Polycaprolactone Foam for Scaffold Development

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1 STR/4/6/FT Polycaprolactone Foam for Scaffold Development B. Y. Tay, M. H. Myint and F. L. Ng Abtract The tudy invetigate the proceing of biodegradable porou caffold of polycaprolactone (PCL). A commercially available PCL powder i blended with a poly(vinyl alcohol) powder at variou compoition to fabricate precaffold uing the three-dimenional printing (3DP) technique followed by particulateleaching. The propertie of the caffold are characteried uing differential canning calorimetry, dynamic mechanical analyer, canning electronic micrography and gel-permeable chromotography. The caffold produced in thi route diplay open cellular tructure with macropore. No ignificant degradation of PCL i detected. Keyword: Polycaprolactone, Poly (vinyl alcohol), Scaffold, Pre-caffold, Degradation 1 BACKGROUND In the pat 4 year, ynthetic biodegradable polymer have found a multitude of ue in the medical indutry. Since the approval of biodegradable uture by the FDA in the 196 [1], medical product baed on lactic acid, glycolic acid, poly(dioxanone), poly(trimethylene carbonate) copolymer and polycaprolactone homopolymer and copolymer have been accepted for ue a medical device [2]. The development of ynthetic biodegradable polymer ha in recent year benefited the deign and development of three-dimenional template or caffold for tiue-engineered product to upport, reinforce and in ome cae organie the regenerating tiue [3-4]. Thee function require a porou caffold with interconnected poroity and deirable chemical propertie [5]. A the polymer will degrade over time in the body during which the tiue i growing, the need for a econd urgery to remove the implant i eliminated [6]. In addition, ynthetic polymer have the advantage over natural biodegradable polymer in that they can be eaily ma-produced. The propertie, in particular, the degradation rate, can be tailored to uit pecific application [7]. The teriliability and biocompatibility of thee polymer have alo been welldocumented [8]. Polycaprolactone (PCL) i one of the mot flexible among the ynthetic biodegradable polymer and eay to proce. It i being ued in clinic a a urgical material and it biomedical application have been reported in controlled drug delivery ytem [9-1] and implant for orthopaedic urgery [11]. It wa alo uggeted a a delivery vehicle for recombinant growth hormone [12]. PCL ha a low gla-tranition temperature (~ -6 o C) and a low melting point (6 o C). Becaue of it low gla-tranition temperature, the PCL amphorou phae diplay high molecular mobility at body temperature. Furthermore, with it ignificant degree of crytallinity and ubtantial hydrophobicity, high molecular PCL ha hown remarkably long in-vivo degradation time [13]. Capronor, a 1-year contraceptive repreent uch a ytem [1]. A an aliphatic polyeter, PCL alo degrade by hydrolyi and the hydrolyed product are reorbed by the body with minimal reaction of the tiue [11,14]. Thi unique et of characteritic fill a gap in the property pectrum unmatched by any other aborbable material. Mot of the conventional method for caffold fabrication uch a olvent cating and particulate-leaching [15], extruion [16], ga foaming [17], freeze drying [18] and phae eparation [19] involve toxic olvent and incomplete removal of reidual particulate in the polymer matrix [2]. Furthermore, thee method are retricted in hape control. The ue of a olid freeform fabrication technique uch a Three- Dimenional Printing will circumvent the limitation [21]. 2 OBJECTIE The invetigation of the proceing of polycaprolactone caffold with a olid freeform fabrication method, pecifically Three-Dimenional Printing (3DP) i conducted here. 3 METHODOLOGY PCL and polyvinyl alcohol (PA) powder were blended for the fabrication of pre-caffold uing a Three-Dimenional Printing (3DP) machine. The pre-caffold were ubequently proceed by particulate-leaching to generate the porou caffold. Blending PCL with PA, which acted a a tranient binder and wa removed later on during particulate-leaching in thi work, ha two advantage. The firt i that PA i wateroluble and potentially toxic organic olvent are 34

