Mechanically strengthened hybrid peptide-polyester hydrogel and potential applications in spinal cord injury repair.

ADA16 peptide hydrogels have been broadly used in tissue engineering due to their good biocompatibility and nanofibrous structure mimicking the native extracellular matrix (ECM). However, the low mechanical strength often fails them as implantable scaffolds. To improve the mechanical stability of the RADA16 peptide hydrogel, a photocrosslinkable diacrylated poly(ϵ-caprolactone)-b-poly(ethylene glycol)-b-poly(ϵ-caprolactone) triblock copolymer (PCECDA) was physically combined with RADA16 peptide pre-modified with cell adhesive Arg-Gly-Asp sequence (RADA16-RGD). Consequently, an interpenetrating network, RADA16-RGD/PCECDA, was formed with highly enhanced mechanical property. The storage modulus (G') of RADA16-RGD/PCECDA (6% w/v, mass ratio mRADA16-RGD/mPCECDA = 1:5) hybrid hydrogel was elevated to ∼2000 Pa, compared to the RADA16-RGD (1% w/v) hydrogel alone (∼700 Pa). Furthermore, this hybrid hydrogel retained the nanofibrous structure from RADA16-RGD peptide, but underwent much slower degradation than RADA16-RGD alone. In vitro, the hybrid hydrogel exhibited excellent cytocompatibility and promoted the differentiation of the seeded neural stem cells. Finally, the RADA16-RGD/PCECDA hydrogel demonstrated capability in reducing cavitation, glial scar formation and inflammation at the lesion sites of hemi-sectioned spinal cord injury model in rats, which holds great potential for application in neural tissue engineering and regenerative medicine.

Promoting Neurite Growth and Schwann Cell Migration by the Harnessing Decellularized Nerve Matrix onto Nanofibrous Guidance.

Synergistic intercellular interactions have been widely acknowledged in tuning functional cell behaviors in vivo, and these interactions have inspired the development of a variety of scaffolds for regenerative medicine. In this paper, the promotion of Schwann cell (SC)-neurite interactions through the use of a nerve extracellular matrix-coated nanofiber composite in vitro was demonstrated using a cell culturing platform consisting of either random or aligned electrospun poly(l-lactic acid) nanofibers and decellularized peripheral nerve matrix gel (pDNM gel) from porcine peripheral nervous tissue. The pDNM-coated nanofiber platform served as a superior substrate for dorsal root ganglion culturing. Furthermore, SC migration was facilitated by pDNM gel coating on the nanofibers, accompanied with much faster axonal extension, in comparison with the effect of topographical guidance from the aligned electrospun fibers only. Finally, the decellularized nerve matrix promoted the ability of SCs to wrap around bundled neurites, triggering axonal remyelination toward nerve fiber functionalization.

Nano-fibrous and ladder-like multi-channel nerve conduits: Degradation and modification by gelatin.

We recently fabricated multi-channel PLLA nerve conduits (NCs, conduits diameter: ~3mm, channels diameter: ~200µm) with nano-fibrous microstructure (NNCs) and ladder-like microstructure (LNCs), and found the nanofibers in the NNCs promote differentiation of nerve stem cells (NSCs) into neurons. In the present study, we evaluated the degradation profile of NNCs and LNCs, and observed that NNCs degraded too fast to implant. To delay the degradation and retain the nano-scale effect of NNCs, we used gelatin to wrap (2% w/v gelatin) or embed (8% w/v gelatin) NNCs and LNCs via vacuum infusion and chemical cross-linking with genipin. NNCs-wrapped maintained their original nano-fibrous microstructure, but NNCs-embedded presented a porous morphology without nanofibers appearing. Incorporation of gelatin did not change their compressive moduli, but increased the creep recovery ratios of LNCs and NNCs. In vitro degradation revealed that integrity was maintained and the mass loss was <5% for NNCs-wrapped after 10weeks, in comparison with 15% mass loss and collapsed structure of the pure NNCs after 4weeks. Meanwhile, there were no obvious changes in the degradation of LNCs with modification. Nerve stem cells (NSCs) were then seeded onto the six NCs represented as: NNCs, NNCs-wrapped, NNCs-embedded, LNCs, LNCs-wrapped, and LNCs-embedded. Immunocytochemistry analysis demonstrated that gelatin coating enhanced the adhesion and proliferation of NSCs, and the NNCs-wrapped scaffold promoted the differentiation proportion of NSCs into neurons from 25.8% (on pure NNCs) to 53.4% after 14days of seeding. On the other hand, only 14.3% of neurons were derived from the differentiation of the seeded NSCs on the NNCs-embedded. NNCs-wrapped would be a good choice for future studies in nerve injury repair in vivo due to its appropriate degradation rate, flexibility, and nano-scale effect.

Magnetic solid-phase extraction of five pyrethroids from environmental water samples followed by ultrafast liquid chromatography analysis.

In this study, the polystyrene-coated magnetic nanoparticles (MNPs/PSt) were successfully prepared and characterized by Fourier transform infrared spectroscopy, transmission electron microscopy and vibrating sample magnetometry. The as-prepared MNPs/PSt were used as the adsorbent in magnetic solid phase extraction of five pyrethroids, including lambda-cyhalothrin, deltamethrin, esfenvalerate, permethrin, bifenthrin, in environmental water samples. The five pyrethroids were determined by ultra fast liquid chromatography-ultraviolet spectrometry. The influencing factors, including amount of MNPs/Pst, extraction time, pH value, type and volume of desorption solvent and desorption time, were examined and optimized. The extraction recoveries obtained with merely 50mg of MNPs/Pst were very satisfactory. The whole extraction process could be completed within 0.5h. The MNPs/PSt can be reused after an easy washing process. Thus, a simple, green, economical, time saving and effective method for pyrethroids analysis in environmental water samples was established. A high enrichment factor of 500 was achieved and the limits of detection for lambda-cyhalothrin, deltamethrin, esfenvalerate, permethrin, bifenthrin were 0.015±0.001 ng mL(-1), 0.012±0.001 ng mL(-1), 0.026±0.001 ng mL(-1), 0.020±0.001 ng mL(-1), 0.013±0.001 ng mL(-1), respectively. Recoveries obtained by analyzing spiked water samples at three concentration levels (0.100±0.001 ng mL(-1), 1.000±0.001 ng mL(-1), 10.000±0.001 ng mL(-1)) were between 78.97±8.38% and 96.05±8.38%. The standard curves for the five pyrethroids showed good linearity with the correlation coefficients in the range of 0.9994-0.9999. The intra-day and inter-day precision were satisfactory with the RSDs in the range of 2.05-5.52% and 2.73-8.38%, respectively.