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Fundamentals and Biomedical Applications of Smart Hydrogels

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Biomaterials and Biopolymers

Part of the book series: AAPS Introductions in the Pharmaceutical Sciences ((AAPSINSTR,volume 7))

Abstract

Hydrogels are three-dimensional elastic networks containing a large amount of water formed from crosslinked hydrophilic polymer chains, which possess tunable tissue-like physicochemical properties. This chapter thoroughly introduces the definition, classification, formation, properties, and typical representative and biomedical applications of natural and synthetic hydrogels. In detail, the essential features of hydrogels relate to swelling, mechanical strength, rheology, self-healing, and injectability. As biomaterials, biocompatibility, biodegradability, and toxicity properties should be considered preferentially. Then, we expound on several typical hydrogels, such as self-healing hydrogels, injectable hydrogels, and stimuli-responsive hydrogels, including shape memory hydrogels and hydrogel actuators. Eventually, we summarize the major attractive applications of hydrogels in biomedical fields such as contact lenses, hygiene products, drug delivery, tissue engineering, and wound healing.

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Author information

Authors and Affiliations

  1. The Laboratory for Advanced Functional/Medicinal Polymers & Smart Drug Delivery Technologies, The Wolfson Faculty of Chemical Engineering, Technion-Israel Institute of Technology, Haifa, Israel

    Qi Wu, Eid Nassar-Marjiya, Mofeed Elias & Shady Farah

  2. The Russell Berrie Nanotechnology Institute, Technion-Israel Institute of Technology, Haifa, Israel

    Shady Farah

Authors
  1. Qi Wu
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  2. Eid Nassar-Marjiya
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  3. Mofeed Elias
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  4. Shady Farah
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Corresponding author

Correspondence to Shady Farah .

Editor information

Editors and Affiliations

  1. School of Pharmacy-Faculty of Medicine, The Hebrew University of Jerusalem and Centre for Cannabis Research and the Institute of Drug Research The Alex Grass Centre for Drug Design and Synthesis, Jerusalem, Israel

    Avi Domb

  2. Laboratory for Bio-materials Faculty of Biotechnology and Food Engineering, Technion-Israel Institute of Technology, Haifa, Israel

    Boaz Mizrahi

  3. The Laboratory for Advanced Functional/Medicinal Polymers & Smart Drug Delivery Technologies, The Wolfson Faculty of Chemical Engineering Technion-Israel Institute of Technology, Haifa, Israel

    Shady Farah

Quizzes

Quizzes

  1. 1.

    Which cross-linking mechanism is irreversible?

    1. (a)

      Self-assembly

    2. (b)

      Crystallization

    3. (c)

      Ionic interactions

    4. (d)

      Enzymatic crosslinking

    Answer: d.

    Explanation: The other crosslinking mechanisms are considered as physical crosslinking, which are dependent on the polymer chemical environment, while for the enzymatic crosslinking, the polymeric chains are bounded through stable covalent bound.

  2. 2.

    Swelling affects the mechanical properties by:

    1. (a)

      Disturbing/reducing the interactions between the polymeric chains.

    2. (b)

      Altering the chains configuration by changing the polymer network density.

    3. (c)

      Volume expansion.

    4. (d)

      All the mentioned above.

    Answer: d.

    Explanation: As the solvent defuse through the polymeric network, it reduces the polymer-polymer interactions and moves the chains apart, while increasing the polymer-solvent interactions, thus, imbibing water in the polymer structure. In other words, altering the chain configurations and expanding the network to a new design according to the new environment.

  3. 3.

    All the non-toxic hydrogels are considered as biocompatible materials.

    1. (a)

      True

    2. (b)

      False

    Answer: b.

    Explanation: Biocompatibility is a different property from nontoxicity, e.g., alumina and poly(tetrafluoroethylene) (PTFE), which are not toxic but often exhibit poor biocompatibility.

  4. 4.

    Which of the tests does not deform the sample?

    1. (a)

      Atomic Force Microscopy (AFM)

    2. (b)

      Compression test

    3. (c)

      Fracture test

    4. (d)

      Uniaxial test

    Answer: a.

    Explanation: The Atomic Force Microscopy (AFM) is performed by a very thin needle that scans the surface at the atomic surface providing accurate data about the atomic surface topography, where it can identify even absorbed molecules on the surface. In the compression test, the sample will be pressed between two disks. In the fracture test, the sample will be ruptured, while in the uniaxial testing, stress will be applied simultaneously in one or two directions. During all these tests, the sample will be deformed and ruptured.

