More than nine months after its outbreak, the Covid-19 pandemic’s infection curve in Indonesia is still on the rise. The virus is so contagious that personal protective equipment is imperative for survival. Therefore, during this so-called new normal, masks are a must-wear item for everyone. However, the huge demand for medical masks worldwide has threatened supply.
Besides, waste from medical masks is cause for environmental concern. Consequently, the search for sustainable and environmentally friendly raw materials to produce masks is intensifying. We all know that bacterial cellulose (BC) has been around for ages. In Indonesia and other Asian countries, BC is known as “nata de coco”. However, with the unique properties of BC, including its high purity, high crystallinity, light weight, network morphology, fiber strength, excellent biocompatibility, high polymerisation and good moldability, BC applications could go far beyond food.
BC has already gained attention as a natural biofabric in a nonwoven and tailor-shaped form for the biocouture industry. Due to its physicochemical and biological characteristics, its application has been noticed for medical garments. However, can BC compete with or replace other approved materials?
BC is produced extracellularly by Komagataiebacter xylinum through fermentation. Since the BC producing-bacteria can only unite fibrils on a nanoscale (diameter of 10 nm and length of 0.5 µm), all BC is nanocellulose.
In terms of chemical composition, BC has the same molecular formula as cellulose from plants (C5H10O)n. However, they are very different in terms of physical and chemical characteristics. Five parameters are generally used to measure whether material meets the requirements of medical masks or not. The parameters are bacterial infiltration efficiency, differential pressure, sub-micron particulate filtration efficiency at 0.1 microns, splash resistance, flame spread and microbial cleanliness.
Bacterial filtration efficiency (BFE) represents the percentage of aerosol particulates, which in this case is Staphylococcus aureus, filtered at 3 µm with a flow rate of 28.3 litre/minute. Staphylococcus aureus bacteria is chosen according to clinical purposes, as it is the leading cause of nosocomial infections, or infections which originate in a hospital or healthcare centre.
Splash resistance measures the resistance of the mask to penetration by synthetic blood under pressure. This test shows the ability of the material to reduce fluid passing through the material and reaching the skin of the wearer. The material is tested with three different velocities: 450, 550 and 635 centimetre/second, equivalent to the range of human blood pressure of 80, 120 and 160 mmHg, respectively.
Submicron particulates filtration efficiency complies with ASTM F2299-03, which used aerosolised particles of latex with a size of 0.1 µm at the flow rate of 28.3 litres/minute. The test shows the efficiency of the mask in filtering particulates going through it. The mask acts as a filter that provides resistance when fluid passes through it, resulting in a total difference pressure between the input and the output of the mask, and this is called pressure drop.
An excellent medical mask needs to minimise its pressure drop (ΔP), as it can reduce the consumption of energy to have better efficiency. This parametre affects the ventilation rate related to the breathability and comfortability of the wearer. The ΔP (differential pressure) indicates the comfort and breathability of a medical mask by measuring the differential air pressure on either side at a flow rate of 8 litres/minute. The higher the Delta P, the more difficult the mask is to breathe through.
Flame spread is a rating of flammability to measure the material’s tendency to burn and spread the fire. The testing method uses the 16 CFR 1610 “Standard for the Flammability of Clothing Textiles”. ASTM F2100 requires all medical masks to be in flammability class 1.
Meanwhile, the microbial cleanliness test calculates the total amount of viable microorganisms on the surface of the mask (cfu/g, colony-forming unit/gram). To understand the requirements thoroughly, let us take a look at the commercial medical mask as a reference.
A medical mask with a thickness of 0.4417 mm, a weight of 95,775 g/m3 and pore size of 16.90 µm is capable of achieving 100 per cent efficiency of synthetic blood resistance at all three pressure levels (80, 120 and 160 mmHg) and the highest BFE 92.19 per cent.
The differential pressure of the medical mask is around 1.7 mmH2O/cm2. BC has high porosity 92 – 99 per cent and a small pore size (5 – 400 µm), with a wet and dry thickness of 11.60mm and 0.1mm, respectively. Therefore, analogously, in terms of BFE, splash resistance and sub-micron particulate filtration efficiency with the properties that BC possesses, we can presume that BC can also be used for medical masks.
Although no current research looks into BC’s utilisation as a fabric for medical masks, judging from its characteristics and compared it with commercial medical masks, BC has a chance to achieve comparable results. However, further research needs to be done to reach all the requirements. In non-medical applications, the leather-like BC performed well compared to cloth masks from natural and synthetic fiber, though some significant issues still need to be addressed, including mechanical durability and comfortability.
Economically speaking, the utilisation of BC remains questionable. However, research has been conducted to bring down the cost of production in terms of strain, medium and fermentation process for BC make it commercially viable. BC provides hope for a green and sustainable biofabric.
Dian Burhani is a researcher at Research Centre for Biomaterial, Indonesian Institute of Sciences(LIPI)
THE JAKARTA POST/ASIA NEWS NETWORK