Humans are incredibly intricate and complex organisms. As you zoom into the individual components that make us human, things seem to get even more complex.
Human tissue is quite literally what holds us together. It is the substance that makes up every component of our bodies. It is what gives us shape and structure internally and externally. It comprises our skin, bones, muscles, organs, nerves…you get the idea.
There are four basic types of human tissue, but within each type, there is a vast array of variability and individuality. For this reason, human tissue was not possible to emulate accurately until relatively recent technological and engineering advances occurred. Today, it is not only possible but necessary.
The Building Blocks
Replicating human tissue is vital to medical and scientific research and development, as well as demonstration and training. Without these important fields, we can’t move forward with certainty and confidence.
There are essentially two categories of tissue replication: biologic and non-biologic. Biologic tissue replication means that live cells are used. A popular example of this was discussed in a previous Ask Allison article: 3D tissue printing.
3D printing of cells is typically used for regenerative medicine, drug discovery and development, and 3D cell culture. This is a fascinating and truly powerful advancement in medical technology, but it comes with its downfalls. Due to the high cost and fragility of the structures produced with 3D tissue printing, it is not an ideal option for medical demonstration and training.
That brings us to the second category: non-biologic. Non-biologic tissue replication is also commonly referred to as synthetic tissue replication. As the name implies, no live cells are used in this category.
The Options
Within the non-biologic category, we can break things down further into the two most common types of synthetic tissue: hydrogels and rubbers.
Without getting more in-depth than you probably care to know, hydrogels are essentially a polymer that doesn’t dissolve in water. Their chemical makeup allows them to be three-dimensional, absorbent, and demonstrate a defined structure (much like native human tissue). This makes them an excellent tool for biomedical purposes, including research and development, but also demonstration and training where a high degree of multi-layer tissue precision is necessary.
Rubbers, on the other hand, are generally more broadly understood because we see and use many types of rubberized substances and objects every day. As you can imagine, based on how widely rubbers are used in so many industries, they provide an easily customizable and moldable medium.
Hydrogels and rubbers each play an important, yet unique, role in the synthetic replication of human tissue. For instance, rubber is ideal for replicating tissues that require specificity in these traits:
- Hardness
- Elasticity
- Puncture strength
- Tear resistance
- Mechanical cutting behavior of native human tissue
- Ultrasound and x-ray contrast
Meanwhile, hydrogels are best used for tissues where these properties require a higher degree of specificity:
- Permittivity
- Conductivity
- Energy-based cutting behavior of native human tissue
- Coefficient of friction
- Adhesion between tissue layers
How Are Synthetic Tissues Used?
Due to the complexity of the chemical composition of hydrogels, a polymer scientist is typically involved in the production process. The expertise of polymer scientists allows for a quantitative and scientific level of precision that is not as prevalent during the production of rubbers.
Because of this level of scientific analysis, hydrogel tissue replication is generally more expensive but also provides an enhanced experience in the following areas:
- Casts of major organs, cancer tissue, plaque formation, and lesions for surgical training
- Skin substitutes for testing suturing and pull-out forces
- Multi-layer models for surgical dissection
- Tissue for lasers and electrocautery
Rubbers also provide excellent customization opportunities and typically rely on more qualitative information. If a customer wants a rubber-based synthetic tissue to look or feel a certain way, the recipe can be infinitely adjusted based on the descriptions provided. Since rubbers do not require the highly quantitative expertise of a polymer scientist, they are generally less expensive while providing the best option for tissues in these areas:
- Amniotic tissue replicas
- Bone fragment replicas
- Skin tissue that is compatible with bandage adhesive
Just because hydrogels and rubbers provide different advantages doesn’t mean they need to be thought about independently of one another. Rubbers and hydrogels can, and often are, used in conjunction to provide an optimal experience. For instance, an entire model can be created using the more cost-effective customized rubbers, but one specific structure within that model can be created using hydrogels. This combination of synthetic materials reveals an endless stream of possibilities.
The Benefits of Synthetic Tissue
Many people falsely assume that biologic tissue provides a more “realistic” experience than non-biologic tissue. Due to the downfalls of biologic tissue replication discussed earlier, this is often not the case.
Synthetic tissue replication offers a level of precision and customizability that biologic tissue cannot. Both rubbers and hydrogels can be adjusted to match the targeted tissue properties desired by a customer. This creates infinite opportunities for medical demonstration, training, research, and development.
The primary benefits of utilizing hydrogel and rubber models include:
- Reliability and repeatability of the tissue. Precisely the same formulation can be used as many times as necessary to eliminate the variability and lack of precision we find from animal tissue.
- Cost-effectiveness. Synthetic tissues are reusable, practical, portable, and expedient compared with animal tissue and biological tissue replication.
- Cruelty-free. No animals are harmed in the making of synthetic tissues!
- Increased shelf-life and durability. Models made with synthetic tissue are always on-hand the moment they’re needed and can be reused over and over again.
- Convenience. All the reasons above boil down to convenience. This convenience encompasses medical salespeople and trainers being able to easily transport and demonstrate with the models, clinicians who utilize the models, the organizations that keep them on hand, and the long-term financial advantages to all entities involved throughout the process.
Wrap-Up
The beauty and fascinating nature of non-biologic tissue replication come with the convenience and customizability it provides. It’s amazing to think that this advancement that was unimaginable in the not-too-distant past is happening today. Not only can human tissue be replicated, it can be replicated with a level of precision that most didn’t even know was possible.