Biocompatibility of poly(ethylene glycol) and poly(acrylic acid) interpenetrating network hydrogel by intrastromal implantation in rabbit cornea.

We evaluated the biocompatibility of a poly(ethylene glycol) and poly(acrylic acid) (PEG/PAA) interpenetrating network hydrogel designed for artificial cornea in a rabbit model. PEG/PAA hydrogel measuring 6 mm in diameter was implanted in the corneal stroma of twelve rabbits. Stromal flaps were created with a microkeratome.

In vivo biocompatibility of two PEG/PAA interpenetrating polymer networks as corneal inlays following deep stromal pocket implantation.

This study compared the effects of implanting two interpenetrating polymer networks (IPNs) into rabbit corneas. The first (Implant 1) was based on PEG-diacrylate, the second (Implant 2) was based on PEG-diacrylamide. There were inserted into deep stromal pockets created using a manual surgical technique for either 3 or 6 months.

Diffusion of protein through the human cornea.

Aims: To determine the rate of diffusion of myoglobin and bovine serum albumin (BSA) through the human cornea. These small proteins have hydrodynamic diameters of approximately 4.4 and 7.

Toward the development of an artificial cornea: improved stability of interpenetrating polymer networks.

A novel interpenetrating network (IPN) based on poly(ethylene glycol) (PEG) and poly(acrylic acid) was developed and its use as an artificial cornea was evaluated in vivo. The in vivo results of a first set of corneal inlays based on PEG-diacrylate precursor showed inflammation of the treated eyes and haze in the corneas. The insufficient biocompatibility could be correlated to poor long-term stability of the implant caused by hydrolytic degradation over time.

Bioactive interpenetrating polymer network hydrogels that support corneal epithelial wound healing.

The development and characterization of collagen-coupled poly(ethylene glycol)/poly(acrylic acid) (PEG/PAA) interpenetrating polymer network hydrogels is described. Quantitative amino acid analysis and FITC-labeling of collagen were used to determine the amount and distribution of collagen on the surface of the hydrogels. The bioactivity of the coupled collagen was detected by a conformation-specific antibody and was found to vary with the concentration of collagen reacted to the photochemically functionalized hydrogel surfaces.

Progress in the development of interpenetrating polymer network hydrogels.

Interpenetrating polymer networks (IPNs) have been the subject of extensive study since their advent in the 1960s. Hydrogel IPN systems have garnered significant attention in the last two decades due to their usefulness in biomedical applications. Of particular interest are the mechanical enhancements observed in "double network" IPN systems which exhibit nonlinear increases in fracture properties despite being composed of otherwise weak polymers.

Development of hydrogel-based keratoprostheses: a materials perspective.

Research and development of artificial corneas (keratoprostheses) in recent years have evolved from the use of rigid hydrophobic materials such as plastics and rubbers to hydrophilic, water-swollen hydrogels engineered to support not only peripheral tissue integration but also glucose diffusion and surface epithelialization. The advent of the AlphaCor core-and-skirt hydrogel keratoprosthesis has paved the way for a host of new approaches based on hydrogels and other soft materials that encompass a variety of materials preparation strategies, from synthetic homopolymers and copolymers to collagen-based bio-copolymers and, finally, interpenetrating polymer networks. Each approach represents a unique strategy toward the same goal: to develop a new hydrogel that mimics the important properties of natural donor corneas.

Glucose-permeable interpenetrating polymer network hydrogels for corneal implant applications: a pilot study.

Epithelialization of a keratoprosthesis requires that the implant material be sufficiently permeable to glucose. We have developed a poly(ethylene glycol)/poly(acrylic acid) (PEG/PAA) interpenetrating polymer network (IPN) hydrogel that can provide adequate passage of glucose from the aqueous humor to the epithelium in vivo. A series of PEG/PAA IPNs with varying PEG macromonomer molecular weights were synthesized and evaluated through swelling studies to determine their water content and diffusion experiments to assess their permeability to glucose.

Design and fabrication of an artificial cornea based on a photolithographically patterned hydrogel construct.

We describe the design and fabrication of an artificial cornea based on a photolithographically patterned hydrogel construct, and demonstrate the adhesion of corneal epithelial and fibroblast cells to its central and peripheral components, respectively. The design consists of a central "core" optical component and a peripheral tissue-integrable "skirt." The core is composed of a poly(ethylene glycol)/poly(acrylic acid) (PEG/PAA) double-network with high strength, high water content, and collagen type I tethered to its surface.

Undulatory delamination of thin polymer films on gold surfaces.

Using two-dimensional surface plasmon resonance measurements, we have observed the formation of traveling waves in the delamination of thin films of polydimethylsilane (PDMS) exposed to methanol. Films were spin-coated on a gold surface and the methanol was added to the top surface. The stress-induced instability caused by the swelling of the PDMS thin film when its edge is pinned to the gold surface leads to wrinkle formation and propagation at the interface.

Glucose permeability of human, bovine, and porcine corneas in vitro.

Purpose: To measure glucose flux across human, bovine, and porcine corneas and to determine the diffusion coefficient of each type of cornea.

Methods: Diffusion of glucose across human (n = 8), bovine (n = 7), and pig corneas (n = 8) was measured using a modified blind well chamber apparatus (Boyden chamber). Dialysis membranes (n = 7) and nonporous Mylar membranes (n = 7) were used as positive and negative controls, respectively.

