Soft tissue augmentation is one of the most common aesthetic medical procedures performed worldwide. It is a highly sought-after and popular medical aesthetic procedure. Fortune magazine predicts its market worth will be around 4000 million US dollars by 2026.

For such a widely prevalent procedure, it is essential to understand the different ways in which this can be done. There are different materials used for soft tissue augmentation, based on their chemical properties as well as their longevity in the human body. This can be broadly classified into two major ways:
• Permanent vs Temporary fillers
• Type of chemical composition of product

Hydrophilic Polyacrylamide Gel (HPG)

Hydrophilic Polyacrylamide Gel (HPG): This is a kind of ‘permanent’ filler. It is composed of 2.5-5% polyacrylamide (a synthetic polymer), suspended in 95-97.5% of water. Polyacrylamides are non-absorbable, synthetic compounds that are used to perform protein separation in molecular biology. They have been available for more than three decades and used in biomedical industry. They remain important constituents of manufacturing soft contact lenses and cosmetics such as sunscreens. Because they are non-biodegradable and non-absorbable, they cannot be metabolized by human enzymes and so, they remain in human tissues ‘permanently’.

They cannot be removed using non-invasive means from the body and require invasive, and often, surgical interventions for removal.

Manufacturers have claimed HPG to be a safe product that can be used as filler material. Polyacrylamide is processed to remove all toxic components and injectable material is then deemed safe for human use. However, a close review of medical literature shows a significant number of cases with the following complications:
• Filler displacement
• Granuloma formation (seen as swelling or induration)
• Deformed facial contours over the years, requiring surgery
• Persistent draining nodules
• Infection with bacteria, including biofilm formation
• Filler leaking from site due to rupture of fibrous capsules that are normally formed around the filler

Due to the various complications and difficulty in dealing with removal, these filler materials have lost a lot of popularity among physicians and injectors worldwide.

Hyaluronic Acid Gel (HA Gel)

Hyaluronic Acid Gel: This is the most common substance used currently for soft tissue augmentation. Hyaluronic acid is a glycosaminoglycan, which is a naturally-occurring component of human extracellular matrix. Extracellular matrix is a network of compounds which helps support cellular structures within the human body. The synthetic form of HA has close resemblance to human tissue. It is identical in all species, and has limited immunogenic potential. This makes allergic reactions to HA a very rare occurrence.

HA can not only volumize tissues but also provide hydration and hence used more commonly due to this anti-aging effect. It is biodegradable and can be completely hydrolyzed by human enzymes within 6-8 months.

It’s rheologic (flow-related) properties ensure the gel interacts adequately and integrates well with human tissues. This is achieved by having good viscoelastic properties.

HA gel related complications are much less common, given the safety of the product used. Most complications are technical in nature due to injector variables (different techniques among injectors and doctors) or inflammatory (due to injection process itself, size of needles and cannula used). The rare dangerous complication is vascular occlusion, which can be reversed if dealt with, in time. The rate of granuloma formation or infections is estimated to be between 0.01-0.1%.

Conclusion

While both substances can be used for the same purpose (i.e., soft tissue augmentation), there are marked differences in their composition as well as their tissue interaction. These must be kept in mind when dealing with patients and for educating patients and clients about these substances.