Lipids and Minerals, Interplay in Biomineralization: Nature's Alchemy.

The main focus of this article is the role of lipids in biomineralization. Much of the discussion on biomineralization focuses on proteins in these decades. Indeed, collagen and acidic noncollagenous proteins effectively serve as templates for mineralization. However, other macromolecules such as lipids and polysaccharides have received less attention despite their abundance at mineralization sites. The matrix vesicle (MV) theory is widely accepted as the induction of early mineralization. Although ion concentration within the vesicles has been discussed in the initial mineralization in this theory, the role of phospholipids that constitute the vesicle membrane has not been discussed much. Comprehensive considerations, including pathological mineralization, exist regardless of the localization of MVs, the involvement of bacteria in dental calculus formation, and biomineralization caused by marine organisms such as corals, suggesting that initial mineralization found in these biological conditions might be a common reaction relating to lipids. In contrast, despite the abundance of lipids, mineralization occurs only in the limited tissue within our body. In other words, gathering knowledge and creating a path to understanding about lipid-based mineralization is extremely important in proposing new bone disease treatment methods. This article describes how lipids influence nucleation, mineralization, and expansion during hard tissue formation.

Fabrication of a Fish-Bone-Inspired Inorganic-Organic Composite Membrane.

Biological materials have properties like great strength and flexibility that are not present in synthetic materials. Using the ribs of crucian carp as a reference, we investigated the mechanisms behind the high mechanical properties of this rib bone, and found highly oriented layers of calcium phosphate (CaP) and collagen fibers. To fabricate a fish-rib-bone-mimicking membrane with similar structure and mechanical properties, this study involves (1) the rapid synthesis of plate-like CaP crystals, (2) the layering of CaP-gelatin hydrogels by gradual drying, and (3) controlling the shape of composite membranes using porous gypsum molds. Finally, as a result of optimizing the compositional ratio of CaP filler and gelatin hydrogel, a CaP filler content of 40% provided the optimal mechanical properties of toughness and stiffness similar to fish bone. Due to the rigidity, flexibility, and ease of shape control of the composite membrane materials, this membrane could be applied as a guided bone regeneration (GBR) membrane.

Bioavailability Enhancement Techniques for Poorly Aqueous Soluble Drugs and Therapeutics.

The low water solubility of pharmacoactive molecules limits their pharmacological potential, but the solubility parameter cannot compromise, and so different approaches are employed to enhance their bioavailability. Pharmaceutically active molecules with low solubility convey a higher risk of failure for drug innovation and development. Pharmacokinetics, pharmacodynamics, and several other parameters, such as drug distribution, protein binding and absorption, are majorly affected by their solubility. Among all pharmaceutical dosage forms, oral dosage forms cover more than 50%, and the drug molecule should be water-soluble. For good therapeutic activity by the drug molecule on the target site, solubility and bioavailability are crucial factors. The pharmaceutical industry's screening programs identified that around 40% of new chemical entities (NCEs) face various difficulties at the formulation and development stages. These pharmaceuticals demonstrate less solubility and bioavailability. Enhancement of the bioavailability and solubility of drugs is a significant challenge in the area of pharmaceutical formulations. According to the Classification of Biopharmaceutics, Class II and IV drugs (APIs) exhibit poor solubility, lower bioavailability, and less dissolution. Various technologies are discussed in this article to improve the solubility of poorly water-soluble drugs, for example, the complexation of active molecules, the utilization of emulsion formation, micelles, microemulsions, cosolvents, polymeric micelle preparation, particle size reduction technologies, pharmaceutical salts, prodrugs, the solid-state alternation technique, soft gel technology, drug nanocrystals, solid dispersion methods, crystal engineering techniques and nanomorph technology. This review mainly describes several other advanced methodologies for solubility and bioavailability enhancement, such as crystal engineering, micronization, solid dispersions, nano sizing, the use of cyclodextrins, solid lipid nanoparticles, colloidal drug delivery systems and drug conjugates, referring to a number of appropriate research reports.

