoblast (C2C12) and endothelial (HUVEC) cells as well as in maintaining cell viability and growth. We also developed a simple and robust protocol for co-culture of these cells. Combined application of the GelMA hydrogels and the DEP technique is suitable for creating highly complex microscale tissues with important applications in fundamental cell biology and regenerative medicine in a rapid, accurate, and scalable manner.

In vitro angiogenesis assay for the study of cell-encapsulation therapy

Cell encapsulation within alginate beads has potential as a sustained release system for delivering therapeutic agents in vivo while protecting encapsulated cells from the immune system. There is, however, no in vitro model for cell-encapsulation therapy that provides a suitable platform for quantitative assessment of physiological responses to secreted factors. Here we introduce a new microfluidic system specifically designed to evaluate and quantify the pro-angiogenic potential of factors secreted from human fetal lung fibroblasts encapsulated in beads on an intact endothelial cell monolayer. We confirmed that cell-encapsulating beads induced an angiogenic response in vitro, demonstrated by a strong correlation between the encapsulated cell density in the beads and the length of the vascular lumen formed in vitro. Conditions established by in vitro tests were then further shown to exert a pro-angiogenic response in vivo using a subcutaneous mouse model, forming an extensive network of functional luminal structures perfused with red blood cells.

The effect of glycomimetic functionalized collagen on peripheral nerve repair

Increasing evidence suggests that the improper synaptic reconnection of regenerating axons is a significant cause of incomplete functional recovery following peripheral nerve injury. In this study, we evaluate the use of collagen hydrogels functionalized with two peptide glycomimetics of naturally occurring carbohydrates-polysialic acid (PSA) and human natural killer cell epitope epitope (HNK-1)-that have been independently shown to encourage nerve regeneration and axonal targeting. Our novel biomaterial was used to bridge a critical gap size (5 mm) in a mouse femoral nerve injury model. Functional recovery was assessed using gait and hind limb extension, and was significantly better in all glycomimetic peptide-coupled collagen conditions versus non-functional scrambled peptide-coupled collagen, native collagen, and saline controls. Analysis of cross-sections of the regenerated nerve demonstrated that hydrogels coupled with the PSA glycomimetic, but not HNK, had significant increases in the number of myelinated axons over controls. Conversely, hydrogels coupled with HNK, but not PSA, showed improvement in myelination. Additionally, significantly more correctly projecting motoneurons were observed in groups containing coupled HNK-1 mimicking peptide, but not PSA mimicking peptide. Given the distinct morphological outcomes between the two glycomimetics, our study indicates that the enhancement of recovery following peripheral nerve injury induced by PSA- and HNK-functionalized collagen hydrogels likely occurs through distinct mechanisms.

UV-photo graft functionalization of polyethersulfone membrane with strong polyelectrolyte hydrogel and its application for nanofiltration

