Investigating skin penetration depth and shape following needle-free injection at different pressures: A cadaveric study

Needleless laser injector versus needle injection for skin enhancement and rejuvenation effect of dermal filler

BACKGROUND AND OBJECTIVES

A needleless laser-induced microjet injector is a novel transdermal drug delivery system that can rapidly inject a very small and precise drug dose into the skin with minimal pain and downtime. In this study, we aimed to compare the laser-induced microjet injection versus needle injection of polylactic acid/hyaluronic acid filler for skin enhancement and rejuvenation.

PATIENTS AND METHODS

A 24-week prospective, single-center, assessor-blinded, randomized, split-face study was conducted. The enrolled patients underwent one treatment session of dermal filler injection using a laser-induced microjet injector on one half of the face or a traditional needle injection on the other half of the face. Evaluation was conducted at baseline before treatment and at 4, 12, and 24 weeks after treatment.

RESULTS

A single treatment of filler injection with a laser-induced microjet injector resulted in similar improvements in skin hydration and elasticity as a single treatment of filler injection by using manual needle injection, with reduced pain, side effects, and decreased treatment time.

CONCLUSIONS

Laser-induced microjet injector enabled not only the application of a controlled dose and filler depth but also even distribution, improved clinical efficacy, reduced pain and side effects, and sufficient time for clinicians to perform treatment.

Experimental investigation of the optimal driving pressure for a larger-volume controllable jet injection system

Jet injection technology has become the alternative drug delivery method of conventional needle-based injection due to its obvious advantages. In order to meet the demand for larger volume injection, the pneumatic jet injection systems have efficiently administrated vaccine up to 1 mL in human. Our recent study has also demonstrated that controlling the driving pressure enabled the pneumatic jet injection system to deliver larger volumes of drugs to target sites at desired rates and times. This work continues to explore the optimal two-phase driving pressure combination with better injection efficiency for typical larger-volume (1.0 mL) jet injection with controllable pneumatic jet injection system. Under the combination of a first phase driving pressure of 1.00 MPa and a second phase driving pressure ranging from 0.25 to 0.90 MPa, dynamic characteristics, dispersion characteristics and pharmacokinetic characteristics of this controllable jet injection system were quantitatively analyzed. In all experiments, it was confirmed that the optimal driving pressure combination of 1.0 mL ejection volume was close to (1.00-0.50) MPa. That is, the injection velocities of 151.85 m/s and 102.01 m/s for the first and second phase respectively facilitated better injection performance with a controlled release of 1.0 mL ejection volume. This strategy is practical for facilitating the clinical application of large-volume controllable jet injection systems.

Bubble dynamics and speed of jets for needle-free injections produced by thermocavitation

Significance

The number of injections administered has increased dramatically worldwide due to vaccination campaigns following the COVID-19 pandemic, creating a problem of disposing of syringes and needles. Accidental needle sticks occur among medical and cleaning staff, exposing them to highly contagious diseases, such as hepatitis and human immunodeficiency virus. In addition, needle phobia may prevent adequate treatment. To overcome these problems, we propose a needle-free injector based on thermocavitation.

Aim

Experimentally study the dynamics of vapor bubbles produced by thermocavitation inside a fully buried 3D fused silica chamber and the resulting high-speed jets emerging through a small nozzle made at the top of it. The injected volume can range from ∼ 0.1 to 2    μ L per shot. We also demonstrate that these jets have the ability to penetrate agar skin phantoms and ex-vivo porcine skin.

Approach

Through the use of a high-speed camera, the dynamics of liquid jets ejected from a microfluidic device were studied. Thermocavitation bubbles are generated by a continuous wave laser (1064 nm). The 3D chamber was fabricated by ultra-short pulse laser-assisted chemical etching. Penetration tests are conducted using agar gels (1%, 1.25%, 1.5%, 1.75%, and 2% concentrations) and porcine tissue as a model for human skin.

Result

High-speed camera video analysis showed that the average maximum bubble wall speed is about 10 to 25 m/s for almost any combination of pump laser parameters; however, a clever design of the chamber and nozzle enables one to obtain jets with an average speed of ∼ 70    m / s . The expelled volume per shot (0.1 to 2    μ l ) can be controlled by the pump laser intensity. Our injector can deliver up to 20 shots before chamber refill. Penetration of jets into agar of different concentrations and ex-vivo porcine skin is demonstrated.