Localized chemical release from an artificial synapse chip.

A device that releases chemical compounds in small volumes and at multiple, well defined locations would be a powerful tool for clinical therapeutics and biological research. Many biomedical devices such as neurotransmitter-based prostheses or drug delivery devices require precise release of chemical compounds. Additionally, the ability to control chemical gradients will have applications in basic research such as studies of cell microenvironments, stem cell niches, metaplasia, or chemotaxis.

Fluid flow past an aperture in a microfluidic channel.

Electroosmotically driven flow in neurotransmitter-based retinal prostheses offers a novel approach to interfacing the nervous system. Here, we show that electroosmotically driven flow in a microfluidic channel can be used either to eject or to withdraw fluid through a small aperture in the channel wall. We study this fluid movement numerically using a finite-element method and experimentally using microfabricated channels and apertures.

The Artificial Synapse Chip: a flexible retinal interface based on directed retinal cell growth and neurotransmitter stimulation.

The Artificial Synapse Chip is an evolving design for a flexible retinal interface that aims to improve visual resolution of an electronic retinal prosthesis by addressing cells individually and mimicking the physiological stimulation achieved in synaptic transmission. We describe three novel approaches employed in the development of the Artificial Synapse Chip: (i) micropatterned substrates to direct retinal cell neurite growth to individual stimulation sites; (ii) a prototype retinal interface based on localized neurotransmitter delivery; and (iii) the use of soft materials to fabricate these devices. By patterning the growth of cells to individual stimulation sites, we can improve the selectivity of stimulation and decrease the associated power requirements.

Streptavidin tetramerization and 2D crystallization: a mean-field approach.

A mean-field theoretical approach is applied to streptavidin tetramerization and two-dimensional (2D) crystallization. This theory includes, in particular, solvent-residue interactions following the inhomogeneous Flory-Huggins model for polymers. It also takes into account residue-residue interactions by using tabulated pair interaction parameters.

Meanfield approach to the thermodynamics of protein-solvent systems with application to p53.

We present a meanfield theoretical approach for studying protein-solvent interactions. Starting with the partition function of the system, we develop a field theory by introducing densities for the different components of the system. At this point, protein-solvent interactions are introduced following the inhomogeneous Flory-Huggins model for polymers.

A meanfield approach to the thermodynamics of a protein-solvent system with application to the oligomerization of the tumor suppressor p53.

The thermodynamic stability and oligomerization status of the tumor suppressor p53 tetramerization domain have been studied experimentally and theoretically. A series of hydrophilic mutations at Met-340 and Leu-344 of human p53 were designed to disrupt the hydrophobic dimer-dimer interface of the tetrameric oligomerization domain of p53 (residues 325-355). Meanfield calculations of the free energy of the solvated mutants as a function of interdimer distance were compared with experimental data on the thermal stability and oligomeric state (tetramer, dimer, or equilibrium mixture of both) of each mutant.

Electrophoresis between sieving and reptation: an investigation of the role of shape fluctuations in electrophoresis.

We present numerical simulation results of electrophoretic mobilities of flexible polyelectrolytes over a wide molecular size range moving through gels with various pore sizes. The data are compared to existing models for different molecular size regimes and to experimental results. We observe rather pronounced shape fluctuations of the polyelectrolytes which, especially for larger gel pores or small molecules, have a strong impact on the dynamics of the molecules.

Preparation, manipulation, and pulse strategy for one-dimensional pulsed-field gel electrophoresis (ODPFGE).

The underlying principles for zero-integrated-field electrophoresis (ZIFE) pulses and more general forward-biased pulse schemes are reviewed for one-dimensional pulsed-field gel electrophoresis (ODPFGE) separations of large DNA molecules. Detailed descriptions of materials, preparation protocols, hardware requirements, and procedures are given. A variety of gel pictures for known yeast DNA markers are shown.

Sequencing using pulsed field and image reconstruction.

The use of pulsed fields in a standard manual sequencing set-up results in the separation of > 2 kb on a single gel, as compared to 300-400 bases with a dc field. However, visual reading of the sequence from a film exposed to a pulsed-field gel is not possible for more than 800-900 bases under the best conditions. The use of image reconstruction and enhancement techniques allows the reading of the M13mp18 sequence to > 1 kb, and individual bands can be identified at > 2 kb.

A new concept for separating nucleic acids by electrophoresis in solution using hybrid synthetic end labelled-nucleic acid molecules.

Analogy between the symmetry breaking of the electrical driving force and the opposing friction force in gels using pulsed electric fields is made with the corresponding effect for polyelectrolyte coils in solution related to the molecular weight-independent charge density. The synthesis of hybrid molecules to break the symmetry of constant charge density is proposed, in which standard polypeptide end labels are attached to nucleic acid fragments. The combinatorial chemical library scheme of Brenner and Lerner (Proc.

Effect of one-dimensional pulsed-field gel electrophoresis on linear and circular DNA.

A summary of the three main one-dimensional pulsed-field strategies (zero-integrated field, forward-biased field, and high frequency modulation) used for separating DNA molecules without band inversion within a preselected size range is given. Each of these strategies has size-specific features which make separations up to 6 Mbp possible. We applied the same methodology to circular DNAs varying in size from 2 kbp to about 4 Mbp.