2 not neceary to diolve thi phae. The econd i that PA i itelf biocompatible and any reidual polymer hould not induce an inflammatory repone [22, 23]. 3.1 Raw material Powder form polycaprolactone (PCL) CAPA653 and poly(vinyl alcohol) (PA) GL-5S were obtained from Solvay Caprolactone (Chehire, UK) and Nippon Gohei, Singapore, repectively. The peak melting point of the material were determined with a TA Differential Scanning Calorimeter and their denitie, by a pcynometer. The reult are hown in Table 1. Table 1. Melting peak and denitie of the raw material ued. Material Melting peak [ o C] Denity [kg m -3 ] PCL 59± PA 84± Preparation of caffold A commercial 3DP machine (ZCorp, Burlington, USA) wa ued in thi application to fabricate the pre-caffold, which would later be proceed to generate poroity within, and hence became a caffold. Rectangular bar of 15 (length) x 9 (width) x 3.5 (thickne) mm 3 were fabricated on the 3DP equipment uing a waterbaed ink. The a-received powder of PCL and PA were ieved to obtain particle range of 15 to 212 µm and 16 to 15 µm, repectively, with a vibratory ieve haker and the morphology of the ieved particle i hown in Fig. 1. Cumulative wt / % PA PCL Size / µm Fig. 1. Particle ize ditribution of PCL and PA. Three blend, 5PCL5PA, 4PCL6PA and 3PCL7PA of different PCL/PA proportion, a hown in Table 2, were mixed in an Inverina-Shaker-Mixer (Bioengineering AG, Sagenraintrae, Switzerland) for 3,6 revolution. Table 2. Blend of PCL and PA prepared. Blend ID PCL PA Proportion (w/w %) Range (µm) Proportion (w/w %) Range (µm) 5PCL5PA PCL6PA PCL7PA The printed pre-caffold were left air-dried at room temperature and had ufficient trength to be handled manually. They were ubequently heated at 65 o C. Scaffold were generated by particulate-leaching in which PA i the leachable component. To determine the optimal leaching duration, the pre-caffold were immered in deionied water for a et of duration. At 2, 4, 6, 1, 14, 24 h after immerion, the ample were withdrawn from the water, evaporated and air-dried at room temperature for at leat 12 hour after which their mae were meaured. 3.3 Scaffold characteriation Differential canning calorimetry wa employed to determine the thermal propertie of the powder, blend, a-printed pre-caffold, a-heated pre-caffold and a-leached caffold. Sample were heated from 5 o C to 15 o C at 1 o C/min, in nitrogen ga atmophere. Three meaurement were made to obtain the average. The torage modulu of the pre-caffold and caffold wa determined by a Perkin Elmer dynamic mechanical analyer. Before teting, the ample were hold for 1 minute at 2 o C and thereafter heated from 2 o C to 4 o C at a can rate of 1 o C/min. The caffold were gold coated and examined in a canning electron microcope (SEM). The molecular weight of the PCL in the a-printed ample, a-heated ample and a-leached caffold during proceing wa examined by a gel permeation chromatography (Agilent 11 GPC) at 25 o C. PLgel mixed bed column, which could detect molecular weight range of 2 3,,, wa ued. Tetrahydrofuran (THF) (HPLC grade) wa ued a the mobile phae at a flow rate of 1 ml/min and the injection volume wa 5 µl. The molecular weight calibration wa etablihed uing polytyrene tandard covering a molecular weight range of 9,86 to 35

426,6. Three meaurement were made to obtain the average. (a) The poroity in the caffold wa etimated by the following formula, auming that all the PA wa removed at leaching and no PCL wa leached.

volume of the a-leached caffold and = l x d x t of which l, d and t are the length, depth and thickne a meaured on the caffold, repectively.

