Georgios Sarakinos

Laminated three-dimensional biodegradable foams for use in tissue engineering

A novel processing technique is reported to construct three-dimensional biodegradable polymer foams with precise anatomical shapes. The technique involved the lamination of highly-porous membranes of porosities up to 90%. Implants with specific shapes were prepared made of poly(L-lactic acid) and copolymers of poly(DL-lactic-co-glycolic acid) to evaluate feasibility. The biomaterials produced have pore morphologies similar to those of the constituent membranes. The pores of adjacent layers of laminated devices are interconnected, resulting in continuous pore structures. The compressive creep behaviour of multilayered devices is also similar to that of the individual layers. Recent discoveries from our group and others that organs and tissues can be regenerated and reconstructed, using cells cultured on synthetic biodegradable polymers, renders this method useful in creating polymer-cell graft for use in cell transplantation.

Cell seeding in porous transplantation devices.

Porous laminated discs of 1.35 cm diameter and thickness of 0.5 cm fashioned from biodegradable polymers were used as scaffolds for the transplantation of isolated cell populations. The distribution of cells seeded in these devices via injection was modelled with a system of dyed polymeric microparticles. Optimization of parameters related to device design and surgical injection conditions was carried out to maximize the device volume effectively employed in cell transplantation. The area of distribution on the top surface of each device was determined by image analysis techniques and used as a measure of the spatial distribution of injected particles. For poly(L-lactic acid) devices of porosity of 0.83 and median pore diameter of 166 microns seeded with 6 microns beads under standard injection conditions, the average surface area of distribution was 44.45% (+/- 3.36%). The device pore size was found to be a crucial determinant of particle distribution, whilst particle size in the range of 1-10 microns was not found to be important for the devices tested. Application of these results to the seeding of hepatocyte suspensions was made.

Dynamics of fibrovascular tissue ingrowth in hydrogel foams

We have investigated and quantified the degree of fibrovascular tissue ingrowth in cylindrical poly(vinyl alcohol) (PVA) foams of 12.5 mm diameter, 5 mm thickness, and 71% porosity implanted in the mesentery of rats over a period of 25 days. Fibrovascular tissue penetrated the center of PVA foams 5 days postimplantation yet the void fraction available for cell seeding was 55% and the volume average pore diameter was 190 (+/- 39) microns. By 10 days postimplantation the void fraction had decreased to 32% and the volume average pore diameter was 121 (+/- 20) microns. As time elapsed fibrovascular tissue continued to expand and fill the remaining pore space. At 15 days postimplantation the void space was impractical for cell seeding and continued to decrease through the remainder of the study. Our data suggest that hydrogel foams with a polydispersed pore morphology can be prevascularized with adequate space for cell seeding as the volume of tissue penetrating the foam is limited by the smaller pores in the foam structure; however, available void space for cell seeding decreases with time.

Catalytic enantioselective Diels-Alder reactions using titanium complexes of cis-N-sulfonyl-2-amino-1-indanols

Abstract A titanium complex derived from (1R, 2S)-N-(2,4,6-trimethylbenzenesulfonyl)-2-amino-1-indanol catalyzes the Diels-Alder reaction of 2-bromoacrolein and cyclopentadiene with 96.5:3.5 enantioselectivity. A new and efficient synthesis of 2-amino-1-indanol ( 6 ) contributes to the potential of this methodology.

DIAXIAL CONFORMERS OF TRANS-1,2-DITHIACYCLOHEXANE DERIVATIVES

Abstract As a result of steric repulsion between the equatorial substituents of the trans -(2-thiacyclohexyl)sulfone 3 , the preferred molecular geometry in solution and in the solid state is the diaxial conformer.