Conclusions

The needle-free injectors based on thermocavitation may hold promise for commercial development, due to their cost and compactness.

Dynamic interaction of injected liquid jet with skin layer interfaces revealed by microsecond imaging of optically cleared ex vivo skin tissue model

BACKGROUND

Needle-free jet injection (NFJI) systems enable a controlled and targeted delivery of drugs into skin tissue. However, a scarce understanding of their underlying mechanisms has been a major deterrent to the development of an efficient system. Primarily, the lack of a suitable visualization technique that could capture the dynamics of the injected fluid-tissue interaction with a microsecond range temporal resolution has emerged as a main limitation. A conventional needle-free injection system may inject the fluids within a few milliseconds and may need a temporal resolution in the microsecond range for obtaining the required images. However, the presently available imaging techniques for skin tissue visualization fail to achieve these required spatial and temporal resolutions. Previous studies on injected fluid-tissue interaction dynamics were conducted using in vitro media with a stiffness similar to that of skin tissue. However, these media are poor substitutes for real skin tissue, and the need for an imaging technique having ex vivo or in vivo imaging capability has been echoed in the previous reports.

METHODS

A near-infrared imaging technique that utilizes the optical absorption and fluorescence emission of indocyanine green dye, coupled with a tissue clearing technique, was developed for visualizing a NFJI in an ex vivo porcine skin tissue.

RESULTS

The optimal imaging conditions obtained by considering the optical properties of the developed system and mechanical properties of the cleared ex vivo samples are presented. Crucial information on the dynamic interaction of the injected liquid jet with the ex vivo skin tissue layers and their interfaces could be obtained.

CONCLUSIONS

The reported technique can be instrumental for understanding the injection mechanism and for the development of an efficient transdermal NFJI system as well.

A clinical observation study on the effect of needle-free insulin syringe on blood glucose control and well-being index in patients with early-onset type 2 diabetes mellitus

OBJECTIVE

To explore the effect of using needle-free insulin syringe on blood sugar control and well-being index in patients with early-onset type 2 diabetes mellitus.

METHODS

A total of 42 patients with early-onset type 2 diabetes mellitus treated with insulin aspart 30 injection in a stable condition in the Endocrinology Department of a tertiary hospital from January 2020 to July 2021 were randomly divided into two groups, one group received insulin pen injections followed by needle-free injections, and the other group received needle-free injections followed by insulin pen injections. Transient scanning glucose monitoring was performed during the last two weeks of each injection modality phase. Comparison of the two injection methods in terms of test indicators and differences in injection site pain scores, the number of red spots on the skin at the injection site and the number of bleeding spots on the skin at the injection site.

RESULTS

The FBG of the needle-free injection group was lower than that of the Novo Pen group (p<0.05); the 2-hour postprandial blood glucose of the needle-free injection group was lower than that of the Novo Pen group, but there was no statistical significant difference. The amount of Insulin in the needle-free injector group was lower than that in the Novo pen group, but there was no statistical significant difference between the two groups. The WHO-5 score of the needle-free injector group was higher than that of the Novo Pen group(p<0.05); the pain score at the injection site was lower than that of the Novo Pen group (p<0.05). The number of skin red spots using the needle-free syringe was more than that of the Novo pen group(p<0.05); the number of skin bleeding at the site of injection was similar between the two injection methods.

CONCLUSION

Compared to traditional insulin pens, subcutaneous injection of premixed insulin using a needle-free syringe is effective in controlling fasting blood glucose in patients with early onset type 2 diabetes and is less painful at the injection site. In addition, blood glucose monitoring should be strengthened and insulin dosage should be adjusted in a timely manner.

