Single Hydrogel Research Articles

Sequential interpenetrating poly(ethylene glycol) hydrogels prepared by UV‐initiated thiol–ene coupling chemistry

AbstractPoly(ethylene glycol) (PEG)‐diallyls, ranging from 2 to 8 kDa, were successfully reacted with a trifunctional thiol crosslinker via thiol–ene coupling reaction to construct four different primary PEG hydrogels. These systems were used as scaffolds for the preparation of a library of sequential interpenetrating networks (SeqIPNs). The solid content of the secondary networks varied between 21 and 34% and was dependent on the length of the absorbing PEGs. The gel fractions for the IPNs were above 85%. Additionally, the lowest degree of swelling was found for the IPN based on 2‐kDa PEG (315%), whereas the 8‐kDa PEG IPN exhibited a value of 810%. The SeqIPN strategy facilitated hydrogel systems that cover a larger domain of tensile modulus (192–889 kPa) when compared with single hydrogel networks (175–555 kPa). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013

A micelle-shedding thermosensitive hydrogel as sustained release formulation

In this paper it is shown that when a thermosensitive hydrogel based on poly(N-isopropylacrylamide)-poly(ethylene glycol)-poly(N-isopropylacrylamide) (pNIPAm-PEG-pNIPAm) was transferred into water, flower-like micelles were continuously released as long as the medium was regularly refreshed. On the other hand, if the medium was not refreshed the concentration of micelles reached an equilibrium. When this gel was loaded with the cytostatic agent paclitaxel (PTX), the released micelles solubilized PTX, as evidenced by a PTX concentration in the release medium above its aqueous solubility. To test the applicability of these micelle-releasing gels for sustained and systemic delivery of PTX an in vivo experiment was performed in tumor-bearing mice. pNIPAm-PEG-pNIPAm gels (without and with 1.2% and 6.0% PTX loading) were administered i.p. in nude mice bearing 14C human squamous cell carcinoma tumor xenografts to obtain doses corresponding to one and five times the maximum tolerated dose of PTX (when given i.v. as the standard formulation in Cremophor EL/ethanol). All gel formulations were well tolerated and no signs of acute systemic toxicity were observed. After injection of the highest dose, PTX levels in serum could be determined for 48h with a comparatively long elimination half-life of 7.4h pointing to a sustained release of PTX. A bioavailability of 100% was calculated from the area under the curve of plasma concentration vs time. Furthermore, at the highest dose, PTX was shown to completely inhibit tumor growth for at least 3weeks with a single hydrogel injection. This promising concept may find application as a depot formulation for sustained, metronomic dosing of chemotherapeutics.

Inherent Interfacial Mechanical Gradients in 3D Hydrogels Influence Tumor Cell Behaviors

Cells sense and respond to the rigidity of their microenvironment by altering their morphology and migration behavior. To examine this response, hydrogels with a range of moduli or mechanical gradients have been developed. Here, we show that edge effects inherent in hydrogels supported on rigid substrates also influence cell behavior. A Matrigel hydrogel was supported on a rigid glass substrate, an interface which computational techniques revealed to yield relative stiffening close to the rigid substrate support. To explore the influence of these gradients in 3D, hydrogels of varying Matrigel content were synthesized and the morphology, spreading, actin organization, and migration of glioblastoma multiforme (GBM) tumor cells were examined at the lowest (<50 µm) and highest (>500 µm) gel positions. GBMs adopted bipolar morphologies, displayed actin stress fiber formation, and evidenced fast, mesenchymal migration close to the substrate, whereas away from the interface, they adopted more rounded or ellipsoid morphologies, displayed poor actin architecture, and evidenced slow migration with some amoeboid characteristics. Mechanical gradients produced via edge effects could be observed with other hydrogels and substrates and permit observation of responses to multiple mechanical environments in a single hydrogel. Thus, hydrogel-support edge effects could be used to explore mechanosensitivity in a single 3D hydrogel system and should be considered in 3D hydrogel cell culture systems.

