Name: fabrication of a bioactive, pcl-based "self-fitting" shape memory polymer scaffold
Uploaded: 2015-10-23T15:00:00
Description: Watch this Scientific Journal Video about Fabrication of a Bioactive, PCL-based "Self-fitting" Shape Memory Polymer Scaffold at JoVE.com

The authors thank Texas A&#38;M University Engineering and Experiment Station (TEES) for financial support of this research. Lindsay Nail gratefully acknowledges support from the Texas A&#38;M University Louis Stokes Alliance for Minority Participation (LSAMP) and the National Science Foundation (NSF) Graduate Research Fellowship Program (GRFP). Dawei Zhang thanks the Texas A&#38;M University Dissertation Fellowship.

1. Synthesizing PCL-DA Macromer
<ol>
	<li>Run the acrylation reaction.
	<ol>
		<li>Weigh 20 g of PCL-diol (Mn = ~10,000 g/mol) into a 250 ml&#160;round bottom flask equipped with a Teflon-covered magnetic stir bar.</li>
		<li>Dissolve the PCL-diol in DCM.
		<ol>
			<li>Add 120 mLlof DCM to the flask (concentration = 0.17 g/ml).</li>
			<li>Place a rubber septum loosely into the neck of the flask so as to avoid pressure build-up while also preventing evaporation of DCM.</li>
			<li>Stir solution for ~30 min&#...

<ol>
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B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Polydopamine-mediated+immobilization+of+multiple+bioactive+molecules+for+the+development+of+functional+vascular+graft+materials.">Polydopamine-mediated immobilization of multiple bioactive molecules for the development of functional vascular graft materials.</a> Biomaterials. 33, 8343-8352 (2012).</li><li>Wu, C., Fan, W., Chang, J., Xiao, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mussel-inspired+porous+SiO+2+scaffolds+with+improved+mineralization+and+cytocompatibility+for+drug+delivery+and+bone+tissue+engineering.">Mussel-inspired porous SiO 2 scaffolds with improved mineralization and cytocompatibility for drug delivery and bone tissue engineering.</a> J Mater Chem. 21, 18300-18307 (2011).</li><li>Ku, S. H., Ryu, J., Hong, S. K., Lee, H., Park, C. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=General+functionalization+route+for+cell+adhesion+on+non-wetting+surfaces.">General functionalization route for cell adhesion on non-wetting surfaces.</a> Biomaterials. 31, 2535-2541 (2010).</li><li>Schoener, C. A., Weyand, C. B., Murthy, R., Grunlan, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Shape+memory+polymers+with+silicon-containing+segments.">Shape memory polymers with silicon-containing segments.</a> J Mater Chem. 20, 1787-1793 (2010).</li><li>Zhang, D., Giese, M. L., Prukop, S. L., Grunlan, M. 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A., Kratz, K., Klein, F., L&#252;zow, K., Lendlein, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermomechanical+behaviour+of+biodegradable+shape-memory+polymer+foams.">Thermomechanical behaviour of biodegradable shape-memory polymer foams.</a> 1190, (2009).</li><li>Luo, X., Mather, P. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+and+characterization+of+shape+memory+elastomeric+composites.">Preparation and characterization of shape memory elastomeric composites.</a> Macromolecules. 42, 7251-7253 (2009).</li><li>Lendlein, A., Schmidt, A. 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This protocol describes the preparation of a polydopamine-coated, PCL-based scaffold whose self-fitting behavior, as well as osteoinductivity and bioactivity, makes it of interest in the treatment of irregular CMF bone defects. Aspects of the protocol may be altered to change various scaffold features.
The protocol begins with acrylation of a PCL-diol to permit UV cure. In the reported example, the PCL-diol Mn is ~10,000 g/mol. However, by appropriately adjusting amount of acryloyl ...