Jet injectors: Perspectives for small volume delivery with lasers

Needle-free jet injectors have been proposed as an alternative to injections with hypodermic needles. Currently, a handful of commercial needle-free jet injectors already exist. However, these injectors are designed for specific injections, typically limited to large injection volumes into the deeper layers beneath the skin. There is growing evidence of advantages when delivering small volumes into the superficial skin layers, namely the epidermis and dermis. Injections such as vaccines and insulin would benefit from delivery into these superficial layers. Furthermore, the same technology for small volume needle-free injections can serve (medical) tattooing as well as other personalized medicine treatments. The research dedicated to needle-free jet injectors actuated by laser energy has increased in the last decade. In this case, the absorption of the optical energy by the liquid results in an explosively growing bubble. This bubble displaces the rest of the liquid, resulting in a fast microfluidic jet which can penetrate the skin. This technique allows for precise control over volumes (pL to µL) and penetration depths (µm to mm). Furthermore, these injections can be tuned without changing the device, by varying parameters such as laser power, beam diameter and filling level of the liquid container. Despite the published research on the working principles and capabilities of individual laser-actuated jet injectors, a thorough overview encompassing all of them is lacking. In this perspective, we will discuss the current status of laser-based jet injectors and contrast their advantages and limitations, as well as their potential and challenges.

Needle-free Mental Incisive Nerve Block:In vitro, Cadaveric, and Pilot Clinical Studies

The present study aimed to optimize Needle-Free Liquid Jet Injection (NFLJI) for Mental Incisive Nerve Blocks (MINB) and evaluate its clinical safety and feasibility. A MINB protocol was developed and optimized by series of NFLJI experiments in soft tissue phantoms and cadavers, then validated in two pilot Randomized Controlled Trials (RCT). The NFLJI penetration depth was found to be directly proportional to the supply pressure and volume. High-pressure NFLJIs (620 kPa or above) created maximum force and total work significantly greater than needle injections. Low-pressure NFLJIs (413 kPa), however, produced results similar to those of needle injections. Additionally, high-pressure NFLJIs created jet impingement pressure and maximum jet penetration pressure higher than low-pressure NFLJIs. Pilot RCTs revealed that high-pressure NFLJI caused a high risk of discomfort (60%) and paresthesia (20%); meanwhile, low-pressure NFLJI was less likely to cause complications (0%). The preliminary success rates of MINB from cadavers using NFLJIs and needles were 83.3% and 87.5%. In comparison, those from RCTs are 60% and 70%, respectively. To conclude, NFLJI supply pressure can be adjusted to achieve effective MINB with minimal complications. Furthermore, the cadaver study and pilot RCTs confirmed the feasibility for further non-inferiority RCT.

Dispersion profile of a needle-free jet injection depends on the interfacial property of the medium

Injections into or through the skin are common drug or vaccine administration routes, which can be achieved with conventional needles, microneedles, or needle-free jet injections (NFJI). Understanding the transport mechanism of these injected fluids is critical for the development of effective drug administration devices. NFJI devices are distinct from traditional injection techniques by their route and time scale, which relies on a propelled microjet with sufficient energy to penetrate the skin surface and deliver the drug into the targeted region. The injected fluid interacts with multiple skin tissue layers and interfaces, which implies that the corresponding injection profile is dependent on their mechanical properties. In this study, we address the lack of fundamental knowledge on the impact of these interfaces on the injection profiles of NFJI devices.

Transient modelling of impact driven needle-free injectors

Needle-free jet injectors (NFJIs) are one of the alternatives to hypodermic needles for transdermal drug delivery. These devices use a high-velocity jet stream to puncture the skin and deposit drugs in subcutaneous tissue. NFJIs typically exhibit two phases of jet injection - namely - an initial peak-pressure phase (< 5 ms), followed by a constant jet speed injection phase (≳ 5 ms). In NFJIs, jet velocity and jet diameter are tailored to achieve the required penetration depth for a particular target tissue (e.g., intradermal, intramuscular, etc.). Jet diameter and jet velocity, together with the injectant volume, guide the design of the NFJI cartridge and thus the required driving pressure. For device manufacturers, it is important to rapidly and accurately estimate the cartridge pressure and jet velocities to ensure devices can achieve the correct operational conditions and reach the target tissue. And thus, we seek to understand how cartridge design and fluid properties affect the jet velocity and pressure profiles in this process. Starting with experimental plunger displacement data, transient numerical simulations were performed to study the jet velocity profile and stagnation pressure profile. We observe that fluid viscosity and cartridge-plunger friction are the two most important considerations in tailoring the cartridge geometry to achieve a given jet velocity. Using empirical correlations for the pressure loss for a given cartridge geometry, we extend the applicability of an existing mathematical approach to accurately predict the jet hydrodynamics. By studying a range of cartridge geometries such as asymmetric sigmoid contractions, we see that the power of actuation sources and nozzle geometry can be tailored to deliver drugs with different fluid viscosities to the intradermal region.

