Particle size and shape effects in medical syringe needles: experiments and simulations for polymer microparticle injection

Evaluating the influence of particle morphology and density on the viscosity and injectability of a novel long-acting local anesthetic suspension

Proper pain management is well understood to be one of the fundamental aspects of a healthy postoperative recovery in conjunction with mobility and nutrition. Approximately, 10% of patients prescribed opioids after surgery continue to use opioids in the long-term and as little as 10 days on opioids can result in addiction. In an effort to provide physicians with an alternative pain management technique, this work evaluates the material properties of a novel local anesthetic delivery system designed for controlled release of bupivacaine for 72 hours. The formulation utilizes solid-lipid microparticles that encapsulate the hydrophobic molecule bupivacaine in its free-base form. The lipid microparticles are suspended in a non-crosslinked hyaluronic acid hydrogel, which acts as the microparticle carrier. Two different particle manufacturing techniques, milling and hot homogenization, were evaluated in this work. The hot homogenized particles had a slower and more controlled release than the milled particles. Rheological techniques revealed that the suspension remains a viscoelastic fluid when loaded with either particle type up to 25% (w/v) particles densities. Furthermore, the shear thinning properties of the suspension media, hyaluronic acid hydrogel, were conserved when bupivacaine-loaded solid-lipid microparticles were loaded up to densities of 25% (w/v) particle loading. The force during injection was measured for suspension formulations with varying hyaluronic acid hydrogel concentrations, particle densities, particle types and particle sizes. The results indicate that the formulation viscosity is highly dependent on particle density, but hyaluronic acid hydrogel is required for lowering injection forces as well as minimizing clogging events.

Sub-100-micron calcium-alginate microspheres: Preparation by nitrogen flow focusing, dependence of spherical shape on gas streams and a drug carrier using acetaminophen as a model drug

We developed a miniature gas-liquid coaxial flow device using glass capillaries, aiming to produce sub-100-μm Ca-alginate microspheres. Depending on collecting distance and the flow rates of nitrogen gas and alginate solution, however, Ca-alginate microparticles of different shapes were obtained. Spherical, monodisperse microparticles (microspheres) could only be obtained at certain gas flow rates and within a corresponding range of collecting distance. The result suggests that, for particles of this size, the gas flow rate and collecting distance are crucial for the formation of the spherical shape. We evaluated, as an example of its applications, the microsphere as a drug carrier using acetaminophen as a model drug. Large (~150 μm) and small (~70 μm) drug-loaded microspheres were prepared using two respective devices. Specifically, the drug-loaded microspheres were complexed with chitosan of different molecular weights. The dependence of in vitro drug release on the microsphere size and the chitosan molecular weight was examined. CHEMICAL COMPOUNDS STUDIED IN THIS ARTICLE: Alginic acid sodium salt (PubChem CID: 5102882); Chitosan (PubChem CID: 71853); Calcium chloride (PubChem CID: 5284359); Sodium chloride (PubChem CID: 5234); Acetaminophen (PubChem CID: 1983); Polydimethylsiloxane (PubChem CID: 24771); n-Octadecyltrimethoxysilane (PubChem CID: 76486).

Enhancing the Injectability of High Concentration Drug Formulations Using Core Annular Flows

Highly concentrated biological drug formulations would offer tremendous benefits to global health, yet they cannot be manually injected using commercial syringes and needles due to their high viscosities. Current approaches to address this problem face several challenges such as crosscontamination, high cost, needle clogging, and protein inactivation. This work reports a simple method to enhance formulation injectability using a core annular flow, where the transport of highly viscous fluids through a needle is enabled by coaxial lubrication by a less viscous fluid. A phase diagram to ensure optimally lubricated flow while minimizing the volume fraction of lubricant injected is established. The technique presented here allows for up to a 7x reduction in injection force for the highest viscosity ratio tested. The role of buoyancy-driven eccentricity in governing nominal pressure reduction is also examined. Finally, the findings are implemented into the development of a double barreled syringe that significantly expands the range of injectable concentrations of several biologic formulations.