Currently considered the gold standard of cranio-maxillofacial (CMF) bone defect treatments, transplantation of harvested autologous grafts is hindered by complex grafting procedures, donor site morbidity and limited availability1. A particular difficulty is shaping and fixing the rigid autograft tightly into the defect in order to obtain osseointegration and to prevent graft resorption. Tissue engineering has been investigated as an alternative strategy to autografting and synthetic bone substitutes (e.g. bone cement)2,3. Critical to the success of a tissue engineering approach is a scaffold with a specific set of properties. First, in order to achieve osseointegration, the scaffold must form close contact with adjacent bone tissue4. The scaffold should also be osteoconductive, permitting cell migration, nutrient diffusion and neotissue deposition4,5. This behavior is generally achieved with biodegradable scaffolds exhibiting a highly interconnected pore morphology. Lastly, the scaffold should be bioactive so as to promote integration and bonding with surrounding bone tissue5.
Here, we present a protocol to prepare a tissue engineering scaffold with these properties. Importantly, this scaffold exhibits the ability to &#8220;self-fit&#8221; into irregular CMF defects due to its shape memory behavior6. Thermoresponsive shape memory polymers (SMPs) are known to undergo shape change upon exposure to heat7,8. SMPs are comprised of &#8220;netpoints&#8221; (i.e. chemical or physical crosslinks) which determine the permanent shape and &#8220;switching segments&#8221; which maintain the temporary shape and recover the permanent shape. The switching segments exhibit a thermal transition temperature (Ttrans) corresponding to either the glass transition (Tg) or melt transition (Tm) of the polymer. As a result, SMPs may be sequentially deformed into a temporary shape at T &#62; Ttrans, fixed in the temporary shape at T &#60; Ttrans, and recovered to the permanent shape at T &#62; Ttrans. Thus, an SMP scaffold could achieve &#8220;self-fitting&#8221; within a CMF defect as follows6. After exposure to warm saline (T &#62; Ttrans), an SMP scaffold would become malleable, permitting a generically prepared cylindrical scaffold to be hand-pressed into an irregular defect, with shape recovery promoting expansion of the scaffold to the defect boundary. Upon cooling (T &#60; Ttrans), the scaffold would return to its relatively more rigid state, with shape fixity maintaining its new temporary shape within the defect. In this protocol, an SMP scaffold is prepared from polycaprolactone (PCL), a biodegradable polymer studied extensively for tissue regeneration and other biomedical applications9-11. For shape memory, the Tm of PCL serves as the Ttrans and varies between 43 and 60 &#186;C, depending on the molecular weight of the PCL12. In this protocol, the Ttrans (i.e. Tm) of the scaffold is 56.6&#177;0.3 &#186;C6.
In order to achieve osteoconductivity, a protocol was developed to make PCL-based SMP scaffolds with highly interconnected pores based on a solvent-casting particulate-leaching (SCPL) method6,13,14. Polycaprolactone diacrylate (PCL-DA) (Mn = ~10,000 g/mol) was utilized to permit rapid, photochemical crosslinking and was dissolved in dichloromethane (DCM) to allow solvent-casting over the salt template. Following photochemical cure and solvent evaporation, the salt template was removed by leaching into water. The average salt size regulates scaffold pore size. Importantly, the salt template was fused with water prior to solvent-casting to achieve pore interconnectivity.
Bioactivity was imparted to the SMP scaffold by the in situ formation of a polydopamine coating onto pore walls6. Bioactivity is often introduced into scaffolds by the inclusion of glass or glass-ceramic fillers15. However, these may give rise to unwanted brittle mechanical properties. Dopamine has been shown to form an adherent, thin polydopamine layer on a variety of substrates16-19. In this protocol, the SMP scaffold was subjected to a slightly basic solution (pH = 8.5) of dopamine to form a nanothick coating of polydopamine on all pore wall surfaces6. In addition to enhancing surface hydrophilicity for improved cell adhesion and spreading, polydopamine has been shown to be bioactive in terms of formation of hydroxyapatite (HAp) upon exposure to simulated body fluid (SBF)18,20,21. In a last step, the coated scaffold is exposed to heat treatment at 85 &#186;C (T &#62; Ttrans) which leads to scaffold densification. Heat treatment was previously noted to be essential for scaffold shape memory behavior, perhaps due to PCL crystalline domains reorganizing to closer proximity14.
We additionally describe the methods to characterize the self-fitting behavior within an irregular model defect, shape memory behavior in terms strain-controlled cyclic-thermal mechanical compression tests (i.e. shape recovery and shape fixity), pore morphology, and in vitro bioactivity. Strategies to tailor scaffold properties are also presented.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>Polycaprolactone-diol (Mn ~ 10,000 g/mol)</td>
			<td>Sigma-Aldrich</td>
			<td>440752</td>
			<td></td>
		</tr>
		<tr>
			<td>Dichloromethane (DCM)</td>
			<td>Sigma-Aldrich</td>
			<td>D65100</td>
			<td>Dried over 4A molecular sieves</td>
		</tr>
		<tr>
			<td>4-dimethylaminopyridine (DMAP)</td>
			<td>Sigma-Aldrich</td>
			<td>D5640</td>
			<td></td>
		</tr>
		<tr>
			<td>Triethylamine (Et3N)</td>
			<td>Sigma-Aldrich</td>
			<td>T0886</td>
			<td></td>
		</tr>
		<tr>
			<td>Acryloyl chloride</td>
			<td>Sigma-Aldrich</td>
			<td>A24109</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethyl Acetate</td>
			<td>Sigma-Aldrich</td>
			<td>319902</td>
			<td></td>
		</tr>
		<tr>
			<td>Potassium Carbonate (K2CO3)</td>
			<td>Sigma-Aldrich</td>
			<td>209619</td>
			<td></td>
		</tr>
		<tr>
			<td>Anhydrous magnesium sulfate (MgSO4)</td>
			<td>Fisher</td>
			<td>M65</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium chloride (NaCl)</td>
			<td>Sigma-Aldrich</td>
			<td>S9888</td>
			<td></td>
		</tr>
		<tr>
			<td>2,2-dimethoxy-2-phenyl acetophenone (DMP)</td>
			<td>Sigma-Aldrich</td>
			<td>196118</td>
			<td></td>
		</tr>
		<tr>
			<td>1-vinyl-2-pyrrolidinone (NVP)</td>
			<td>Sigma-Aldrich</td>
			<td>V3409</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Sigma-Aldrich</td>
			<td>459844</td>
			<td></td>
		</tr>
		<tr>
			<td>Dopamine Hydrochloride</td>
			<td>Sigma-Aldrich</td>
			<td>H8502</td>
			<td></td>
		</tr>
		<tr>
			<td>Tris buffer (2mol/L)</td>
			<td>Fisher</td>
			<td>BP1759</td>
			<td>Used at 10 mM concentration, pH = 8.5</td>
		</tr>
		<tr>
			<td>Sieve</td>
			<td>VWR</td>
			<td>47729-972</td>
			<td></td>
		</tr>
		<tr>
			<td>UV-Transilluminator (365 nm, 25 W)</td>
			<td>UVP</td>
			<td>95-0426-02</td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge</td>
			<td>Eppendorf</td>
			<td>5810 R</td>
			<td></td>
		</tr>
		<tr>
			<td>Dynamic Mechanical Analyzer (DMA)</td>
			<td>TA Instruments</td>
			<td>Q800</td>
			<td></td>
		</tr>
		<tr>
			<td>High Resolution Sputter Coater</td>
			<td>Cressington</td>
			<td>208HR</td>
			<td></td>
		</tr>
		<tr>
			<td>Scanning Electron Microscope (SEM)</td>
			<td>FEI</td>
			<td>Quanta 600</td>
			<td></td>
		</tr>
	</tbody>
</table>