3 426,6. Three meaurement were made to obtain the average. (a) The poroity in the caffold wa etimated by the following formula, auming that all the PA wa removed at leaching and no PCL wa leached. Poroity = = pore PCL (1) (b) Where PCL i the volume of PCL content in the mpcl a-leached caffold and PCL =, m PCL ρ PCL and ρ PCL refer to the ma and denity of PCL in the caffold, repectively i the volume of the a-leached caffold and = l x d x t of which l, d and t are the length, depth and thickne a meaured on the caffold, repectively. pore i the volume of poroity in the a-leached caffold 4 RESULTS & DISCUSSION 4.1 Pot-printing proceing Although the pre-caffold produced at printing had ufficient handling trength, it collaped and lot it form immediately when immered in the deionied water. Heat treatment near the melting point of PCL at 65 o C helped to enhance integrity and the part could be immered in the water for at leat 24 h without loing it form. The average torage modulu (E ) value for the a-printed part were.78 ±.7 MPa,.66 ±.8 MPa and.6 ±.7 MPa for 5PCL5PA, 4PCL6PA and 3PCL7PA, repectively, at 25 o C. A for the a-heated part, the value were 2.63 ±.3 MPa, 1.89 ±.3 MPa and 1.6 ±.8 MPa for 5PCL5PA, 4PCL6PA and 3PCL7PA, repectively, at the ame temperature. Only light decreae in the E value in the printed part wa noted with the reduction of PCL amount. With heat treatment, E increaed by about three time. The increae in trength in the a-heated pre-caffold wa made poible with the melting of PCL particle, which diffued over the matrix a een in Fig. 2. Thi reulted in a tronger network in the a-heated precaffold. Fig. 2. Micrograph of (a) a-printed and (b) aheated pre-caffold. Remaining ma of the pre-caffold at different duration of leaching wa determined and hown in Fig. 3. The amount of ma lo correponded to the amount of PA in the precaffold and mall amount (< 1 wt%) of PCL. By the 1 th hour, no ignificant lo of binder could be detected. In Fig. 4, which compare the differential canning calorimetry of the a-leached ample to thoe of the a-received raw material, blended material and printed part, no ignificant melting peak correponding to thoe of PA were detected in the leached ample. It how the complete removal of PA in the caffold. % Ma Remaining PCL5PA 4PCL6PA 3PCL7PA Time / h Fig. 3. Leaching time curve. 36

Heat flow / W g -1 1 5-5 -1-15 PCL CAPA653 PA A-blended A-printed A-leached PA peak Fig.

4 Heat flow / W g PCL CAPA653 PA A-blended A-printed A-leached PA peak Fig. 5 ummarie the change in the molecular weight of PCL in the a-printed pre-caffold, a-heated pre-caffold and a-leached caffold. No ignificant degradation in molecular weight wa oberved in the PCL of the three blend a they were progreively proceed from printing to leaching. 4.2 Scaffold characteritic Temperature / o C Fig. 4. Calorimetric curve of PCL, PA, a-blended material, a-printed pre-caffold and a-leached caffold. Table 3 tabulate the melting peak of PCL (T m ) in the a-printed, a-heated and a-leached precaffold and caffold of 5PCL5PA, 4PCL6PA and 3PCL7PA. In general, the data reveal a ditinct but mall increae ( o C) in the average T m a the part wa progreively proceed from printing to leaching with T m(a-printed) < T m(a-heated) < T m (a-leached). The lowering of T m of PCL in the a-printed and aheated pre-caffold may be attributed to the preence of PA, which melted over a wider range of temperature. With the removal of PA in the a-leached ample, T m of PCL wa brought back to a level cloer to the T m of the a-received raw material. The average torage modulu (E ) value for the a-leached caffold were meaured to be.19 ±.1 MPa and.3 ±.1 MPa, for 5PCL5PA and 4PCL6PA, repectively, at 25 o C. A before, the trength decreaed with decreaing amount of PCL. It wa not ucceful to meaure the trength value for the caffold fabricated from 3PCL7PA a the tructure crumbled upon teting. The SEM image in Fig. 6 how a uniform ditributed microtructure in the a-leached caffold. The leached ample wa oft and pongy. No obviou urface degradation wa oberved on them although the corner lot it harpne. The exterior wa uniform and the form of the printed part retained reaonably well after leaching. The open pore tructure reveal that the poroity network within caffold ha a high degree of connectivity. Table 3. Melting peak of PCL (T m) in a-printed, aheated and a-leached ample. 5PCL5 PA 4PCL6 PA 3PCL7 PA T m ( o C) A-Printed A-Heated A-Leached ± ± ± ± ± ± ± ± ±.5 Fig. 6. A typical leached ample. Mw Pre-caffold Heat-treated Scaffold 5PCL5PA 4PCL6PA 3PCL7PA Fig. 5. Change in molecular weight of PCL at different tage of proceing. Fig. 7 how the internal morphologie of the caffold produced by leaching different amount of PA. The caffold fabricated from the three blend exhibited almot imilar open cellular tructure at the urface and interior. A poroity wa generated by the removal of PA, the level of poroity in the caffold alo increaed from 5PCL5PA to 3PCL7PA. The etimated poroity (from equation 1) wa.8,.85 and.88 for the caffold fabricated from blend 5PCL5PA, 4PCL6PA and 3PCL7PA, repectively. With 5 and 6 wt% of PA incorporated in the pre-caffold, macropore in the range of 1 to 5 µm could be oberved in the caffold. The pore generated in the caffold 37

Polycaprolactone Foam for Scaffold Development of 3PCL7PA blend were larger. Thee were formed not only by the leaching of PA but alo the removal of a mall amount of PCL particle alongide with it.

