Prefilled syringes (PFS) increasingly serve as standalone injection systems and as critical components in autoinjectors, where device performance and patient safety depend on tightly controlled component attributes. Silicone oil (SO) is widely used as a lubricant on syringe barrels, plungers, needles, and elastomeric needle shields to reduce frictional forces; however, accurately quantifying the microgram‑level SO present on individual elastomeric components remains analytically challenging. Here, we present a rapid and sensitive proton nuclear magnetic resonance (¹H NMR) method for direct measurement of SO amount on single elastomeric needle shields. A calibration curve constructed from SO standard demonstrated excellent linearity (R² = 0.999), and the method achieved a limit of detection of approximately 0.2 µg SO per component. Applied to two elastomeric needle shield batches with vendor‑controlled siliconization, the method successfully distinguished between low‑ and high‑SO conditions. In a separate PFS batch with known variability in pull‑off force (POF), an inverse relationship was observed between SO mass and POF: syringes with lower POF exhibited higher SO levels, whereas those with higher POF contained less SO. Overall, this ¹H NMR approach enables fast (<10 min per sample), specific, and quantification of SO on single elastomeric needle shields, providing a practical tool for routine quality control and for correlating siliconization levels with critical device performance attributes.

Needle clogging is one of the key challenges in delivery of suspension (i.e., multi-phase) formulations. It is a phenomenon by which the particles (i.e., solid phase) accumulate locally to occlude the flow, leading to injection failure. This work proposes alternative needle hub designs for suspension delivery systems, enabling enhanced injection process by reducing the risk of particle jamming. Rapid prototyping was harnessed to experimentally evaluate the injection behavior using our custom-built injection characterization set-up by monitoring plunger force throughout injection. Improved performance of several proposed designs was demonstrated compared to standard (unmodified) needles across a range of high-concentration suspension formulations. The proposed tapered contractions offer competitive advantage of enabling clog-free delivery of high-concentration suspension formulations that would otherwise exhibit failure using conventional syringe/needle systems, thereby potentially accelerating time to market.

Elastomeric components such as closures and stoppers play key roles in providing container closure integrity (CCI), supporting a portfolio of injectable combination products and primary containers including needle shields (NSs) in prefilled syringes (PFSs). Upon piercing through the elastomeric (i.e., synthetic rubber) components, the physical interaction between the needle and the deformable elastomer could result in the formation of small, random-shaped particles fragmented and dislodged from the NS material due to cutting processes. This phenomenon, called coring, poses a major risk in drug product contamination, as elastomer particle fragments can potentially be aspirated with the medication and injected into a patient or prevent injection. Here, we present a combined computational and experimental approach to assess the incidence of coring. In particular, we first experimentally characterized the nonlinear finite deformation behavior of five commonly used NS elastomers and calibrated constitutive models. Then, we performed finite element simulations validated with needle insertion experiments to compare the coring behavior of the NS elastomers. We demonstrated that higher maximum failure strain under tension and higher deformation-stiffening properties of the elastomer are contributing factors that attenuate coring and fragmentation. The experimental-numerical framework presented is suitable for quantifying broad correlative and discovering relationships between device properties governing the incidence of coring and fragmentation.

Pre-filled syringes (PFS) have been in use in the pharmaceutical industry for over 60 years. For syringe functionality, a layer of silicone oil is often added as lubrication to promote smooth plunger stopper movement. Importantly, current technologies that generate this silicone oil layer often produce inhomogeneous layers displaying topographical features such as dimples. Additionally, the equipment that generates these layers is generally inaccessible in non-commercial settings. Here, we present a new silicone oil coating technique that addresses the shortcomings of traditional methods to generate a uniform silicone oil layer utilizing commonplace centrifuge technology. Our method creates silicone layers in PFS with improved homogeneity and tunable thickness, ranging from 400-1800 nm, by adjusting centrifuge speed and temperature.

Myelination is a key biological process wherein glial cells such as oligodendrocytes wrap myelin around neuronal axons, forming an insulative sheath that accelerates signal propagation down the axon. A major obstacle to understanding myelination is the challenge of visualizing and reproducibly quantifying this inherently three-dimensional process in vitro . To this end, we previously developed Artificial Axons (AAs), a biocompatible platform consisting of 3D-printed hydrogel-based axon mimics designed to more closely recapitulate the micrometer-scale diameter and sub-kilopascal mechanical stiffness of biological axons. First, we present our platform for fabricating AAs with tunable axon diameter, stiffness, and inter-axonal spacing. Second, we demonstrate that increasing the Young’s modulus E or stiffness of polymer comprising the AAs increases the extent of myelin ensheathment by rat oligodendrocytes. Third, we demonstrate that the responses of oligodendrocytes to pro-myelinating compounds are also dependent on axon stiffness, which can affect compounds efficacy and the relative ranking. These results reinforce the importance of studying myelination in mechanically representative environments, and highlight the importance of considering biophysical cues when conducting drug screening studies.