A strong polyelectrolyte hydrogel was graft copolymerized on a polyethersulfone (PES) ultrafiltration (UF) membrane using vinyl sulfonic acid (VSA) as the functional monomer, and N,N'-methylenbisacrylamide (MBAA) as the cross-linker monomer. This was carried out in one simple step using the UV photoirradiation method. The effect of the polymerization conditions on the degree of grafting (DG) was investigated using the gravimetric method which measures the total hydrogel grafted on the membrane, and with ATR-FTIR spectroscopy which indicates the functional monomer fraction in the hydrogel layer. The VSA could not graft polymerize without the cross-linker as comonomer. An increase in the cross-linker fraction from 0.25 to 2.5 mol % (relative to the functional monomer VSA) resulted in a higher DG. Although the surface morphology changed upon modification, the resulting surface roughness as measured by AFM was very low. From the monitoring of DG with UV time (4.5-30 min) at constant conditions, it was deduced that during the early stages of the polymerization mainly the cross-linker was grafted, thus inducing the graft copolymerization of the functional monomer. Polymerization using a higher monomer concentration (12.5-40% VSA) at constant monomer/cross-linker ratio resulted in a higher VSA fraction in the grafted hydrogel, although the gravimetric DG was similar. Ion exchange capacity and X-ray photoelectron spectroscopy measured after modification under the different conditions supported these findings. The new membranes were tested under nanofiltration (NF) conditions. A NF membrane could be obtained when the MBAA fraction was above 0.25%. The Na2SO4 rejection was 90-99% and the permeability 10-1 L m(-2) h(-1) bar(-1) when the MBAA fraction increased from 0.75 to 2.5%. The order of rejection of single salts solution was Na2SO4 > MgSO4 ≈ NaCl > CaCl2, as expected on the basis of Donnan exclusion for negatively charged NF membranes. An increase in the salts rejection with increasing degree of cross-linking and VSA fraction was attributed to an increase in the membrane charge density and to steric exclusion that also resulted in an increase of rejection for uncharged solutes such as sucrose or glucose. The new membrane presented a high, essentially unchanged Na2SO4 rejection (>97%) in the range of salt concentrations up to 4 g/L, and only slightly reduced rejection (>92%) at a concentration of 8 g/L; this can be related to its high barrier layer charge density measured by ion exchange capacity. In addition, because poly(vinyl sulfonic acid) (PVSA) is a strong polyelectrolyte the membrane separation performance was stable in the range of pH 1.5 to pH 10.

Hydrogel particles as a particulate stabilizer for dispersion polymerization

Hydrogel particles composed of poly(N-isopropylacrylamide) were used as a particulate steric stabilizer for the dispersion polymerization of styrene for the first time. The effects of the size and concentration of the hydrogel particles on the resultant polystyrene particles were investigated. As expected, the hydrogel particles indeed play the role of steric stabilizer for dispersion polymerization. Moreover, some of the resultant polystyrene particles were covered with hydrogel particles, which was confirmed by electron microscopy and X-ray photoelectron spectroscopy.

Smart self-assembled hybrid hydrogel biomaterials

Hybrid biomaterials are systems created from components of at least two distinct classes of molecules, for example, synthetic macromolecules and proteins or peptide domains. The synergistic combination of two types of structures may produce new materials that possess unprecedented levels of structural organization and novel properties. This Review focuses on biorecognition-driven self-assembly of hybrid macromolecules into functional hydrogel biomaterials. First, basic rules that govern the secondary structure of peptides are discussed, and then approaches to the specific design of hybrid systems with tailor-made properties are evaluated, followed by a discussion on the similarity of design principles of biomaterials and macromolecular therapeutics. Finally, the future of the field is briefly outlined.

In vitro and in vivo testing of glucose-responsive insulin-delivery microdevices in diabetic rats

We have developed glucose-responsive implantable microdevices for closed-loop delivery of insulin and conducted in vivo testing of these devices in diabetic rats. The microdevices consist of an albumin-based bioinorganic membrane that utilizes glucose oxidase (GOx), catalase (CAT) and manganese dioxide (MnO(2)) nanoparticles to convert a change in the environmental glucose level to a pH stimulus, which regulates the volume of pH-sensitive hydrogel nanoparticles and thereby the permeability of the membrane. The membrane is integrated with microfabricated PDMS (polydimethylsiloxane) structures to form compact, stand-alone microdevices, which do not require tethering wires or tubes. During in vitro testing, the microdevices showed glucose-responsive insulin release over multiple cycles at clinically relevant glucose concentrations. In vivo, the microdevices were able to counter hyperglycemia in diabetic rats over a one-week period. The in vitro and in vivo testing results demonstrated the efficacy of closed-loop biosensing and rapid response of the 'smart' insulin delivery devices.