Modulation of Properties through Covalent Bond Induced Formation of Strong Ion Pairing between Polyelectrolytes in Injectable Conetwork Hydrogels.

In situ simultaneous formation of both covalent linkages and ion pair is challenging yet necessary to control the biological properties of a hydrogel. We report that the generation of covalent linkages (+N-C) facilitates the simultaneous formation of ion pairs between polyelectrolytes (PEs) in a hydrogel network. Co-injection of tertiary amine functional macromolecules and reactive poly(ethylene glycol) (PEG) containing negatively charged PE leads to the formation of hydrogel conetworks consisting of covalent junctions and ion pairs. Our design is based on the gradual appearance of +N-C junctions followed by formation of ion pairs. This strategy provides an easy access to hydrogel networks bearing a predetermined proportion of ion pair and covalent cross-linking junction. The proportion of ion pair could be varied by introducing a precalculated proportion of mono- and difunctional reactive PEG in the hydrogel system. The topology of the prepolymer and the hydrogel could be modulated (graft) during hydrogel formation. This approach is applicable to obtain covalent/ionic, covalent bond induced purely ionic, and purely covalent hydrogels of several macromolecular entities. The effect of ion pairing in the hydrogels is strongly reflected in the modulus, strain bearing, degradation, free volume, swelling, and drug release properties. The hydrogels exhibit microscopic recovery of modulus after application of high amplitude strain depending on the prepolymer concentration (chain entanglement) and nature of hydrogel network. The hydrogels are hemocompatible, and the covalent/ionic hydrogels show a slower release of methotrexate than that of the purely covalent hydrogel. This work provides an understanding for the in situ construction and manipulation of biological properties of hydrogels through the covalent bond induced formation of a strong ion pair.

Library of Derivatizable Multiblock Copolymers by Nucleophilic Substitution Polymerization and Targeting Specific Properties.

Multiblock copolymers (MBCs) are fascinating in the field of biology-polymer chemistry interfaces. Synthesizing libraries of MBCs with tailor-made functionality is challenging as it involves multiple steps. Herein, a simple synthesis, analogous to polyurethane/Michael addition reactions, has been introduced to obtain a library of derivatizable MBCs. Nucleophilic substitution polymerization (SNP) of poly(ε-caprolactone) and poly(ethylene glycol) blocks containing activated halide termini by primary mono/di/coamines or clickable amines provides functional MBCs. The structure of amines directs the properties of the MBCs. The self-assembly of small molecular weight primary diamine-based MBCs shows controlled release of hydrophobic model guest molecules and therapeutics. The primary diamine (no dangling chain) helps to form MBC micelles having a relatively tight core with a low diffusion property. Antimicrobial property in the MBCs has been introduced by separating the cationic centers from the lipophilic groups using a coamine as a nucleophilic agent and a small molecular weight dihalide as a chain extender. Clickable MBCs were synthesized by changing the structure of the nucleophile to obtain degradable amphiphilic conetworks and hydrogels. Varieties of macromolecular entities could be obtained by switching the nucleophilic agent and introducing a small molecular weight chain extender. This synthesis approach provides an opportunity to tune the chemical functionality, topological structure, and biological properties of macromolecular entities.

Gold Nanoparticle Promoted Formation and Biological Properties of Injectable Hydrogels.