Needle-free injection: Dental infiltration anesthesia

This study aimed to develop an optimal Needle-Free Liquid Jet Injection (NFLJI) technique for dental infiltration anesthesia and evaluate its clinical safety and feasibility. The fluid dynamics of NFLJI in the dentoalveolar region were investigated using soft tissue phantoms supported by rigid glass. NFLJIs were performed at different incident angles and recorded using a high-speed camera. Accordingly, an optimal NFLJI for infiltration anesthesia was developed and validated on cadavers, then assessed in two pilot Randomized Controlled Trials (RCT): one for validating the safety of optimal NFLJI technique, the other for evaluating its feasibility and safety. High-speed videos showed that perpendicular NFLJIs induced significantly more regurgitation than oblique NFLJIs, which was confirmed in cadavers. Clinical trials revealed that perpendicular NFLJIs induced a high risk of bleeding (83.3%) and laceration (83.3%), whereas oblique NFLJIs induced a low risk of bleeding (33.3%) and laceration (16.7%). Moreover, the preliminary success rates of oblique NFLJIs and needle injections were both 83.3%. The recruitment took 3-5 weeks with a rate of 100%. Oblique NFLJIs could be a promising approach for dental infiltration anesthesia, causing minimal drug regurgitation with a relatively low risk of complication. The pilot RCTs confirmed the feasibility for conducting a non-inferiority RCT.

Mechanism and clinical applications of needle-free injectors in dermatology: Literature review

BACKGROUND

Needle-free jet injectors are devices that deliver drugs using a high-speed jet without a needle. Recent studies have significantly increased our understanding of the mechanisms of needle-free jet injectors, and technical advancements have broadened the scope of application of the device.

AIMS

We aimed to provide an up-to-date review of previous literature regarding the mechanism of action and clinical applications of needle-free jet injectors in dermatology field.

METHODS

We conducted a PUBMED search for studies on needle-free jet injectors using the following parameters: "Pneumatic injector" OR "needleless injector" OR "needle-free injector" OR "jet injector." Among 191 results, 72 articles focusing on their mechanisms of action, cutaneous delivery patterns, and clinical applications in dermatology were selected for review.

RESULTS

Significant clinical evidence has been published confirming the potential of needle-free jet injectors in treating various dermatologic conditions. In particular, these devices have the potential to be used in various skin remodeling treatment, especially in skin rejuvenation procedures by injecting various esthetic materials.

CONCLUSION

As proven by accumulated experience, the applications of NFJIs are not restricted to vaccine or insulin delivery in dermatology field. However, this literature review shows that until now, there are no clinical guidelines that standardize the optimal parameters when using NFJIs on various clinical settings. Therefore, further studies should be performed in order to investigate the full potential of these devices in dermatology, to ensure safe and effective outcomes in clinical practice.

Predictive mechanics-based model for depth of cut (DOC) of waterjet in soft tissue for waterjet-assisted medical applications

