Scott D. Fitzpatrick

PNIPAAm-Grafted-Collagen as an Injectable, In Situ Gelling, Bioactive Cell Delivery Scaffold

We synthesized two thermoresponsive, bioactive cell scaffolds by decorating the backbone of type I bovine collagen with linear chains of poly(N-isopropylacrylamide) (PNIPAAm), with the ultimate aim of providing facile delivery via injection and support of retinal pigment epithelial (RPE) cells into the back of the eye for the treatment of retinal degenerative diseases. Both scaffolds displayed rapid, subphysiological phase transition temperatures and were capable of noninvasively delivering a liquid suspension of cells that gels in situ forming a cell-loaded scaffold, theoretically isolating treatment to the injection site. RPE cells demonstrated excellent viability when cultured with the scaffolds, and expulsion of cells arising from temperature-induced PNIPAAm chain collapse was overcome by incorporating a room-temperature incubation period prior to scaffold phase transition. These results indicate the potential of using PNIPAAm-grafted-collagen as a vehicle for the delivery of therapeutic cells to the subretinal space.

Cell-adhesive thermogelling PNIPAAm/hyaluronic acid cell delivery hydrogels for potential application as minimally invasive retinal therapeutics †

Copolymers of N-isopropylacrylamide (NIPAAm) and acrylic acid N-hydroxysuccinimide (NAS) were synthesized via free radical polymerization and conjugated with amine-functionalized hyaluronic acid (HA) and cell adhesive RGDS peptides. These novel copolymers were designed to facilitate noninvasive delivery of a liquid suspension of cells into the delicate subretinal space for treatment of retinal degenerative diseases such as age-related macular degeneration (AMD) and diabetic retinopathy. The various synthesized copolymers all displayed subphysiological phase transition temperatures, thereby allowing temperature-induced scaffold formation and subsequent entrapment of transplanted cells within an adhesive support matrix. Successful grafting of HA and RGDS peptides were confirmed with Fourier Transform Infrared (FTIR) spectroscopy and quantified with (1)H Nuclear Magnetic Resonance (NMR) spectroscopy. All copolymers demonstrated excellent compatibility with retinal pigment epithelial (RPE) cells in culture and minimal host response was observed following subcutaneous implantation into hairless SKH1-E mice (strain code 447).

Temperature-sensitive polymers for drug delivery

The ability to undergo rapid changes in response to subtle environmental cues make stimuli- responsive materials attractive candidates for minimally invasive, targeted and personalized drug delivery applications. This special report aims to highlight and provide a brief description of several of the significant natural and synthetic temperature-responsive materials that have clinical relevance for drug delivery applications. This report examines the advantages and disadvantages of natural versus synthetic materials and outlines various scaffold architectures that can be utilized with temperature-sensitive drug delivery materials. The authors provide a commentary on the current state of the field and provide their insight into future expectations for temperature-sensitive drug delivery, emphasizing the importance of the emergence of dual and multiresponsive systems capable of responding precisely to an expanding set of stimuli, thereby allowing the development of disease-specific drug delivery vehicles.

Strategies for ocular siRNA delivery: Potential and limitations of non-viral nanocarriers.

Controlling gene expression via small interfering RNA (siRNA) has opened the doors to a plethora of therapeutic possibilities, with many currently in the pipelines of drug development for various ocular diseases. Despite the potential of siRNA technologies, barriers to intracellular delivery significantly limit their clinical efficacy. However, recent progress in the field of drug delivery strongly suggests that targeted manipulation of gene expression via siRNA delivered through nanocarriers can have an enormous impact on improving therapeutic outcomes for ophthalmic applications. Particularly, synthetic nanocarriers have demonstrated their suitability as a customizable multifunctional platform for the targeted intracellular delivery of siRNA and other hydrophilic and hydrophobic drugs in ocular applications. We predict that synthetic nanocarriers will simultaneously increase drug bioavailability, while reducing side effects and the need for repeated intraocular injections. This review will discuss the recent advances in ocular siRNA delivery via non-viral nanocarriers and the potential and limitations of various strategies for the development of a ‘universal’ siRNA delivery system for clinical applications.

Development of injectable, resorbable drug-releasing copolymer scaffolds for minimally invasive sustained ophthalmic therapeutics.

Copolymers based on N-isopropylacrylamide (NIPAAm), acrylic acid N-hydroxysuccinimide (NAS) and varying concentrations of acrylic acid (AA) and acryloyloxy dimethyl-γ-butyrolactone (DBA) were synthesized to create thermoresponsive, resorbable copolymers for minimally invasive drug and/or cell delivery to the posterior segment of the eye to combat retinal degenerative diseases. Increasing DBA content was found to decrease both copolymer water content and lower critical solution temperature. The incorporation of NAS provided an amine-reactive site, which can be exploited for facile conjugation of bioactive agents. Proton nuclear magnetic resonance analysis revealed the onset of hydrolysis-dependent opening of the DBA lactone ring, which successfully eradicated copolymer phase transition properties and should allow the gelled polymer to re-hydrate, enter systemic circulation and be cleared from the body without the production of degradation byproducts. Hydrolytic ring opening occurs slowly, with over 85% copolymer mass remaining after 130 days of incubation in 37°C phosphate buffered saline. These slow-degrading copolymers are hypothesized to be ideal delivery vehicles to provide minimally invasive, sustained, localized release of pharmaceuticals within the posterior segment of the eye to combat retinal degenerative diseases.

Effect of anti-TGF-β2 surface modification of polydimethylsiloxane on lens epithelial cell markers of posterior capsule opacification

Posterior capsule opacification is the most common complication of cataract surgery. Lens epithelial cells remaining in the capsular bag following surgery can undergo epithelial-to-mesenchymal transition and migrate from the anterior to the posterior capsule, leading to fibrosis, capsular wrinkling, and ultimately vision loss. Transforming growth factor-beta 2 has been shown to play a major role in epithelial-to-mesenchymal transition. Covalent tethering of anti-transforming growth factor-beta 2 to the surface of the intraocular lens material may inhibit epithelial-to-mesenchymal transition and the subsequent events, thus leading to a reduction in posterior capsule opacification. In this work, the antibody was tethered to the surface of polydimethylsiloxane as a model lens material via a poly(ethylene) glycol spacer. Surface characterization using a variety of methods demonstrated successful modification. The surface density of the anti-transforming growth factor-beta 2 was approximately 0.5 µg/cm2. The presence of transforming growth factor-beta 2 in cell culture medium stimulated production of extracellular matrix components such as collagen, fibronectin, laminin, and the fibrotic marker α-smooth muscle actin, by HLE-B3 cells. These effects were decreased but not completely eradicated by the presence of the anti-transforming growth factor-beta 2 antibody on the polydimethylsiloxane surface. These results suggest that surface modification with appropriate antifibrotic molecules has the potential to modulate cellular changes following cataract surgery and lead to a reduction in posterior capsule opacification.