Sureable degradation would occur within the timeframe of the study. Specimens (2 mm by 12 mm) were cut and enclosed in cylindrical stainless steel mesh cages (1.5 mm length, 3 mm diameter). [32] Three month old female Sprague Dawley rats were anesthetized before and during the procedure with 2 isoflurane. Their sides were shaved, and incision sites were scrubbed with chlorhexidine. Incisions (approximate 1 cm long) were made on the side of the rats, and blunt dissection was used to prepare implant pockets (2 per side). Specimens were introduced through the incision and positioned within the pocket away from the incision site. The incisions were then closed with stainless steel surgical wound clips. Clips were removed 7 days post-implantation. After 4, 8, or 12 weeks, rats were euthanized via carbon dioxide inhalation. A subsequent bilateral thoracotomy was performed to ensure death. The stainless steel cages were explanted, and hydrogel specimens were carefully removed from the stainless steel cages. Swelling ratio and modulus of explants were measured as described above to measure the extent of degradation.NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript 3.Equilin Results3.1 Initial Hydrogel Properties Initial swelling ratio and modulus of 10 PEG (10k) DA and DAA hydrogels were measured to ensure that the two systems were comparable, Figure 3. Both swelling ratio and modulus were statistically similar (p0.05) between the two gel systems prior to degradation. It should be noted that the PEGDAA gel had a slightly higher initial modulus (94 11 vs. 77 19) than the PEGDA gel. However, the lack of statistical difference inJ Biomed Mater Res A. Author manuscript; available in PMC 2015 December 01.Browning et al.Pagethese measurements indicates that the two systems had similar initial crosslink densities and can be directly compared in subsequent degradation studies.NIH-PA Author Manuscript NIH-PA Author Manuscript NIH-PA Author Manuscript3.2 Hydrogel In Vitro Degradation 3.2.1 Accelerated Hydrolytic In Vitro Degradation–Hydrogel degradation occurs via cleavage of networked groups and results in a reduced crosslink density over time. These changes in crosslink density can be monitored via measurements of swelling ratio and/or modulus. [19] To this end, swelling ratio and compressive modulus measurement were utilized to assess the extent of sample degradation in the varied media at the selected time points. Only swelling ratio was measured for samples that exhibited rapid declines in structural integrity that prevented accurate measurement of compressive modulus, including PEGDA under accelerated hydrolytic conditions and both PEGDA and PEGDAA under accelerated oxidative conditions.SP-13786 Thus, to analyze PEGDA accelerated hydrolytic degradation, swelling ratio of samples in 5 mM NaOH was measured every 24 hours, Figure 4.PMID:24458656 PEGDA hydrogels experienced significant increases in swelling each day, indicating that rapid degradation was occurring under these alkaline conditions. A loss of mechanical integrity was observed at 5 days, and complete dissolution occurred within 10 days. Singificant increases in swelling occurred every day except for day 5; the insignificant change in swelling ratio between days 4 and 5 may indicate that some samples were beginning to physically break apart, which may have prevented measurement of full swollen weight due to loss of smaller pieces. Both swelling ratio and modulus of PEGDAA hydrogels were mea.
