Viscoelastic and Thermoreversible Networks Crosslinked by Non-covalent Interactions Between "Clickable" Nucleic Acids Oligomers and DNA

Smart stimuli-responsive injectable gels and hydrogels for drug delivery and tissue engineering applications: A review

Hydrogels are widely used biomaterials in the delivery of therapeutic agents, including drugs, genes, proteins, etc., as well as tissue engineering, due to obvious properties such as biocompatibility and their similarity to natural body tissues. Some of these substances have the feature of injectability, which means that the substance is injected into the desired place in the solution state and then turns into the gel, which makes it possible to administer them from a way with a minimal amount of invasion and eliminate the need for surgery to implant pre-formed materials. Gelation can be caused by a stimulus and/or spontaneously. Suppose this induces due to the effect of one or many stimuli. In that case, the material in question is called stimuli-responsive because it responds to the surrounding conditions. In this context, we introduce the different stimuli that cause gelation and investigate the different mechanisms of the transformation of the solution into the gel in them. Also, we study special structures, such as nano gels or nanocomposite gels.

Athermal, Chemically Triggered Release of RNA from Thioester Nucleic Acids

An athermal approach to mRNA enrichment from total RNA using a self-immolative thioester linked nucleic acids (TENA) is described. Oligo(thymine) (oT) TENA has a six-atom spacing between bases which allowed TENA to selectively base-pair with polyadenine RNA. As a result of the neutral backbone of TENA and the hydrophobicity of the octanethiol end group, oT TENA is water insoluble and efficiently pulled down 93±2 % of EGFP mRNA at a concentration of 10 ng μL^-1 . Self-immolative degradation of TENA upon ambient temperature exposure to nucleophilic buffer components (Tris, DTT) allowed recovery of 55±27 ng of mRNA from 3.1 μg of total RNA, which was not statistically different from the amount recovered using Dynabeads® mRNA DIRECT Kit (89±24 ng). Gene expression as measured by RT-qPCR was comparable for both enrichment methods, suggesting that the mild conditions required for enrichment of mRNA using oT TENA are compatible with RT-qPCR and other downstream molecular biology applications.

Polypeptide Composition and Topology Affect Hydrogelation of Star-Shaped Poly(L-lysine)-Based Amphiphilic Copolypeptides

In this research, we studied the effect of polypeptide composition and topology on the hydrogelation of star-shaped block copolypeptides based on hydrophilic, coil poly(L-lysine)20 (s-PLL20) tethered with a hydrophobic, sheet-like polypeptide segment, which is poly(L-phenylalanine) (PPhe), poly(L-leucine) (PLeu), poly(L-valine) (PVal) or poly(L-alanine) (PAla) with a degree of polymerization (DP) about 5. We found that the PPhe, PLeu, and PVal segments are good hydrogelators to promote hydrogelation. The hydrogelation and hydrogel mechanical properties depend on the arm number and hydrophobic polypeptide segment, which are dictated by the amphiphilic balance between polypeptide blocks and the hydrophobic interactions/hydrogen bonding exerted by the hydrophobic polypeptide segment. The star-shaped topology could facilitate their hydrogelation due to the branching chains serving as multiple interacting depots between hydrophobic polypeptide segments. The 6-armed diblock copolypeptides have better hydrogelation ability than 3-armed ones and s-PLL-b-PPhe exhibits better hydrogelation ability than s-PLL-b-PVal and s-PLL-b-PLeu due to the additional cation-π and π-π interactions. This study highlights that polypeptide composition and topology could be additional parameters to manipulate polypeptide hydrogelation.