Fill volume and stopper insertion depth are important parameters that require definition and de-risking prior to commercial-scale manufacture of pre-filled syringe combination products. Due to cost and time constraints, it is not practical to conduct extensive development runs in the manufacturing facility to optimize and validate process parameter settings. In response to this need, we used Monte Carlo simulations to predict the outcome variability by modeling input parameters using their expected statistical distributions. Governing equations were developed for the desired outcomes of deliverable volume and air gap size. Input variables included sterile barrier height, frictional force, and syringe and stopper dimensions, for which the values were determined either by laboratory measurement, specifications provided by vendors, or conservative assumptions representing worst-case scenarios. Results from these simulations were used to set the target values and tolerance ranges for both fill volume and stopper insertion depth to maximize the probability that manufactured PFS batches would meet acceptable criteria for deliverable volume and sterility.

Autoinjectors with dual-chamber cartridges (AIDCs) are single-use, self-administrable injection devices that facilitate automated reconstitution and injection of lyophilized products. We report the development and application of a physics-based model to understand and optimize AIDC behavior, predicting its response as a function of formulation properties and injection device parameters. Our model is based on the equations of motion for the AIDC's dual stoppers, as well as the ideal gas law and an experimentally derived stopper friction vs. glide speed relationship. Our model provides estimates for some of the key essential performance requirements that yield good device performance, including injection time, stopper trajectories, and the maximum diluent volume. We validated our model using experimental injection time data demonstrating good agreement for a range of diluent volumes, reconstituted solution viscosities, and stopper positions. The model allows different device and formulation configurations to be tested virtually without requiring the physical device and formulation, reducing the need for extensive experimental testing and ensuring the robustness of the injector performance for successful drug delivery. The modeling framework applies to a broad class of spring-driven AIDCs for lyophilized drug and vaccine delivery and enables informed device selection through simulation-led technical due diligence.

Administration of high-concentrated suspension formulations (i.e., solid particles dispersed in a liquid vehicle) can be limited due to their greater propensity for needle occlusion. The physical interaction between the solid phase (i.e., particles), the vehicle (i.e., flow field), and injection devices could result in the formation of particle bridging or filtering, posing a major risk in dose delivery accuracy and injectability. Here, given the limited understanding on how clogging initiates in syringe and needle delivery systems, we report an experimental approach to fully characterize the transient injection behavior of suspensions. In particular, we first established a custom fluorescence tagging and imaging technique with integrated force sensor to enable visual observation of local particle concentrations and plunger force monitoring throughout injection. Then, we investigated the effects of key formulation properties and device parameters including particle concentration and morphology, carrier viscosity, injection rate, needle and syringe sizes, and tissue backpressure on the incidence of suspension particle jamming and needle clogging. We performed systematic benchmark studies demonstrating that increasing needle inner diameter (ID) and particle density considerably reduced clogging risk, while increasing vehicle viscosity, particle size, and tissue backpressure significantly increased clogging. The experimental framework presented is amenable to quantifying clogging risk in drug-loaded particle suspensions and provides a guideline to make informed decisions on the tradeoffs between creating particles for pharmaceutical impact and feasibility of injection delivery.

PURPOSE:Acoustic streaming induced by applying transcranial focused ultrasound (FUS) promotes localized advective solute transport in the brain and has recently garnered research interest for drug delivery and enhancement of brain waste clearance. The acoustic streaming behavior in brain tissue is difficult to model numerically and thus warrants an in vitro examination of the effects of using different sonication parameters, in terms of frequency, intensity, and pulse duration (PD).METHODS:Melamine and polyvinyl alcohol (PVA) foams were used to mimic the porous brain tissue, which contains leptomeningeal fenestrations and perivascular space, while agar hydrogel was used to emulate denser neuropil. FUS was delivered to these media, which were immersed in a phosphate-buffered saline containing toluidine blue O dye, across various frequencies (400, 500, and 600 kHz; applicable to transcranial delivery) in a pulsed mode at two different spatialpeak pulse-average intensities (3 and 4 W/cm2).RESULTS:Image analysis showed that the use of 400 kHz yielded the greatest dye infiltration in melamine foam, while sonication had no impact on infiltration in the agar hydrogel due to the dominance of diffusional transport. Using a fixed spatial-peak temporal-average intensity of 0.4 W/cm2 at 400 kHz, a PD of 75 ms resulted in the greatest infiltration depth in both melamine and PVA foams among the tested range (50-150 ms).CONCLUSION:These findings suggest the existence of a specific frequency and PD that induce greater enhancement of solute/fluid movement, which may contribute to eventual in vivo applications in promoting waste clearance from the brain.