The use of waterjet technology is now prevalent in medical applications including surgery, soft tissue resection, bone cutting, waterjet steerable needles, and wound debridement. The depth of the cut (DOC) of a waterjet in soft tissue is an important parameter that should be predicted in these applications. For instance, for waterjet-assisted surgery, selective cutting of tissue layers is a must to avoid damage to deeper tissue layers. For our proposed fracture-directed waterjet steerable needles, predicting the cut depth of the waterjet in soft tissue is important to develop an accurate motion model, as well as control algorithms for this class of steerable needles. To date, most of the proposed models are only valid in the conditions of the experiments and if the soft tissue or the system properties change, the models will become invalid. The model proposed in this paper is formulated to allow for variation in parameters related to both the waterjet geometry and the tissue. In this paper, first the cut depths of waterjet in soft tissue simulants are measured experimentally, and the effect of tissue stiffness, waterjet velocity, and nozzle diameter are studied on DOC. Then, a model based on the properties of the tissue and the waterjet is proposed to predict the DOC of waterjet in soft tissue. In order to verify the model, soft tissue properties (constitutive response and fracture toughness) are measured using low strain rate compression tests, Split-Hopkinson-Pressure-Bar (SHPB) tests, and fracture toughness tests. The results show that the proposed model can predict the DOC of waterjet in soft tissue with acceptable accuracy if the tissue and waterjet properties are known. Graphical Abstract (Left) An overview of the problems of traditional steerable needles and the solutions provided by waterjet steerable needles. (A) Traditional tip-steerable needles and tip-bent needles suffer from poor curvature, especially in soft tissues. (B) Traditional steerable needles are unable to accomplish many bends because the cutting force only results from drastic tissue deformation. (C) The first step for realization of waterjet steerable needles is to understand and model the interaction between waterjet and soft tissues at the tip (predictive model for depth of cut). (D) Then, the equilibrium between shapes cut in the tissue and the straight elastic needle should be understood. (Right) Waterjet steerable needles in which the direction of the tissue fracture is contr olled by waterjet and then the flexible needle follows. The first step for waterjet steerable needle realization is to predict the depth of waterjet cut.

Electronic Pneumatic Injection-Assisted Dermal Drug Delivery Visualized by Ex Vivo Confocal Microscopy

Background and Objectives

Electronic pneumatic injection (EPI) is a technique for dermal drug delivery, which is increasingly being used in clinical practice. However, only few studies have been reported on cutaneous drug distribution and related clinical endpoints. We aimed to visualize the immediate cutaneous drug distribution, changes in skin architecture, and related clinical endpoint of EPI.

Study Design/Materials and Methods

Acridine orange (AO) solution was administered to ex vivo porcine skin by EPI at pressure levels from 4 to 6 bar with a fixed injection volume of 50 µl and nozzle size of 200 µm. Immediate cutaneous distribution was visualized using ex vivo confocal microscopy (EVCM). Changes in skin architecture were visualized using both EVCM and hematoxylin and eosin‐stained cryosections.

Results

The defined immediate endpoint was a clinically visible papule formation on the skin. The pressure threshold to consistently induce a papule was 4 bar, achieving delivery of AO to the deep dermis (2319 µm axial and 5944 µm lateral distribution). Increasing the pressure level to 6 bar did not lead to significant differences in axial and lateral dispersion (P = 0.842, P = 0.905; respectively). A distinctively hemispherical distribution pattern was identified. Disruption of skin architecture occurred independently of pressure level, and consisted of subepidermal clefts, dermal vacuoles, and fragmented collagen.

Conclusions

This is the first study to relate a reproducible clinical endpoint to EPI‐assisted immediate drug delivery using EVCM. An EPI‐induced skin papule indicates dermal drug delivery throughout all layers of the dermis, independent of pressure level settings. Lasers Surg. Med. © 2020 The Authors. Lasers in Surgery and Medicine published by Wiley Periodicals LLC

Effect of geometrical parameters on the fluid dynamics of air-powered needle-free jet injectors

Needle-free jet injectors are non-invasive systems having intradermal drug delivery capabilities. At present, they revolutionize the next phase of drug delivery and therapeutic applications in the medical industry. An efficiently designed injection chamber can reduce the energy consumption required to achieve the maximum penetration depth in skin tissue. In this study, the authors explored the effect of various geometrical parameters using a computational fluid dynamics tool. Peak stagnation pressure during the initial phase of the injection procedure was considered as the quantifier for comparison because of its proportional relationship with the initial penetration depth during the injection process. Peak stagnation pressure indicates the maximum energy transformation that could happen between the microjet and skin tissues for an injection procedure. The results of this study indicated a tradeoff that exists between the attainable density and velocity of the microjet on the skin surface with variation in nozzle diameter; the optimum nozzle diameter was found to be within 200-250 μm under the present conditions. The authors also observed a discrepancy in the peak stagnation pressure value for lower filling ratios with variation in chamber diameter; hence, filling ratio of at least 50% was recommended for such systems. Furthermore, a 150% increase in the peak stagnation pressure was obtained with an angle of entry of 10°. In general, this study could provide valuable insights into the effect of geometrical parameters in the fluid dynamics characteristics of propelled microjets from the nozzle of a needle-free jet injector. Such information could be useful for the design of a mechanically driven needle-free jet injector having limited control over the energizing mechanism.