A Single Component Conducting Polymer Hydrogel as a Scaffold for Tissue Engineering

AbstractConducting polymers (CPs) have exciting potential as scaffolds for tissue engineering, typically applied in regenerative medicine applications. In particular, the electrical properties of CPs has been shown to enhance nerve and muscle cell growth and regeneration. Hydrogels are particularly suitable candidates as scaffolds for tissue engineering because of their hydrated nature, their biocompatibility, and their tissue‐like mechanical properties. This study reports the development of the first single component CP hydrogel that is shown to combine both electro‐properties and hydrogel characteristics. Poly(3‐thiopheneacetic acid) hydrogels were fabricated by covalently crosslinking the polymer with 1,1′‐carbonyldiimidazole (CDI). Their swelling behavior was assessed and shown to display remarkable swelling capabilities (swelling ratios up to 850%). The mechanical properties of the networks were characterized as a function of the crosslinking density and were found to be comparable to those of muscle tissue. Hydrogels were found to be electroactive and conductive at physiological pH. Fibroblast and myoblast cells cultured on the hydrogel substrates were shown to adhere and proliferate. This is the first time that the potential of a single component CP hydrogel has been demonstrated for cell growth, opening the way for the development of new tissue engineering scaffolds.

Actuating individual electrospun hydrogel nanofibres

The actuation of a single hydrogel nanofibre is measured for the first time by AFM. The actuation stress generated was comparable to that produced by skeletal muscle and the actuation rate was significantly increased by the nanoscale dimensions of the fibre.

Influence of care system and wearing modality on clinical performance of a single silicone hydrogel contact lens

Purpose: Silver-infused contact lenses (CLs) may provide benefits to CL wearers by reducing adherence of potential pathogens to CL surfaces; however, they have the potential to modify the normal ocular biota during wear. This study investigated the effect of silverinfused silicone hydrogel CLs on conjunctival flora over six months of daily wear (DW). Method: A prospective, randomised, doublemasked, contralateral study was conducted. Sixty subjects were randomly assigned to wear silverinfused (galyfilcon A with incorporated silver ions, test) and standard (galyfilcon A, control) silicone hydrogel CLs on a contralateral basis for six months of DW. Prior to assignment of the test and control CLs, all subjects were fitted with etafilcon A daily disposable CLs for a one week wearin period. Conjunctival flora were cultured at screening/pre-baseline (with subjects’ habitual CLs), baseline (after daily disposable wear) and four weeks, three and six months following commencement of test and control CL wear, using sterile calcium alginate swabs moistened with sterile unpreserved 0.9% saline. Results: There were no statistically significant differences between the conjunctivae of test and control eyes in incidence of positive cultures (p>0.05), culture classification grades (p>0.05), microorganism levels (p>0.05) or numbers of different types of microorganisms isolated (p>0.05). Wear of the test CLs did not promote fungal or yeast colonisation of the conjunctivae. The most frequently isolated microorganisms were Gram-positive bacteria considered to be part of the normal ocular flora. Conclusions: Wear of the silver-infused CLs did not result in any statistically or clinically significant alterations to the ocular biota over six months of DW.

Single nonfouling hydrogels with mechanical and chemical functionality gradients

Hydrogels are widely studied as tissue engineering scaffolds, but the biological tissues they are designed to mimic are often complex tissues with non-uniform chemical and mechanical profiles. This work reports a new strategy to create hydrogels composed of a continuous sheet of a single nonfouling but functionalizable material with mechanical and/or chemical functionality gradients. By using different combinations of functionalizable or nonfunctionalizable versions of nonfouling carboxybetaine methacrylate (CBMA) and carboxybetaine dimethacrylate crosslinker (CBMAX), various hydrogels with gradients of crosslinking densities and/or functionalizable groups can be created. In this work, we demonstrate this concept with two nonfouling hydrogels, both with a mechanical gradient: one with uniform functionalizability and the other with a gradient in chemical functionalizability. With this versatile system, hydrogels with built-in gradient profiles of various types can be controlled at will for a given application.

Computational Study of pH-sensitive Hydrogel-based Microfluidic Flow Controllers.