fabrication of a bioactive, pcl-based "self-fitting" shape memory polymer scaffold

Tissue engineering has been explored as an alternative strategy for the treatment of critical-sized cranio-maxillofacial (CMF) bone defects. Essential to the success of this approach is a scaffold that is able to conformally fit within an irregular defect while also having the requisite biodegradability, pore interconnectivity and bioactivity. By nature of their shape recovery and fixity properties, shape memory polymer (SMP) scaffolds could achieve defect &#8220;self-fitting.&#8221; In this way, following exposure to warm saline (~60 &#186;C), the SMP scaffold would become malleable, permitting it to be hand-pressed into an irregular defect. Subsequent cooling (~37 &#186;C) would return the scaffold to its relatively rigid state within the defect. To meet these requirements, this protocol describes the preparation of SMP scaffolds prepared via the photochemical cure of biodegradable polycaprolactone diacrylate (PCL-DA) using a solvent-casting particulate-leaching (SCPL) method. A fused salt template is utilized to achieve pore interconnectivity. To realize bioactivity, a polydopamine coating is applied to the surface of the scaffold pore walls. Characterization of self-fitting and shape memory behaviors, pore interconnectivity and in vitro bioactivity are also described.

The resulting PCL-based SMP scaffold is capable of self-fitting into a model CMF defect (Figure 2). After brief exposure to warm saline (~60 &#176;C), the cylindrical scaffold softens allowing the scaffold to be manually pressed into and expand within the model defect. After cooling to RT, the scaffold is fixed into its new temporary shape which is retained upon removal from the defect.
The shape memory behavior of an SMP scaffold is quantified by strain-controlled cyclic-ther...

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Fabrication of a Bioactive, PCL-based "Self-fitting" Shape Memory Polymer Scaffold

Scaffolds capable of fitting within cranio-maxillofacial (CMF) bone defects while exhibiting osteoconductivity and bioactivity are of interest. This protocol describes the preparation of a shape memory scaffold based on polycaprolactone diacrylate (PCL-DA) using a solvent-casting particulate-leaching (SCPL) method employing a fused salt template and application of a bioactive polydopamine coating.

Tissue engineering has been explored as an alternative strategy for the treatment of critical-sized cranio-maxillofacial (CMF) bone defects. Essential to ...

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Fabrication of Inverted Colloidal Crystal Polyethylene glycol Scaffold: A Three-dimensional Cell Culture Platform for Liver Tissue Engineering

The ability to maintain hepatocyte function in vitro, for the purpose of testing xenobiotics&#39; cytotoxicity, studying virus infection and developing ...

Fabrication and Characterization of Optical Tissue Phantoms Containing Macrostructure

The rapid development of new optical imaging techniques is dependent on the availability of low-cost, customizable, and easily reproducible standards. By ...

Microdissection of Primary Renal Tissue Segments and Incorporation with Novel Scaffold-free Construct Technology

Kidney transplantation is now a mainstream therapy for end-stage renal disease. However, with approximately 96,000 people on the waiting list and only ...