Biomacromolecules 2008, 9, 1527–1534
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Compatibilized Polymer Blends Based on PDLLA and PCL for Application in Bioartificial Liver Luigi Calandrelli,† Anna Calarco,‡ Paola Laurienzo,*,† Mario Malinconico,† Orsolina Petillo,‡ and Gianfranco Peluso*,‡ Institute of Polymers Chemistry and Technology, CNR, Via Campi Flegrei 34, 80078 Pozzuoli (Naples), Italy, and Institute of Protein Biochemistry, CNR, Via Pietro Castellino 111, 80131 Naples, Italy Received November 27, 2007; Revised Manuscript Received March 28, 2008
Porous scaffolds for tissue engineering applications based on poly(D,L-lactide)/poly(ε-caprolactone) compatibilized blends are described. The addition of a third polymer, namely poly(D,L-lactide-co-caprolactone) copolymer, has a profound effect on morphological properties of the blends scaffolds. In fact, the copolymer acts as compatibilizing agent and reduces the dimension of the dispersed phase of an order of magnitude. Such effect is function of the polymer composition. The efficiency of scaffolds obtained with poly(D,L-lactide) based blends containing 30% by weight of poly(ε-caprolactone) as dispersed phase toward hepatocytes has been tested by several biological assays and we found that they are able to promote a perfect adhesion, proliferation and growth of cells. Moreover, the addition of the copolymer significantly improves the biomedical performance of the scaffold.
Introduction Many organs, such as liver, lung, and epithelial surfaces, have regenerative capacity and will regenerate rather than scar in the absence of extracellular matrix destruction. In case of extracellular matrix destruction, one strategy with possible relevance to surgical therapy is the replacement of damaged tissue with engineered matrices, such as biomaterials, to restore a normal cell adhesion environment. The guidance provided by biomaterials may facilitate restoration of structure and function of damaged or dysfunctional tissues, both in cell-based therapies, such as those where carriers deliver transplanted cells or matrices induce morphogenesis in bioengineered tissues constructed ex vivo and in acellular therapies, such as those where materials induce ingrowth and differentiation of cells from healthy residual tissues in situ.1 In the last case, materials should provide a provisional support to interact with cells to control their function, guiding the spatially and temporally complex multicellular processes of tissue formation and regeneration.2,3 Despite numerous attempts, engineering of functional tissue using this type of biomaterials has proven elusive because of the challenges involved in the differentiation and sustenance of the different cell types. Recently, the bioactivity of the biomaterials has been improved by combining polymers with different characteristics. Indeed, the technique of blending is particularly relevant for biomedical application, as it permits to merge and optimize some characteristics of interest of the single components (i.e., biodegradation rate, mechanical properties, cellular adhesion, and so on) working with already tested and approved components without introducing new polymers that are accepted with extreme caution in this field. Actually, several studies on blends based on biocompatible polymers with respect to cell adhesion and proliferation can be found in literature.4–6 Particularly, blends of poly(D,L-lactide) (PDLLA) and poly(ε-caprolactone) (PCL) in the form of nonporous films have been evaluated, and the * To whom correspondence should be addressed. E-mail: paola.laurienzo@ ictp.cnr.it (P.L.);
[email protected] (G.P.). † Institute of Polymers Chemistry and Technology. ‡ Institute of Protein Biochemistry.
effects of microstructure and roughness of the surface on cell adhesion and proliferation of osteoblast cells have been discussed.5 In this study, the authors applied composition and annealing temperature gradients to create different surface morphologies of the films and demonstrated the existence of a relationship between microstructure and cell response. Because the use of temperature gradients destroys the scaffold porous structure, we have used a new approach, the addition of a compatibilizer to porous PDLLA/PCL polymer blend membranes, to modify the material microstructure. PCL by itself is reported to be able to promote a good cell adhesion with many different cells, as fibroblasts,7 osteoblasts,8 and hepatocytes;9 nevertheless, scaffolds based on PCL are hardly obtainable and lack the structural stability to withstand biomechanical loading due to the extreme softness of PCL.10 On the contrary, PDLLA possesses an adequate structural stability and a rate of biodegradation which is compatible with tissue regeneration. PCL has been proven to support desirable cellular response in culture more than PDLLA.11 To obtain homogeneous scaffolds of the said polymer blend, we have attempted to apply the principles of polymer blends compatibilization, already described in bulk biodegradable blends,12–14 to the realization of porous membranes. Such a target was very ambitious, as not many examples of heterogeneous polymer blend membranes were found in the scientific literature and even less examples of the effect of the addition of a copolymer minor phase as emulsifying agent on blends membrane structure.15 In a previous paper,16 we verified that the addition of a P(DLLA-co-CL) copolymer as compatibilizing agent in blends of PDLLA and PCL really influences the dispersion of the minor phase, either in blends obtained by melt mixing or in porous membranes obtained by the well-known solvent/nonsolvent phase inversion method. In the present paper, we focus our attention on the influence of the addition of the copolymer to porous membranes made of the said homopolymers on biological response. It is in fact still to be understood if the realization of more entangled morphologies is beneficial or not in terms of cellular response. We have, hence, prepared two copolymers of different composition and characterized them through vis-
10.1021/bm7013087 CCC: $40.75 2008 American Chemical Society Published on Web 05/22/2008
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Biomacromolecules, Vol. 9, No. 6, 2008
cometry, GPC, 1H- and 13C NMR spectroscopy, and thermal analysis and verified the influence of their addition as compatibilizing agents on the dispersed phase dimension of PDLLA/ PCL membranes of different composition. Adhesion, proliferation, and differentiation of hepatocytes on a selected blend (with and without the addition of one of the copolymer) have been examined.
Experimental Section Materials. Poly(D,L-lactide) (PDLLA, 100000 mau) was furnished by Resomer; poly(ε-caprolactone) (PCL, 50000 mau) was a Solvay product. D,L-Lactide (Boehringer-Ingelheim, Mannheim, Germany) was purified by recrystallization from ethyl acetate and then dried under vacuum at 40-50 °C. ε-Caprolactone (Aldrich, Milan, Italy) was dried on molecular sieves until a water content