Fast-degradable microbeads encapsulating human umbilical cord stem cells in alginate for muscle tissue engineering

Human umbilical cord mesenchymal stem cells (hUCMSCs) are inexhaustible and can be obtained without an invasive surgery. To date, there has been no report on seeding hUCMSCs in three-dimensional scaffolds for muscle tissue engineering. The objectives of this study were to (1) investigate hUCMSC seeding in a scaffold for muscle engineering and (2) develop a novel construct consisting of hUCMSC-encapsulating and fast-degradable microbeads inside a hydrogel matrix. The rationale was that the hydrogel matrix would maintain the defect volume, while the microbeads would degrade to release the cells and concomitantly create macropores in the matrix. hUCMSCs were encapsulated in alginate-fibrin microbeads, which were packed in an Arg-Gly-Asp (RGD)-modified alginate matrix (AM). This construct is referred to as hUCMSC-microbead-AM. The control consisted of the usual cell encapsulation in AM without microbeads (referred to as hUCMSC-AM). In the hUCMSC-AM construct, the hUCMSCs showed as round dots with no spreading at 1-14 days. In contrast, cells in the hUCMSC-microbead-AM construct had a healthy spreading and elongated morphology. The microbeads successfully degraded and released the cells at 8 days. Myogenic expressions for hUCMSC-microbead-AM were more than threefold those of hUCMSC-AM (p<0.05). Immunofluorescence for myogenic markers was much stronger for hUCMSC-microbead-AM than hUCMSC-AM. Muscle creatine kinase of hUCMSC-microbead-AM at 14 days was twofold that of hUCMSC-AM (p<0.05). In conclusion, hUCMSC encapsulation in novel fast-degradable microbeads inside a hydrogel matrix was investigated for muscle engineering. Compared to the usual method of seeding cells in a hydrogel matrix, hUCMSC-microbead-AM construct had greatly improved cell viability and myogenic differentiation, and hence, is promising to enhance muscle regeneration.

Mosaic hydrogels: one-step formation of multiscale soft materials

The one-step, continuous formation of mosaic hydrogel sheets is presented. A microfluidic device allows controllable incorporation of secondary biopolymers within a flowing biopolymer sheet followed by a cross-linking step that retains the microscale composition. Information is encoded; mosaic stiffness and diffusivity patterns are created; tessellations are populated with biomolecules, microparticles and viable primary cells; and 3D soft material assemblies are demonstrated.

A hydrogel derived from decellularized dermal extracellular matrix

The ECM of mammalian tissues has been used as a scaffold to facilitate the repair and reconstruction of numerous tissues. Such scaffolds are prepared in many forms including sheets, powders, and hydrogels. ECM hydrogels provide advantages such as injectability, the ability to fill an irregularly shaped space, and the inherent bioactivity of native matrix. However, material properties of ECM hydrogels and the effect of these properties upon cell behavior are neither well understood nor controlled. The objective of this study was to prepare and determine the structure, mechanics, and the cell response in vitro and in vivo of ECM hydrogels prepared from decellularized porcine dermis and urinary bladder tissues. Dermal ECM hydrogels were characterized by a more dense fiber architecture and greater mechanical integrity than urinary bladder ECM hydrogels, and showed a dose dependent increase in mechanical properties with ECM concentration. In vitro, dermal ECM hydrogels supported greater C2C12 myoblast fusion, and less fibroblast infiltration and less fibroblast mediated hydrogel contraction than urinary bladder ECM hydrogels. Both hydrogels were rapidly infiltrated by host cells, primarily macrophages, when implanted in a rat abdominal wall defect. Both ECM hydrogels degraded by 35 days in vivo, but UBM hydrogels degraded more quickly, and with greater amounts of myogenesis than dermal ECM. These results show that ECM hydrogel properties can be varied and partially controlled by the scaffold tissue source, and that these properties can markedly affect cell behavior.

