Not quite a solid, not quite a liquid: Meet hydrogels

Recommendable!

3D-printed hydrogel structure using peptide inks could be gamechanger for regenerative medicine

Good news!

"... scientists have developed a revolutionary solution for constructing complex structures for housing cells using a soft, Jell-O-like material. By using a self-assembling peptide ink, researchers ... have figured out how to 3D-print well-defined structures, which could be used to grow muscles and — perhaps one day — entire organs fit for transplant. ...
These core peptides used as ink are designed to be hydrophobic (rejecting water) on one side and hydrophilic (attracting water) on the other, which allows them to stack onto one another like a ‘hydrophobic sandwich’ and form long fibers, which then form a hydrogel — a water-based material with a gelatinous texture that can be useful for a wide range of applications, ranging from tissue engineering and soft robotics to wastewater treatment. ..."

From the abstract:

"3D printing has become one of the primary fabrication strategies used in biomedical research. Recent efforts have focused on the 3D printing of hydrogels to create structures that better replicate the mechanical properties of biological tissues. These pose a unique challenge, as soft materials are difficult to pattern in three dimensions with high fidelity. Currently, a small number of biologically derived polymers that form hydrogels are frequently reused for 3D printing applications. Thus, there exists a need for novel hydrogels with desirable biological properties that can be used as 3D printable inks. In this work, the printability of multidomain peptides (MDPs), a class of self-assembling peptides that form a nanofibrous hydrogel at low concentrations, is established. MDPs with different charge functionalities are optimized as distinct inks and are used to create complex 3D structures, including multi-MDP prints. Additionally, printed MDP constructs are used to demonstrate charge-dependent differences in cellular behavior in vitro. This work presents the first time that self-assembling peptides have been used to print layered structures with overhangs and internal porosity. Overall, MDPs are a promising new class of 3D printable inks that are uniquely peptide-based and rely solely on supramolecular mechanisms for assembly."

3D-printed Jell-O-like structure using peptide inks could be gamechanger for regenerative medicine

3D Printing of Self-Assembling Nanofibrous Multidomain Peptide Hydrogels (no public access)

Sunlight-activated "loofah hydrogel" excels at off-grid water purification without fouling

Good news! Like desalination, better water filters are salvation too!

Can you believe it, it can filter microplastics! (Caution: Irony)

"... the hydrogel is hydrophilic (water-attracting) at cool temperatures, but becomes hydrophobic (water-repelling) when heated. Pollutants such as organic dyes (which were used in lab tests) do get pulled in along with the water at cool temperatures, but because their molecules stick to the gel, they don't get expelled when the water is released at warmer temps. Droplets of oil pollution don't get drawn in in the first place, as the (then) hydrophilic gel rejects them. ... loofah hydrogel can be reused simply by rinsing it with diluted acid or ethanol. ..."

From the abstract:

"Hydrogels are promising soft materials for energy and environmental applications, including sustainable and off-grid water purification and harvesting. A current impediment to technology translation is the low water production rate well below daily human demand. To overcome this challenge, we designed a rapid-response, antifouling, loofah-inspired solar absorber gel (LSAG) capable of producing potable water from various contaminated sources at a rate of ∼26 kg m–2 h–1, which is sufficient to meet daily water demand. The LSAG─produced at room temperature via aqueous processing using an ethylene glycol (EG)–water mixture─uniquely integrates the attributes of poly(N-isopropylacrylamide) (PNIPAm), polydopamine (PDA), and poly(sulfobetaine methacrylate) (PSBMA) to enable off-grid water purification with enhanced photothermal response and the capacity to prevent oil fouling and biofouling. The use of the EG–water mixture was critical to forming the loofah-like structure with enhanced water transport. Remarkably, under sunlight irradiations of 1 and 0.5 sun, the LSAG required only 10 and 20 min to release ∼70% of its stored liquid water, respectively. Equally important, we demonstrate the ability of LSAG to purify water from various harmful sources, including those containing small molecules, oils, metals, and microplastics."

Sunlight-activated "loofah hydrogel" excels at purifying water

Quick-Release Antifouling Hydrogels for Solar-Driven Water Purification

Figure 1. Fabrication and hierarchical porous structures of the hydrogel. (a) Schematic of the fabrication method for L-PNIPAm and LSAG. (b) Schematic of the thermally driven water release process for LSAG. (c) Photograph and microstructure of natural loofah sponge and LSAG.

How to make hydrogels more injectable to e.g. treat diseased tissues

Good news! Of course, this is based on computer modeling! In practice, this may not work.

"Gel-like materials that can be injected into the body hold great potential to heal injured tissues or manufacture entirely new tissues.  ...
researchers have created a set of computational models to predict the material’s structure, mechanical properties, and functional performance outcomes. The researchers hope that their new framework could make it easier to design materials that can be injected for different types of applications, which until now has been mainly a trial-and-error process. ...
When individual hydrogel blocks are densely compacted together, they form a gel-like material known as a granular matrix. These materials can act as a solid or a liquid, depending on the conditions, which makes them good candidates for applications such as 3D-bioprinting engineered tissues. Once injected or implanted into the body, they could release drugs or help to regenerate injured tissue. ...
[researchers] now plan to use this modeling approach to try to develop materials that could be used for medical applications such as repairing heart defects or delivering drugs to the gastrointestinal tract. ..."

