“Using a micro-pipette, add trypsin into the cell culture flask and wait for five minutes. Check that the cells are detached before transferring the cell suspension into a Falcon tube. Next, centrifuge the Falcon tube for five minutes. Finally, count the cell density using a hemocytometer and transfer desired numbers of cells back into the culture flask.”
Does this protocol for cell culture look familiar? What about the lab supplies listed in the protocol? Lab supplies such as micro-pipettes and cell culture flasks are so common that no researcher pays much attention to them anymore. However, unknown to many, the designs of common lab supplies have evolved tremendously to suit modern scientific endeavors. Their sophisticated and standardized designs have enabled protocols to be rigorously established—a major factor driving scientific progress. This article outlines the chronological evolution of popular lab consumables and equipment, and discusses future developments in their designs.
A centrifuge is a piece of equipment that makes use of centrifugal forces to separate substances based on their densities. This rotation-based mechanism causes denser substances to be collected at the bottom while less dense substances rise to the top.
As early as 1864, driven by the commercial need of the dairy industry to quickly separate cream from denser milk, the German brewer Antonin Prandtl invented the first dairy centrifuge. However, its rotational speed was inadequate for biomedical research as biomolecules are much smaller and lighter, and different species of biomolecules required faster speed to be separated from one another. The breakthrough came in 1926 when Nobel Laureate Theodor Svedberg invented an ultra-centrifuge capable of reaching a speed as high as 900,000 g. This speed was three to four times faster than most centrifuges at that time, providing sufficient forces to separate small biomolecules such as proteins, which facilitated the study of complex protein structures.
The next few decades witnessed huge progress in the development of centrifuges for isolating sub-cellular organelles like mitochondria and even enriched uranium for the atomic bomb project. Nevertheless, these centrifuges remained bulky, expensive, and were not widely available. It was not until 1962 that Eppendorf commercialized the first micro-centrifuge for benchtop use. Since then, materials like lightweight titanium have replaced bulky steel to provide even stronger centrifugal forces. Modern-day centrifuges also offer sophisticated features such as temperature control, user-programmed acceleration/deceleration rates, automatic imbalance detection, and noise reduction.
A micro-pipette is a spring-loaded piston fitted with a disposable plastic tip for transferring precise volumes of liquid. Through an air buffer, the piston is separated from the liquid, which minimizes biological contamination. The modern-day micro-pipette is also fitted with a second spring that can be activated by applying stronger pressure to dislodge the pipette tip automatically.
The first glass pipette was invented by the French scientist Louis Pasteur (do you recall Pasteur pipettes that you used in chemistry labs?), to prevent cross-contamination of samples. Following rapid developments in plastic technology, plastic pipettes were eventually developed in the 1940s.
In 1957, Heinrich Schnitger, then a postdoc in the University of Marburg, Germany, was frustrated with having to continually make and calibrate new glass pipettes to suck precise volumes of analytes for his experiments. He channeled his frustration into positive output by developing the first prototype of the modern-day micro-pipette with spring-loaded piston and refillable liquid plastic tips that he also patented in the same year. Although Schnitger’s design made pipetting easier and safer, it did not offer researchers the flexibility of adjustable volume. After consulting multiple users, Warren Gilson and Henry Lardy, who were then that the University of Wisconsin-Madison, incorporated the feature of flexible volumes into the micro-pipette.
Since then, multiple features such as rubber grip and lock have been introduced to improve the ergonomics and precision of micro-pipettes. A variety of new products such as the multi-channel micro-pipette for handling large sample numbers has also entered the market. Companies have even color-coded micro-pipettes with their corresponding pipette tips to make changing pipette tips more convenient and intuitive for users.
Cell culture flasks
Cell culture flasks come in different sizes ranging from surface areas of 25 cm2 to 225 cm2. Therefore, they are commonly referred to as Tx flasks with x corresponding to their respective surface area. Cell culture flasks can be used to grow a variety of cells including immortalized cell lines and even primary cells from patients.
Traditionally, cells were being cultured in glass flasks. However, most cells have difficulty attaching to glass surfaces and consequently, glass flasks have to be specially treated with expensive proteins such as collagen to induce cell attachment. Even then, with batch-to-batch variability in protein quality, protein coating may not be uniform, causing uneven cell attachment. More importantly, the process of cleaning glass may also leave behind toxic detergent residues that can affect biological interpretations.