This computational study investigates the sensing and actuating behavior of a pH-sensitive hydrogel-based microfluidic flow controller. This hydrogel-based flow controller has inherent advantage in its unique stimuli-sensitive properties, removing the need for an external power supply. The predicted swelling behavior the hydrogel is validated with steady-state and transient experiments. We then demonstrate how the model is implemented to study the sensing and actuating behavior of hydrogels for different microfluidic flow channel/hydrogel configurations: e.g., for flow in a T-junction with single and multiple hydrogels. In short, the results suggest that the response of the hydrogel-based flow controller is slow. Therefore, two strategies to improve the response rate of the hydrogels are proposed and demonstrated. Finally, we highlight that the model can be extended to include other stimuli-responsive hydrogels such as thermo-, electric-, and glucose-sensitive hydrogels.

Three-dimensional photolithographic patterning of multiple bioactive ligands in poly(ethylene glycol) hydrogels

The biomaterials community is faced with the challenge of imitating a vastly complex, physiological tissue environment. While cellular systems towards this end have been traditionally studied in two dimensions (2D), most cells require three-dimensional (3D) cues to produce a physiologically relevant response. Two-photon absorption laser scanning lithography (TPA-LSL) may be applied to photosensitive hydrogel systems to engineer heterogeneous, 3D microenvironments consisting of precisely patterned bioactive signals. In this work, we have developed new operating parameters and system capabilities for TPA-LSL through the patterning of fluorescently labeled monoacrylate PEG-RGDS within PEG-DA hydrogels. Specifically, we have demonstrated a flexible pattern size range, with features ranging from 1 µm to nearly 1 mm. We have also shown patterns of differing concentrations of the cell adhesive ligand RGDS and correlated observed RGDS fluorescence with laser scan speed and intensity. Finally, we have micropatterned multiple, unique bioactive ligands into distinct, 3D forms within a single hydrogel. The results presented here have significantly developed the capabilities of the TPA-LSL micropatterning technique to allow for the fabrication of heterogeneous, 3D cellular microenvironments, which should prove highly useful for future biomimetic applications.

One-Shot Synthesis of a Poly(N-isopropylacrylamide)/Silica Hybrid Gel

Class I hybrid poly(N-isopropylacrylamide)/silica hydrogels, PNIPAM/SiO2, were prepared by a new one shot synthesis. In this approach, the free-radical polymerization of vinyl groups of N-isopropylacrylamide (NIPAM) and the hydrolysis-condensation of alkoxy groups of tetramethoxysilane (TMOS) are performed concomitantly using sodium persulfate and 3-(dimethylamino)-propionitrile, a well-known couple to initiate the organic polymerization. The cross-linker is N,N-methylenebisacrylamide. The kinetic study of mechanical properties from the sol-to-gel state for different ratios of TMOS/NIPAM was investigated by rheological ultrasonic measurements. The thermoresponse of hybrid materials was investigated by differential scanning calorimetry and the measurements showed that hybrid gels present a lower critical solution temperature, which is similar with one of single organic hydrogel.

A novel single precursor-based biodegradable hydrogel with enhanced mechanical properties

A mechanically tough biodegradable hydrogel is developed from a single precursor comprising poly(ethylene glycol) and oligo(trimethylene carbonate), where both the crosslink density and swelling properties of the polymer network are independently controlled through c and hydrophilic-hydrophobic balance. These highly cost effective hydrogels are also biocompatible and can be degraded both hydrolytically and enzymatically.

Photopatterned anisotropic swelling of dual-crosslinked hyaluronic acid hydrogels

The purpose of a tissue engineered (TE) scaffold is to provide a support structure that can aid the regeneration of damaged tissue. Unlike native tissues, currently existing TE scaffolds are structurally simple, with homogeneous bulk properties that are unable to induce cells to regenerate architecturally complex healthy tissue. Thus, there is a need for methods that can create structural complexity within TE scaffolds to guide tissue regeneration. In this paper we have engineered novel dual-crosslinked hyaluronic acid hydrogel scaffolds with photopatterned anisotropic swelling. Anisotropic swelling can produce zonal distributions of crosslink density, water content and viscoelasticity on the macro- and micro-scales within the hydrogel scaffold. We have found that anisotropically swelling hydrogels can be obtained by a combination of chemical crosslinks and patterned photocrosslinks within a single dual-crosslinked hydrogel. According to our method an unswollen chemically crosslinked hydrogel substrate was spatially patterned with photocrosslinks that restricted swelling at selected sites. The resulting dual-crosslinked hydrogel swelled anisotropically because of differential crosslink densities between the photopatterned and non-photopatterned regions. Anisotropic swelling permitted the hydrogel to contort and evolve a shape different from that of the unswollen hydrogel. A biodegradable hydrogel with this unique swelling behavior yields a new, unexplored type of shape-changing TE scaffold.

