Subscribe“Necessity is the mother of invention”
This quotation from the dialogue Republic by ancient Greek philosopher Plato, could be considered one of the mantras of scientific research and product development. Many specialized products used in research were developed out of a specific need that was not already addressed in the marketplace. We often use these products without even thinking about their history, their development, or the imagination of the person who invented them.
WPI's NanoFil is a perfect example of this scientific mantra. Dr. Tawfik El-Samman of Lexicon Genetics Incorporated needed to inject sub microliter samples into the retinal pigment epithelium of mice. He wanted to hold the syringe himself and activate the injection using a pump with a footpedal. Currently, there are no systems of the kind on the market. WPI's Vice-President of Research and Development, Suyi Liu, PhD, considered this problem and went to work inventing a solution. Thus, NanoFil was born.
NanoFil is a unique low-volume syringe with a patented gasket that allows tip exchanges during an experiment. Backfill the 10 microliter syringe with sample using the large 26 gauge needle provided, then exchange the needle for the tip of your choice and begin injections.
The patented silicone gasket makes it possible to hold not only metal tips but also glass and quartz tubing. Many types of tubing can be easily connected to the syringe as long as the outer diameter (OD) is close to, but not more than, the inner diameter (ID) of the inside barrel. The application potential of this design is tremendous.
Flexible quartz capillaries used in Gas Chromotography (GC) and Capillary Electrophoresis (CE) can also be easily coupled to the syringe. The replaceable needles used with the NanoFil are available with either blunt or beveled tips. The blunt tip is used for injection into soft tissue and when a uniform solution distribution is needed.
The beveled style is used for applications that involve the penetration of a tough tissue. One of the main factors that limit the resolution and accuracy of conventional micro syringes to the upper tens of nanoliters range is diffusion in the large tip ID. When the tip ID is equal or larger than 100 microns, the error caused by tip diffusion is in the nanoliter range level ( (100 micron)^3 = 1 nanoliter ).
With a 36 gauge needle installed on the NanoFil, the error caused by diffusion will be reduced to the sub nanoliter level, making accurate injection of a nanoliter possible. All of WPI's beveled tips have a unique 25 degree tri-surface bevel that is optimized for microinjection. A 10 degree single-surface beveled tip penetrates better than one with a 25 degree angle, however the distance between the upper opening to the tip is longer.
As a result, it requires a deeper penetration of the tip to achieve the same level of liquid delivery. Deeper penetration means more tissue damage. WPI's unique 25 degree beveled tip solves this problem with two extra beveled surfaces. The tip of a single surface beveled tip is actually a blade instead of a point. It dulls very quickly. In contrast, the trisurfaced tip has a real point. It not only penetrates much better but is also much more durable.
Our tests show that our 33 gauge, 25 degree beveled tip penetrates easier and lasts longer than other manufacturer's 33 gauge, 10 degree single beveled tips. With a 35 gauge tri-surface beveled tip, the resistance to the penetration becomes even less. Each of our tips undergo a penetration test before leaving the factory to guarantee the best results for our customers.
Selecting the correct tip for your application
Specially designed tips as small as 36 gauge (110 micron OD) are offered in both blunt and beveled styles. Our studies have shown that these tips will cause less trauma to the tissue than any other form of micro syringe currently in use. NanoFil has a unique coupling mechanism that allows many different forms of small tubing and tips to be coupled with the syringe barrel. Based on application requirements, NanoFil can be used in several different configurations
Direct injection by hand: This is the simplest and most economical way to inject. Any of our tips can be inserted directly into the NanoFil syringe. Even the SilFlex tubing can be inserted to switch from hand injection to the other methods listed below. The limitation of this method is the difficulty achieving sub microliter resolution. One user has this comment:
"I think this is a fantastic product. I am using the hand-held syringes for in utero, intraventricular cortical injections in embryonic mice to perturb and elucidate developmental mechanisms during neurogenesis. The tribeveled Flexifil syringes deliver precise volumes, minimize surgery trauma, and increase post-procedure survival in younger embryos."
- Yun C. Yung, Graduate Student, The Scripps Research Institute
Installed on WPI's UMP-II microsyringe pump: This will allow the user to achieve nanoliter resolution and reproducibility. For neural system injection, mount the UMPII on a stereotaxic frame. Jeff Skaggs of Oklahoma University uses the NanoFil with the UMPII pump and had this comment: "Overall the system is very nice. It has drastically increased my throughput."
