The development of needle-free drug injection systems is of great importance to global healthcare. However, in spite of its great potential and research history over many decades, these systems are not commonly used .
One of the main problems is that existing methods use diffusive jets, which result in scattered penetration and severe deceleration of the jets, causing frequent pain and insufficient penetration . We experimentally demonstrate that these unique jets are able to penetrate human skin: the focused nature of these microjets creates an injection spot smaller than a mosquito’s proboscis and guarantees a high percentage of the liquid being injected .
The liquid substances can be delivered to a much larger depth than conventional methods, and create a well-controlled dispersion pattern . Thanks to the excellent controllability of the microjet, small volume injections become feasible . Furthermore, the penetration dynamics is studied through experiments performed on gelatin mixtures (human soft tissue equivalent) and human skin, agreeing well with a viscous stress model which we develop .
This model predicts the depth of the penetration into both human skin and soft tissue . The results presented here take needle-free injections a step closer to widespread use . Needle-free liquid jet injectors have been used for more than 50 years for parenteral delivery of vaccines and drugs.
Although excellent bioavailability has been reported for a number of drugs, occasional pain and bruising have limited wide acceptance of jet injectors. There are numerous examples of jet injection some of which are described here . Liquid jet injections employ a high-speed jet to puncture the skin and deliver drugs without the use of a needle.
They have been used to deliver a number of macromolecules including vaccines and insulin, as well as small molecules, such as anesthetics and antibiotics. It indicates that liquid jet injectors with respect to their historical perspective, clinical applications, mechanisms and future prospects are very significant .
The central principle of this injection is “if an abundant pressure can be generated by an aqueous in confined contact with the skin, then the liquid will verve a hole in to the skin and be transferred into the tissues in and beneath the skin.” Although the same principle is applied as in powder, there is a difference in the absolute design and action of the powder injection devices.
These systems use gas or springs, pistons, drug loaded chambers and nibs. Typically, the nozzle has an aperture size of about 150 to 300μm . Particular attention is paid to the mechanistic understanding of jet injections, especially the dependence of jet penetration on parameters such as nozzle diameter, velocity and jet power.
The search for methods of vaccine delivery not requiring a needle and syringe has been accelerated by recent concerns regarding pandemic disease, bioterrorism, and disease eradication campaigns .
Needle-free vaccine delivery could aid in these mass vaccinations by increasing ease and speed of delivery, and by offering improved safety and compliance, decreasing costs, and reducing pain associated with vaccinations.
Jet injectors are needle-free devices that deliver liquid vaccine through a nozzle orifice and penetrate the skin with a high-speed narrow stream. They generate improved or equivalent immune responses compared with needle and syringe. Powder injection, a form of jet injection using vaccines in powder form, may obviate the need for the “cold chain .
These injections composed of a enclosed volume in a body filled with solid drug mixture and a nib for discharging drug minims into the skin by using the power source which typically is tightly pressured gas. The injection has a diaphragm (a few microns thick) on either side of the enclosed volume in body to cover the drug enclosed space .
Transcutaneous immunization involves applying vaccine antigen and adjuvant to the skin, using a patch or “microneedles,” and can induce both systemic and mucosal immunity. Improved knowledge regarding the immune system and its responses to vaccination continues to inform vaccine technologies for needle-free vaccine delivery .
Depot or projectile injections are made for transfer of a drug into muscles. They build a lode of drug into muscles that is set free forever over a wanted time period.  Needle-free injection systems are original and of a kind not seen before way to introduce distinct medicines into patients without piercing the skin with ordinary and painful needle.
Needle-free systems were first described by Marshall Lockhart in 1936 in his plain jet injection. Then in the early 1940’s Higson and others developed high pressure “guns” using a fine jet of liquid to pierce the skin and deposit the drug in underlying tissue .
Needle free injection methods include:
- Spring load jet injector:
This technique depends on a spring mechanism which is stressed back. The spring is set free by hitting trigger governing to propagation of jet stream of drug for below the epidermis, within a muscle or trans. Dermal transfer of a drug. The activated spring load must be dead end by hand for the next conduct . Following are its examples: Dermojet® , Medi-jector® .
- Battery powdered jet injector:
This method has a small rechargeable battery pack to retract the dosing device. The dosing device has an electric piston which is automatically redrawn after dosing. This is good for continuous use. This type of injector is similar to a battery powered hand drill.
Used for subcutaneous, intramuscular or transdermal delivery of drug depending on the recommended method . Examples: Intra Dermal Application of Liquids (IDAL) ®Intervet, Boxmeer .
- Gas powdered jet injector:
This system contains of an air/gas ball which is associated to the gun through a tubing system that transfers power to the piston after the propulsion of trigger; it releases the piston and creates jet stream of drug. It is suitable for subcutaneous, intramuscular or trans. dermal use.  Its examples are: Biojector®, Pulse® Needle-Free Felton, Lenexa, Ks. Agro-Jet®/Med-Jet®- Mit, Montreal, Quebec,Canada .
Advantages of needle-free injection
- Escape skin puncture dangers and its abolition; also does not cause problem of bleeding or black mark and basal skin vibes.
- Convey fast drug delivery and fine reproducibility as balanced to aggressive attack drug delivery systems and hence increasers bioavailability when match with invasive drug delivery systems.
- Better drug stableness during accumulation as it is transferred in dry powder form especially for water sensitive drugs.
- Averts problems of reconstitution and any effect of cutting or clipping.
- Abrogation of needle phobia.
- Self-administration is appropriate with needle free injections.
- Helps in improving immune response to vaccines. Immunization of influenza, tetanus, typhoid, diphtheria, pertussis, and hepatitis A vaccines can be injected by needle free injections.
- Bio-equivalence has been demonstrated enabling the development of generic drug proteins.
- A good dose response with increased drug doses .
These systems have been in employment to deliver moderately, DNA-based vaccines to the intradermal layer  The system delivers the drug at a very low depth that is, between the layer of the skin.
One of the most developed NFIT systems working for intramuscular drug management. Drug delivery via this system is the deepest among all. Drug delivery through NFIT devices has been most successful for vaccination .
Certain therapeutic proteins including the human growth hormones have been administered by this system. The medicament is delivered to the adipose layer just below the skin .
The development of this drug delivery system aims to go in to the skin has been reliant on the simple engineering concepts. Needle free technology are capable of delivering a extensive range of medicinal formulations into the body with the same bioequivalence as that which could have been achieved by drug management by a two-piece syringe system, without inflating pointless pain to the patients.
These devices are very easy to be used, don’t require any skilled administration or conduct, easy to store, and set out. These devices are suitable for delivery of drugs to some of the most sensitive parts of the body like cornea.
They are efficient to administer intra-muscular, subcutaneous and intra-dermal injections. However some facts about these injections such as these are complicated and expensive. All systems are not fitted into one size. Need for personnel training and maintenance. It is not applicable for Intravenous route.