Why Glass Microfluidic chips are popular in Life Science applications

Microfluidic products used in life sciences and health applications can be made from a range of materials. Yet these products are remarkably often glass based. Why is that? What are the specific properties of glass that cause the popularity of this material for microfluidic chips? This blog will give insight into the benefits of glass as a base material for microfluidic chips. We take a closer look at a range of typical life science applications that use glass microfluidic products and compare the properties of glass to those of other materials.

 

General Benefits of Glass in Microfluidics

Glass is widely used in the life science industry. Especially in applications for multi-omics and drug delivery. The popularity glass as a base material for microfluidic chips comes from its following characteristics:

• excellent optical transparency
• extreme flatness of the material
• high thermal shock resistance / thermal stability
• high mechanical stability
• chemically inert, it will not affect active ingredients or leach
• non-permeable, content is protected from external influences
• very precise and smooth micro and nano structuring
• high seal resistance
• low autofluorescence

These properties ensure state-of-the-art, robust, and stable microfluidic products. The most used glass processing steps are wet etching, dry etching, powder blasting, and laser processing.

 

The use of Glass Microfluidics in Life Sciences applications

Let us look at some of the most common microfluidic applications within the life sciences and medical field.

 

Multiomics

In multi omicsapplications like DNA sequencing, fluorescent markers play an essential role. Glass is used in this process for its superior optical properties. Glass is the prime material for transmittance of light. Thin glass layers support the short focus length of the lenses that are typically used for large magnifications. Low background fluorescence greatly benefits the visibility of the emission of fluorescent markers. There is a large amount of biochemical functionalization protocols available for glass.

Glass flow cells have contributed enormously to the growth of Next Gen Sequencing and the success of players in this field. These flow cells are used in FDA certified NGS diagnostics solutions. In DNA synthesis, typically very aggressive chemicals are used. This is challenging for most alternative materials, but makes glass microfluidics a perfect fit.

 

Cell Analysis & Therapy

For cell analysis there is a range of microfluidic cell sorting techniques that can separate cells based on, for example, shape, size, or electrical charge. Think of pinched flow fractionation, dielectrophoresis, and acoustophoresis. Often the feature sizes and required tolerances are reasons to choose glass for these applications. Another advantage is that glass survives heavy chemical cleaning, which offers re-use potential that helps to lower the costs per use.

 

Drug Delivery

Microfluidic devices for drug delivery ensure that drugs are delivered at the right place in the body and at desired volumes and times. Think of flow distributors, spray nozzles or microneedles. Glass or a glass-silicon combination is usually chosen for its inertness, non-leaching qualities, and geometric stability.

 

Other Materials for Microfluidic chips

What about other materials used in microfluidic device fabrication? The mother material for MEMS applications is of course silicon. Also, polymers such a Cyclic olefin copolymers (COC) often serve as substrates for microfluidic chips. Silicon-glass or glass-polymer hybrid combinations are also frequently used. Nevertheless, glass-based microfluidic devices remain a stable factor in life sciences. A short comparison shows why:

 

Pros of Glass in comparison to Silicon

Glass has optical transparency, whilst silicon is only transparent to infrared. Moreover, silicon is a more expensive base material compared to glass. Due to the crystal orientation, it is mostly processed using more expensive dry etching techniques.

 

Pros of Glass in comparison to Polymer

Glass is a more worry-free material compared to polymer for its chemical compatibility. Also, it can withstand aggressive cleaning, which allows multiple-use scenarios, where polymer is typically a one-use material. Disposables are not always the most ecological or economic option. The stability of glass is much higher than that of polymers. Furthermore, glass can tolerate higher temperatures and pressure and has resistance to organic solvents.

 

Technical specs of Glass

• General data on the most used types of glass: borosilicate glass and fused silica.
• Thickness: 0.1mm-2mm (per layer)
• Thermal resistance: up to 450 °C
• Chemical inertness: high resistance to water, acids, alkalis, and organic substances
• Surface roughness: optical quality (≤ 1nm RMS)
• Autofluorescence: very low
• Refractive index: n = 1.5-1.9