Preparation And Characterization Of Poly (DL-lactic Acid) Porous 3-D Scaffolds For Bone Tissue Engineering

Poly (lactic acid) (PLA) has been widely used as scaffolds for tissue engineering because of its good biocompatibility, biodegradability and plasticity. How to acquire the connected porous structures that not only have high porosity (>75%) but also have proper mechanical strength is the problem of tissue engineering, which is badly in need of solution.In this paper, solution casting / particulate leaching technique (SC/PL), thermally induced phase separation technique (TIPS) and gas foaming & particulate leaching technique (GF&PL) were used to prepare Poly (DL-lactic acid) porous scaffolds. The density and porosity of samples were determined by "liquid draining" method. Three-dimensional video microscope and scanning electronic microscope were used to observe the appearance of the surfaces and cross-sections of porous scaffolds, so as to determine the structures and the size of pores. Studied the factors of each method to see which could control porosity, the structure and the size of pores. The advantages and disadvantages of each method were compared.Honeycomb-like structures had been obtained by solution casting / particulate leaching technique. Porosity can reach 90-92%, which was mainly determined by porogen weight fraction. Pore diameter was between 50 and 450um, which depended on the size of porogen particles. Specific area of pores increased with the increase of porogen weight fraction and the decrease of porogen particle size. All of them had no relationship with the kind of porogen and solvent. SC/PL technique is simple and economic, with the advantage of controllable pore diameter and porosity and beautiful appearance of pores. But because the pores were not distributed evenly and porogen was left in the matrix, the connected ability of pores became worse. So the shape of scaffolds was limited (the thickness was generally less than 2mm).Three-dimensional reticulate structures had been obtained by thermally induced phase separation technique. Porosity was generally high (>75%) and mainly determined by the concentration of polymer solution. Low concentration of polymer solution, weak mutual action between solvent and polymer, long coarsening time were good for the swell of pore diameter. Neither higher nor lower coarsening temperaturewas good for the swell of pore diameter. The shape of pores was close to globularity when the coarsening time was prolonged. The scaffolds prepared by this technique didn't have porogen left and had no cuticle. The pores were distributed evenly, connected well and with beautiful appearance. Because the mechanism hasn't been studied thoroughly now, the preparation is hard to repeat and control. But this method assuredly had potential.Floc-like structures had been obtained by gas foaming & particulate leaching technique. Pores diameter was mainly regulated by the size of porogen particles. Porosity was determined by the porogen weight fraction. The concentration and temperature of aqueous citric acid solution and the kinds of solvent mainly affected the structure of pores and the mechanical strength of scaffolds. This method had the advantage of both the solution casting / particulate leaching technique and the thermally induced phase separation technique. The process was simple and economic. Pores were distributed evenly and connected well. What's more, pore diameter and porosity could be controlled easily. But a small quantity of poregen would be left in matrix and cuticle existed. The appearance of pores wasn't tidy enough.With all the aspects considered, gas foaming & particulate leaching technique was thought to be the most appropriate method for the preparation of porous scaffolds used in bone-tissue engineering now.