One-Component DNA Mechanoprobes for Facile Mechanosensing in Photopolymerized Hydrogels and Elastomers

DNA mechanosensors offer unique properties for mechano-adaptive and self-reporting materials, such as programmable bond strength and geometrical strain response, tunable fluorescent strain sensing, interfacing to biological systems, and the ability to store mechanical information. However, the facile incorporation of advanced DNA motifs into polymer networks and achieving robustness in application settings remain difficult. Herein, we introduce one-component DNA mechanoprobes that can be easily polymerized into polymer hydrogels and even elastomers to allow strain-induced fluorescence sensing. The all-in-one mechanoprobe contains a DNA hairpin for programmable force sensing, an internal fluorophore-quencher pair as a reporter, and methacrylamide groups on both ends for rapid and facile photopolymerization into networks based on the nontoxic water-soluble monomer methoxy triethylene glycol acrylate (mTEGA). In addition to mechanosensing hydrogels, we utilize the low T_g of p(mTEGA) to develop the first bulk elastomer materials with DNA force sensors, which show high elasticity and stronger mechanofluorescence. The system makes decisive steps forward for DNA-based mechanoprobes by overcoming the classical multicomponent design of such probes, allowing photopolymerization useful for the design of complex objects or even 3D printing and demonstrating that such motifs may even be useful in dry bulk materials.

Development of a modular, biocompatible thiolated gelatin microparticle platform for drug delivery and tissue engineering applications

The field of biomaterials has advanced significantly in the past decade. With the growing need for high-throughput manufacturing and screening, the need for modular materials that enable streamlined fabrication and analysis of tissue engineering and drug delivery schema has emerged. Microparticles are a powerful platform that have demonstrated promise in enabling these technologies without the need to modify a bulk scaffold. This building block paradigm of using microparticles within larger scaffolds to control cell ratios, growth factors and drug release holds promise. Gelatin microparticles (GMPs) are a well-established platform for cell, drug and growth factor delivery. One of the challenges in using GMPs though is the limited ability to modify the gelatin post-fabrication. In the present work, we hypothesized that by thiolating gelatin before microparticle formation, a versatile platform would be created that preserves the cytocompatibility of gelatin, while enabling post-fabrication modification. The thiols were not found to significantly impact the physicochemical properties of the microparticles. Moreover, the thiolated GMPs were demonstrated to be a biocompatible and robust platform for mesenchymal stem cell attachment. Additionally, the thiolated particles were able to be covalently modified with a maleimide-bearing fluorescent dye and a peptide, demonstrating their promise as a modular platform for tissue engineering and drug delivery applications.

Synthesis and Characterization of Click Nucleic Acid Conjugated Polymeric Microparticles for DNA Delivery Applications

Microparticle-mediated nucleic acid delivery is a popular strategy to achieve therapeutic outcomes via antisense gene therapy. However, current methods used to fabricate polymeric microparticles suffer from suboptimal properties such as particle polydispersity and low encapsulation efficiency. Here, a new particulate delivery system based on step-growth thiol-Michael dispersion polymerization is reported in which a low polydispersity microparticle is functionalized with a synthetic nucleic acid mimic, namely, click nucleic acids (CNA). CNA oligomers, exhibiting an average length of approximately four nucleic acid repeat units per chain for both adenine and thymine bases, were successfully conjugated to excess thiols present in the microparticles. Effective DNA loading was obtained by simple mixing, and up to 6 ± 2 pmol of complementary DNA/mg of particle was achieved, depending on the length of DNA used. In addition, DNA loading was orders of magnitude less for noncomplementary sequences and sequences containing an alternating base mismatch. The DNA release properties were evaluated, and it was found that release could be triggered by sudden changes in temperature but was unaffected over a range of pH. Finally, phagocytosis of loaded microparticles was observed by confocal microscopy and corroborated by an increase in cellular metabolic activity up to 90%. Overall, this work suggests that CNA functionalized microparticles could be a promising platform for controlled DNA delivery.