Acceleration of gelation in the biological environment and improvement of overall biological properties of a hydrogel is of enormous importance. Biopolymer stabilized gold (Au) nanoparticles (NPs) exhibit cytocompatibility and therapeutic activity. Hence, in situ gelation and subsequent improvement in the property of a hydrogel by employing Au NPs is an attractive approach. We report that stable Au NPs accelerate the conventional nucleophilic substitution reaction of activated halide-terminated poly(ethylene glycol) and tertiary amine functional macromolecules, leading to the rapid formation of injectable nanocomposite hydrogels in vivo and ex vivo with improved modulus, cell adhesion, cell proliferation, and cytocompatibility than that of a pristine hydrogel. NP surfaces with low chain grafting density and good colloidal stability are crucial requirements for the use of these NPs in the hydrogel formation. Influence of the structure of the amine functional prepolymer, the spacer connecting the halide leaving groups of the substrate, and the structure of the stabilizer on the rate promoting activity of the NPs have been evaluated with model low-molecular-weight substrates and macromolecules by 1H NMR spectroscopy, rheological experiments, and density functional theory. Results indicate a significant effect of the spacer connecting the halide leaving group with the macromolecule. The Au nanocomposite hydrogels show sustained co-release of methotrexate, an anti-rheumatic drug, and the Au NPs. This work provides insights for designing an injectable nanocomposite hydrogel system with multifunctional property. The strategy of the use of cytocompatible Au NPs as a promoter provides new opportunity to obtain an injectable hydrogel system for biological applications.

PEGylated gold nanoparticles promoted rapid macromolecular chain-end transformation and formation of injectable hydrogels.

Azide-alkyne click cycloaddition and Michael addition reactions are useful for the synthesis and modification of biologically relevant macromolecules. Acceleration of these reactions at the macromolecular chain-ends and backbone has been achieved by gold [Au-(PEG-SH)n] nanoparticles (NPs) stabilized with multi-thiol-functional poly(ethylene glycol) containing tertiary amine groups in its backbone. The Au NPs successfully activate electron rich alkyne and acrylate functionalities of macromolecules at low substrate concentration leading to the enhancement of the reaction rate. The Au NPs successfully accelerate the gelation rate of reactive prepolymers leading to the rapid formation of injectable hydrogels. The Au nanocomposite hydrogels exhibited higher ultimate modulus and porosity than those of the pristine hydrogels. The grafting density (chains per nm2) of the stabilizer onto the Au NP surface plays a crucial role towards the activity of the NPs. The conversion of the chain-end functionality and gelation rate increase with decreasing grafting density onto the NP surface. A high grafting density lowers the activity of the Au NPs through blocking the active metal surface. The developed Au NPs may be a potential agent for the rapid preparation of biologically relevant macromolecular entities.

Self-Assembly of Partially Alkylated Dextran- graft-poly[(2-dimethylamino)ethyl methacrylate] Copolymer Facilitating Hydrophobic/Hydrophilic Drug Delivery and Improving Conetwork Hydrogel Properties.

Key issues of injectable hydrogels are incapability of loading hydrophobic drugs due to insolubility of drugs in aqueous prepolymer solution as well as in hydrogel matrix, and high water swelling, which leads to poor mechanical and bioadhesive properties. Herein, we report that self-assembly of partially long-chain alkylated dextran- graft-poly[(2-dimethylamino)ethyl methacrylate] copolymer in aqueous solution could encapsulate pyrene, a hydrophobic probe, griseofulvin, a hydrophobic antifungal drug, and ornidazole, a hydrophilic antibiotic. Addition of activated chloride terminated poly(ethylene glycol) (PEG) into the guest molecules loaded copolymer solution produced an injectable dextran- graft-poly[(2-dimethylamino)ethyl methacrylate]-linked-PEG conetwork hydrogel. The alkylated hydrogels exhibited zero order release kinetics and were mechanically tough (50-54 kPa storage modulus) and bioadhesive (8-9 kPa). The roles of alkyl chains and dextran on the drug loading-release behavior, degradation behavior, gelation time, and the mechanical property of the hydrogels have been studied in details. Additionally, DNA hybrid composite hydrogel was formed owing to the cationic nature of the prepolymer solution and the hydrogel. Controlled alkylation of a prepolymer thus highlights the potential to induce and enhance the hydrogel property.

Liquid Prepolymer-Based in Situ Formation of Degradable Poly(ethylene glycol)-Linked-Poly(caprolactone)-Linked-Poly(2-dimethylaminoethyl)methacrylate Amphiphilic Conetwork Gels Showing Polarity Driven Gelation and Bioadhesion.