Diagnostic microchip to assay 3D colony-growth potential of captured circulating tumor cells

Microfluidic technology has been successfully applied to isolate very rare tumor-derived epithelial cells (circulating tumor cells, CTCs) from blood with relatively high yield and purity, opening up exciting prospects for early detection of cancer. However, a major limitation of state-of-the-art CTC-chips is their inability to characterize the behavior and function of captured CTCs, for example to obtain information on proliferative and invasive properties or, ultimately, tumor re-initiating potential. Although CTCs can be efficiently immunostained with markers reporting phenotype or fate (e.g. apoptosis, proliferation), it has not yet been possible to reliably grow captured CTCs over long periods of time and at single cell level. It is challenging to remove CTCs from a microchip after capture, therefore such analyses should ideally be performed directly on-chip. To address this challenge, we merged CTC capture with three-dimensional (3D) tumor cell culture on the same microfluidic platform. PC3 prostate cancer cells were isolated from spiked blood on a transparent PDMS CTC-chip, encapsulated on-chip in a biomimetic hydrogel matrix (QGel™) that was formed in situ, and their clonal 3D spheroid growth potential was assessed by microscopy over one week in culture. The possibility to clonally expand a subset of captured CTCs in a near-physiological in vitro model adds an important element to the expanding CTC-chip toolbox that ultimately should improve prediction of treatment responses and disease progression.

Layer-shaped alginate hydrogels enhance the biological performance of human adipose-derived stem cells

BACKGROUND

The reconstruction of adipose tissue defects is often challenged by the complications that may occur following plastic and reconstructive surgery, including donor-site morbidity, implant migration and foreign body reaction. To overcome these problems, adipose tissue engineering (ATE) using stem cell-based regeneration strategies has been widely explored in the last years. Mounting evidence has shown that adipose-derived stem cells (ADSCs) represent a promising cell source for ATE. In the context of a small number of reports concerning adipose tissue regeneration using three-dimensional (3-D) systems, the present study was designed to evaluate the biological performance of a novel alginate matrix that incorporates human ADSCs (hADSCs).

RESULTS

Culture-expanded cells isolated from the stromal vascular fraction (SVF), corresponding to the third passage which showed the expression of mesenchymal stem cell (MSC) markers, were used in the 3-D culture systems. The latter represented a calcium alginate hydrogel, obtained by the diffusion of calcium gluconate (CGH matrix), and shaped as discoid-thin layer. For comparative purposes, a similar hADSC-laden alginate hydrogel cross-linked with calcium chloride was considered as reference hydrogel (RH matrix). Both hydrogels showed a porous structure under scanning electron microscopy (SEM) and the hADSCs embedded displayed normal spherical morphologies, some of them showing signs of mitosis. More than 85% of the entrapped cells survived throughout the incubation period of 7 days. The percentage of viable cells was significantly higher within CGH matrix at 2 days post-seeding, and approximately similar within both hydrogels after 7 days of culture. Moreover, both alginate-based hydrogels stimulated cell proliferation. The number of hADSC within hydrogels has increased during the incubation period of 7 days and was higher in the case of CGH matrix. Cells grown under adipogenic conditions for 21 days showed that both analyzed 3-D culture systems support adipogenic differentiation in terms of neutral lipid accumulation and perillipin expression. Furthermore, the cells encapsulated in CGH matrix displayed a more differentiated phenotype.

CONCLUSIONS

The results of this study suggest that both CGH and RH matrices successfully support the survival and adipogenesis of hADSC. An enhancement of biological performance was detected in the case of CGH matrix, suggesting its promising application in ATE.

Microfluidic encapsulation of cells in polymer microgels

In this Concept article, recent advances in microfluidic platforms for the generation of cell-laden hydrogel particles (microgels) are reported. Advances in the continuous microfluidic encapsulation of cells in droplets and microgels are critically reviewed, and currently used methods for the encapsulation of cells in polymer microgels are discussed. An outlook on current applications and future directions in this field of research are also presented. This article will be of interest to chemists, materials scientists, cell biologists, bioengineers, and pharmacologists.