Transport of interstitial fluid and solutes plays a critical role in clearing metabolic waste from the brain. Transcranial application of focused ultrasound (FUS) has been shown to promote localized cerebrospinal fluid solute uptake into the brain parenchyma; however, its effects on the transport and clearance of interstitial solutes remain unknown. We demonstrate that pulsed application of low-intensity FUS to the rat brain enhances the transport of intracortically injected fluorescent tracers (ovalbumin and high molecular-weight dextran), yielding greater parenchymal tracer volume distribution compared to the unsonicated control group (ovalbumin by 40.1% and dextran by 34.6%). Furthermore, FUS promoted the drainage of injected interstitial ovalbumin to both superficial and deep cervical lymph nodes (cLNs) ipsilateral to sonication, with 78.3% higher drainage observed in the superficial cLNs compared to the non-sonicated hemisphere. The application of FUS increased the level of solute transport visible from the dorsal brain surface, with ~ 43% greater area and ~ 19% higher fluorescence intensity than the unsonicated group, especially in the pial surface ipsilateral to sonication. The sonication did not elicit tissue-level neuronal excitation, measured by an electroencephalogram, nor did it alter the molecular weight of the tracers. These findings suggest that nonthermal transcranial FUS can enhance advective transport of interstitial solutes and their subsequent removal in a completely non-invasive fashion, offering its potential non-pharmacological utility in facilitating clearance of waste from the brain.

Multiple sclerosis (MS), a chronic neurodegenerative disease driven by damage to the protective myelin sheath, is currently incurable. Today, all clinically available treatments modulate the immune-mediated symptoms of the disease but they fail to stop neurodegeneration in many patients. Remyelination, the regenerative process of myelin repair by oligodendrocytes, which is considered a necessary step to protect demyelinated axons and stop neuronal death, is impaired in MS patients. One of the major obstacles to finding effective remyelinating drugs is the lack of biomimetic drug screening platforms that enable quantification of compounds' potential to stimulate 3D myelination in the physiologically relevant axon-like environment. To address this need, we built a unique myelination drug discovery platform, by expanding our previously developed technology, artificial axons (AAs), which enables 3D-printing of synthetic axon mimics with the geometry and mechanical properties closely resembling those of biological axons. This platform allows for high-throughput phenotypic myelination assay based on quantification of 3D wrapping of myelin membrane around axons in response to compounds. Here, we demonstrate quantification of 3D myelin wrapping by rat oligodendrocytes around the axon mimics in response to a small library of known pro-myelinating compounds. This assay shows pro-myelinating activity for all tested compounds consistent with the published in vitro and in vivo data, demonstrating predictive power of AA platform. We find that stimulation of myelin wrapping by these compounds is dose-dependent, providing a facile means to quantify the compounds' potency and efficacy in promoting myelin wrapping. Further, the ranking of relative efficacy among these compounds differs in this 3D axon-like environment as compared to a traditional oligodendrocyte 2D differentiation assay quantifying area of deposited myelin membrane. Together, we demonstrate that the artificial axons platform and associated phenotypic myelin wrapping assay afford direct evaluation of myelin wrapping by oligodendrocytes in response to soluble compounds in an axon-like environment, providing a predictive tool for the discovery of remyelinating therapies.

