Crystalline Antibody-Laden Alginate Particles: A Platform for Enabling High Concentration Subcutaneous Delivery of Antibodies

Subcutaneous (SC) administration is a desired route for monoclonal antibodies (mAbs). However, formulating mAbs for small injection volumes at high concentrations with suitable stability and injectability is a significant challenge. Here, this work presents a platform technology that combines the stability of crystalline antibodies with injectability and tunability of soft hydrogel particles. Composite alginate hydrogel particles are generated via a gentle centrifugal encapsulation process which avoids use of chemical reactions or an external organic phase. Crystalline suspension of anti-programmed cell death protein 1 (PD-1) antibody (pembrolizumab) is utilized as a model therapeutic antibody. Crystalline forms of the mAb encapsuled in the hydrogel particles lead to stable, high concentration, and injectable formulations. Formulation concentrations as high as 315 mg mL^-1 antibody are achieved with encapsulation efficiencies in the range of 89-97%, with no perceivable increase in the number of antibody aggregates. Bioanalytical studies confirm superior maintained quality of the antibody in comparison with formulation approaches involving organic phases and chemical reactions. This work illustrates tuning the alginate particles' disintegration by using partially oxide alginates. Crystalline mAb-laden particles are evaluated for their biocompatibility using cell-based in vitro assays. Furthermore, the pharmacokinetics (PK) of the subcutaneously delivered human anti-PD-1 mAb in crystalline antibody-laden alginate hydrogel particles in Wistar rats is evaluated.

Micro flow photochemical synthesis of Ca-sensitive fluorescent sensor particles

Fluorescence probes have widely been used for detecting and imaging Ca2+-enriched parts of cells but more rarely for quantitative determination of concentrations. In this study we show how this can be achieved by a novel approach using hydrogel particles. In a microfluidic co-flow arrangement spherical droplets were generated from an aqueous solution of acrylamide, N,N'-methylenebisacrylamide crosslinker and photoinitiator and subsequently photo-cured in situ yielding gel particles in a sub millimeter range. These particles were separated, dried under reduced pressure and re-swollen in water containing Rhod-5N tri potassium salt as calcium ion selective fluorescence probe. After that the particles were dried again and stored for further investigations. Upon exposure of dried particles to calcium chloride solutions they swell and take up Ca2+-ions forming a strong fluorescing complex with Rhod-5N. Thus, fluorescence intensity increases with calcium ion concentration. Up to ca. 0.50 mM the enhancement effect is strong and then becomes considerably weaker. The intensity-concentration-dependence is well described by an equation derived from the equilibrium of the formation of a 1:1 Ca2+:Rhod-5N complex. The particles allow for a fast optical determination of Ca2+-concentrations up to 0.50 mM in analyte volumes down to below 10 μL.

Design and Use of a Thermogelling Methylcellulose Nanoemulsion to Formulate Nanocrystalline Oral Dosage Forms

Oral drug products have become indispensable in modern medicine because of their exceptional patient compliance. However, poor bioavailability of ubiquitous low-water-soluble active pharmaceutical ingredients (APIs) and lack of efficient oral drug formulations remain as significant challenges. Nanocrystalline formulations are an attractive route to increase API solubility, but typically require abrasive mechanical milling and several processing steps to create an oral dosage form. Using the dual amphiphilic and thermoresponsive properties of methylcellulose (MC), a new thermogelling nanoemulsion and a facile thermal dripping method are developed for efficient formulation of composite particles with the MC matrix embedded with precisely controlled API nanocrystals. Moreover, a fast and tunable release performance is achieved with the combination of a fast-eroding MC matrix and fast-dissolving API nanocrystals. Using the versatile thermal processing approach, the thermogelling nanoemulsion is easily formulated into a wide variety of dosage forms (nanoparticle suspension, drug tablet, and oral thin film) in a manner that avoids nanomilling. Overall, the proposed thermogelling nanoemulsion platform not only broadens the applications of thermoresponsive nanoemulsions but also shows great promise for more efficient formulation of oral drug products with high quality and tunable fast release.

A platform for multiplexed colorimetric microRNA detection using shape-encoded hydrogel particles

We report a platform utilizing a reporter enzyme, which produces a chromogenic indigo precipitate that preferentially localizes within a hydrogel microparticle. The 3D network of the hydrogel maintains the rapid target binding kinetics found in solution, while multiplexed target detection is achieved through shape-encoding of the particles. Moreover, the precipitate-laden hydrogels can be imaged with a simple phone camera setup. We used this system to detect microRNA (miRNA) down to 0.22 fmol. We then showed the compatibility of this system with real samples by performing multiplexed miRNA measurements from total RNA from matched colon cancer and normal adjacent tissue.