Collagens, stromal cell‐derived factor‐1α and basic fibroblast growth factor increase cancer cell invasiveness in a hyaluronan hydrogel

Beyond to control of cell migration, differentiation and proliferation, the extracellular matrix (ECM) also contributes to invasiveness of human cancers. As the roles of hyaluronan (HA) and collagens in this process are still controversial, we have investigated their involvement in cancer pathogenesis. With this aim in view, we developed a three-dimensional matrix, as reticulate HA hydrogel alone or coated with different collagens, in which cells could invade and grow. We show that cancer cells, which were non-invasive in a single HA hydrogel, acquired this capacity in the concomitant presence of type I or III collagens. Both types of ECM compound, HA and collagens, possess the capacity to stimulate production of metalloprotease-2, recognized otherwise as a factor for poor cancer prognosis. HA-provoked cellular invasiveness resulted from CD44-mediated increase in cytosolic [Ca2+] and its subsequent hydrolysis due to ADAM (a disintegrin and metalloprotease) proteolytic activity. Interestingly, this mechanism seemed to be absent in non-invasive cancer cell lines. Furthermore, using basic fibroblast growth factor and stromal cell-derived factor-1alpha, we also show that this three-dimensional reticulate matrix may be considered as a valuable model to study chemokinetic and chemotactic potentials of factors present in tumour stroma.

Photon Force-Induced Phase Transition Dynamics of Single Hydrogel Nanoparticles in Water

--isopropylacrylamide) gel particles labeled with a polarity-sensitive °uores-cent probe monomer were optically trapped by a focused laser beam and its°uorescence dynamics was analyzed. The °uorescence intensity of trappedsingle gel particles was increased with the trapping laser power, while the °u-orescence peak wavelength was not changed. Temperature-induced changesof °uorescence properties of the single particle were conflrmed to be simi-lar to those of the bulk solution. These behaviors are well interpreted byconsidering that the °uorescence intensity and °uorescence peak re°ect lo-cal interactions between the °uorescent probe and attaching (bound) watermolecules and efiective polarity determined by (free) water content in theparticle, respectively. A change in the °uorescence peak wavelength afterlaser trapping was followed and its blue-shift was conflrmed to occur withina few hundreds seconds, indicating that a single gel particle gradually attainsto a globular state on this timescale, expelling initially free water moleculesand then bound ones.PACS numbers: 87.80.Cc, 33.50.Dq, 61.25.Hq, 87.64.{t

In-Situ AFM Studies of the Phase-Transition Behavior of Single Thermoresponsive Hydrogel Particles

The volume phase transition (VPT) behavior of individual thermally responsive poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAm-co-AAc) hydrogel microparticles was studied by in-situ dynamic mode atomic force microscopy (AFM) and force spectroscopy during heating and cooling cycles. Hydrogel samples were prepared by electrostatic immobilization of microparticles to amine-modified gold surfaces. The AFM studies of particle deswelling were performed by varying the force applied on the particles during imaging as a function of the geometry and material of the AFM probe. Aluminum-coated silicon cantilevers were found to influence substantially the behavior of the particles during the VPT, leading to a significant shape change. Low force impact magnetic excitation of the AFM probe (MAC mode) during dynamic mode measurements resulted in an undisturbed deswelling behavior enabling observation of the expected volume changes of the particles without significant tip-sample interaction. Hence, MAC-mode AFM was determined to be the most suitable technique for in-situ AFM studies on volume and shape changes at single hydrogel particles during VPT. Elasticity measurements performed at single particles at temperatures below and above the VPT revealed a 15-fold increase in the Young's modulus after passing the VPT, indicating the transition from a soft, swollen network to a stiffer, deswollen state.

