An injectable, in situ-forming, mechanically resilient, and degradable hydrogel for cell delivery for nucleus pulposus regeneration
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Authors
Riahinezhad, Hossein
Date
Type
thesis
Language
eng
Keyword
Nucleus pulposus regeneration , Injectable hydrogel , Cell encapsulation
Alternative Title
Abstract
Intervertebral disk degeneration, occurring mainly in the nucleus pulposus (NP), is a main cause of back pain. Tissue engineering has emerged as a promising approach for regenerating the damaged tissue by delivering cells of interest within an appropriate scaffold. Hydrogels have received great attention for cell encapsulation due to their potential for mimicking the extracellular matrix environment. This thesis focused on development of an injectable, in situ-forming, mechanically resilient and degradable hydrogel for cell delivery for nucleus pulposus regeneration.
The hydrogel design employed a Michael addition reaction for hydrogel formation through reaction with thiol modified chondroitin sulfate (CS-SH) with an amphiphilic synthetic copolymer made of a functionalized 4-arm-[poly(ethylene glycol)-block-poly(trimethylene carbonate)] (4a-[P(EG)m-b-P(TMC)n]). CS was selected as it is present in the NP tissue and it can support the degradability of the hydrogel, and the amphiphilic copolymer was employed to create a range of mechanical properties through the contributions of the P(TMC) block. Two different thiol reactive functional groups were considered: vinyl sulfone and acrylate. Vinyl sulfone group were initially examined, and in particular a vinyl sulfone carbonate monomer that could be polymerized using 4a-[P(EG)] as a macroinitiator. During examination of hydrogels formed with this polymer and chondroitin sulfate, it was discovered that the hydrogels unexpectedly underwent rapid degradation. Further investigation into degradation mechanism revealed that the carbonate linkage in poly(vinyl sulfone carbonate) was hydrolyzed due to the electron withdrawing capacity of the pendant vinyl sulfone group, making the carbonyl bond of the polymer backbone susceptible to the nucleophile attack by a hydroxyl group.
Due to the rapid degradation of the VSC based hydrogels, focus shifted to use of an acrylate functionalized amphiphilic synthetic copolymer. A library of hybrid hydrogels prepared through crosslinking CS-SH with acrylate functionalized 4a-[P(EG)m-b-P(TMC)n] was created to find a candidate hydrogel with mechanical properties similar to those of native human NP tissue for NP cell delivery. Changing the polymer volume fraction of the hydrogels or the length of P(TMC) block resulted in a wide range of Young’s moduli from 24 to 150 kPa. Additionally, the hydrogels had high water content and were resistant to cyclic compressive loads, which are criteria to mimic the NP tissue.
Subsequent studies investigated the injectability and potential of the candidate hydrogel for the encapsulation of bovine NP cells (NPCs) under static hypoxic culture condition (5 % CO2, 5 % O2). The 5 w/v % polymer solution of acrylate functionalized 4a-[P(EG)3.75kDa-b-P(TMC)0.65kDa] and CS-SH was injectable at 25 °C and formed a crosslinked network within 30 minutes at 37 °C. The hydrogel supported the viability (>83 %) and proliferation of the NPCs. Additionally, the encapsulated NPCs maintained their spherical shape and deposited collagen type II with no deposition of collagen type I. Finally, the hydrogel supported the encapsulated NPCs up to 28 days, after which the hydrogel was fully degraded. Overall, the 5 w/v % hydrogel formulation has potential for NP tissue regeneration, given its injectability, high NPC viability and deposition of collagen type II.
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Queen's University's Thesis/Dissertation Non-Exclusive License for Deposit to QSpace and Library and Archives Canada
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ProQuest PhD and Master's Theses International Dissemination Agreement
Intellectual Property Guidelines at Queen's University
Copying and Preserving Your Thesis
This publication is made available by the authority of the copyright owner solely for the purpose of private study and research and may not be copied or reproduced except as permitted by the copyright laws without written authority from the copyright owner.