Fabrication of poly(phosphoester) nerve guides by immersion precipitation and the control of porosity

Immersion precipitation was employed as a method for the fabrication of pol ymeric conduits from P(BHET-EOP/TC), a poly(phosphoester) with an ethylene terephthalate backbone, to be applied as guidance channels for nerve regene ration. Coatings of various porosities could be obtained by immersing mandr els coated with a solution of the polymer in chloroform into non-solvent im mersion baths, followed by freeze or vacuum-drying. The porosity of the coa tings decreased with an increase in polymer molecular weight, drying time b efore precipitation and concentration of polymer solution. The effects of t hese parameters can be rationalized by employing ternary phase diagrams, wh ere porosity is directly related to the degree of phase separation availabl e to the system before gelation occurs. To afford improved porosity control , a new system was developed which employed the contrasting phase-separatio n behavior of P(BHET-EOP/TC)/chloroform solution in methanol and water. As water is essentially a non-solvent for the polymer, the demixing boundary o f the P(BHET-EOP/TC)-CHCl3-H2O system is located close to the polymer-solve nt edge of the phase diagram, while that of the P(BHET-EOP/TC)-CHCl3 -MeOH system is located further away. A mixture of methanol and water allows the demixing boundary to be shifted to intermediate coordinates. By immersing P (BHET-EOP/TC) coatings in immersion baths containing different ratios of wa ter and methanol, then gradually titrating the bath with methanol to a conc entration of 70% (v/v) methanol, surface porosities ranging From 2 to 58% c ould be achieved. (C) 2001 Elsevier Science Ltd. All rights reserved.