Photolithographic patterning of polyethylene glycol hydrogels

A simple, inexpensive photolithographic method for surface patterning deformable, solvated substrates is demonstrated using photoactive poly(ethylene glycol) (PEG)-diacrylate hydrogels as model substrates. Photolithographic masks were prepared by printing the desired patterns onto transparencies using a laser jet printer. Precursor solutions containing monoacryloyl-PEG-peptide and photoinitiator were layered onto hydrogel surfaces. The acrylated moieties in the precursor solution were then conjugated in monolayers to specific hydrogel regions by exposure to UV light through the transparency mask. The effects of UV irradiation time and precursor solution concentration on the levels of immobilized peptide were characterized, demonstrating that bound peptide concentration can be controlled by tuning these parameters. Multiple peptides can be immobilized to a single hydrogel surface in distinct patterns by sequential application of this technique, opening up its potential use in co-cultures. In addition, 3D structures can be generated by incorporating PEG-diacrylate into the precursor solution. To evaluate the feasibility of using these patterned surfaces for guiding cell behavior, human dermal fibroblast adhesion on hydrogel surfaces patterned with acryloyl–PEG–RGDS was investigated. This patterning method may find use in tissue engineering, the elucidation of fundamental structure–function relationships, and the formation of immobilized cell and protein arrays for biotechnology.

Lamellar Liquid Single Crystal Hydrogels: Synthesis and Investigation of Anisotropic Water Diffusion and Swelling

The synthesis and characterization of anisotropic liquid single crystal hydrogels (LSCHs) via photoinduced radical polymerization of magnetically aligned samples in the lyotropic mesophase are reported, which are stable against tensile stresses in all three dimensions. The hydrogels exhibit a lamellar phase (Lα) in the swollen state. The high mechanical stability is achieved by using a new type of cross-linker. Monomer and cross-linker molecules have almost the same chemical constitution, varying only in the number of polymerizable groups. The cross-linker is incorporated perfectly into the liquid-crystalline phase structure of the lyotropic liquid-crystalline monomers, yielding a network which has covalent bridges between the lamellae. The anisotropic hydrogels are characterized by a variety of methods on micro- and macroscopic length scales. Swelling with the nonselective solvent toluene shows that cross-linking within the liquid-crystalline phase causes an anisotropic topology of the network, which sho...

Single Component Chitosan Hydrogel Microcapsule from a Layer-by-Layer Approach

Smart biomaterials have found broad applications in modern medical technologies.1 However, the development of smart hydrogels with rapid response, good biocompatibility, and controllable degradability is still a formidable challenge. Chitosan, a biodegradable, nontoxic, and renewable linear polysaccharide, has been considered for various biomedical and pharmaceutical applications.2,3 To these ends, microparticles of chitosan in hundreds of micrometers have been prepared in different ways, including coacervation/ precipitation, spray-drying, emulsion cross-linking, emulsiondroplet coalescence, reverse micellization, ionic gelation, and sieving method.3,4 Complexation between chitosan and oppositely charged polysaccharides in solution is another way to synthesize chitosan microparticles; however, this process often leads to the formation of fibers.5 A new strategy, the so-called “layer-by-layer (LbL) assembly”, has been used here to fabricate microcapsules from chitosan. This strategy, based on the electrostatic interaction between oppositely charged polyelectrolytes, was first introduced by Decher et al. to fabricate thin films on planar supports by alternate adsorption of polycation and polyanion.6 Because of its advantages of fine control of the compositions and the thickness of the capsules, the LbL method received more and more attention in recent years.7-9 It was extended to three-dimensional (3D) systems by Mohwald et al. to fabricate core-shell particles and hollow capsules by further removal of the sacrificial core.10 In previous works, we first extended the LbL method based on hydrogen and covalent bonding to 3D systems and synthesized hydrogen or covalent bonded capsules.11,12 Chitosan bears positive charges and is a polycation at low pH. It has been used widely to fabricate LbL films13-19 and capsules20-22 with other polyelectrolytes. For the normal LbL methods, the capsule wall has at least two compositions. In certain applications, one may take advantage of the feasibility of several components by combining their individual material properties. On the other hand, the presence of a second polymer component for LbL assembling may limit the specific functionality of materials. For instance, the biocompatibility and biodegradability of chitosan could be destroyed by a second polymer component. Moya et al. fabricated a nearly single component capsule of polyallylamine hydrochloride (PAH) from the polystyrene sulfonate (PSS)/PAH LbL assembly by using cells as the template.23 The PAH in the capsule wall was oxidized and cross-linked, and then most of PSS was removed while removing the cell core template with sodium hypochlorite. However, this strategy could not be a general method for fabrication of single component capsules. Zhang et al. reported the preparation of single component 2-dimensional films from hydrogen-bonded LbL films, but these films were not cross-linked.24,25 Our new strategy is to selectively crosslink the chitosan chains and remove the second polymer component that was built up in the capsule walls (see Scheme 1). Using this strategy, single component chitosan hydrogel microcapsules were successfully synthesized. The pHresponsive volume phase transition of the chitosan hydrogel microcapsules could be controlled through the cross-linking density. The resultant chitosan gel microcapsules are nearly monodispersed, and the shell thickness is tunable, which is a big advantage to control the releasing kinetics of encapsulated drug or other molecules in response to pH or salt concentration changes. More importantly, although many shell cross-linked capsules have been made from synthetic block copolymers through a strategy of self-assembly of block copolymers with selective cross-linking on the shell block,26-31 it is very challenging, if not impossible, to synthesize well-defined block copolymers from natural polysaccharides. Our novel strategy here can provide a general method to synthesize shell cross-linked microcapsules from natural polysaccharides that have many applications in the pharmaceutical and medical field due to their biocompatibility and degradability.