SilFlex tubing and holder: The needle is mounted on a small plastic holder that is connected to the NanoFil by a 35 cm length of flexible tubing. The NanoFil is mounted on the UMP II pump. This configuration allows the user to hold the animal in one hand and insert the needle with the other.
When the needle reaches the desired location, activate the pump using the footswitch and the pre-programmed injection volume will be delivered. This configuration gives a nanoliter level of accuracy and reproducibility. It is best suited for applications such as the RPE (Retinal Pigment Epithelial) and IO (Intra Ocular) injection.
Available Tips
33 gauge: This tip is similar to Hamilton's 7762 and 7803 series removable needles in both tip length and outer diameter. However, our beveled tip version is shorter, more durable, and penetrates better due to the special tri-surface grinding technique. In the past, 33 gauge tips were the smallest size sold by other manufacturers and were frequently cited in literature. However, our new 35 gauge tip is much better for injections involving small animals, especially mice.
Compared with Hamilton' 33 gauge, 10 degree beveled tip, our 35 gauge 25 degree beveled tip can reduce the depth of penetration by almost 80%. The distance between the tip and the upper rim of the opening is 1024 microns for the 33 gauge tip. The distance for our 35 gauge tip is only 230 microns. In addition, the smaller tip size significantly reduces the required penetration force. In nearly all applications, a 33 gauge tip can be replaced with our 35 gauge tip and produce better results.
34 gauge: This is a transitional size between the 33 gauge and 35 gauge. If the 35 gauge is too weak and the 33 gauge is too large, this makes a good alternative.
35 gauge: This was the most popular and preferred tip of most scientists during our field trial. The combination of its strength, length, durability, and clogging resistance creates a balance with very little compromising of the individual properties. It is much smaller than the 33 gauge tip offered by other manufacturers. It is only slightly larger than the 36 gauge tip but is much stronger and less likely to be clogged. Samples can be directly loaded with this tip. Its 5 mm length is sufficient enough for almost all injection applications in mice.
36 gauge: This is the smallest tip that is commercially available. The tip is so small that it can be inserted into the opening of the 33 gauge needle tip. Because this is pushing the limits of what current technology can produce, there are some limitations to consider before using. Its thin diameter makes it necessary to limit its length to 2.5 to 3.0 mm and still maintain a usable strength. Since the tip ID is in the 25 to 50 micron range, it is very easily clogged. Therefore, only well filtered solutions can be used. We recommend using the 35 gauge tip instead of the 36 gauge unless it is absolutely necessary.
Flexifil: The Flexifil tip is made of a titanium alloy. The advantage of this tubing is its durability. This "semi-flexible" tip can be bent up to 90 degrees without damage. It is also much more corrosion resistant than the stainless steel tip. Saline solutions left in the tip will be less likely to clog it. Although this tip is specified as a 33 gauge tip, its outer diameter is slightly smaller than our 33 gauge stainless steel tip.
Flexible Quartz Tubing: The flexible quartz tubing tip is made of 160 micron OD polyimide coated quartz tubing with a special adapter sleeve mounted at the end. It is designed for filling glass capillary electrodes or pipettes, just like WPI's traditional MF34G Microfil. However, unlike the traditional MicroFil, which has about 50 microliters of dead volume in its luer hub, the dead volume of this tip is less than 0.6 microliters. It is useful for loading electrodes with solutions that have a limited volume or are too expensive to waste.
Application Kits
These kits are specially designed for eye research for injecting retinal pigment epithelium (RPE) and intraocular (IO) in addition to brain injection in mice. They need to be used with a NanoFil syringe and UMP2 to achieve accurate, repetitive, and oil free injection in the submicroliter range.
Each kit includes two pieces of Silflex tubing (one for a spare), a holder assembly, spare gaskets, and an assortment of four tips - blunt for the RPE kit and beveled tips for the IO kit. Each kit comes with one each of 33, 34, 35 and 36 gauge tips so that first time users can find the best size for their application.
The Silflex tubing is the most critical component of the kit. This 35 cm long, flexible tubing has a very precise outer diameter for airtight fitting with the syringe. It also has a small inner diameter for minimum dead volume, and is very durable when handled correctly. The SilFlex is coupled to the injection tip with a mechanism similar to that of the NanoFil. The dead volume of the entire kit (including the tubing) is less than 3 microliters. All of the components in the kit are constructed of inert, solvent resistant, and autoclaveable materials for easy cleaning after viral injection.
NanoFil has become a solution for many problems with sub microliter injection. It is constantly evolving and improving as new users stretch the boundaries of its initial intended use.