Particulate leaching

In later work, PEO and PCL PUs were blended by simple mixing to form three-dimensional sponges using solvent cast/particulate leaching methods. 

In order to overcome some of the drawbacks associated with the fiber bonding preparation, a solvent-casting and particulate-leaching technique was developed [32], With appropriate thermal treatment porous constructs of synthetic biode-... 

Fig. 4a, b. Scanning electron photomicrographs of amorphous poly(L-lactic acid) foams a 92% porosity and 30 pm median pore diameter b and 91% porosity and 94 pm median pore diameter. Prepared by a solvent-casting and particulate-leaching method [32] using 90 wt% sieved sodium chloride particles of size range between 0-53 pm and 106-150 pm, respectively... 

Highly porous membranes with an inter-connected pore structure were produced using this solvent-casting and particulate-leaching technique (Fig. 4a, b). The porosity of porous PLLA membranes could be controlled by varying the amount of salt used to construct the composite material (Fig. 5a). 

The authors described several other fabrication techniques, but their conclusions are the important parts of their report Conventional scaffold fabrication techniques are incapable of precisely controlling pore size, pore geometry, spatial distribution of pores and construction of internal channels within the scaffold. They also state that scaffolds produced by the solvent casting-particulate leaching technique cannot guarantee interconnection of pores because interconnection is dependent on whether the adjacent salt particles are in contact. Moreover, only thin scaffold cross sections can be produced due to difficulty in removing salt particles deep in the matrix. 

Figure 1. The highly porous, interconnected structure of a particulate leached PCL tissue scaffold.

Various techniques, such as intrusion methods, image analysis and weight determinations are used to provide estimates of the porosity and the distribution of pore sizes within a tissue scaffold. This preliminary study of the structural features of particulate-leached PCL scaffolds has shown that reliable measures of porosity can be obtained from simple weighing measurements (Buoyancy method). 

The distribution of pore sizes can be obtained from both mercury porosimetry and capillary flow porometry. These distributions are only representations of the actual scaffold structure reflecting the limitations of the underlying physics behind each technique. For this reason it is very difficult to compare pore size distributions for complex structures, such as particulate-leached tissue scaffolds. 

A gas foaming/particulate leaching process can be employed to fabricate interconnected open pore structures of PLGA for controlled release of DNA [113,199]. This process employs carbon dioxide to process a mixture of polymer and porogen, in order to fuse adjacent polymer particles into an interconnected structure. The DNA can be lyophilized with the microspheres [113] or encapsulated within the microspheres [200,201]. Lyophilization of DNA with the microspheres can provide large quantities of incorporated DNA, with relatively rapid release kinetics. Incorporation of DNA into the microspheres provides for a more sustained release relative to the lyophilization method [200], with the release kinetics dependent on the polymer molecular weight and microsphere size [201]. DNA can be incorporated into polymer microspheres using several approaches [201-205]. Subcutaneous implantation of scaffolds results in transfected cells observed within the scaffold... 

Wu L, Jing D, Ding JA (2006) room-temperature injection molding/particulate leaching approach for fabrication of biodegradable three-dimensional porous scaffolds. Biomaterials 27 185-191... 

Solvent-casting, particulate-leaching is a common method of creating porous foams. 

Human mesenchymal stromal cells (hMSCs) Triton X-lOO-rNH H-t DNase hMSCs Macroporous poly(lactic-co-glycolic acid) (PLGA) scaffold fabricated by gas foaming/ particulate leaching method Rat Decaris et al. (2012a)... 

Solvent casting and particulate leaching This approach allows the preparation of porous structures with regular porosity. Other than the small thickness range that can be obtained, another drawback of such scaffolds lies in the use of organic solvents, which must be fully removed to avoid any possible damage... 

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