Mechanical Characteristics of SPG-178 Hydrogels: Optimizing Viscoelastic Properties through Microrheology and Response Surface Methodology

Background: Self-assembling peptides (SApeptides) have growing applications in tissue engineering and regenerative medicine. The application of SApeptide-based hydrogels depends strongly on their viscoelastic properties. Optimizing the properties is of importance in tuning the characteristics of the hydrogels for a variety of applications. Methods: In this study, we employed statistical modeling, conducted with the response surface methodology (RSM) and particle tracking microrheology, to investigate the effects of self-assembling SPG-178 peptide and added NaCl salt concentrations and milieu type (deionized water or blood serum) on the viscoelastic properties of SPG-178 hydrogels. A central composite RSM model was employed for finding the optimum value of the parameters to achieve the highest storage modulus and the lowest tan δ. Results: Viscoelastic properties of each sample, including storage modulus, loss modulus, and tan δ, were determined. Storage modulus and tan δ were modeled, accounting for the impact of the SPG-178 peptide and NaCl concentrations and milieu type on the viscoelastic properties. It was found that the SPG-178 hydrogel storage modulus was positively influenced by the SPG-178 peptide concentration and the serum. Conclusion: A combination of microrheology and RSM is a useful test method for statistical modeling and analysis of rheological behavior of solid-like gels, which could be applied in various biomedical applications such as hemostasis.

On the analysis of microrheological responses of self-assembling RADA16-I peptide hydrogel.

This work aims to obtain a hydrogel based on self-assembling RADA16-I with proper rheological properties for hemostasis application. Response surface methodology (RSM) was performed to predict the gelation and stiffness of the hydrogel in different concentrations of peptide and NaCl in water and blood serum milieus. Particle tracking microrheology technique was used to evaluate Brownian motion of polystyrene particles in the peptide solutions to obtain their trajectories and measure the viscoelastic properties (G'', G″, and tan δ). Formation of gel was influenced by the concentrations of peptide and salt and their interactions. Optimum response for maximizing elastic modulus was obtained in the presence of blood serum in comparison with water. Negative effect of excess amount of NaCl was predicted by RSM model and confirmed by animal study. Circular dichroism (CD) analysis showed formation of ß-sheet secondary structure in water. On the other hand, in the presence of blood serum, tertiary structure was formed. Dimensional characterization of peptide fibers was performed by means of AFM. Peptide self-assembly in blood serum (pH around 7) which contains different ions, led to enhancing bonds between fibers, caused increasing the fiber diameter and length by 20 and 10 times, respectively. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 330-338, 2019.

Evaluation of the hemocompatibility of RADA 16-I peptide.

RADA 16-I is an ionic self-assembling peptide that can form macroscopic scaffolds through ß-sheet structures which are used in favor of cell growth and tissue engineering. This peptide has also the ability to stop bleeding effectively and quickly (∼20 seconds) when applied directly to the injuries. This study is focused on coagulation process, platelet aggregation, C3 and C4 concentrations, CBC counting, hemolysis, and white blood cell morphology tests to analyze hemocompatibility of RADA 16-I at different concentrations - 0.1, 0.2, 0.3 and 0.5%. According to the results, RADA 16-I hydrogel decreased the number of blood cells, slightly increased clot formation time and platelet aggregation, and yielded negligible hemolysis and only small changes in C3 and C4 concentrations and white blood cell morphology. All by all, the in vitro tests of hemocompatibility showed no perturbation in the blood composition when the peptides were in contact with the blood. The observed rapid hemostasis might be a result of increasing local concentrations of molecules involved in the formation of clot near the peptide hydrogel, thereby making a barrier which ended up with complete hemostasis. In conclusion, our experiments strongly supported further development of biomaterials based on RADA 16-I peptide.

An efficient method for the application of PHA-poor solvents to extract polyhydroxybutyrate from Cupriavidus necator.

There are many published studies presenting ethanol and acetone as PHAs-poor solvents, where these two solvents are shown to dissolve <2% (w/v) of PHAs at low temperatures. In this study, the suitability of ethanol and acetone for the recovery of PHB at different temperatures (from room temperature to near boiling point) in Cupriavidus necator was investigated. Experiments were performed using response surface methodology to examine the effects of different temperatures and heating incubation times on recovery percentage using the two solvents. The highest recovery percentage (92.3%) and product purity (up to 99%) were obtained with ethanol-assisted extraction at 76°C for 32 min of incubation time. Under these conditions the extracted PHB exhibited a molecular mass of 1.2 × 106 . The present strategy showed that at temperatures near its boiling point, ethanol, as a nonhalogenated solvent, represents a good alternative to halogenated solvents, like chloroform, when PHB recovery is concerned. DSC analysis showed good thermal properties for ethanol- and acetone-extracted biopolymers. GC and 1 H NMR analysis confirmed the extracted biopolymer to be polyhydroxybutyrate of good purity. © 2016 American Institute of Chemical Engineers Biotechnol. Prog., 32:1480-1486, 2016.

High production of bacteriorhodopsin from wild type Halobacterium salinarum.

Bacteriorhodopsin (bR) is a trans-membrane proton pump found in the purple membrane of Halobacterium salinarum. This protein has high photochemical and photoelectric conversion efficiency and thermal stability, allowing it to withstand high temperatures, high salinity, and nutritionally-limited environments. The ability of this protein to convert light energy into chemical energy has applications that are mainly therapeutic/diagnostic and research-oriented. There is increasing demand for bacteriorhodopsin production in different fields. The present study maximized bacteriorhodopsin production using H. salinarum. The physical parameters of illumination, agitation speed, temperature, and nitrogen source were studied using a fractional factorial design to determine the optimal levels of each. The most suitable nitrogen source was determined to be peptone from meat. The optimal temperature was 39 °C, agitation speed was 150 rpm, and light intensity was 6300 lux for bR production. Under these conditions, the maximum bR yield was 196 mg/l, which is about 4.23 fold greater than those obtained with basal medium. The proposed strategies could be used for bR production using this archaeobacterium; the results are the highest reported thus far from a batch culture of H. salinarum.