Careful handling wa required for caffold fabricated from 3PCL7PA. There i thu a limit to which the amount of PA could be increaed for the attainment of higher poroity.

the level of poroity increaed with the tarting amount of PA in the pre-caffold with a concomitant decreae in torage modulu. Pore of ize 1 to 5 µm were obtained.

5 Polycaprolactone Foam for Scaffold Development of 3PCL7PA blend were larger. Thee were formed not only by the leaching of PA but alo the removal of a mall amount of PCL particle alongide with it. Although thi created a greater poroity than expected, the ituation wa undeirable a the creation of larger pore with the removal of the PCL particle would weaken the tructure. Careful handling wa required for caffold fabricated from 3PCL7PA. There i thu a limit to which the amount of PA could be increaed for the attainment of higher poroity. It i poible to improve it handling trength by reinforcing the material with hydroxyapatite [24]. the level of poroity increaed with the tarting amount of PA in the pre-caffold with a concomitant decreae in torage modulu. Pore of ize 1 to 5 µm were obtained. No ignificant reduction in molecular weight wa detected in the PCL during caffold fabrication. 6 INDUSTRIAL SIGNIFICANCE Medical engineering i a young and growing indutry in Singapore. However, reearch i more active in the univerity and hopital. Thi article illutrated the ue of a commercial prototyping equipment (i.e. 3D printer) to proce biodegradable polymer for caffold development for potential application in tiue engineering. Minimum modification wa made in the equipment for thi tudy. (a) REFERENCES [1] (b) [2] [3] [4] (c) [5] [6] Fig. 7. Morphology of leached ample prepared from (a) 5PCL5PA, (b) 4PCL6PA and (c) 3PCL7PA. 5 [7] CONCLUSION [8] In thi tudy, fabrication of caffold of ynthetic biodegradable polymer polycaprolactone (PCL) uing the three-dimenional printing (3DP) with poly (vinyl alcohol) both a a binder during printing and a pore-generating medium during particulate-leaching, wa invetigated. The binder wa non-toxic, completely removed from the caffold and with no uage of toxic olvent during proceing. Scaffold with macropore and open-cellular tructure were produced and [9] 38 D.K. Gilding and A.M. Reed, Biodegradable polymer for ue in urgerypolyglycolic/ poly(actic acid) homo- and copolymer: 1, Polymer, ol. 2(12), pp , (1979). T.H. Barrow, Degradable implant material: a review of ynthetic aborbable polymer and their application, Clin. Mater., ol. 1, pp , (1986). R. Langer and J.P. acanti, Tiue Engineering. Science, ol. 26(511), pp , (1993). B.S. Kim and D.J. Mooney, Development of biocompatible ynthetic extracellular matrice for tiue engineering, Trend Biotech., ol. 16(5), pp , (1998). S.. Madihally and H.W.T. Matthew, Porou chitoan caffold for tiue engineeering, Biomater., ol. 2(12), pp , (1999). J.S. Temenoff and A.G. Miko, Review: tiue engineering for regeneration of articular cartilage, Biomater., ol. 21(5), pp , (2). J.C. Middleton and A.J. Tipton, Synthetic biodegradable polymer a orthopaedic device, Biomater., ol. 23(23), pp , (2). C. Chu, Biodegradable polymeric biomaterial: an updated overview, in The Biomedical Engineering Handbook, J.D. Bronzino, CRC Pre, Florida, pp , (2). P.M. Hombreiro, C. Zinutti, A. Lamprecht, N. Ubrich, A. Atier, M. Hoffman, R. Bodmeier and P. Maincent, The preparation and evaluation of poly(epiloncaprolactone) microparticle containing both a lipophilic and a hydrophilic drug. J.