Combating iron overload: a case for deferoxamine-based nanochelators

While iron is a nutrient metal, iron overload can result in multiple organ failures. Iron chelators, such as deferoxamine, are commonly used to ameliorate iron overload conditions. However, their uses are limited due to poor pharmacokinetics and adverse effects. Many novel chelator formulations have been developed to overcome these drawbacks. In this review, we have discussed various nanochelators, including linear and branched polymers, dendrimers, polyrotaxane, micelles, nanogels, polymeric nanoparticles and liposomes. Although these research efforts have mainly been focused on nanochelators with longer half-lives, prolonged residence of polymers in the body could raise potential safety issues. We also discussed recent advances in nanochelation technologies, including mechanism-based, long-acting nanochelators.

Ex vivo biomechanical characterization of syringe-needle ejections for intracerebral cell delivery

Intracerebral implantation of cell suspensions is finding its clinical translation with encouraging results in patients with stroke. However, the survival of cells in the brain remains poor. Although the biological potential of neural stem cells (NSCs) is widely documented, the biomechanical effects of delivering cells through a syringe-needle remain poorly understood. We here detailed the biomechanical forces (pressure, shear stress) that cells are exposed to during ejection through different sized needles (20G, 26G, 32G) and syringes (10, 50, 250 µL) at relevant flow rates (1, 5, 10 µL/min). A comparison of 3 vehicles, Phosphate Buffered Saline (PBS), Hypothermosol (HTS), and Pluronic, indicated that less viscous vehicles are favorable for suspension with a high cell volume fraction to minimize sedimentation. Higher suspension viscosity was associated with greater shear stress. Higher flow rates with viscous vehicle, such as HTS reduced viability by ~10% and also produced more apoptotic cells (28%). At 5 µL/min ejection using a 26G needle increased neuronal differentiation for PBS and HTS suspensions. These results reveal the biological impact of biomechanical forces in the cell delivery process. Appropriate engineering strategies can be considered to mitigate these effects to ensure the efficacious translation of this promising therapy.

Improved delivery of PLGA microparticles and microparticle-cell scaffolds in clinical needle gauges using modified viscosity formulations

Polymer microparticles are widely used as acellular drug delivery platforms in regenerative medicine, and have emerging potential as cellular scaffolds for therapeutic cell delivery. In the clinic, PLGA microparticles are typically administered intramuscularly or subcutaneously, with the clinician and clinical application site determining the precise needle gauge used for delivery. Here, we explored the role of needle diameter in microparticle delivery yield, and develop a modified viscosity formulation to improve microparticle delivery across a range of clinically relevant needle diameters. We have identified an optimal biocompatible formulation containing 0.25% pluronic F127 and 0.25% carboxymethyl cellulose, which can increase delivery payload to 520% across needle gauges 21-30G, and note that needle diameter impacts delivery efficacy. We use this formulation to increase the delivery yield of PLGA microparticles, and separately, PLGA-cell scaffolds supporting viable mesenchymal stem cells (MSCs), demonstrating the first in vitro delivery of this cell scaffold system. Together, these results highlight an optimal formulation for the delivery of microparticle and microparticle-cell scaffolds, and illustrate how careful choice of delivery formulation and needle size can dramatically impact delivery payload.

Microcryogels as injectable 3-D cellular microniches for site-directed and augmented cell delivery

The success of cell therapy for tissue repair and regeneration demands efficient and reliable cell delivery methods. Here we established a novel microengineered cryogel (microcryogel) array chip containing microcryogels with predefined size and shape as injectable cell delivery vehicles. The microscale macroporous cryogels enabled automatic and homogeneous loading of tailored cellular niches (e.g. cells, matrices, bioactive factors) and could be easily harvested from the ready-to-use array chip. In contrast to microscale hydrogels, microcryogels exhibited excellent elasticity and could retain their shape and integrity after injection through the microsyringe routinely used for cell therapy. Human mesenchymal stromal cells loaded within microcryogels could be shielded from the mechanical insult and necrosis caused by during direct cell injection. After subcutaneous injection to the mice, cell-loaded microcryogels exhibited concentrated localization and enhanced retention at the injection site compared to dissociated cells. To demonstrate the potential therapeutic application for ischemic diseases, site-directed induction of angiogenesis was achieved subcutaneously in mice 2weeks after injection of NIH/3T3 fibroblast-loaded microcryogels, indicating long-term engraftment, accumulative paracrine stimulation and augmented host tissue integration. Our results convincingly showed the great promise of microcryogels as 3-D cellular microniches and injectable cell delivery vehicles to tackle major challenges faced by cell therapy-based regenerative medicine including shear-induced damages, uncontrolled localization, poor retention, limited cellular survival and functionalities in vivo.