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Module 1: Release Systems and Hydrogels

    Study Reminders
    Support

    Lesson Summary:
    Hydrogels- Three dimensional, hydrophilic polymer networks capable of swelling by absorbing large amounts of fluid.
    -can expand to thousand of times their dry weight in fluid
    -Insoluble due to physical or chemical crosslinks which provide the network structure and physical integrity
    - bioerodible or non-erodible
    -Numerous Applications


    Advantages of Swelling-controlled Matrix Hydrogels
    Low burst effect
    Known or predictable swelling rates
    Reformulation of vehicle not necessary for different drugs
    Disdvantages of Swelling-controlled Matrix Hydrogels
    Generally short release periods
    Not suitable for all delivery routes or targets

    Classification of Hydrogels:

    Physical Hydrogels:

    - polymer network held together by neutral or ionic bonds
    - Not Homogeneous, clusters of molecular entanglements, or hydrophobically/ionically associated
    - Single physical cross-link, formed by hydrophobic association/Van der Waals bonding, ionic bonding, or hydrogen bonding between two monomers in water (lower strengths than singular covalent bond)
    - Formation of transiently stable hydrogels requires block copolymer structures where cooperative binding can occur
    - Formation of one physical bond is immediately followed by bonding of several other adjacent monomer units

    Ionic Hydrogels:

    - Polymer chains within hydrogels contains pendant groups that are cationic or anionic
    - Ionic- Gels are unionized above (cationic) or below (anionic) the pKa of the groups. For pH above (anionic) or below (cationic) pKa, the pendant groups are ionized and repel each other = large swelling