Safe Needle Insertion Locations for Motor Point Injection of the Triceps Brachii Muscle: A Pilot Cadaveric and Ultrasonography Study

Objective

To determine the location of the motor endplate zones (MoEPs) for the three heads of the triceps brachii muscles during cadaveric dissection and estimate the safe injection zone using ultrasonography.

Methods

We studied 12 upper limbs of 6 fresh cadavers obtained from body donations to the medical school anatomy institution in Seoul, Korea. The locations of MoEPs were expressed as the percentage ratio of the vertical distance from the posterior acromion angle to the midpoint of the olecranon process. By using the same reference line as that used for cadaveric dissection, the safe injection zone away from the neurovascular bundle was identified in 6 healthy volunteers via ultrasonography. We identified the neurovascular bundle and its location with respect to the distal end of the humerus and measured its depth from the skin surface.

Results

The MoEPs for the long, lateral, and medial heads were located at a median of 43.8%, 54.8%, and 60.4% of the length of the reference line in cadaver dissection. The safe injection zone of the medial head MoEPs corresponded to a depth of approximately 3.5 cm from the skin surface and 1.4 cm away from the humerus, as determined by sonography.

Conclusion

Correct identification of the motor points for each head of the triceps brachii would increase the precision and efficacy of motor point injections to manage elbow extensor spasticity.

Delivery Strategies for Skin: Comparison of Nanoliter Jets, Needles and Topical Solutions

Drug diffusion within the skin with a needle-free micro-jet injection (NFI) device was compared with two well-established delivery methods: topical application and solid needle injection. A permanent make-up (PMU) machine, normally used for dermal pigmentation, was utilized as a solid needle injection method. For NFIs a continuous wave (CW) laser diode was used to create a bubble inside a microfluidic device containing a light absorbing solution. Each method delivered two different solutions into ex vivo porcine skin. The first solution consisted of a red dye (direct red 81) and rhodamine B in water. The second solution was direct red 81 and rhodamine B in water and glycerol. We measured the diffusion depth, width and surface area of the solutions in all the injected skin samples. The NFI has a higher vertical dispersion velocity of 3 × 10⁵μm/s compared to topical (0.1 μm/s) and needle injection (53 μm/s). The limitations and advantages of each method are discussed, and we conclude that the micro-jet injector represents a fast and minimally invasive injection method, while the solid needle injector causes notable tissue damage. In contrast, the topical method had the slowest diffusion rate but causes no visible damage to the skin.

Characterization of skin blebs from intradermal jet injection: Ex-vivo studies

This paper presents results from an ex-vivo study of intradermal jet injections, which is an attractive method to achieve both needle-free and fractional dose delivery of vaccines. Due to the fact that fluid properties of many novel therapeutics and vaccines can vary significantly, a key parameter for our study is the fluid viscosity, whilst the main focus is on determining the best correlation between the delivered volume and geometrical dimensions of the fluid deposit. For this we use a combination of top-view (skin wheal), underside (below the dermis), and cross-section (true skin bleb) perspectives and find that the top-view alone, as done in clinical practice, is insufficient to estimate the volume deposited in the dermis. Overall, the best correlation is found between the injection volume and cross-sectional diameter, however there is significant variation amongst the different fluids. For mean injection volumes of 60 μL the mean bleb diameter is ≈8 mm, with mean aspect ratio h¯/d=0.38, indicating the blebs are mostly oblate. However, the shape varies with viscosity and the higher viscosity does not spread laterally to the same degree as lower viscosity fluids. In addition, our high-speed video observations of the injection process, reveal some interesting dynamics of the jet injection method, and we modeled the bleb growth with an exponential saturation.

