Bioresponsive Hydrogels for Controlled Drug Delivery
Deepa H. Patel in Bioresponsive Polymers, 2020
In general, the three parts of hydrogels preparation are, monomer, initiator, cross-linker. Hydrogel can be obtained by copolymerization or crosslinking free radical polymerization of hydrophilic monomers with multifunctional cross-linkers. Or mostly water-soluble natural or synthetic linear polymers are cross-linked to form hydrogel. The crosslinking techniques are described below: Physical crosslinking (entanglements, electrostatic, and crystallite formation);Chemical crosslinking, using chemical reactions to link polymers;Radiation crosslinking (using ionizing radiation to generate main chain free radicals).
Injectable Scaffolds for Bone Tissue Repair and Augmentation
Naznin Sultana, Sanchita Bandyopadhyay-Ghosh, Chin Fhong Soon in Tissue Engineering Strategies for Organ Regeneration, 2020
Injectable scaffolds for bone tissue regeneration are particularly interesting, not only because the use of these materials can potentially avoid the surgical interventions to implant the scaffolds at defective/fractured areas, but they can also reassemble within a short interval and can fill any irregularly shaped defects once inside the body (Hou et al. 2004, Jin et al. 2009, Naahidi et al. 2017). An injectable system also takes the advantage of a more homogeneous distribution of bioactive molecules within the matrix, that can readily be obtained by virtue of the scaffold components being in suspension or solution before solidification in vivo. The promising injectable materials that can be used as bone scaffolds are primarily based on hydrogel (Temenoff and Mikos 2000, Hou et al. 2004, Nourmohammadi et al. 2016) and paste (Migliaresi et al. 2007). Hydrogels are soft materials, having cross-linked hydrophilic networks that can absorb large quantities of water (or biological fluids) while maintaining their original structure (Ahmed and Aggor 2010, Jung et al. 2017, Portnov et al. 2017). When hydrogels are injected, they can readily wet all surfaces of the injured site and create a low-density aqueous cavity that contains the components necessary for bone tissue regeneration. Paste based injectable scaffolds are usually developed from calcium phosphate cements (CPC) and are also considered to be clinically important owing to their biocompatibility, bioactivity, ease of handling, moldability, and injectability (Li et al. 2009).
Treatment of Pressure Sores
J G Webster in Prevention of Pressure Sores, 2019
Many synthetic occlusive dressings are available and can be divided into four groupings, each with its advantages and disadvantages (Mulder and LaPan 1988). Figure 14.6 points out the advantages and disadvantages of each type of synthetic occlusive dressing when used on pressure sores. Hydrocolloid dressings are adhesive, gel-producing, water-impermeable membranes. They can be left on for up to one week, and commonly have an adhesive wound contact face, an impermeable outer face, and an exudate-absorbing component that is usually carboxymethylcellulose. They are easy to apply, but may be messy and disruptive when used on high-exudate wounds. Polyurethane and thin film dressings are transparent-adhesive dressings that are often difficult to use. They can be troublesome to apply and may be disrupted or removed by patient movement. It is also common to have exudate leakage due to the minimal absorption of the dressing. Bio-dressings and gels are similar groupings of dressings. They are usually hydrogels of water and polyethylene oxide, have a reinforced polyethylene film, and have a high water content. They are more appropriate for use on abrasions and superficial wounds than pressure sores.
Nano-composite hydrogels of Cu-Apa micelles for anti-vasculogenic mimicry
Published in Journal of Drug Targeting, 2023
Rui Kang, Mengdi Song, Zhou Fang, Kehai Liu
The APsGels degraded relatively slowly in the cellular microenvironment (Figure 2H). The mass loss of the hydrogels increased as the degradation time increased. More specifically, 19.17 ± 0.71% and 62.15 ± 0.58% of the total weight were degraded after 1 and 16 d, respectively. The APsGels prepared by the Schiff base reaction had a high degree of cross-linking, which increased the steric hindrance effect between molecules, thereby resisting external forces. The degradation rate of the APsGels decreased, suggesting that they had better stability. Additional properties of the APsGels are listed in Table 3. It has been claimed that the phase transition temperature of in situ gels is generally between 25 °C and 35 °C. This is due to the addition of polysaccharides that increase the crosslinking degree, leading to a higher phase transition temperature [51]. These indicate that hydrogel was used for biomedical applications, such as drug release and tissue engineering. However, APsGels can still undergo rapid phase transformation (77.33 ± 2.05 s) at body temperature, which meets the design requirements of in situ gel application in vivo.
Hydrogels for localized chemotherapy of liver cancer: a possible strategy for improved and safe liver cancer treatment
Published in Drug Delivery, 2022
Jianyong Ma, Bingzhu Wang, Haibin Shao, Songou Zhang, Xiaozhen Chen, Feize Li, Wenqing Liang
Despite their numerous advantages, hydrogels do have a few limitations. Several hydrogels cannot be used in load-bearing applications due to their low tensile strength. These hydrogels prematurely dissolve or flow away from a designated site (Bai et al., 2020). This constraint may be more relevant in many conventional drug delivery applications (e.g. subcutaneous injection, in situ injection, and intratumoral injection). Perhaps a more significant concern is about the drug delivery capabilities of hydrogels. Drug loading into hydrogels may be limited in terms of amount and uniformity, particularly for hydrophobic drugs. The large pore diameters and high-water content of most hydrogels result in the rapid release of payloads, or burst release (Tsirigotis-Maniecka et al., 2021). The ease of application is also a significant concern. Some hydrogels can be injected, but many cannot be, so they have to be implanted through surgery. Due to these limitations, the use of hydrogel-based therapies in clinical applications may be restricted (Table 4).
Polysaccharide-based hydrogels for drug delivery and wound management: a review
Published in Expert Opinion on Drug Delivery, 2022
Dhruv Sanjanwala, Vaishali Londhe, Rashmi Trivedi, Smita Bonde, Sujata Sawarkar, Vinita Kale, Vandana Patravale
Hydrogels are three-dimensional crosslinked networks of hydrophilic polymers, synthesized using physical or chemical crosslinking, and are capable of absorbing large quantities of water or aqueous fluids. Hydrogels can entrap large volumes of water (in some cases, several times their own weight) in their crosslinked networks and swell greatly. This high hydrophilicity of hydrogels can be attributed to the abundant hydrophilic groups present in the polymeric chains. Hydrogels can be fabricated from synthetic as well as natural polymers. Synthetic polymer-based hydrogels are usually non-biodegradable as opposed to natural hydrogels, which are environment-friendly and easily degradable. Natural polymers commonly used for fabricating hydrogels include biological macromolecules such as proteins (collagen, gelatin), polysaccharides (cellulose, chitosan, hyaluronic acid (HA), agarose), and nucleic acids. Among these, carbohydrate polymers are used extensively, mainly due to their abundance, nontoxicity, renewability, and high biocompatibility. Moreover, they can be chemically modified to accurately mimic various body tissues [1–3]. Table 1 lists the most common natural polysaccharides and their semisynthetic derivatives used to fabricate hydrogels for biomedical applications.