Patent Application Review

The invention relates to a microfluidic switch for stopping a liquid flow for a period of time comprising a switch with at least one first channel, at least one second channel, a common area where the paths of the first and second channels meet, and a stopping mechanism at the end of the first channel. An example of an embodiment of the microfluidic switch is provided below. As can be seen, the switch is shown by 20, the first channel by 3 and the second channel by 4.
There are three independent claims for the invention. The first claim (i.e. claim 1) is directed to a microfluidic switch which covers all the eight embodiments described in the specification. As long as a switch comprises two channels with the first channel comprising a stopping mechanism and a second channel for continuing the flow in the first channel, it falls within the scope of the present invention. The dependent claims (i.e. claims 2 to 22) further define the microfluidic switch according to the embodiments provided in the invention.
The second independent claim (i.e. claim 23) is directed to a carrier comprising the switch as disclosed in claim 1. The third independent claim (i.e. claim 24), relates to a process for operating the switch as disclosed in claim 1. Together, the claims cover the product (i.e. the microfluidic switch), the process of using the switch and a product comprising the switch.
As can be seen, the microfluidic switch will be useful for various wet, chemical, biochemical and diagnostic analyses which involve the mixing of the sample liquid with other reagents for a defined time interval where the sample liquid will react with the reagent to produce a product. The product may then be removed for further analysis. Before the present invention, stopping mechanisms comprised of mechanical valves which would most likely be controlled by external means e.g. computers which are time consuming, complex and more expensive.
The present switch may be used to control the time interval for the reaction to take place by varying the length and the contours of the second channel. It may also be possible to connect several of the microfluid channels in series so that the sample liquid may undergo various steps by coming in contact with various reagents without having to be exposed to the environment. This will reduce the chances of the sample liquid being contaminated by the environment.
Although the science of microfluids is well known in the art, using the dynamics of microfluids as a switch is novel and not within the confines of a skilled person. A brief review of the prior art has revealed that there are two main prior art documents that may possibly disclose similar subject matter. The prior art documents are a US patent application, US2002/036018 (Fluid circuit components based upon passive fluid dynamics) and a US patent US-A-6090251 (Microfabricated structures for facilitating fluid introduction into microfluidic devices).
US2002/036018 is related to methods of controlling fluid flow through microchannels with the use of valves that are passive or a means of stopping within the microchannels itself. The passive valves act as pressure barriers preventing flow of any solution beyond the stopping means until enough force is built up within the microchannels to overcome the force of the pressure barrier. The use of such stopping means as passive valves may have several functions including regulating fluid flow through microchannels which enable the contact of different fluids with each other, allowing for the dilution of liquids which have been introduced through a single channel, allowing liquids to be split into multiple channels without there being a need for pipetting the different liquids individually into the reaction chamber and many more other functions. Flow through the multiple channels can also be regulated to enable a series of similar wells to all fill up prior to the fluid flowing past any one of the wells. This method of filling of sister wells or chambers ensures that all wells or chambers are able to undergo the reactions simultaneously. Air ducts may be further included in the present invention in order to prevent trapping of air in the microchannels. An embodiment is provided below.
US-A-6090251 discloses a microfluidic system comprising a substrate having an upper and lower surface, and a microfluidic channel found between both the upper and lower surface. The substrate further comprises a wall bordering a port suited for receiving a fluid, wherein the port and the channel are in fluid communication. The port is further defined by being open at the upper surface of the substrate and at the lower surface of the substrate. The port also has a cross-section capable of inducing sufficient capillary force in the fluid to restrain the fluid within the port; and a mechanism to transport the fluid to the port from outside the substrate, the transport mechanism comprises a pin which extends downward toward the port to transfer fluid on the pin to the port. Fluid introduction is facilitated through the use of a port which extends entirely through a microfluidic substrate. Capillary forces can be used to retain the fluid within the port, and a series of samples or other fluids may be introduced through a single port by sequentially blowing the fluid out through the substrate and replacing the removed fluid with an alternate fluid, or by displacing the fluid in part with additional fluid. In another aspect, microfluidic substrates have channels which varying in cross-sectional dimension so that capillary action spreads a fluid only within a limited portion of the channel network. In yet another aspect, the introduction ports may include a multiplicity of very small channels leading from the port to a fluid channel, so as to filter out particles or other contaminants which might otherwise block the channel at the junction between the channel and the introduction port. An example of an embodiment is provided below.