Hierarchical formation of supramolecular transient networks in water: a modular injectable delivery system

A modular one-component supramolecular transient network in water, based on poly(ethylene glycol) and end-capped with four-fold hydrogen bonding units, is reported. Due to its nonlinear structural formation, this system allows active proteins to be added to the hydrogel during formation. Once implanted in vivo it releases the protein by erosion of both the protein and polymer via dissolution.

Efficient inhibition of colorectal peritoneal carcinomatosis by drug loaded micelles in thermosensitive hydrogel composites

In this work, we aim to develop a dual drug delivery system (DDDS) of self-assembled micelles in thermosensitive hydrogel composite to deliver hydrophilic and hydrophobic drugs simultaneously for colorectal peritoneal carcinomatosis (CRPC) therapy. In our previous studies, we found that poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone) (PCEC) copolymers with different molecular weight and PEG/PCL ratio could be administered to form micelles or thermosensitive hydrogels, respectively. Therefore, the DDDS was constructed from paclitaxel (PTX) encapsulated PCEC micelles (PTX-micelles) and a fluorouracil (Fu) loaded thermosensitive PCEC hydrogel (Fu-hydrogel). PTX-micelles were prepared by self-assembly of biodegradable PCEC copolymer (M(n) = 3700) and PTX without using any surfactants or excipients. Meanwhile, biodegradable and injectable thermosensitive Fu-hydrogel (M(n) = 3000) with a lower sol-gel transition temperature at around physiological temperature was also prepared. The obtained PTX-micelles in thermosensitive Fu-hydrogel (PTX-micelles-Fu-hydrogel) composite is a free-flowing sol at ambient temperature and rapidly turned into a non-flowing gel at physiological temperature. In addition, the results of cytotoxicity, hemolytic study, and acute toxicity evaluation suggested that the PTX-micelles-Fu-hydrogel was non-toxic and biocompatible. In vitro release behaviors of PTX-micelles-Fu-hydrogel indicated that both PTX and Fu have a sustained release behavior. Furthermore, intraperitoneal application of PTX-micelles-Fu-hydrogel effectively inhibited growth and metastasis of CT26 peritoneal carcinomatosis in vivo (p < 0.001), and induced a stronger antitumor effect than that of Taxol® plus Fu (p < 0.001). The pharmacokinetic study indicated that PTX-micelles-Fu-hydrogel significantly increased PTX and Fu concentration and residence time in peritoneal fluids compared with Taxol® plus Fu group. Thus, the results suggested the micelles-hydrogel DDDS may have great potential clinical applications.

Contactless laser-assisted patterning of surfaces for bio-adhesive microarrays

Micropatterned surfaces with cell adhesive areas, delimited by protein repellent microstructures, are in high demand for its potential use as relevant biological assays. This is not only because such surfaces allow directing cell growth in a spatially localized and restricted manner, but also because they can be used to elucidate basic cell growth and orientation mechanisms. Here, it is presented a laser-assisted micropatterning technique to fabricate large area microstructures of poly (ethylene glycol) hydrogel onto a cell adhesive surface: a biofunctional maleic anhydride copolymer. By varying photoinitiator, laser intensity, copolymer as well as the hydrogel layer thickness, the optimum conditions to produce high quality features were found. The suitability of these micropatterned substrates for bioassay applications was proved by cell adhesion studies. The introduced procedure could be used to prepare a broad range of microarrays for certain bioanalytical approaches and to create different types of biofunctional surfaces.

Reductively responsive siRNA-conjugated hydrogel nanoparticles for gene silencing

