Manoj B. Charati

Injectable and bioresponsive hydrogels for on-demand matrix metalloproteinase inhibition

Inhibitors of matrix metalloproteinases (MMPs) have been extensively explored to treat pathologies where excessive MMP activity contributes to adverse tissue remodeling. While MMP inhibition remains a relevant therapeutic target, MMP inhibitors have not translated to clinical application due to the dose-limiting side effects following systemic administration of the drugs. Here, we describe the synthesis of a polysaccharide-based hydrogel that can be locally injected into tissues and releases a recombinant tissue inhibitor of MMPs (rTIMP-3) in response to MMP activity. Specifically, rTIMP-3 is sequestered in the hydrogels through electrostatic interactions and is released as crosslinks are degraded by active MMPs. Targeted delivery of the hydrogel/rTIMP-3 construct to regions of MMP over-expression following a myocardial infarction (MI) significantly reduced MMP activity and attenuated adverse left ventricular remodeling in a porcine model of MI. Our findings demonstrate that local, on-demand MMP inhibition is achievable through the use of an injectable and bioresponsive hydrogel.

Injectable shear-thinning hydrogels engineered with a self-assembling Dock-and-Lock mechanism

Injected therapeutics, such as cells or biological molecules, may have enhanced efficiency when delivered within a scaffold carrier. Here, we describe a dual-component Dock-and-Lock (DnL) self-assembly mechanism that can be used to construct shear-thinning, self-healing, and injectable hydrogels. One component is derived from the RIIα subunit of cAMP-dependent kinase A and is engineered as a telechelic protein with end groups that dimerize (docking step). The second component is derived from the anchoring domain of A-kinase anchoring protein (AD) and is attached to multi-arm crosslinker polymers and binds to the docked proteins (locking step). When mixed, these two DnL components form robust physical hydrogels instantaneously and under physiological conditions. Mechanical properties and erosion rates of DnL gels can be tuned through the AD peptide sequence, the concentration and ratio of each component, and the number of peptides on the cross-linking polymer. DnL gels immediately self-recover after deformation, are resistant to yield at strains as high as 400%, and completely self-heal irrespective of prior mechanical disruption. Mesenchymal stem cells mixed in DnL gels and injected through a fine needle remain highly viable (>90%) during the encapsulation and delivery process, and encapsulated large molecules are released with profiles that correspond to gel erosion. Thus, we have used molecular engineering strategies to develop cytocompatible and injectable hydrogels that have the potential to support cell and drug therapies.

Light-Sensitive Polypeptide Hydrogel and Nanorod Composites†

Stimuli-responsive hydrogels exhibit structural changes based on changes in local temperature or pH and analytes and are highly valued in fields ranging from controlled drug release to tissue repair and also in microdevices. Hydrogels that respond to external stimuli, such as light or magnetic fields, offer additional advantageswith respect to on-demandand triggered response. With this in mind, we formulated a composite of thermoreversible polypeptide-based hydrogels, formed from a genetically engineered multiblock polypeptide that exhibits a temperature-dependent transition from a solid to liquid state, and gold nanorods. Near-infrared-light (NIR) exposure of the nanorods induces local heating and, consequently, melting of the gels. These networks were explored for the controlled release of a macromolecule and the release profiles were controlled by the extent and timing of light exposure, including stepwise release with intermittent light. The infrared-lightcontrolled dissociation of these hydrogels offers unique opportunities, such as for the delivery of drugs and growth factors with transdermal light exposure or for incorporation of hydrogel actuators in microdevices. Smart biopolymeric hydrogels are a new generation of biomaterials that may exhibit reversible physicochemical changes in response to their environment. These stimuliresponsivegels arefindingapplications inmanyfields, suchas for the delivery of therapeutic molecules, biomedical devices, such as actuators and biosensors/diagnostics, and as scaffolds for tissue engineering and regenerative medicine. A unique feature of such materials is that they undergo significant conformational changes upon variation in one or more physicochemical stimuli such as pH, temperature, analytes, or light. Although many variables have been explored, hydrogels that reversibly respond to temperature changes have been the subject of major investigation over the past two decades. These thermoresponsive systems are typically centered around synthetic polymers suchas poly(N-isopropylacrylamide) (PNIPAm) and its derivatives or biomimetic elastin-based

Elastomeric polypeptide-based biomaterials.

Elastomeric proteins are characterized by their large extensibility before rupture, reversible deformation without loss of energy, and high resilience upon stretching. Motivated by their unique mechanical properties, there has been tremendous research in understanding and manipulating elastomeric polypeptides, with most work conducted on the elastins but more recent work on an expanded set of polypeptide elastomers. Facilitated by biosynthetic strategies, it has been possible to manipulate the physical properties, conformation, and mechanical properties of these materials. Detailed understanding of the roles and organization of the natural structural proteins has permitted the design of elastomeric materials with engineered properties, and has thus expanded the scope of applications from elucidation of the mechanisms of elasticity to the development of advanced drug delivery systems and tissue engineering substrates.

Regulation of electronic behavior via confinement of PPV-based oligomers on peptide scaffolds

Intermolecular interactions dramatically affect the structure/property relationships of electroactive molecules in device environments and have been the subject of significant research effort. Purposeful manipulation of the distance between chromophores is a key parameter in such investigations, although such manipulation has proven difficult. Systems in which distances between chromophores can be controlled serve both as model systems for understanding structure/property relationships in more depth, as well as potential active components in devices. In this work, oxadiazole-containing poly(phenylenevinylene) (Oxa-PPV) oligomers have been chemically attached in specific positions to an α-helical peptide scaffold, which permits the presentation of the Oxa-PPV side-chains at distances of nominally 6 A and 11 A apart on the same side and also 7 A apart on opposite sides of the peptide. The Oxa-PPV side-chains were attached to the peptide scaffolds via straightforward Heck coupling strategies; the resulting modified peptides were characterized by a variety of spectroscopic methods. Circular dichroic spectroscopy (CD) confirmed the helical conformation of the scaffolds modified with the bulky conjugated side-chains, and suggested that side-chain interactions may improve the thermal stability of the molecules. Exciton-coupled CD measurements confirmed the interactions of the conjugated side-chains and detected subtle apparent differences in side-chain orientation that were also indicated in computational modeling of the molecules. Photoluminescence spectroscopy confirmed the electronic interaction of the side-chains; the results clearly captured differences in luminescence as a function of chromophore presentation, and further indicated differences in excited state species with differences in chromophore presentation. The observed effects indicate not only that bulky chromophores can be presented on helical peptide templates without loss of template conformation, but also that such presentation may accurately capture details of electronic transport between molecules commonly employed in organic electronic applications.

Photophysical Consequences of Interactions Between Conjugated Chromophores

We study phenylenevinylene chromophore pairs whose spacing and orientation can be varied by coupling them to peptide backbones. Copious interchromophore excitations are observed and explain reduced fluorescence yields in conjugated polymer films relative to solutions.