Contents
rGO Binding
From a review of current literature, we found that the most promising avenue for binding graphene to our silk fibres involved using suspensions of graphene oxide (GO) particles, before reducing them in situ after binding to produce reduced graphene oxide (rGO) [1]. When consulting Dr Ana Neves, a senior lecturer and associate research fellow with the Nano-Engineering, Science and Technology Group at the University of Exeter, we were informed that directly binding rGO particles is a more efficient method for fibre coating with a conductive layer of graphene.
Thus, we adapted the GO binding protocol in [1]. Preliminary investigations involved cleaning native spider silk samples via heating in a water bath, after vortexing with dish soap. rGO-coated fibres and films were prepared from the silk samples via submersion in a diluted rGO suspension and ultrasonication. Multimeter testing indicated rGO coating increased electrical conductivity of the fibre and film by factors of 5.14 and 5.43 respectively over the baseline conductivity of dragline silk - 4.4 x 10-6 Sm-1 [2].
Figure 1 - Natural spider silk following cleaning with hot water bath and dish soap. The sample is still contaiminated with colourful fibres
Examination under an optical microscope (10-400x magnification) showed spider silk samples were heavily contaminated with dust and other debris (as shown in Figure 1), limiting the validity of conclusions drawn from these investigations. To reduce contamination from dust and debris we switched to using silk samples from commercially bought silkworm cocoons. Cocoons were cut into millimetre long strips, boiled in sodium carbonate solution to remove glue-like sericin proteins and again sonicated with diluted suspensions of rGO, producing samples such as that shown in Figure 2.
Figure 2 - A fibroin fibre sample ultrasonicated with an RGO suspension
Investigations showed that whilst ultrasonication caused reaggregation of silk fibres, reducing efficiency of film formation, it did increase the efficiency of the rGO coating procedure and consequently increased conductivity. This procedure yielded a film with a conductivity of 3.7 x 10-5 Sm-1, compared with around 3.5 x 10-5 Sm-1 for a film with ionic impurities resulting from exposure to calcium chloride and glycerol [3]. rGO coating was further augmented by submerging the rGO-coated film again in undiluted rGO suspension, yielding samples such as that shown in Figure 3. This yielded a sample with a conductivity of 1.7 x 10-3 Sm-1, a factor of around 50 times greater than for the uncoated fibroin film.
Figure 3 - A twice-coated fibroin fibre sample which has been submerged in undiluted RGO suspension
Thus preliminary investigations established that coating silk with rGO rather than GO followed by an in situ reduction step, is favourable for coating our final recombinant spidroin-derived protein fibres. Moreover, the most efficient rGO coating is achieved when protein fibres are ultrasonicated with rGO suspension, dried to create a film and then submerged in undiluted rGO, as shown by conductivity results displayed in Figure 4.
Figure 4 - Graph showing the conductivity of different RGO-bound silk sample types
Accessible Micropipette
As part of our work for the Inclusivity Award, we used 3D CAD modelling to design a modified micropipette grip to make it more accessible to people with poor motor coordination, weak grip strength, or hand tremors. This micropipette grip is designed to fit securely around the base of the pipette body, and allows for the attachment of a velcro or elastic strap at both the top and bottom of the pipette, without interfering with the function of the pipette. The attachment point has also been reinforced to ensure that it will not wear out over time. Due to the position in which the pipette grip has to be attached, the body of the brace attachment has been made longer, so that a window can be added over the volume display, allowing for the pipette grip to be used with micropipettes that have both fixed and adjustable volume.
Figure 5 - Main Body Pipette Brace
To test the micropipette brace, a series of technical assessments were conducted using a P100 Satorius BioHit micropipette to transfer variable quanities of water. The results of our technical assessment showed improvements in precision and accuracy when participants used the brace compared to without, as participants more consistently transferred the correct volume of liquid when using the brace. Participants were also able to hold the micropipette in the manner recommended by manufacturers and experienced fewer tremors when using the pipette. When participants were asked to provide feedback, participant's stated that they felt more confident when using the pipette, and that they found the brace more comfortable to use compared to the unmodified pipette. However, participants also stated that the thickness of the brace occasionally made it more difficult to press the button to change the volume of the pipette, however the participants also quickly found that the brace itself could be used to gain more leverage against the button by lifting the brace up over the button and using it to depress it. Future iterations of this hardware would likely include a built-in lever that would make it easier to depress the button.