A critical need still remains for effective delivery of RNA interference (RNAi) therapeutics to target tissues and cells. Self-assembled lipid- and polymer-based systems have been most extensively explored for transfection with small interfering RNA (siRNA) in liver and cancer therapies. Safety and compatibility of materials implemented in delivery systems must be ensured to maximize therapeutic indices. Hydrogel nanoparticles of defined dimensions and compositions, prepared via a particle molding process that is a unique off-shoot of soft lithography known as particle replication in nonwetting templates (PRINT), were explored in these studies as delivery vectors. Initially, siRNA was encapsulated in particles through electrostatic association and physical entrapment. Dose-dependent gene silencing was elicited by PEGylated hydrogels at low siRNA doses without cytotoxicity. To prevent disassociation of cargo from particles after systemic administration or during postfabrication processing for surface functionalization, a polymerizable siRNA pro-drug conjugate with a degradable, disulfide linkage was prepared. Triggered release of siRNA from the pro-drug hydrogels was observed under a reducing environment while cargo retention and integrity were maintained under physiological conditions. Gene silencing efficiency and cytocompatibility were optimized by screening the amine content of the particles. When appropriate control siRNA cargos were loaded into hydrogels, gene knockdown was only encountered for hydrogels containing releasable, target-specific siRNAs, accompanied by minimal cell death. Further investigation into shape, size, and surface decoration of siRNA-conjugated hydrogels should enable efficacious targeted in vivo RNAi therapies.

Three-dimensional biomimetic patterning in hydrogels to guide cellular organization

An image-guided micropatterning method is demonstrated for generating biomimetic hydrogel scaffolds with two-photon laser scanning photolithography. This process utilizes computational methods to directly translate three-dimensional cytoarchitectural features from labeled tissues into material structures. We use this method to pattern hydrogels that guide cellular organization by structurally and biochemically recapitulating complex vascular niche microenvironments with high pattern fidelity at the microscale.

Flexible and microporous chitosan hydrogel/nano ZnO composite bandages for wound dressing: in vitro and in vivo evaluation

Current wound dressings have disadvantages such as less flexibility, poor mechanical strength, lack of porosity, and a tendency for dressings to adhere onto the wound surface; in addition, a majority of the dressings did not possess antibacterial activity. Hydrogel-based wound dressings would be helpful to provide a cooling sensation and a moisture environment, as well as act as a barrier to microbes. To overcome these hassles, we have developed flexible and microporous chitosan hydrogel/nano zinc oxide composite bandages (CZBs) via the incorporation of zinc oxide nanoparticles (nZnO) into chitosan hydrogel. The prepared nanocomposite bandages were characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD), and scanning electron microscopy (SEM). In addition, swelling, degradation, blood clotting, antibacterial, cytocompatibility, cell attachment on the material, and cell infiltration into the composite bandages were evaluated. The nanocomposite bandage showed enhanced swelling, blood clotting, and antibacterial activity. Cytocompatibility of the composite bandage has been analyzed in normal human dermal fibroblast cells. Cell attachment and infiltration studies showed that the cells were found attached to the nanocomposite bandages and penetrated into the interior. Furthermore, the in vivo evaluations in Sprague-Dawley rats revealed that these nanocomposite bandages enhanced the wound healing and helped for faster re-epithelialization and collagen deposition. The obtained data strongly encourage the use of these composite bandages for burn wounds, chronic wounds, and diabetic foot ulcers.

Differential effects of substrate modulus on human vascular endothelial, smooth muscle, and fibroblastic cells

Regenerative medicine approaches offer attractive alternatives to standard vascular reconstruction; however, the biomaterials to be used must have optimal biochemical and mechanical properties. To evaluate the effects of biomaterial properties on vascular cells, heparinized poly(ethylene glycol) (PEG)-based hydrogels of three different moduli, 13.7, 5.2, and 0.3 kPa, containing fibronectin and growth factor were utilized to support the growth of three human vascular cell types. The cell types exhibited differences in attachment, proliferation, and gene expression profiles associated with the hydrogel modulus. Human vascular smooth muscle cells demonstrated preferential attachment on the highest-modulus hydrogel, adventitial fibroblasts demonstrated preferential growth on the highest-modulus hydrogel, and human umbilical vein endothelial cells demonstrated preferential growth on the lowest-modulus hydrogel investigated. Our studies suggest that the growth of multiple vascular cell types can be supported by PEG hydrogels and that different populations can be controlled by altering the mechanical properties of biomaterials.