Characterization of jet injection efficiency with mouse cadavers

Needle-free drug delivery is highly sought after for reduction in sharps waste, prevention of needle-stick injuries, and potential for improved drug dispersion and uptake. Whilst there is a wealth of literature on the array of different delivery methods, jet injection is proposed as the sole candidate for delivery of viscous fluids, which is especially relevant with the advent of DNA-based vaccines. The focus of this study was therefore to assess the role of viscosity and jet configuration (i.e. stand-off relative to the skin) upon injection efficiency for a fixed spring-loaded system (Bioject ID Pen). We performed this assessment in the context of mouse cadavers and found that the dominant factor in determining success rates was the time from euthanasia, which was taken as a proxy for the stiffness of the underlying tissue. For overall injection efficiency, ANOVA tests indicated that stiffness was highly significant (P <  < 0.001), stand-off was moderately significant (P < 0.1), and viscosity was insignificant. In contrast, both viscosity and standoff were found to be significant (P < 0.01) when evaluating the percentage delivered intradermally. Using high-resolution micro-computed tomography (μ-CT), we also determined the depth and overall dispersion pattern immediately after injection.

Needle-free pneumatic injection device; histologic assessment using a rat model and parameter comparison in predicting collagen synthesis degree

BACKGROUND

Needle-free pneumatic injections have been recently introduced to the field of dermatology to inject such substances as hyaluronic acid. However, data on the influence of various pneumatic injection parameters on collagen synthesis are lacking.

OBJECTIVE

Compare the effect of diameter, pressure, and volume of a pneumatic injection jet on collagen synthesis and fluid dispersion pattern using a rat model. Investigate if the total work force of the injection jet is useful in predicting the degree of collagen synthesis.

MATERIALS AND METHODS

We injected fluid with 1 mg/ml of hyaluronic concentration to adult rats. Different injection pressures and volumes were tested using devices with nozzles of different diameters. Collagen synthesis areas were then measured, and statistical analyses were performed.

RESULTS

The area of collagen fibers increased for up to two months. The injection pressure and volume did not correlate with the degree of collagen synthesis. The nozzle diameter showed a significant after two and four weeks of injection. The total work force correlated with collagen synthesis 2, 4, and 8 weeks post-injection. (P = 0.043, 0.027, and 0.000, respectively).

CONCLUSION

Collagen formation is more prominent 2 months post-hyaluronic acid injection than after 1 month when using a needle-free pneumatic injection device. The total work force, which is affected by both the nozzle diameter and injection pressure, can be helpful in predicting the degree of collagen synthesis. Lasers Surg. Med. 51:278-285, 2019. © 2019 Wiley Periodicals, Inc.

Split-face comparison study of transcutaneous pneumatic injection therapy with isotonic and hypertonic glucose solutions

BACKGROUND

Transcutaneous pneumatic injection (TPI) is a minimally invasive, needle-free modality that can be used to forcefully deliver solution into soft tissues of the face and scalp.

OBJECTIVE

To evaluate the effects of TPI of 5% isotonic and 20% hypertonic glucose solutions in in vivo human skin for face lifting.

METHODS AND MATERIALS

A prospective, split-face, evaluator-blinded comparison study was performed on 10 Korean participants who were treated with three sessions of TPI using 5% isotonic and 20% hypertonic glucose solutions.

RESULTS

The following assessment parameters were improved after TPI therapy using 5% isotonic glucose solution in descending order of mean global aesthetic improvement scale (GAIS) score: perioral expression wrinkles, zygomatic wrinkles or mid-cheek furrows, eyebrow ptosis, jowl sagging, marionette line, horizontal forehead lines, nasolabial folds, and blepharochalasis. Meanwhile, TPI therapy using 20% hypertonic glucose solution improved the following assessment parameters: zygomatic wrinkles or mid-cheek furrows, perioral expression wrinkles, eyebrow ptosis, blepharochalasis, marionette line, jowl sagging, nasolabial folds, and horizontal forehead lines. Linear mixed models revealed a significant interaction between treatment groups and time.

CONCLUSION

Our data demonstrated that TPI treatment with 20% hypertonic glucose solution elicited earlier and more pronounced therapeutic responses, compared to 5% isotonic glucose solution.

