Jiřı́ Kotek

Abstract The commercial grade of isotactic polypropylene was modified by a specific β‐nucleating agent in a broad concentration range. The supermolecular structure of the specimens prepared by injection molding was characterized by X‐ray scattering and correlated with mechanical behavior. It was found that at a critical nucleant concentration of 0.03 wt % the content of the β‐modification virtually reaches a saturation level. With further addition of the nucleant, the β‐phase content increases only slightly. The long period passes through a distinct maximum at the same nucleant concentration. This singularity in structure remarkably correlates with a minimum of the yield stress and maxima of strain at break and fracture toughness. Such general behavior is also reflected in the correlation between the β‐phase concentration and fracture toughness profiles along the injection‐molded bars. It is suggested that in the critically nucleated material an optimum thickness of the amorphous interlayer with connecting chains between the β‐crystallites is established, rendering the material the highest possible ductility and toughness. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1174–1184, 2002

The architecture and mechanical properties of a scaffold for spinal cord injury treatment must provide tissue integration as well as effective axonal regeneration. Previous work has demonstrated the cell-adhesive and growth-promoting properties of the SIKVAV (Ser-Ile-Lys-Val-Ala-Val)-modified highly superporous poly(2-hydroxethyl methacrylate) (PHEMA) hydrogels. The aim of the current study was to optimize the porosity and mechanical properties of this type of hydrogel in order to develop a suitable scaffold for the repair of spinal cord tissue. Three types of highly superporous PHEMA hydrogels with oriented pores of ~60 µm diameter, porosities of 57-68% and equivalent stiffness characterized by elasticity moduli in the range 3-45 kPa were implanted into a spinal cord hemisection, and their integration into the host tissue, as well as the extent of axonal ingrowth into the scaffold pores, were histologically evaluated. The best tissue response was found with a SIKVAV-modified PHEMA hydrogel with 68% porosity and a moderate modulus of elasticity (27 kPa in the direction along the pores and 3.6 kPa in the perpendicular direction). When implanted into a spinal cord transection, the hydrogel promoted tissue bridging as well as aligned axonal ingrowth. In conclusion, a prospective oriented scaffold architecture of SIKVAV-modified PHEMA hydrogels has been developed for spinal cord injury repair; however, to develop an effective treatment for spinal cord injury, multiple therapeutic approaches are needed.