The development of disposable plastic cell culture flasks was catalyzed by a progress in plastic technology. By the 1960s, polystyrene, a type of plastic, was being tested to manufacture cell culture flasks. This plastic is transparent, easily moldable into different sizes and shapes, and can be sterilized by irradiation, making it an ideal material. Unfortunately, polystyrene is also a hydrophobic plastic, which means that it repels water and cells do not attach well to it.
It wasn’t before long scientists figured out a way to modify the hydrophobic surface of polystyrene to a hydrophilic (water-loving) one. Using high energy plasma that produces reactive oxygen ions, oxygen can be incorporated into polystyrene, making it hydrophilic and cell attachment-friendly.
Starting from the 1970s, disposable plastic cell culture flasks became a mainstay in labs. The modern-day flask is also fitted with a filtered cap at its opening to regulate the flow of gases and to prevent biological contaminants from entering the flask. Evolving with biomedical needs, cell culture flasks with different surfaces have also been commercialized. For instance, Corning introduced the Ultra-Wet® Synthetic Surfaces that resemble 3D fiber-like topography that cells would experience in vivo. This is useful for culturing stem cells that differentiate differently in a 2D versus 3D environment. With increasing popularity in organoid (3D tissue-like structures with different cell types originating from stem cells) research, Thermo Fisher Scientific also commercialized the Nunclon™ Sphera™ flasks that have ultra-low attachment to avoid uncontrolled stem cell attachment and spontaneous differentiation.
The word “hemocytometer” means blood cell counter and its invention was linked to the popularity of hematology in the mid-1700s and optical microscope in the 1850s. A standard hemocytometer comes with a counting chamber with four squares, each measuring 1 mm2, that is etched into the surface of glass. A specific volume of liquid, usually 10 μL, is added to the counting chamber and cell density can be determined with the following formula:
Cell density (per mL) = Total number of cells in the 4 squares *1000
The humble hemocytometer has experienced substantial design evolution. The initial idea was first conceived by Louis-Charles Malassez, who in 1874, used a capillary tube to transfer fixed volumes of cell suspension into a glass slide with grids. Nevertheless, it remained challenging to reproducibly count cells as sample uniformity was poor with this technique. Over the next 30 years, multiple innovative features were being incorporated into hemocytometers including counting chambers with fixed volumes so that cell concentration could be back calculated. Finally, in 1913, Karl Bürker invented the closest version of the modern-day hemocytometer that exploited capillary action to draw fixed liquid volumes into counting chambers. His hemocytometer design also had two sides that facilitated duplicate counting, which subsequent designs followed.
Factors such as user preferences, experimental needs, and plastic technology have dramatically influenced the designs of many lab consumables and equipment, but this evolution is nowhere near completion. Automation, including the introduction of robots in labs, has dramatically impacted the designs of lab equipment. Labs, especially those working in high throughput screening, are increasingly relying on robots to perform pipetting. Robotically-controlled pipetting (also known as liquid handling robots) can significantly reduce human labor, translating to cost savings. Automated cell counters, which perform counting much faster than a human, are also replacing traditional hemocytometers. Automated systems supported by rigorous check and control algorithms are expected to become widely used. Researchers can also look forward to future designs with wireless systems for remote control.
Lab supplies and equipment are also undergoing the miniaturization revolution to become more price-friendly for democratizing scientific research. One great example is the evolution of cheaper benchtop centrifuges from bulky, expensive floor model centrifuges. Some research groups have taken the idea of “miniaturization” and “cost-savings” even further by adapting unconventional materials as lab supplies. For instance, the Whitesides group at Harvard University has created handheld centrifuges modified from an egg-beater to separate blood cells. The same group has even creatively used bubble wraps to store and transport liquid samples for analytical assays. Similarly, the Prakash Lab at Stanford University pioneered a low-cost paper-based microscope with up to 140x magnification and 2 μm resolution.
University College London, the largest university in the United Kingdom, recently announced that it plans to phase out single-use plastics including lab consumables like pipette tips and cell culture flasks within the next five years. One way to achieve this ambitious goal is to look into alternative materials. It may not be surprising that reusable materials and equipment with low carbon footprints like handheld centrifuges may be used even in well-funded and established labs. Interestingly, similar to the fashion industry, the design of lab supplies may be going “retro” with greater environmental objections regarding single-use plastic. Glass, an old friend of biological experiments, may regain its long-lost popularity.
The design of lab supplies and equipment is continually undergoing creative reinventions. Beyond considering users’ preferences, manufacturers should anticipate factors such as environmental considerations and institutional research policies that could influence how they design and manufacture lab supplies. It will be an exciting time ahead.