Low-intensity transcranial focused ultrasound (FUS) has gained momentum as a non-/minimally-invasive modality that facilitates the delivery of various pharmaceutical agents to the brain. With the additional ability to modulate regional brain tissue excitability, FUS is anticipated to confer potential neurotherapeutic applications whereby a deeper insight of its safety is warranted. We investigated the effects of FUS applied to the rat brain (Sprague-Dawley) shortly after an intracortical injection of fluorescent interstitial solutes, a widely used convection-enhanced delivery technique that directly (i.e., bypassing the blood–brain-barrier (BBB)) introduces drugs or interstitial tracers to the brain parenchyma. Texas Red ovalbumin (OA) and fluorescein isothiocyanate-dextran (FITC-d) were used as the interstitial tracers. Rats that did not receive sonication showed an expected interstitial distribution of OA and FITC-d around the injection site, with a wider volume distribution of OA (21.8 ± 4.0 µL) compared to that of FITC-d (7.8 ± 2.7 µL). Remarkably, nearly half of the rats exposed to the FUS developed intracerebral hemorrhaging (ICH), with a significantly higher volume of bleeding compared to a minor red blood cell extravasation from the animals that were not exposed to sonication. This finding suggests that the local cerebrovascular injury inflicted by the micro-injection was further exacerbated by the application of sonication, particularly during the acute stage of injury. Smaller tracer volume distributions and weaker fluorescent intensities, compared to the unsonicated animals, were observed for the sonicated rats that did not manifest hemorrhaging, which may indicate an enhanced degree of clearance of the injected tracers. Our results call for careful safety precautions when ultrasound sonication is desired among groups under elevated risks associated with a weakened or damaged vascular integrity.

Photocrosslinkable polymers have been exploited to attain impressive advantages in printing freestanding, micrometer-scale, mechanically compliant features. However, a more integrated understanding of both the polymer photochemistry and the microfabrication processes could enable new strategic design avenues, unlocking far-reaching applications of the light-based modality of additive manufacturing. One promising approach for achieving high-aspect-ratio structures is to leverage the phenomenon of light self-trapping during the photopolymerization process. In this review, we discuss the design of materials that facilitate this optical behavior, the computational modeling and practical processing considerations to achieve high aspect-ratio structures, and the range of applications that can benefit from architectures fabricated using light self-trapping—especially those demanding free-standing structures and materials of stiffnesses relevant in biological applications. Coupled interactions exist among material attributes, including polymer composition, and processing parameters such as light intensity. We identify strong opportunities for predictive design of both the material and the process. Overall, this perspective describes the wide range of existing polymers and additive manufacturing approaches, and highlights various future directions to enable constructs with new complexities and functionalities through the development of next-generation photocrosslinkable materials and micromanufacturing methods.

Low-intensity transcranial focused ultrasound (tFUS) offers new functional neuromodulation opportunities, enabling stimulation of cortical as well as deep brain areas with high spatial resolution. Brain stimulation of awake sheep, in the absence of the confounding effects of anesthesia on brain function, provides translational insight into potential human applications with safety information supplemented by histological analyses. We examined the effects of tFUS pulsing parameters, particularly regarding pulse durations (PDs), on stimulating the cortical motor area (M1) and its thalamic projection in unanesthetized, awake sheep (n = 8). A wearable tFUS headgear, custom-made for individual sheep, enabled experiments to be conducted without using anesthesia. FUS stimuli, each 200 ms long, were delivered to the M1 and the thalamus using three different PDs (0.5, 1, and 2 ms) with the pulse repetition frequency (PRF) adjusted to maintain a 70% duty cycle at a derated in situ spatial-peak temporal-average intensity (Ispta) of 3.6 W/cm2. Efferent electromyography (EMG) responses to stimulation were quantified from both hind limbs. Group-averaged EMG responses from each of the hind limbs across the experimental conditions revealed selective responses from the hind limb contralateral to sonication. The use of 0.5 and 1 ms PDs generated higher EMG signal amplitudes compared to those obtained using a 2 ms PD. Faster efferent response was also observed from thalamic stimulation than that from stimulating the M1. Post-sonication behavioral observation and histological assessment performed 24 h and 1 month after sonication were not indicative of any abnormalities. The results suggest the presence of pulsing scheme-dependent effects of tFUS on brain stimulation and attest its safety in awake large animals.

Efficient transport of solutes in the cerebrospinal fluid (CSF) plays a critical role in their clearance from the brain. Convective bulk flow of solutes in the CSF in the perivascular space (PVS) is considered one of the important mechanisms behind solute movement in the brain, before their ultimate drainage to the systemic lymphatic system. Acoustic pressure waves can impose radiation force on a medium in its path, inducing localized and directional fluidic flow, known as acoustic streaming. We transcranially applied low-intensity focused ultrasound (FUS) to rats that received an intracisternal injection of fluorescent CSF tracers (dextran and ovalbumin, having two different molecular weights–M w ). The sonication pulsing parameter was determined on the set that propelled the aqueous solution of toluidine blue O dye into a porous media (melamine foam) at the highest level of infiltration. Fluorescence imaging of the brain showed that application of FUS increased the uptake of ovalbumin at the sonicated plane, particularly around the ventricles, whereas the uptake of high-M w dextran was unaffected. Numerical simulation showed that the effects of sonication were non-thermal. Sonication did not alter the animals’ behavior or disrupt the blood-brain barrier (BBB) while yielding normal brain histology. The results suggest that FUS may serve as a new non-invasive means to promote interstitial CSF solute transport in a region-specific manner without disrupting the BBB, providing potential for enhanced clearance of waste products from the brain.