From the highlights and abstract:

"Highlights

• Built flexible ML pipeline for robust model selection, validation, and explanation

• Applied modular ML approach to stepwise empirical material development workflow

• Optimized hydrogel bioblocks, granular matrices, complex rheology, and extrudability

• Produced data-driven models and extracted human-readable predictive design insights

Progress and potential

Granular hydrogel matrices are promising for biomedical applications ranging from extrusion-based bioprinting to injectable tissue engineering. However, they remain challenging to design, assemble, and optimize. Each development stage involves multidimensional input-output spaces affected by poorly understood multi-scale, multi-physics phenomena. Here, we demonstrate the utility of a flexible and modular machine learning (ML) approach to advance complex materials in a stepwise fashion. We apply our ML approach to automatically construct, validate, and explain predictive design frameworks for each set of empirical results. These data-driven models allow one to assess each experimental design space and provide condensed design insights extracted from high-dimensional input-output maps. The resulting bioblock materials have broad biomedical applications, yet our approach should be applicable for data-driven advancement of any complex material system.

Summary

Granular hydrogel matrices have emerged as promising candidates for cell encapsulation, bioprinting, and tissue engineering. However, it remains challenging to design and optimize these materials given their broad compositional and processing parameter space. Here, we combine experimentation and computation to create granular matrices composed of alginate-based bioblocks with controlled structure, rheological properties, and injectability profiles. A custom machine learning pipeline is applied after each phase of experimentation to automatically map the multidimensional input-output patterns into condensed data-driven models. These models are used to assess generalizable predictability and define high-level design rules to guide subsequent phases of development and characterization. Our integrated, modular approach opens new avenues to understanding and controlling the behavior of complex soft materials."

How to make hydrogels more injectable | MIT News | Massachusetts Institute of Technology A new computational framework could help researchers design granular hydrogels to repair or replace diseased tissues.

Integrated data-driven modeling and experimental optimization of granular hydrogel matrices (open access)

Graphical abstract

Hydrogel casing keeps vaccines stable without refrigeration up to 65°C

Good news! Besides vaccines it can also stabilize enzymes, diagnostics and other biologics.

"Most vaccines need to be refrigerated, which makes it difficult and expensive to get them to remote areas where they’re often needed most. Now, researchers at ETH Zurich have developed a new method for encapsulating vaccines in hydrogels so they can be transported and stored at much higher temperatures. ...
The key ingredient is a synthetic polymer called polyethylene glycol (PEG), and the resulting hydrogel encapsulates the vaccine’s proteins and keeps them separated. This allows the medicine to remain viable at room temperature and indeed, much higher – up to 65 °C (149 °F). ..."

Hydrogel casing keeps vaccines stable without refrigeration up to 150 °F

Thermal stabilization of diverse biologics using reversible hydrogels (open access)

Improved hydrogel could make artificial tendons

Recommendable! Amazing stuff! Looks like synthetic hydrogels are in the news these days. See also my recent blog about this subject here. And it appears that researchers are making good progress regarding hydrogels. 

"... Here we present a strategy to produce a multi-length-scale hierarchical hydrogel architecture using a freezing-assisted salting-out treatment. The produced poly(vinyl alcohol) hydrogels are highly anisotropic, comprising micrometre-scale honeycomb-like pore walls, which in turn comprise interconnected nanofibril meshes. ..."

Improved hydrogel could make artificial tendons – Physics World A strong, flexible and tough hydrogel that contains more than 70% water could be used to make durable artificial tendons and other load-bearing biological tissues.

Here is the underlying research article:

Strong tough hydrogels via the synergy of freeze-casting and salting out (no public access)

Lipid-containing hydrogels Inspired by Cartilage

Recommendable!

"What copes with heavy pressure and exists in a state of constant friction, decade after decade, yet barely gets worn down? The answer is the cartilage padding our joints – actually a marvelous system that both absorbs shocks and lubricates the joints, allowing bones to slide easily against one another. ...
A new gel with better lubricating properties could have applications in the near future in uses such as stent insertion and tissue engineering. It could also lead to the development of artificial joints that can better withstand wear and tear, so that replacement joints last longer and cause fewer problems than those inserted today.  ..."

"... By contrast, the lubricity of articular cartilage, a complex biohydrogel, has been at least partially attributed to nonfluid, lipid-exposing boundary layers. We emulated this behavior in synthetic hydrogels by incorporating trace lipid concentrations to create a molecularly thin, lipid-based boundary layer that renews continuously. We observed a 80% to 99.3% reduction in friction and wear relative to the lipid-free gel, over a wide range of conditions. ..."

Inspired by Cartilage The clever addition of lipids to water-based hydrogels makes them excellent lubricants for biomedical uses

Here is the link to the underlying research article:

Cartilage-inspired, lipid-based boundary-lubricated hydrogels