Effective Suppression of Oxidative Stress on Living Cells in Hydrogel Particles Containing a Physically Immobilized WS2 Radical Scavenger

We report a tungsten disulfide (WS₂) nanosheet-immobilized hydrogel system that can inhibit oxidative stress on living cells. First, we fabricated a highly stable suspension of WS₂ nanosheets as a radical scavenger by enveloping them with the amphiphilic poly(ε-caprolactone)- b-poly(ethylene oxide) copolymer (PCL- b-PEO) during in situ liquid exfoliation in aqueous medium. After the PCL- b-PEO-enveloped WS₂ nanosheets were embedded in three types of hydrogel systems, including carrageenan gum/locust bean gum bulk hydrogels, physically cross-linked alginate microparticles, and covalently cross-linked PEG hydrogel microparticles, they retained their characteristic optical properties. Intriguingly, the WS₂ nanosheet-immobilized hydrogel particles exhibited sustainable radical scavenging performance without any deterioration in the original activity of the WS₂ nanosheets, even after repeated use. This implies that the hydrogen atoms dissociated from the chalcogen of the WS₂ nanosheets effectively scavenged free radicals through the hydrogel mesh. Because of this unique behavior, the coexistence of the WS₂ nanosheets with living cells in the hydrogel matrix improved cell viability up to 40%, which demonstrates that the WS₂ nanosheets can suppress oxidative stress on living cells.

Shape-Preserved Transformation of Biological Cells into Synthetic Hydrogel Microparticles

The synthesis of materials that can mimic the mechanical, and ultimately functional, properties of biological cells can broadly impact the development of biomimetic materials, as well as engineered tissues and therapeutics. Yet, it is challenging to synthesize, for example, microparticles that share both the anisotropic shapes and the elastic properties of living cells. Here, a cell-directed route to replicate cellular structures into synthetic hydrogels such as polyethylene glycol (PEG) is described. First, the internal and external surfaces of chemically fixed cells are replicated in a conformal layer of silica using a sol-gel process. The template is subsequently removed to render shape-preserved, mesoporous silica replicas. Infiltration and cross-linking of PEG precursors and dissolution of the silica result in a soft hydrogel replica of the cellular template as demonstrated using erythrocytes, HeLa, and neuronal cultured cells. The elastic modulus can be tuned over an order of magnitude (≈10-100 kPa) though with a high degree of variability. Furthermore, synthesis without removing the biotemplate results in stimuli-responsive particles that swell/deswell in response to environmental cues. Overall, this work provides a foundation to develop soft particles with nearly limitless architectural complexity derived from dynamic biological templates.

Influence of formulation and process parameters on the properties of Cu2+/alginate particles prepared by external ionic gelation evaluated by principal component analysis

Currently, the method of external ionic gelation for the preparation of alginate particles is successfully used not only in the field of pharmacy and medicine, but also especially in the field of biotechnology. Therefore, the preparation of alginate particles and their subsequent evaluation using principal component analysis was the key task of our experiment. To optimize this method, we focused on the evaluation of the effect of formulation (the polymer concentration, the hardening solution concentration) and process parameters (the outer diameter of the injection needle) on the properties of the resulting beads (yield, sphericity factor, equivalent diameter and swelling capacity at pH 6). Using multivariate data analysis, the major influence on the resulting properties of the prepared particles was confirmed only in sodium alginate concentration. Obtained results verified the reliable and safe potential of the external ionic gelation for preparation alginate-based particulate dosage forms.

Photo-Crosslinkable Unnatural Amino Acids Enable Facile Synthesis of Thermoresponsive Nano- to Microgels of Intrinsically Disordered Polypeptides

Hydrogel particles are versatile materials that provide exquisite, tunable control over the sequestration and delivery of materials in pharmaceutics, tissue engineering, and photonics. The favorable properties of hydrogel particles depend largely on their size, and particles ranging from nanometers to micrometers are used in different applications. Previous studies have only successfully fabricated these particles in one specific size regime and required a variety of materials and fabrication methods. A simple yet powerful system is developed to easily tune the size of polypeptide-based, thermoresponsive hydrogel particles, from the nano- to microscale, using a single starting material. Particle size is controlled by the self-assembly and unique phase transition behavior of elastin-like polypeptides in bulk and within microfluidic-generated droplets. These particles are then stabilized through ultraviolet irradiation of a photo-crosslinkable unnatural amino acid (UAA) cotranslationally incorporated into the parent polypeptide. The thermoresponsive property of these particles provides an active mechanism for actuation and a dynamic responsive to the environment. This work represents a fundamental advance in the generation of crosslinked biomaterials, especially in the form of soft matter colloids, and is one of the first demonstrations of successful use of UAAs in generating a novel material.