Microfabricated Cell-based Biosensor Arrays.

Here, we described the fabrication using photolithography of poly(ethylene glycol) (PEG)-based hydrogel microstructures encapsulating viable mammalian cells on glass and silicon substrates. Substrates were treated with 3-(trichlorosilyl) propyl methacrylate to form pendant acrylate group to covalent link the hydrogel microstructure. Cells were encapsulated in arrays of cylindrical hydrogel microstructures 600 and 50 μm in diameter and viability assays demonstrated that encapsulated cells remained viable after photoencapsulation. These microstructures had clearly defined, three-dimensional structure without any residual cells remaining surface and no delamination of hydrogel elements from functionalized substrate occurred in aqueous environment for over a week. By changing spin-coating rates and feature sizes of photomasks, we could create cell-containing microstructures with aspect ratios ranging from 0.12 to 1.4. In case of 50 μm hydrogel microstructure, number of cells could be limited to 1 or 2 cells per element and array consisting of 400 elements could be fabricated in a square of 2 mm2. These cell-containinghydrogel microstructures were also successfully fabricated in poly(dimethylsiloxane) microchannels to create optical biosensor arrays of individually addressable single or multiple cell- containing hydrogel microstructures with potential applications in drug screening or pathogen detection.

Enlargement and Sculpturing of a Small and Deformed Glans

We present 2 techniques of enhancement and sculpturing of a small and/or deformed glans. The small glans in primary or re-do hypospadias repair was enhanced by longitudinal double-faced island flaps incorporated onto the ventral side of the glans between the glans wings. The deformed glans, of small or normal size (with normal urethra or well functioning neourethra), was enlarged and sculptured by injection of hydrogel. Between May 1997 and March 2002, 27 patients underwent glans enhancement and sculpturing. Small deformed glans occurred after failed hypospadias repair in 10 patients, penile trauma in 3, hemangioma sclerozation in 2, primary hypospadias in 8 and normally developed penile body in 4. A double-faced island flap was performed in 14 patients, glans was enhanced by hydrogel injection in 9 and both procedures were performed in 4. Mean followup was 34 months for the double-faced flap technique 17 months for hydrogel injection. Satisfactory enlargement and esthetic appearance were achieved in 13 of the 14 patients who underwent the double-faced flap technique and 1 required surgical correction. Of the 9 patients who underwent either single or multistage hydrogel injection 8 had good results and 1 required partial removal of hydrogel after hypercorrection. The combination of these 2 techniques provided satisfactory results in all 4 cases. Enlargement and sculpturing of a small deformed glans are challenging and difficult. A double-faced island flap and/or injection of hydrogel resolves this problem satisfactorily.