6 Controlled Releae, ol. 65(3), pp , (2). [1] C.G. Pitt, T.A. Mark and A. Schindler, Biodegradable drug delivery ytem baed on aliphatic polyeter: application to contraceptive and narcotic antagonit, in Controlled Releae of Bioactive Material, R. Baker, Academic, New York, pp (198). [11] K.J. Lowry, K.R. Hamon, L. Bear, Y.B. Peng, R. Celaluce, M.L. Evan, O.J. Anglen and W.C. Allen, Polycaprolactone/gla bioaborbable implant in a rabbit humeru fracture model, J. Biomed. Mater. Re., ol. 36(4), pp , (1997). [12] C.J. Goodwin, M. Braden, S. Downe, J.J. Marhall, Releae of bioactive human growth hormone from a biodegradable material: Poly(epilon-caprolactone), J. Biomed Mater. Re., ol. 4(2), pp , (1998). [13] D.E. Pernin and J.P. Englih, in Handbook of biodegradable polymer, A.J. Dome, J. Kot and D.M. Wieman, Harwood Academic, Amterdam, p. 63, (1997). [14] R.R.M. Bo, F.R. Rozema, G. Boering, A.J. Nijenhui, A.J. Penning, A.B. erway, P. Nieuwenhui and H.W.B. Janen, Degradation of and tiue reaction to biodegradable poly(l-lactide) for ue a internalfixation of fracture a tudy in rate, Biomater., ol. 12(1), pp , (1991). [15] A.G. Miko, A.J. Thoren, L.A.Czerwonka, Y. Bao and R. Langer, Preparation and characteriation of poly (l-lactic acid) foam, Polymer, ol. 35(5), pp , (1994). [16] M.S. Widmer, P.K. Gupta, L. Lu, R.K. Mezlenyi, G.R.D. Evan, K. Brandt, T. Savel, A. Gurlek, C.W. Patrick Jr. and A.G. Miko, Manufacture of porou biodegradable polymer conduit by extruion proce for guided tiue regeneration, Biomater., ol. 19(21), pp , (1998). [17] Y.S. Nam, J.J. Yoon and T.G. Park, A novel fabrication method of macroporou biodegradable polymer caffold uing ga foaming alt a a porogen additive, J. Biomed. Mater. Re., ol. 53(1), pp. 1-7, (2). [18] K. Whang, D.C. Tai, E.K. Nam, M. Aitken, S.M. Sprague, P.K. Patel and K.E. Healy, Ectopic bone formation via rhbmp-2 delivery from porou bioaborbable polymer caffold, J. Biomed. Mater. Re., ol. 42(4), pp , (1998). [19] L. Lu and A.G. Miko, The importance of new proceing technique in tiue engineering, MRS Bulletin, ol. 21(11), pp , (1996). [2] C.X.F. Lam, X.M. Mo, S.H. Teo and D.W. Hutmacher, Scaffold development uing 3D printing with a tarch-baed polymer, Mater. Sci. Eng. C, ol. S2(1-2), pp , (22). [21] D.W. Hutmacher, Scaffold in tiue engineering bone and cartilage, Biomater, ol. 21(24), pp , (2). [22] K. Burczak, E. Gamian and A. Kochman, Long-term in vivo performance and biocompatibility of poly(vinyl-alcohol) hydrogenl macrocapule for hybrid-type artificial pancrea, Biomater., ol. 17(24), pp , (1996). [23] S.H. Oh, S.G. Kang, E.S. Kim, S.H. CHo and J.H. Lee, Fabrication and charactertiation of hydrophilic poly(lactic-coglycolic)/poly(vinyl alcohol) blend cell caffold by melt-moulding particulate-leaching method, Biomater., ol. 24(22), pp (23). [24] J.F. Mano, C.M. az, S.C. Mende, R.L. Rei and A.M. Cunha, Dynamic mechanical propertie of hydroxyapatite-reinforced and porou tarch-baed degradable biomaterial, J. Mater. Sci. Med., ol. 1(12), pp , (1999). 39

INVESTIGATION OF HIGHLY POROUS POLY(Ε-CAPROLACTONE)

szerzoi_jav_005_036.qxd 2008.06.20. 16:00 Page 30 INVESTIGATION OF HIGHLY POROUS POLY(Ε-CAPROLACTONE) SCAFFOLDS László Oláh 1, Lajos Borbás 2, Tibor Czigány 3 1 Polymer Competence Center Leoben GmbH 2