Introduction: Progress in the field of tissue engineering and regenerative medicine has been hampered because of limited vascularization. Current approaches to overcome this issue include delivery of angiogenic growth factors (GF), transplantation of endothelial cell, gene delivery, or the utilization of decellularized scaffolds[1]. Our lab discovered a unique material based on poly methacrylic acid (PMAA) that induced the formation of blood vessels instead of a fibrous capsule, without the addition of GF or cells[2]-[4]. Here we report on the properties of a new injectable PMAA-based hydrogel that we envisage can be used for cell delivery.
Materials and Methods: In our approach, poly(ethylene glycol) (PEG) was used as an injectable “delivery vehicle” to administer water-soluble, linear poly(MAA) in vivo. A liquid solution containing multi-arm PEG-vinyl sulfone and poly(MAA) gels upon the addition of a stoichiometric amount of a thiol cross-linker, via Michael-type addition[5]. The resulting material is a semi-interpenetrating polymer network (SIPN), where PMAA is physically “entrapped” in a 3D network made of PEG.
Results and Discussion: Interpenetrating networks (SIPN) of PEG and poly(MAA) were prepared with well-controllable physical properties. At room temperature, gelation times ranged from >11 min to <30 s when changing the nature of the cross-linker or altering the hydrogel formulation, as shown in Figure 1A. SIPN exhibited tunable water uptake accompanied by swelling at 37°C, which did not change over a period of three weeks indicating a stable 3D networks (Figure 1B and C). Two formulations were prepared by changing the mass ratio of PEG to PMAA (80/20 and 60/40) and compared to the base PEG vehicle.
Figure 1: Gelation times (A) and water uptakes (B) of hydrogels prepared from different cross-linkers: 2arms PEG-SH (P-2); 4arms PEG-SH (P-4); 8arms PEG-SH (P-8); and dithiothreitol (DTT). The equilibrium swelling of hydrogels prepared with DTT remains stable for at least 21 days (C).
The generation of blood vessels in the surrounding tissue upon subcutaneous injection of the SIPN in CD1 mice is being investigated, as shown in Figure 2. Studies are underway to optimize the formulation of the SIPN and test its suitability for cell delivery purposes. Chemical modification of PMAA to allow the preparation of injectable PMAA hydrogels without PEG vehicle is also under consideration.
Figure 2: Generation of blood vessels at periphery of hydrogels upon subcutaneous injection is evaluated in vivo. SIPN PEG60-PMAA40 (right) and pure PEG (left). Both hydrogels were prepared using DTT as cross-linker.
Conclusions: A new type of injectable hydrogel made of the vascular regenerating methacrylic acid was prepared. The vascularizing capacity and the suitability for cell delivery purposes is investigated. The findings create the basis for the selective production of such hydrogels for future application in the field of cell-based therapy.
The authors acknowledge the financial support of the Ontario Research Fund
References:
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