  5. 5.

    Injectable hydrogels are considered:

    1. (a)

      Newtonian fluid

    2. (b)

      Dilatant fluid

    3. (c)

      Pseudoplastic fluid

    Answer: c.

    Explanation: During the injection process, pressure will be applied to the syringe to push the fluid outside the needle to its destination. When pressure is applied to the dilatant fluid, its viscosity increases, preventing it from flowing easily. In the case of pseudoplastic fluid, the viscosity decreased as the pressure is applied, allowing the fluid to flow. Polymers are considered non-Newtonian liquids since the presence of the long polymeric chains results in non-negligible friction between the chains, in other words, viscosity. Therefore, injectable polymers are considered pseudoplastic.

  6. 6.

    Regards the Fig. 3d, which of the following is true:

    1. (a)

      The high angular frequency in region B, corresponds with the liquid-like behavior.

    2. (b)

      The low angular frequency in region A, corresponds with the solid-like behavior.

    3. (c)

      The crossover between G′ and G″ confirms the existence of reversible crosslinking network.

    4. (d)

      The crosslinking between G′ and G″ indicates the existence of permanent chemical crosslinking.

    Answer: c.

    Explanation: High angular frequency in region B, corresponds with the solid-like behavior while the low angular frequency in region A, corresponds with liquid-like behavior. The absence of crossover between G′ and G″ curves indicates that there is permanent chemical crosslinking.

  7. 7.

    Which of the following is not true?

    1. (a)

      Liquid biomaterials, as well as gels with shear thinning features which can be injected, are considered injectable hydrogels.

    2. (b)

      Biocompatibility and nontoxicity are the same property, and the existence of one of them is enough.

    3. (c)

      Self-healing ability is a common property among hydrogels, and can happen in two forms, based on the bonding mechanism.

    4. (d)

      Chemically and physically crosslinked hydrogels, react in a different way to temperature changes.

    Answer: b.

    Explanation: Biocompatibility and nontoxicity are different properties, some products are nontoxic, still, not highly biocompatible.

  8. 8.

    Which of the following is not true?

    1. (a)

      UCST (the upper critical solution temperature), in which the hydrogel shrinks when cooled to lower than this level.

    2. (b)

      Chemically crosslinked thermo-gels are positive temperature-responsive hydrogels, while physically crosslinked hydrogels are negative responsive.

    3. (c)

      Light, pressure, ultrasound, and temperature are examples of physical stimuli for hydrogels.

    4. (d)

      Number of crosslinked networks in the polymer structure can affect to which level the polymer is considered a multi-functional.

    Answer: b.

    Explanation: Positive and negative responsive systems are two groups that the polymers are divided to, when they undergo temperature changes, regardless they are chemically or physically crosslinked (these are two different points).

  9. 9.

    From the written above, regards drug delivery hydrogels, one can infer:

    1. (a)

      Synthetic hydrogels, with superior mechanical strength are not compatible for drug release applications.

    2. (b)

      Density and level of network crosslinking are important keys for successful drug delivery process.

    3. (c)

      The acidic environment in the stomach inhibits the drug release process.

    4. (d)

      Hydrogels that undergo degradation are not able to deliver drugs in the human body.

    Answer: b.

    Explanation: Being a hydrogel with high mechanical strength is important for achieving long-term release, thus, it can be applicable in drug delivery. Acidic environment possesses drug release process and doesn’t inhibit it. Drugs loaded in degradable hydrogels is one possible mechanism for drug delivery and release.

  10. 10.

    The properties of being degradable and removable in wound healing field are necessary for:

    1. (a)

      Changing hydrogel dressing.

    2. (b)

      Supplying low-cost hydrogels replacing process.

    3. (c)

      Suppling bioactive multifunctionality.

    4. (d)

      Preserving high efficiency during the healing process, as well as, refraining infections.

    Answer: d.

    Explanation: Hydrogel dressing replacement is essential for preserving high efficiency and preventing infections during the healing process, but this step is highly expensive and can cause injuries, thus, it is important to own the mentioned properties as a substitution.

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Wu, Q., Nassar-Marjiya, E., Elias, M., Farah, S. (2023). Fundamentals and Biomedical Applications of Smart Hydrogels. In: Domb, A., Mizrahi, B., Farah, S. (eds) Biomaterials and Biopolymers . AAPS Introductions in the Pharmaceutical Sciences, vol 7. Springer, Cham. https://doi.org/10.1007/978-3-031-36135-7_4

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