Effect of Polyethylene Glycol, Glycerol and Sodium Chloride on Sodium Alginate and Gelatin blend – A molecular dynamics study

Sodium Alginate and Gelatin blends showed strong response towards the external stimuli of pH and ionic strengths. Molecular dynamics simulations were used to study the hydrogen bonding interactions in these blends when subjected to different pH and different ionic strength medium. The effect of plasticizers viz. glycerol and polyethylene glycols of different molecular weights on the blend were also studied. In addition, the effect of external stimuli and plasticizers upon the individual constituents of the blend viz. Sodium Alginate and Gelatin were also studied in order to understand their combined effect in the properties shown by the Sodium Alginate and Gelatin blend. Polyelectrolytic properties of sodium alginate and polyampholytic properties of gelatin were explored both in presence and absence of salt. Finally, the simulation results for gelatin in salt medium were verified using theoretical expressions and experimental analysis of the same system

Piperine as a Placebo: Stability of Gelatin Capsules without a Cross-Linker

Gelatin has been the biomaterial of choice for decades now. Its low cost, renewable, nontoxic and biodegradable properties make it one of the most desirable materials for controlled release applications. However, the usage of gelatin is limited by its poor mechanical/thermal stability and high water solubility. Chemical cross-linkers and hydrophobic modifications of gelatin have solved this problem but they lead to the problem of toxicity and/ or high processing cost. This research attempts to employ a nontoxic hydrophobic drug molecule to curb early degradation of gelatin in an aqueous environment. We report the design of non-cross-linked gelatin capsules with high dissolution resistance in an aqueous medium. Piperine, a hydrophobic drug (Solubility: 40mg/L in water) was coated on the gelatin capsules to enhance its stability in an aqueous environment. The hydrophobic piperine molecules repelled the water molecules to intensify its dissolution resistance. This stabilization was used to control the release of naproxen sodium, encapsulated inside the gelatin matrix. Piperine, in this case, acts as a placebo i.e it has zero therapeutic effect but its presence was necessary to control the early degradation of gelatin matrix. The deposition of piperine was done using the solvent evaporation method where ethanol was used as the solvent. The wettability studies revealed the hydrophobic nature of surface after the deposition of piperine while SEM analysis showed the presence of long cylindrical (fiber-like) structures over the gelatin surface. Further investigation (FTIR/ATR and molecular dynamics) revealed that the long fiber structures were due to the crystallization of piperine over the surface of gelatin. This crystallization was triggered by the intermolecular association (hydrogen bond) of ethanol and piperine. These observations enabled us to optimize the piperine loading protocol over the gelatin capsules that helped in achieving a zero order naproxen release for 32 hours

Physicochemical Response of Gelatin in a Coulombic Soup of Monovalent Salt: A Molecular Simulation and Experimental Study

The effect of salt on the static properties of aqueous solution of gelatin is studied by molecular dynamics simulation at pH = 1.2, 7, and 10. At the isoelectric point (pH = 7), a monotonic increase in size of the polymer is obtained with the addition of sodium chloride ions. In the positive polyelectrolyte regime (pH = 1.2), collapse of gelatin is observed with increase in salt concentration. In the negative polyelectrolyte regime, we observe an interesting collapse–reexpansion behavior. This is due to the screening of repulsion between the excess charges followed by the screening of attraction of oppositely charged ions as the salt concentration is increased. This mechanism is very different from the charge inversion mechanism which causes the reexpansion in the presence of multivalent ions. The location of salt concentration corresponding to the minimum size of the chain is comparable to the theoretical estimate. The shift in the peak of radial distribution function calculated between monomers and salt ions confirms this spatial reorganization. The predictions from the simulation are verified by dynamic light scattering(DLS) and small-angle X-ray scattering (SAXS) experiments. The size of the hydrodynamic “clusters” obtained from DLS confirms the simulation predictions. Persistence length of the gelatin is calculated from SAXS to get single chain statistics, which also agrees well with the simulation results