Biomedical Engineering Reference
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linear, unbranched polymer. Meyer and co-workers found HA
to be composed of a repeating disaccharide unit that consists of
N
-acetyl-
d
-glucosamine and
d
-glucuronic acid linked by a b (1-4)
glycosidic bond [3]. The disaccharides are linked by b
1-3 bonds
to form the HA chain. In addition to its presence in the vitreous
body, HA occurs in many living substrates such as the extracellular
matrix and synovial fluids [2-5]. In practice, HA is used in wound
healing, because it supports tissue reconstruction. During the first
few days of tissue repair, endogeneous HA is the predominant
glycosaminoglycan present in wounds and forms the template
necessary for reconstruction following injury [2]. A detailed
knowledge of flow and surface properties of HA powder material
is important for practical pharmaceutical applications, e.g., in drug
formulation, construction of wound healing dressings, tablets,
capsules, dry powder inhalation formulations.
That is why, in this chapter, we present the results of our current
research focused on powder flow and surface properties analysis
of HA powder material by means of inverse gas chromatography
(iGC) and powder rheometer testing. These are both excellent tools
for characterisation of the physicochemical properties of powder
materials.
4.2 Methods for Hyaluronic Acid Powder Analysis
4.2.1 Theoretical Background
The surface free energy of a solid can be described as the sum of the
dispersive and specific contributions. Dispersive (apolar) interactions,
also known as Lifshitz-van der Waals interactions, consist of London
interactions which originate from electron density changes but may
include both Keesom and Debye interactions [6, 7]. Other forces
influencing the magnitude of surface energy are Lewis acid-base
interactions which are generated between an electron acceptor (acid)
and an electron donor (base). Details of the widely accepted theoretical
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