Programmable hydrogels for the controlled release of therapeutic nucleic acid aptamers via reversible DNA hybridization

Hydrogel drug delivery systems for minimally invasive local immunotherapy of cancer

Although systemic immunotherapy has achieved durable responses and improved survival for certain patients and cancer types, low response rates and immune system-related systemic toxicities limit its overall impact. Intratumoral (intralesional) delivery of immunotherapy is a promising technique to combat mechanisms of tumor immune suppression within the tumor microenvironment and reduce systemic drug exposure and associated side effects. However, intratumoral injections are prone to variable tumor drug distribution and leakage into surrounding tissues, which can compromise efficacy and contribute to toxicity. Controlled release drug delivery systems such as in situ-forming hydrogels are promising vehicles for addressing these challenges by providing improved spatio-temporal control of locally administered immunotherapies with the goal of promoting systemic tumor-specific immune responses and abscopal effects. In this review we will discuss concepts, applications, and challenges in local delivery of immunotherapy using controlled release drug delivery systems with a focus on intratumorally injected hydrogel-based drug carriers.

Translational Applications of Hydrogels

Advances in hydrogel technology have unlocked unique and valuable capabilities that are being applied to a diverse set of translational applications. Hydrogels perform functions relevant to a range of biomedical purposes-they can deliver drugs or cells, regenerate hard and soft tissues, adhere to wet tissues, prevent bleeding, provide contrast during imaging, protect tissues or organs during radiotherapy, and improve the biocompatibility of medical implants. These capabilities make hydrogels useful for many distinct and pressing diseases and medical conditions and even for less conventional areas such as environmental engineering. In this review, we cover the major capabilities of hydrogels, with a focus on the novel benefits of injectable hydrogels, and how they relate to translational applications in medicine and the environment. We pay close attention to how the development of contemporary hydrogels requires extensive interdisciplinary collaboration to accomplish highly specific and complex biological tasks that range from cancer immunotherapy to tissue engineering to vaccination. We complement our discussion of preclinical and clinical development of hydrogels with mechanical design considerations needed for scaling injectable hydrogel technologies for clinical application. We anticipate that readers will gain a more complete picture of the expansive possibilities for hydrogels to make practical and impactful differences across numerous fields and biomedical applications.

Development of hydrogel-like biomaterials via nanoparticle assembly and solid-hydrogel transformation

Hydrogels for biomedical applications such as controlled drug release are usually synthesized with the chemical or physical crosslinking of monomers or macromers. In this work, we used gelatin to prepare hydrogel nanoparticles and studied whether gelatin nanoparticles (GNPs) could assemble to form a solid biomaterial and whether this solid biomaterial was capable of transforming into a hydrogel upon introduction to a hydrated environment. The data show that GNPs with or without aptamer functionalization could form a nanoparticle-assembled porous solid biomaterial after freezing and lyophilization treatment. This formation did not need any additional crosslinking reactions. More importantly, this solid biomaterial could undergo solid-to-hydrogel transition after contacting a solution and this transformation was tunable to match different shapes and geometries of defined molds. The formed hydrogel could also sequester and release growth factors for the promotion of skin wound healing. Thus, GNP-assembled solid biomaterials hold great potential as an off-the-shelf therapy for biomedical application such as drug delivery and regenerative medicine.

Dynamic DNA nanostructures in biomedicine: Beauty, utility and limits

DNA composite materials are at the forefront, especially for biomedical science, as they can increase the efficacy and safety of current therapies and drug delivery systems. The specificity and predictability of the Watson-Crick base pairing make DNA an excellent building material for the production of programmable and multifunctional objects. In addition, the principle of nucleic acid hybridization can be applied to realize mobile nanostructures, such as those reflected in DNA walkers that sort and collect cargo on DNA tracks, DNA robots performing tasks within living cells and/or DNA tweezers as ultra-sensitive biosensors. In this review, we present the diversity of dynamic DNA nanostructures functionalized with different biomolecules/functional units, imaging smart biomaterials capable of sensing, interacting, delivery and performing complex tasks within living cells/organisms.

Macroporous Hydrogels for Stable Sequestration and Sustained Release of Vascular Endothelial Growth Factor and Basic Fibroblast Growth Factor Using Nucleic Acid Aptamers

Macroporous hydrogels have been widely studied for biological and biomedical applications such as drug delivery and tissue engineering. However, these hydrogels cannot stably sequester molecules of interest due to their high permeability. The purpose of this work was to study the feasibility of using two aptamers to sequester two protein drugs, quantify the apparent diffusivity of protein drugs in aptamer-functionalized macroporous hydrogels, and evaluate the function of aptamer-functionalized macroporous hydrogels in controlling protein release for angiogenesis. Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) were used as model proteins. The data show that anti-VEGF and anti-bFGF aptamers could be uniformly incorporated into macroporous hydrogels for stable and specific sequestration of VEGF and bFGF. The aptamers could reduce the apparent diffusivity of VEGF and bFGF in the macroporous hydrogels by approximately three orders of magnitude. Moreover, as the aptamers could prolong the release of these growth factors, dual aptamer-functionalized macroporous hydrogels could stimulate synergistic angiogenesis. Therefore, this work has successfully demonstrated that aptamer-functionalized macroporous hydrogels hold great potential of stably sequestering multiple molecules of interest for various biological and biomedical applications.

Green-emitting carbon dot loaded silica nanoparticles coated with DNA-cross-linked hydrogels for sensitive carcinoembryonic antigen detection and effective targeted cancer therapy

Bifunctional composite nanospheres for carcinoembryonic antigen sensing and targeted drug delivery, based on carbon dot loaded silica nanoparticles coated with DNA-cross-linked hydrogels.

Hybrid polymeric hydrogels via peptide nucleic acid (PNA)/DNA complexation

This work presents a new concept in hybrid hydrogel design. Synthetic water-soluble N-(2-hydroxypropyl)methacrylamide (HPMA) polymers grafted with multiple peptide nucleic acids (PNAs) are crosslinked upon addition of the linker DNA. The self-assembly is mediated by the PNA-DNA complexation, which results in the formation of hydrophilic polymer networks. We show that the hydrogels can be produced through two different types of complexations. Type I hydrogel is formed via the PNA/DNA double-helix hybridization. Type II hydrogel utilizes a unique "P-form" oligonucleotide triple-helix that comprises two PNA sequences and one DNA. Microrheology studies confirm the respective gelation processes and disclose a higher critical gelation concentration for the type I gel when compared to the type II design. Scanning electron microscopy reveals the interconnected microporous structure of both types of hydrogels. Type I double-helix hydrogel exhibits larger pore sizes than type II triple-helix gel. The latter apparently contains denser structure and displays greater elasticity as well. The designed hybrid hydrogels have potential as novel biomaterials for pharmaceutical and biomedical applications.

An omega-like DNA nanostructure utilized for small molecule introduction to stimulate formation of DNAzyme-aptamer conjugates

An omega (Ω)-like DNA nanostructure was for the first time utilized for homogenous electrochemical monitoring of small molecules (ATP used in this case) based on target-induced formation of DNAzyme-aptamer conjugates without the need for sample separation and washing.