Raspberry-like poly(γ-glutamic acid) hydrogel particles for pH-dependent cell membrane passage and controlled cytosolic delivery of antitumor drugs

In this research, we synthesized bioderived poly(amino acid) hydrogel particles that showed pH-dependent membrane-disrupting properties and controlled cytosolic delivery of antitumor drugs. Poly(γ-glutamic acid) (γ-PGA) that has been produced extensively using bacteria, especially those of Bacillus subtilis species, was modified with cholesterol (γ-PGA/Chol), and the γ-PGA/Chol conjugates were used to form polymeric nanoparticles the size of 21.0±1.1 nm in aqueous solution. When the polymeric nanoparticles were mixed with doxorubicin (Dox), raspberry-like hydrogel particles (RBHPs) were formed by the electrostatic interaction between the cationically charged Dox and the anionically charged nanoparticles. The average size and surface charge of the RBHPs in aqueous solution were 444.9±122.5 nm and −56.44 mV, respectively. The loaded amount of Dox was approximately 63.9 μg/mg of RBHPs. The RBHPs showed controlled drug release behavior in both in vitro and ex vivo cell-based experiments. Through fluorescence microscopy and fluorescence-activated cell sorting, the cellular uptake of RBHPs into human cervical cancer cells (HeLa) was analyzed. The cytotoxic effect, evaluated by the methyl tetrazolium salt assay, was dependent on both the concentration of RBHPs and the treatment time. The pH-dependent membrane-disrupting properties of the RBHPs and the subsequent cytosolic delivery of Dox were evaluated using a standard hemolysis assay. Upon an increase in hydrophobicity at the lysosomal acidic pH, RBHPs could easily interact, penetrate cell membranes, and destabilize them. Taken together, the data suggested that RBHPs could be used as drug delivery carriers after loading with other therapeutic drugs, such as proteins or small interfering RNA for cancer therapy.

Engineering poly(ethylene glycol) particles for improved biodistribution

We report the engineering of poly(ethylene glycol) (PEG) hydrogel particles using a mesoporous silica (MS) templating method via tuning the PEG molecular weight, particle size, and the presence or absence of the template and investigate the cell association and biodistribution of these particles. An ex vivo assay based on human whole blood that is more sensitive and relevant than traditional cell-line based assays for predicting in vivo circulation behavior is introduced. The association of MS@PEG particles (template present) with granulocytes and monocytes is higher compared with PEG particles (template absent). Increasing the PEG molecular weight (from 10 to 40 kDa) or decreasing the PEG particle size (from 1400 to 150 nm) reduces phagocytic blood cell association of the PEG particles. Mice biodistribution studies show that the PEG particles exhibit extended circulation times (>12 h) compared with the MS@PEG particles and that the retention of smaller PEG particles (150 nm) in blood, when compared with larger PEG particles (>400 nm), is increased at least 4-fold at 12 h after injection. Our findings highlight the influence of unique aspects of polymer hydrogel particles on biological interactions. The reported PEG hydrogel particles represent a new class of polymer carriers with potential biomedical applications.

Hyaluronic Acid-Based Hydrogels: from a Natural Polysaccharide to Complex Networks

Hyaluronic acid (HA) is one of nature's most versatile and fascinating macromolecules. Being an essential component of the natural extracellular matrix (ECM), HA plays an important role in a variety of biological processes. Inherently biocompatible, biodegradable and non-immunogenic, HA is an attractive starting material for the construction of hydrogels with desired morphology, stiffness and bioactivity. While the interconnected network extends to the macroscopic level in HA bulk gels, HA hydrogel particles (HGPs, microgels or nanogels) confine the network to microscopic dimensions. Taking advantage of various scaffold fabrication techniques, HA hydrogels with complex architecture, unique anisotropy, tunable viscoelasticity and desired biologic outcomes have been synthesized and characterized. Physical entrapment and covalent integration of hydrogel particles in a secondary HA network give rise to hybrid networks that are hierarchically structured and mechanically robust, capable of mediating cellular activities through the spatial and temporal presentation of biological cues. This review highlights recent efforts in converting a naturally occurring polysaccharide to drug releasing hydrogel particles, and finally, complex and instructive macroscopic networks. HA-based hydrogels are promising materials for tissue repair and regeneration.

Centrifugal deposition of microgels for the rapid assembly of nonfouling thin films

Thin films assembled from microgel building blocks have been constructed using a simple, high-throughput, and reproducible centrifugation (or "active") deposition technique. When compared to a common passive adsorption method (e.g., dip coating), microgels that are actively deposited onto a surface have smaller footprints and are more closely packed. Under both active and passive deposition conditions, the microgel footprint areas decrease during deposition. However, under active deposition, the microgel footprint appears to decrease continually and to a greater degree over the course of the deposition, forming a tightly packed, homogeneous film. Taking advantage of the rapid and uniform assembly of these films, we demonstrate the use of active deposition toward the fabrication of polyelectrolyte multilayers containing anionic microgels and a cationic linear polymer. Microgel multilayers successfully demonstrated effective blocking of the underlying substrate toward macrophage adhesion, which is a highly sought-after property for modulating the inflammatory response to an implanted biomaterial.