A New Phenomenon: Sub-Tg, Solid-State, Plasticity-Induced Bonding in Polymers

Characteristic Evaluation of Gel Formulation Containing Niosomes of Melatonin or Its Derivative and Mucoadhesive Properties Using ATR-FTIR Spectroscopy

Chitosan or polyvinyl pyrrolidone (PVP) were used in combination with hydroxypropyl methylcellulose (HPMC) and poloxamer 407 (P407) as gelling agents for oral drug delivery. The performance interaction with mucin of chitosan-composed gel (F1) and PVP-composed gel (F2) was compared using attenuated total reflectance-Fourier-transform infrared (ATR-FTIR) spectroscopy at controlled temperatures of 25 and 37 °C for 1 and 5 min. F1 containing niosome-entrapped melatonin or its derivatives was investigated for mucoadhesive interaction on mucosa by ATR-FTIR spectroscopy under the same conditions. The results showed that F1-treated mucin gave a significantly lower amide I/amide II ratio than untreated mucin and F2-treated mucin did within 1 min, suggesting improved rapid affinity between mucin and chitosan. The spectra of mucosa treated with F1 incorporating niosomes of melatonin or its derivatives showed peak shifts at C=O (amide I), N-H (amide II), and carbohydrate regions and an associated decrease in the amide I/amide II ratio and increase in the carbohydrate/amide II ratio. These results indicated electrostatic interaction and hydrogen bonding between chitosan and mucin on the mucosa. In conclusion, the molecular interaction between gels and mucin/mucosa detected at amide I and amide II of proteins and the carbohydrate region could lead to an improved mucoadhesive property of the gel on the mucosa.

Surface Damage Influences the JKR Contact Mechanics of Glassy Low-Molecular-Weight Polystyrene Films

Using a surface forces apparatus (SFA), we quantitatively study the influence of surface damage on the contact mechanics of self-mated glassy polystyrene (PS) films. We use the SFA to measure the contact radius, surface profile, and normal force between the films, including the adhesion force. The molecular weight (MW) of the polymer influences the repeatability of the adhesion measurements and the effective surface energy calculated using the Johnson-Kendall-Roberts (JKR) theory. For low-MW PS (MW = 2.33 kDa), the effective surface energy increases over repeated adhesion cycles as the films become progressively damaged. For high-MW PS (MW = 280 kDa), the effective surface energy is constant over repeated adhesion cycles, but hysteresis is still present, manifested in a smaller contact radius during compression of the surfaces than during separation. Our results demonstrate that while the JKR theory is appropriate for describing the contact mechanics of glassy polymer thin films on layered elastic substrates, the contact mechanics of low-MW polymer films can be complicated by surface damage to the films.