Amphiphilic conetwork (APCN) gels suffer from lack of direct injectability due to use of organic solvent, prolonged crosslinking/polymerization process and immiscibility between hydrophilic and hydrophobic prepolymers. On the basis of prepolymers compatibility and polarity, we report the use of an advanced prepolymer liquid system for in situ construction of APCN gels. Solid elastic poly(ethylene glycol)-linked-poly(ε-caprolactone)-linked-poly(2-dimethylaminoethyl)methacrylate (PEG-l-PCL-l-PDMA) APCN gels were formed upon addition of an appropriate amount of PDMA diluted in nonreactive sacrificial liquid PEG into a compatible blend of activated halide terminated PEG and PCL liquids. Compatibility among the prepolymers allowed favorable gelation. The polarity of the prepolymer liquid greatly influenced the gelation time. PEG-l-PCL-l-PDMA APCN gels were cytocompatible/biodegradable and showed storage modulus in the range of 50-200 kPa and bioadhesive strength of 40-90 kPa. The fluorescence experiments showed that the hydrophobic probe, pyrene was distributed in both hydrophilic and hydrophobic phases of the APCN gels. These APCNs exhibited sustained release of hydrophobic and hydrophilic drugs. Effects of polarity, composition, and molecular weight of the liquid prepolymers on the gelation time, rheological property, and swelling behavior of the APCN gels have been investigated in details.

Synthesis and Multi-Responsive Self-Assembly of Cationic Poly(caprolactone)-Poly(ethylene glycol) Multiblock Copolymers.

Individual dissimilar blocks were combined to obtain well-defined An Bn and (A-B-A)n types of cationic amphiphilic multiblock copolymers (MBCs) through mild sequential nucleophilic substitution without formation of byproducts. MBCs were synthesized by reacting end-functional polymer blocks of poly(caprolactone) (PCL), poly(ethylene glycol) (PEG), and PCL-b-PEG-b-PCL. For selective degradation, acid- and base-labile ester as well as reducible disulfide groups were introduced as linkers between the blocks. The micellar self-assemblies of these MBCs showed exceptional stability under normal physiological conditions with negligible release of the guest molecules. Selective disassembly under mildly acidic and basic conditions or in the presence of reducing agents caused triggered release of the guest molecules. This strategy is versatile and opens an opportunity to obtain a variety of tailor-made MBCs for selective and triggered release of therapeutics.

Dually crosslinked injectable hydrogels of poly(ethylene glycol) and poly[(2-dimethylamino)ethyl methacrylate]-b-poly(N-isopropyl acrylamide) as a wound healing promoter.

Rapid gelation, low heat generation, biocompatibility, biodegradability, avoiding the use of a small molecular weight gelator and high gel fraction are the essential criteria for the successful biomedical application of an injectable hydrogel. We have developed a series of dually crosslinked injectable hydrogels of PEG and poly[2-(dimethylamino)ethyl methacrylate]-b-poly(N-isopropyl acrylamide) through extremely simple chemistry. The sequential nucleophilic substitution reaction between PEG containing reactive termini and the copolymer provided chemically crosslinked hydrogels with a gel fraction as high as 96-99% with a gelation time of 1-4 min under physiological conditions. The gelation occurred with ca. 1 °C rise in temperature per gram of the injectable solution, avoids formation of by-products and can be performed in the temperature range of 20-37 °C. The hydrogels undergo hardening at a physiological temperature as confirmed by rheological experiments. The gelation time, water swelling, mechanical properties and degradability of the hydrogels depend on the PEG to copolymer ratio in the injectable solution. The rheological behaviour of the fully hydrated hydrogels showed desirable mechanical properties for soft tissue regeneration. The hydrogels exhibited blood compatibility and retained the viability of HepG2 cells with time. Platelet adhesion and aggregation followed by fibrinogen adsorption ability makes these hydrogels suitable for wound healing applications.