Originally, our micropipette brace was designed specifically for the Satorius BioHit pipette, which has a unique slit along the finger rest that was intended to be used with the BioHit pipette rack. However, when designing our pipette brace, we used this slit to our advantage, as its location and size meant that it could function as the perfect secondary attachment point for our strap, allowing the brace to fit securely along the hand, without interferring with the pipette. This design was incredibily successful, as shown by the data on our Inclusivity page. However, our current design was only compatible with a specific brand of pipettes, requiring laboratories to either already own them or purchase them, suddenly making our inexpensive hardware incredibly costly.
Figure 6 - Comparison of original brace designed for a BioHit pipette and the original brace with the secondary attachment, designed for wider variety of pipettes.
Ensuring that the body of the current pipette brace would be compatible with a wide range of micropipettes was fairly simple, as we chose a highly flexible material, TPU filament, for the brace, which allowed it to fit on a variety of pipette bodies, regardless of their size. As we were initially using the Satorius BioHit pipette, we printed the main body brace at a scale up of about 165.42% of the overall model from its original size as found in the STL file. Depending on the pipette brand, the brace did have to be scaled up slightly for a better fit, however the fundamental design did not need to be altered. While this solved the first hurdle of universal design, we still had to design a secondary attachment point to make the brace compatible for a wide range of pipettes. The body of the pipette brace could not simply be extended with an identical attachment point near the top, as doing so would prevent access to the micropipette plunger.
To address this issue, we designed a second component that could be used in conjunction with the brace to create a second attachment point. This component had to be sleek and non-obstructive during usage, to ensure it did not interfere with the finger rest or the plunger, however it still had to allow for a hand to be afixed to the pipette in the correct position. As a result, we decided that the attachment point should be fitted so that it faced backward, which could then be used with a longer velcro strap that split part way along so that the brace could be securely attached, without obstructing the micropipette.
Figure 7 - Accessory Top Body Pipette Brace
The accessory top brace was printed in slightly varying sizes and have been tested on a range of pipette brands that are available in our teaching labs.
In the printing process of the top brace, we didn't have immediate access to different pipette brands and only knew that the top of micropipettes are generally slightly larger than their main bodies. As a result, we printed several top braces at varying sizes, having upscaled the size by 2mm, 4mm, 6mm, and 8mm on the X-axis and Y-axis. The size-up measurements from the original size, as found in the STL files were as follow:
- - Increase of 2 mm in both directions: Inside measurements are 34.81 mm and 31.56 mm. A 175.54% scale up of the overall model.
- - Increase of 4 mm in both directions: Inside measurements are now 36.81 mm and 33.56 mm. A 189.94% scale up of the overall model.
- - Increase of 6 mm in both directions: Inside measurements are now 38.81 mm and 35.56 mm. A 195.75% scale up of the overall model.
- - Increase of 8 mm in both directions. Inside measurements are now 40.81 mm and 35.56 mm. A 205.80% scale up of the overall model.
The results were as follows: from the pipettes available in our laboratories, the top brace without any additional size increase fitted the BioHit Proline (WOLF) pipette; the brace with a 2mm size increase fitted the Axygen and Gilson pipettes, a 4mm size increase fitted the Labmate and Satoris Transfer pipettes; and a 6mm increase fitted the Alpha Laboratories pipettes. No pipettes were large enough to fit the pipette brace with an 8mm increase.
Figure 8 - Top Pipette Braces Tested on Different Brands
References
- [1] Liang B et al. Fabrication and application of flexible silk-rGO composite film electrodes decorated with spiky Pt nanospheres. Nanoscale. 2014;6: 4264-4274. doi: 10.1039/C3NR06057H
- [2] Steven E et al. Physical characterization of functionalized spider silk: electronic and sensing properties. Sci Technol Adv Mater. 2011;12(5): 055002. doi: 10.1088/1468-6996/12/5/055002
- [3] Yadav R et al. Tailoring of electrical and optical properties of regenerated silk fibroin films with metal oxides. Journal of Materials Science: Materials in Electronics. 2020;31: 17784-17797. doi: 10.1007/s10854-020-04332-4