Current trends in needle-free jet injection: an update

Background

Jet injection can be defined as a needle-free drug delivery method in which a high-speed stream of fluid impacts the skin and delivers a drug. Despite 75 years of existence, it never reached its full potential as a strategic tool to deliver medications through the skin.

Objective

The aim of this review was to evaluate and summarize the evolution of jet injection intradermal drug delivery method including technological advancements and new indications for use.

Methods

A review of the literature was performed with no limits placed on publication date.

Results

Needleless injectors not only reduce pain during drug delivery but also confine the drug more evenly in the dermis. Understanding skin properties of the injection site is a key factor to obtain optimal results as well as setting the right parameters of the jet injector. Until the advent of disposable jet injectors/cartridges, autoclaving of the injector remains the only reliable method to eliminate the risk of infection. Needle-free intradermal injection using corticosteroids and/or local anesthetics is well documented with promising indications being developed.

Limitations

Limitations of the review include low-quality evidence, small sample sizes, varying treatment parameters, and publication bias.

Conclusion

New developments may help reconsider the use of jet injection technology. Future studies should focus on measurable optimized parameters to insure a safe and effective outcome.

A novel combination regimen with intense focused ultrasound and pressure- and dose-controlled transcutaneous pneumatic injection of hypertonic glucose solution for lifting and tightening of the aging face

BACKGROUND

Intense focused ultrasound (IFUS) has demonstrated moderate efficacy for facial laxity of the aging face. Pressure- and dose-controlled transcutaneous pneumatic injections of hypertonic glucose solution (TPIG) are a minimally invasive way to deliver solution into the skin for therapeutic purposes. Recently, its application around temporal areas is known to exert early-onset lifting effects with facial contour rejuvenation.

AIMS

We sought to evaluate the safety and efficacy of this novel combination regimen with IFUS and TPIG for lifting and tightening of aging face.

PATIENTS AND METHODS

Twenty-two Korean subjects with mild-to-moderate facial skin laxity were evaluated after receiving a sequential single session of IFUS and TPIG treatments. Dermatologists' objective assessments for general appearance, and mid- and low faces based on photographic images were performed at 1- and 12-week post-treatment follow-ups. Patients' subjective assessments were also conducted. Skin biopsies were taken at baseline and the last visit.

RESULTS

Among 22 subjects, twenty (91%) demonstrated improvement after 12-week follow-up. We also observed similarly improved state just after 1 week of treatments (82%: 18/22). Specifically, improvement of the mid-face was evident from the first week, while the progress of the low face improvement was observed at the twelve week. Subjective assessments paralleled these findings. No seriously adverse effect was observed during procedures. Histologic evaluation showed greater dermal collagen fibers throughout the dermis after treatments.

CONCLUSION

Combination treatment with IFUS and TPIG has beneficial effects for skin lifting and tightening with early-onset time.

Pressure- and dose-controlled transcutaneous pneumatic injection of hypertonic glucose solution for the treatment of atrophic skin disorders

BACKGROUND

Needleless transcutaneous pneumatic injections (TPIs) are a minimally invasive way to deliver the solution into the skin for therapeutic purposes. The suggested action mechanisms of TPI therapy include mechanical stimulation, immediate tissue shrinkage and late wound healing.

METHODS

Thirteen Korean patients were treated with TPI for atrophic skin disorders, including acne scars, striae albae, post-furuncle, or carbuncle scars, and horizontal wrinkles with lipoatrophy. At each TPI treatment session, a single pass was made along with the atrophic skin lesions without overlapping. Thereafter, two dermatologists objectively evaluated the clinical improvement in the lesions in the photographs via the global aesthetic improvement scale (GAIS).

RESULTS

One month after the final treatment, the overall mean GAIS score was 2.3 ± 0.8. Six of the 13 (46.2%) patients exhibited clinical improvement of grade 3, five (38.5%) patients grade 2 and two (15.4%) patients grade 1. The overall mean subjective satisfaction score with the TPI treatment was 2.3 ± 0.9. Six of the 13 (46.2%) patients achieved subjective satisfaction of grade 3, six (46.2%) patients grade 2 and one (7.7%) patient grade 0.

CONCLUSIONS

The present study demonstrated that the TPI treatment is effective and safe for treating atrophic skin disorders of varying causes in Korean patients.