Wirelessly Powered-Electrically Conductive Polymer System for Stem Cell Enhanced Stroke Recovery.

Effective stroke recovery therapeutics remain limited. Stem cell therapies have yielded promising results, but the harsh ischemic environment of the post-stroke brain reduces their therapeutic potential. Previously, we developed a conductive polymer scaffold system that enabled stem cell delivery with simultaneous electrical modulation of the cells and surrounding neural environment. This wired polymer scaffold proved efficacious in optimizing ideal conditions for stem cell mediated motor improvements in a rodent model of stroke. To further enable preclinical studies and enhance translational potential, we identified a method to improve this system by eliminating its dependence upon a tethered power source. We have herein developed a wirelessly powered, electrically conductive polymer system that eases therapeutic application and enables full mobility. As a proof of concept, we demonstrate that the wirelessly powered scaffold is able to stimulate neural stem cells in vitro, as well as in vivo in a rodent model of stroke. This system modulates the stroke microenvironment and increases the production of endogenous stem cells. In summation, this novel, wirelessly powered conductive scaffold can serve as a mobile platform for a wide variety of therapeutics involving electrical stimulation.

Electrical modulation of transplanted stem cells improves functional recovery in a rodent model of stroke.

Stroke is a leading cause of long-term disability worldwide, intensifying the need for effective recovery therapies. Stem cells are a promising stroke therapeutic, but creating ideal conditions for treatment is essential. Here we developed a conductive polymer system for stem cell delivery and electrical modulation in animals. Using this system, electrical modulation of human stem cell transplants improve functional stroke recovery in rodents. Increased endogenous stem cell production corresponds with improved function. Transcriptome analysis identified stanniocalcin 2 (STC2) as one of the genes most significantly upregulated by electrical stimulation. Lentiviral upregulation and downregulation of STC2 in the transplanted stem cells demonstrate that this glycoprotein is an essential mediator in the functional improvements seen with electrical modulation. Moreover, intraventricular administration of recombinant STC2 post-stroke confers functional benefits. In summation, our conductive polymer system enables electrical modulation of stem cells as a potential method to improve recovery and identify important therapeutic targets.

Conducting polymer-based granular hydrogels for injectable 3D cell scaffolds.

Injectable 3D cell scaffolds possessing both electrical conductivity and native tissue-level softness would provide a platform to leverage electric fields to manipulate stem cell behavior. Granular hydrogels, which combine jamming-induced elasticity with repeatable injectability, are versatile materials to easily encapsulate cells to form injectable 3D niches. In this work, we demonstrate that electrically conductive granular hydrogels can be fabricated via a simple method involving fragmentation of a bulk hydrogel made from the conducting polymer PEDOT:PSS. These granular conductors exhibit excellent shear-thinning and self-healing behavior, as well as record-high electrical conductivity for an injectable 3D scaffold material (~10 S m-1). Their granular microstructure also enables them to easily encapsulate induced pluripotent stem cell (iPSC)-derived neural progenitor cells, which were viable for at least 5 days within the injectable gel matrices. Finally, we demonstrate gel biocompatibility with minimal observed inflammatory response when injected into a rodent brain.

Single-Cell Encapsulation via Click-Chemistry Alters Production of Paracrine Factors from Neural Progenitor Cells.

Extracellular matrix (ECM) properties affect multiple cellular processes such as cell survival, proliferation, and protein synthesis. Thus, a polymeric-cell delivery system with the ability to manipulate the extracellular environment can act as a fundamental regulator of cell function. Given the promise of stem cell therapeutics, a method to uniformly enhance stem cell function, in particular trophic factor release, can prove transformative in improving efficacy and increasing feasibility by reducing the total number of cells required. Herein, a click-chemistry powered 3D, single-cell encapsulation method aimed at synthesizing a polymeric coating with the optimal thickness around neural progenitor cells is introduced. Polymer encapsulation of neural stem cells significantly increases the release of neurotrophic factors such as VEGF and CNTF. Cell encapsulation with a soft extracellular polymer upregulates the ADCY8-cAMP pathway, suggesting a mechanism for the increase in paracrine factors. Hence, the described single-cell encapsulation technique can emerge as a translatable, nonviral cell modulation method and has the potential to improve stem cells' therapeutic effect.

Bioinspired Fibrillary Hydrogel with Controlled Swelling Behavior: Applicability as an Artificial Vitreous.