However, nothing in both the documents disclose the features of the microfluidic switch as disclosed in claim 1 of the present invention. A skilled person reading the two documents would not be led to the present invention at all. Therefore, the microfluidic switch appears to be patentable.
Further, since the claims are directed to the microfluid switch itself, a device comprising the switch and the method of using the switch, the scope of protection is quite large. With regard to infringement, the patent prevents any company from making, disposing of, offering to dispose of, using or importing the product (i.e. microfluidic switch) or keeping it whether for disposal or otherwise. The patent also prevents the end user from using the product provided the microfluidic switch has exactly the same features as that disclosed in the granted claims.
Having said the above, although the microfluidic switch may be granted a patent, the use of it may be complicated as the design of the switch will have to vary depending on the liquid that travels around the channels. This is because, if the liquid is too viscous, the second channel will have to be shorter and with less contours so that the time interval (i.e. reaction time between reagent and sample liquid) will not have to be too long. However, if the liquid is thin and of low viscosity, the second channel will have to be longer and have more contours so that the liquid will have to travel a longer distance in the second channel allowing the reaction time between reagent and sample liquid to be longer. Therefore, it is very difficult and time consuming to determine the actual design of the microfluidic switch.
Also, since there are so many different variants to consider in coming up with a single design for the microfluidic switch, many tests have to be carried out to determine the actual design of the microfluidic switch that will give the desired results (i.e. the desired time interval). This will result in a waste of resources and will be time consuming.
Further, since most of the movement of the liquids is against gravity, there may be a high chance that blockages will occur along the path of the liquids in either one of the channels which may result in the flow being interrupted. This may result in several complications including contamination and wastage of sample.
Having said the above, the microfluidic switch, does make it possible to stop liquid flow at the end of the first channel for a predetermined time interval without the need for electrically triggerable microvalves to restart the liquid flow as what is available in the prior art. This saves cost and keeps the design simple.
It can also be useful in wet chemical, biochemical and diagnostic analyses where it is usually necessary for the sample liquid to be mixed with reagents for a short period before it is transferred to another chamber to be mixed with another liquid. For example, the microfluidic switch may be used in a device with a series of reaction chambers where, in a first reaction chamber, the sample liquid is mixed with reagent A and left for a time period for the reaction to take place because of the presence of the microfluidic switch in the first channel of the first chamber. When the liquid from the second channel fills up to the part where both the paths of the first and second channels meet, the reaction mixture from the first reaction chamber, may be transferred to a second reaction chamber where the reaction mixture comes in contact with a reagent B. Again, both solutions are left to react during a defined time interval, until the second channel connected to the second reaction chamber fills up. This process may be repeated as many times as necessary depending on the number of reagents in the protocol that is being carried out. As mentioned above, this allows the final product from the various steps to be free of contamination from the environment as the various steps are carried out within a controlled and enclosed environment and there is no exposure to the environment.
The final product may then be removed from the reaction chamber in order to be analyzed. The stopping means for well known microfluidic arrangements are usually made as mechanical valves, which are initiated and controlled from the outside. These valves are used to separate individual reaction chambers and analysis chambers one from the other by using fluids. External time control, for example via a computer, the corresponding incubation times, i.e. the time intervals of the residence of the sample or products in the reaction chambers and/or analysis chambers, can be adjusted. These microfluidic switches with microvalves have the property that they have mechanically moving parts, which for example are accordingly electrically triggered. This leads to high hardware complexity. In addition, integration of these microvalves into the microfluidic switches is complex, especially when the microfluidic switch is made of plastic. This allows the microfluidic to be more useful than the current available methods.
To summarise, although the microfluidic switch of the present invention may be considered patentable for it is considered novel and inventive, it appears that the cons in its use outweighs the pros and as such it may not be considered as an efficient means of regulating the flow of liquid in a microfluidic channel and creating a time interval for a reaction to take place. In particular, due to the presence of many variants (i.e. the viscosity of the liquid to be used, the length of the second channel, the contours of the second channel, and the size of the reaction chamber) that affect the functionality and efficiency of the microfluidic switch, it causes the switch to complicate the process instead of simplifying it. Further, in order to get the appropriate time interval, all these factors have to be considered and many tests have to be carried out varying these factors before the perfect combination can be determined. Therefore, it appears that the use of the microfluidic switch in stopping the liquid flow at the end of the first channel for a predetermined time interval without the need for electrically triggerable microvalves to restart the liquid flow may not be the best way of regulating the flow of the liquid.