PURPOSE:The purpose of this study was to evaluate if transcutaneous application of low-intensity ultrasound can locally enhance the effects of finasteride on hair growth in a murine model of androgenic alopecia (AA). METHODS:AA mice (injected twice per week with testosterone enanthate, n=11), under daily oral administration of finasteride, received 1-MHz ultrasound for 1 hour at the unilateral thigh area five times per week for 5 weeks. Non-thermal and non-cavitational ultrasound was delivered in a pulsed manner (55-ms pulse duration with a repetition frequency of 4 Hz). Skin temperature was measured during sonication, and the measurements were validated with numerical simulations of sonication-induced tissue temperature changes. Hair growth was assessed both photographically and histologically. RESULTS:We found more hair growth on the sonicated thigh area than on the unsonicated thigh, beginning from week 3 through the end of the experiment. Histological analyses showed that the number of hair follicles doubled in the skin sections that received sonication compared to the unsonicated zone, with thicker follicular diameter and skin. An over five-fold increase was also observed in the anagen/telogen ratio in the sonicated area, suggesting an enhanced anagen phase. Skin temperature was unaltered by the administered sonication. CONCLUSION:The findings of the present study suggest that pulsed application of ultrasound promotes hair growth, potentially by disrupting the binding of albumin to finasteride. This may suggest further applications to enhance the pharmacological effects of other relevant drugs exhibiting high plasma protein binding.

Additive manufacturing (AM) has become an increasingly powerful technique for fabricating complex three-dimensional micro-architectures for a wide variety of applications. Despite the multitude of AM techniques that support single material printing at progressively higher throughput, larger build size, and finer spatial resolution, multi-material printing of interlaced structures with one of the materials being a filled composite has not been demonstrated. This work aims to demonstrate the technical feasibility of fabricating such heterogeneous structures using a custom-built multi-material digital light processing (MMDLP) 3D printer. The printer was equipped with two resin dispensers and an air-jet that enable fast exchange between the resins—one of which was filled with carbon nanotubes (CNTs) up to 0.25%. The inclusion of CNTs reduced the cure depth of the resins, but significantly lowered the critical exposure required to initiate the photopolymerization. This information was successfully used to select appropriate process parameters for printing complex CNT-filled multi-material structures.

Soft composite actuators can be fabricated by embedding shape memory alloy (SMA) wires into soft poly-mer matrices. Shape retention and recovery of these actuators are typically achieved by incorporating shape memory polymer segments into the actuator structure. However, this requires complex manufac-turing processes. This work uses multimaterial 3D printing to fabricate composite actuators with variable stiffness capable of shape retention and recovery. The hinges of the bending actuators presented here are printed from a soft elastomeric layer as well as a rigid shape memory polymer (SMP) layer. The SMA wires are embedded eccentrically over the entire length of the printed structure to provide the actuation bending force, while the resistive wires are embedded into the SMP layer of the hinges to change the temperature and the bending stiffness of the actuator hinges via Joule heating. The temperature of the embedded SMA wire and the printed SMP segments is changed sequentially to accomplish a large bending deformation, retention of the deformed shape, and recovery of the original shape, without applying any external mechanical force. The SMP layer thickness was varied to investigate its effect on shape retention and recovery. A nonlinear finite element model was used to predict the deformation of the actuators. (c) 2021 Elsevier B.V. All rights reserved.

To address current unmet needs in terms of scalability and material biocompatibility for future photocrosslinking-based additive manufacturing technologies, emergent platform designs are in inexorable demand. In particular, a shift from the present use of cell-damaging UV light sources in light-based three-dimensional (3D) bioprinting methods demands new platforms. We adopted an organic light-emitting diode (OLED) microdisplay as a digital visible light modulator to create a 3D printing platform modality that offers scalability and multi-material capability while forgoing the need for UV photocrosslinking. We formulate biocompatible inks that are visible light-crosslinkable with relatively quick photoinitiation rates. We demonstrated successful attachment and rapid growth of primary human dermal fibroblast-adult (HDF-a) cells on biological substrates fabricated using the OLED platform. This platform incites new possibilities by providing a simple-yet-effective means for low-cost, high-throughput, and multi-material 3D fabrication of functional structures made of polymers, ceramic composites, and biomaterials.