The vitreous humor of the eye is mainly composed of fibrillary collagen and semiflexible hyaluronic acid (HA). To mimic this macromolecular composition of the vitreous, we previously developed an injectable two-component hydrogel composed of a fibrillary gellan and a semiflexible polyelectrolyte, poly[methacrylamide-co-(methacrylic acid)], both endowed with thiol cross-linkers. We optimized the hydrogel formulations for optical, physical, mechanical, and transport properties approximating those of the vitreous. Here, we studied 11 hydrogel formulations with varying concentrations of each component, and, as expected, we found that they all swelled in physiological solution. The two formulations that most closely matched the vitreous properties were investigated further. Judged against nonsurgical control and silicone oil, a clinically accepted vitreous replacement, both hydrogel formulations were biocompatible in rabbits for 30 days. Both hydrogels maintained optical clarity, physiological intraocular pressure, and intact retinal layers that displayed normal electroretinography. The swelling behavior of the gel led us to postulate that the native vitreous may also exhibit controlled swelling, where ionic HA's swelling capacity is restricted by fibrillary collagen. In conclusion, the two hydrogels merit further in vivo evaluation as an artificial vitreous for an extended duration and additionally in mini-pigs for their similarity to human eyes in size.

Biomimetic hydrogel with tunable mechanical properties for vitreous substitutes.

UNLABELLED: The vitreous humor of the eye is a biological hydrogel principally composed of collagen fibers interspersed with hyaluronic acid. Certain pathological conditions necessitate its removal and replacement. Current substitutes, like silicone oils and perfluorocarbons, are not biomimetic and have known complications. In this study, we have developed an in situ forming two-component biomimetic hydrogel with tunable mechanical and osmotic properties. The components are gellan, an analogue of collagen, and poly(methacrylamide-co-methacrylate), an analogue of hyaluronic acid; both endowed with thiol side groups. We used response surface methodology to consider seventeen possible hydrogels to determine how each component affects the optical, mechanical, sol-gel transition temperature and swelling properties. The optical and physical properties of the hydrogels were similar to vitreous. The shear storage moduli ranged from 3 to 358Pa at 1Hz and sol-gel transition temperatures from 35.5 to 43°C. The hydrogel had the ability to remain swollen without degradation for four weeks in vitro. Three hydrogels were tested for biocompatibility on primary porcine retinal pigment epithelial cells, human retinal pigment epithelial cells, and fibroblast (3T3/NIH) cells, by electric cell-substrate impedance sensing system. The two-component hydrogels allowed for the tuning and optimizing of mechanical, swelling, and transition temperature to obtain three biocompatible hydrogels with properties similar to the vitreous. Future studies include testing of the optimized hydrogels in animal models for use as a long-term substitute, whose preliminary results are mentioned. STATEMENT OF SIGNIFICANCE: Although hydrogels are researched as long-term vitreous substitute, none have advanced sufficiently to reach clinical application. Our work focuses on the development of a novel two component in situ forming hydrogel that bio-mimic the natural vitreous. Our thiol-containing copolymers can be injected as an aqueous solution into the vitreous cavity wherein, at physiological temperature, the rigid component will instantaneously form a physical gel imbedding the random coil copolymer. Upon subsequent oxidation, the two components will form disulfide cross-links and a stable reversible hydrogel capable of providing osmotic pressure to reattach the retina. It may be left in the eye permanently or easily removed by injection of a simple reducing agent to cleave the disulfide bonds, rather than surgery. This contribution is significant because it is expected to provide patients with a much better quality of life by improving surgical outcomes, creating much less post-operative burden, and reducing the need for secondary surgeries.

Investigating thiol-modification on hyaluronan via carbodiimide chemistry using response surface methodology.

Hyaluronan (HA) is a naturally occurring glycosaminoglycan widely researched for its use as a biomaterial in tissue engineering, drug delivery, angiogenesis, and ophthalmic surgeries. The mechanical properties of this biomaterial can be altered to a required extent by chemically modifying the pendant reactive groups. However, derivatizing these polymers to a predetermined extent has been the Achilles heel for this process. In this study, we have investigated the factors controlling the derivatization of the carboxyl moieties of HA with amine containing thiol, cystamine dihydrochloride (Cys), via carbodiimide crosslinking chemistry. We used fractional factorial design to screen and identify the significant factor(s) affecting the reaction, and response surface methodology (RSM) to develop a model equation for predicting the degree of thiolation of HA. Also, we analyzed the reaction mechanism for potential side reactions. We observed that N-(3-dimethylaminopropyl)-N'-ethylcarbodiimide hydrochloride (EDC) (mole ratio with repeat unit of HA) is the significant factor controlling the degree of amidation. The quadratic equations developed from RSM predict the formulation for a desired degree of amidation of HA and percentage of potential side product. Hence, derivatizing HA to a predetermined extent with minimal side product can be achieved using the statistical design of experiments.