Chapter 4 results discussions design and development of tissue engineering scafflods using rapid prototyping technology

Chapter Four: Results and Discussions Chapter Four Results and Discussions 91 Chapter Four: Results and Discussions 4.1 Polymer Synthesis Ring-opening polymerization (ROP) of ε-caprolactone initiated by dihydroxyl PEG formed an ABA-type triblock copolymer with a central PEG block and two lateral PCL blocks. Polymers initiated by ethylene glycol can be regarded as PCL homopolymer since ethylene glycol is a small molecule. On the other hand, copolymerization initiated by mPEG propagated at one end only. The hydrophilic segment in the resulted mPEG-PCL copolymers should exhibit higher chain mobility as compared to PCL-PEG-PCL. Based on the now wellknown mechanism of ROP of lactonic compounds initiated by alcohols in the presence of a catalyst like stannous octoate (Kricheldorf et al, 2000; Kowalski et al, 2000), the process of block copolymerization of ε-caprolactone and DLlactide was extended to zinc metal initiation by mPEGOH (Huang et al, 2004). In a first step, the ROP of ε-caprolactone was initiated by mPEG propagating at the OH end only to form a diblock PEG-PCL copolymer terminated by an OH group. This hydroxyl-bearing diblock copolymer was then used as macroinitiator to polymerize the DL-lactide. The main structure of the chain was thus PEG-PCL-P(DL)LA. Table 4.1 summarizes the molecular characteristics of the resulting polymers and of the precursors involved in the synthesis, namely mPEGOH, PEG-PCL. In this study, mPEG with a Mn of 5,000, dihydroxyl PEG with a Mn of 8,000, and an initial [CL]/[EO] ratio of 3/1 were selected as a compromise between the formation of high molecular weights, appropriate PEG content, and the bioresorbability of PEG-rich degradation products. In fact, low molecular weight PEG ([...]... 4. 10: Influence of liquefier temperature on RW and porosity of the scaffolds fabricated with lay-down pattern of 0/90 and nozzle size of 500 µm RW Porosity 90 700 RW (um) 70 500 60 40 0 Porosity 80 600 50 300 40 2.5 3 3.5 4 4.5 5 5.5 Pressure (bar) Figure 4. 11: Influence of extrusion pressure on RW and porosity of the scaffolds fabricated with lay-down pattern of 0/90 and nozzle size of 500 µm 113 Chapter. .. z-direction (Figures 4. 4 - 4. 9 & 4. 18 - 4. 19) This anisotropy was more or less pronounced depending on the processing conditions and other design 125 Chapter Four: Results and Discussions parameter (FD) In this study, all the designs and processing conditions tested led to the development of scaffolds with structural parameters in the range of those of various tissues including trabecular and cancellous bones... demonstrated by Figures 4. 13 and 4. 14 FD 1.5 mm FD 1.25 mm FD 1.0 mm Figure 4. 13: SEM images of PCL scaffolds demonstrating the influence of FD on their morphologies (nozzle size: 500 µm & Pattern 0/90); top row: plan view & bottom row: x-sectional view 116 Chapter Four: Results and Discussions FD 1.5 mm FD 1.25 mm FD 1.0 mm Figure 4. 14: SEM images of PCL-PEG scaffolds demonstrating the influence of FD on their... the main aim of the incorporation of other polymer components into the PCL main chain was to modulate the mechanical properties and resorption rates of the original PCL scaffold 4. 4 Scaffold Design and Processing The requirements for tissue engineering scaffolds like, morphological, mechanical and biochemical properties are application specific i.e different 101 Chapter Four: Results and Discussions. .. extruding pressure and deposition speed It is because of the fact that the fluidity of polymer melt increases with increasing temperature that makes faster and more dispensing of the polymer The overall morphological changes due to change of liquefier temperature are presented in Table 4. 4 An increase of temperature from 80 to 100°C resulted in an increase of road 106 Chapter Four: Results and Discussions. .. Chapter Four: Results and Discussions RW Porosity 600 70 500 60 40 0 50 40 270 320 Porosity (%) 80 300 220 Filament Dia (um) 700 370 Deposition Speed (mm/min) Figure 4. 12: Influence of deposition speed on RW and porosity of the scaffolds fabricated with lay-down pattern of 0/90 and nozzle size of 500 µm Mariani et al (2006) investigated the influence of process parameters (deposition velocity and extrusion... 11.09 100 5.0 623 45 877±90 118±18 47 7.90 100 P1=3.0 bars P2 =4. 0 bars P3=5.0 bars Figure 4. 6: SEM images of PCL scaffolds demonstrating the influence of extrusion pressure on their morphologies (nozzle size: 500 µm & FD: 1.5 mm); top row: plan view & bottom row: x-sectional view 109 Chapter Four: Results and Discussions P1=3.0 bars P2 =4. 0 bars P3=5.0 bars Figure 4. 7: SEM images of PCL-PEG scaffolds... keeping the pattern and FD constant, larger pores and thus, higher porosity can be obtained 121 Chapter Four: Results and Discussions 4. 5 .4 Influence of Lay-Down Pattern Beside the process and design parameters, the influence of lay-down patterns on scaffold morphology was also investigated by analyzing the scaffolds fabricated with three lay-down patterns namely, 0/90, 0/60/120 and 0/30/60/90/120/150... 11.09 100 360 377 48 1123±100 340 ±30 75 12.60 100 S= 240 mm/min S=300 mm/min S=360 mm/min Figure 4. 8: SEM images of PCL scaffolds demonstrating the influence of deposition speed on their morphologies (nozzle size: 500 µm & FD: 1.5 mm); top row: plan view & bottom row: x-sectional view 111 Chapter Four: Results and Discussions S= 240 mm/min S=300 mm/min S=360 mm/min Figure 4. 9: SEM images of PCL-PEG scaffolds... integrity and reproducibility of the scaffold were maintained Therefore, based on the investigated results the best-suited values of the process parameters namely, liquefier temperature, extruding pressure and deposition speed were considered to be 90°C, 4. 0 bars and 300 mm/min respectively that maintained a significant consistency between the theoretical and real values of RW 4. 5.3 Influence of Design . Scaffold 64. 3 51500 1.6 55.3 39. 64 PCL-PEG Raw 63.5 33000 1.6 62 44 .44 PCL-PEG Scaffold 65.3 33600 1.7 61.8 44 .30 PCL-PEG-PCL Raw 64. 4 30000 1.8 48 34. 41 PCL-PEG-PCL Scaffold 65.6 31700 1.7 47 .2. Chapter Four: Results and Discussions Chapter Four Results and Discussions 91 Chapter Four: Results and Discussions 4. 1 Polymer. well-defined melting profiles. 15 20 25 30 35 40 45 0 50 100 150 Temperature (oC) Heat Flow PCL-PEG-PCL PEG-PCL-PLA PCL-PEG PCL 15 20 25 30 35 40 0 50 100 150 Temperature (oC) Heat Flow PCL-PEG-PCL