Supramolecular Biopolymers for Tissue Engineering

Supramolecular biopolymers (SBPs) are those polymeric units derived from macromolecules that can assemble with each other by noncovalent interactions. Macromolecular structures are commonly found in living systems such as proteins, DNA/RNA, and polysaccharides. Bioorganic chemistry allows the generation of sequence-specific supramolecular units like SBPs that can be tailored for novel applications in tissue engineering (TE). SBPs hold advantages over other conventional polymers previously used for TE; these materials can be easily functionalized; they are self-healing, biodegradable, stimuli-responsive, and nonimmunogenic. These characteristics are vital for the further development of current trends in TE, such as the use of pluripotent cells for organoid generation, cell-free scaffolds for tissue regeneration, patient-derived organ models, and controlled delivery systems of small molecules. In this review, we will analyse the 3 subtypes of SBPs: peptide-, nucleic acid-, and oligosaccharide-derived. Then, we will discuss the role that SBPs will be playing in TE as dynamic scaffolds, therapeutic scaffolds, and bioinks. Finally, we will describe possible outlooks of SBPs for TE.

Messenger RNA enrichment using synthetic oligo(T) click nucleic acids

Enrichment of mRNA is a key step in a number of molecular biology techniques, particularly in the rapidly growing field of transcriptomics. Currently, mRNA is isolated using oligo(thymine) DNA (oligo(dT)) immobilized on solid supports, which binds to the poly(A) tail of mRNA to pull the mRNA out of solution through the use of magnets or centrifugal filters. Here, a simple method to isolate mRNA by complexing it with synthetic click nucleic acids (CNAs) is described. Oligo(T) CNA bound efficiently to mRNA, and because of the insolubility of CNA in water, >90% of mRNA was readily removed from solution using this method. Simple washing, buffer exchange, and heating steps enabled mRNA's enrichment from total RNA, with a yield of 3.1 ± 1.5% of the input total RNA by mass, comparable to the yield from commercially available mRNA enrichment beads. Further, the integrity and activity of mRNA after CNA-facilitated pulldown and release was evaluated through two assays. In vitro translation of EGFP mRNA confirmed the translatability of mRNA into functional protein and RT-qPCR was used to amplify enriched mRNA from total RNA extracts and compare gene expression to results obtained using commercially available products.

Scalable One-Pot-Liquid-Phase Oligonucleotide Synthesis for Model Network Hydrogels

Solid-phase oligonucleotide synthesis (SPOS) based on phosphoramidite chemistry is currently the most widespread technique for DNA and RNA synthesis but suffers from scalability limitations and high reagent consumption. Liquid-phase oligonucleotide synthesis (LPOS) uses soluble polymer supports and has the potential of being scalable. However, at present, LPOS requires 3 separate reaction steps and 4-5 precipitation steps per nucleotide addition. Moreover, long acid exposure times during the deprotection step degrade sequences with high A content (adenine) due to depurination and chain cleavage. In this work, we present the first one-pot liquid-phase DNA synthesis technique which allows the addition of one nucleotide in a one-pot reaction of sequential coupling, oxidation, and deprotection followed by a single precipitation step. Furthermore, we demonstrate how to suppress depurination during the addition of adenine nucleotides. We showcase the potential of this technique to prepare high-purity 4-arm PEG-T20 (T = thymine) and 4-arm PEG-A20 building blocks in multigram scale. Such complementary 4-arm PEG-DNA building blocks reversibly self-assemble into supramolecular model network hydrogels and facilitate the elucidation of bond lifetimes. These model network hydrogels exhibit new levels of mechanical properties (storage modulus, bond lifetimes) in DNA bonds at room temperature (melting at 44 °C) and thus open up pathways to next-generation DNA materials programmable through sequence recognition and available for macroscale applications.

Sequence-defined vinyl sulfonamide click nucleic acids (VS-CNAs) and their assembly into dynamically responsive materials

Synthetic DNA analogues are of great interest for their application in information storage, therapeutics, and nanostructured materials, yet are often limited in scalability. Vinyl sulfonamide click nucleic acids (VS-CNAs) have been developed to overcome this limitation using the highly efficient thiol-Michael 'click' reaction. Utilizing all four nucleobases, sequence-defined click nucleic acids (CNAs) were synthesized using a simple and scalabale solution-phase approach. Employing a polyethylene glycol (PEG) support, synthesis of the CNA sequence, GATTACA, was achieved in high yields. CNA crosslinked hydrogels were assembled using multiarm PEG-CNAs resulting in materials that dynamically respond to temperature, strain, and competitive sequences.