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

Summary

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.

Abstract

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 “self-fitting.” In this way, following exposure to warm saline (~60 ºC), the SMP scaffold would become malleable, permitting it to be hand-pressed into an irregular defect. Subsequent cooling (~37 ºC) 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.

Introduction

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 ....

Protocol

1. Synthesizing PCL-DA Macromer

1. Run the acrylation reaction.
   1. Weigh 20 g of PCL-diol (M_n = ~10,000 g/mol) into a 250 ml round bottom flask equipped with a Teflon-covered magnetic stir bar.
   2. Dissolve the PCL-diol in DCM.
      1. Add 120 mLlof DCM to the flask (concentration = 0.17 g/ml).
      2. Place a rubber septum loosely into the neck of the flask so as to avoid pressure build-up while also preventing evaporation of DCM.
      3. Stir solution for ~30 min at ~250 rpm to completely dissolve the polymer.
   3. Add ~6.6 mg of 4-dimethylaminopyridine (DMAP) to the solution and disso....

Results

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 °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-thermal m.......

Discussion

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 M_n is ~10,000 g/mol. However, by appropriately adjusting amount of acryloyl .......

Materials

List of materials used in this article

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