Ultra-Strong Protein-Based Hydrogels via Promoting Intermolecular Entanglement of the Amorphous Region.

Proteins are classified as biopolymers which share similar structural features with semi-crystalline polymers. Although their unique biocompatibility facilitates the universal applications of protein-based hydrogels in the biomedical field, the mechanical performances of protein-based hydrogels fall short of practical requirements. Conventional strategies for enhancing mechanical properties focus on forming regularly folded secondary structures as analogs of crystalline regions. This concept is based on proteins as the analogy of semi-crystalline polymers, in which crystalline regions profoundly contribute to the mechanical performances. Even though the contribution of the amorphous region is equally weighted for semi-crystalline polymers, their capacity to improve the mechanical performances of protein-based structures is still undervalued. Herein, the potential of promoting the mechanical performances is explored by controlling the state of amorphous regions in protein-based hydrogels. A fibril protein is chosen, regenerated silk fibroin (RSF), as a model molecule for its similar viscoelasticity with a semi-crystalline polymer. The amorphous regions in the RSF hydrogels are transformed from extended to entangled states through a double-crosslinking method. The formation of entanglement integrates new physically crosslinked points for remarkable improvement in mechanical performances. A robust hydrogel is not only developed but also intended to provide new insights into the structural-property relationship of protein-based hydrogels.

Bridging Biocondensation and Biomimetic Fibrillation by Regulating Intra- And Interchain Hydrogen Bonds in Artificial Biomacromolecular Condensates.

Utilizing biocondensates as feedstocks can be a state-of-the-art strategy for emulating natural silk spinning. Although current biocondensates can form solid fibers using a biomimetic draw spinning method, the fibrillation is primarily achieved through evaporation of highly concentrated biocondensates rather than structural conversion in natural spinning. Current artificial biocondensates lack biomimetic features of stress-induced fibrillation since they are unable to replicate the structural complexity of native proteins in the dope. Herein, we successfully achieved biomimetic fibrillation at significantly reduced concentrations by constructing artificial biocondensates using naturally derived silk fibroin. The biomimetic features of stress-induced fibrillation in native proteins are replicated in our artificial biocondensates by tailoring multivalent interactions in biocondensation. Our findings unravel the fundamental correlations between biocondensation and stress-induced fibrillation. This work can not only provide a framework for designing artificial biocondensates in biomimetic spinning but also improve the molecular insights into natural spinning.

Non-metallic T2-MRI agents based on conjugated polymers.

Developing non-metallic contrast agents of clinically applied magnetic resonance imaging (MRI) is an alternative strategy to reduce the toxicity of heavy metal elements in current MRI agents. These non-metallic MRI agents usually generate contrasts by unpaired electrons, which are prone to be deactivated by in vivo radical scavenging pathways. Since the unpaired electrons in conjugated polymers exhibit satisfying stability for in vivo imaging, developing conjugated polymers based MRI agents may solve the in vivo stability problem of current non-metallic agents. However, MRI-active properties have not been reported in existing conjugated polymers yet. Herein we report on MRI-active conjugated polymer nanoparticles based on polypyrrole (PPy), which can be used for in vivo imaging. Our method not only introduce a kind of non-metallic MRI agents but extends the applications of conjugated polymers from optical imagings to MRI.

Preparing 3D-printable silk fibroin hydrogels with robustness by a two-step crosslinking method.

Regenerated silk fibroin (RSF) features excellent biocompatibility and high-strength mechanical properties. However, traditional RSF-based materials can hardly be applied in 3D printing, which has shown great potential in producing artificial implants. In this work, we report a 3D printable RSF hydrogel formed by a weak, chemically crosslinked network. After the 3D printing process, the mechanical properties of the above hydrogel can be remarkably improved by a ripening process. The maximum compressive modulus of this RSF hydrogel is 2.5 MPa, reaching the same order of magnitude as natural elastomers such as cartilage. The mechanical properties of this hydrogel are superior to most RSF-based 3D printed hydrogels. The investigation of gelation mechanism reveals that the chemically crosslinked network can constrain the growth of ß-sheet structures of RSF to form a dense and uniform physical network. Such a physically crosslinked network endows the high strength and good resilience of RSF hydrogels. With both good biocompatibility and mechanical properties, this double-network hydrogel has potential in producing 3D printed scaffolds for tissue engineering.

Dual-loaded, long-term sustained drug releasing and thixotropic hydrogel for localized chemotherapy of cancer.

Localized cancer chemotherapy is an intra-tumoral treatment and can effectively prevent locoregional recurrence. In this study, we proposed an environmentally-friendly method to load both hydrophilic (Doxorubicin, Dox) and hydrophobic (Curcumin, Cur) drugs into one hydrogel. The hydrogel was composed of two naturally derived polymers, regenerated silk fibroin (RSF) and hydroxypropylcellulose (HPC), and was endowed with thixotropic properties because of its differently crystalized ß-sheet region. Moreover, by taking advantage of the specific interactions between Cur and the ß-sheet region in the hydrogel, the solubility and stability of the hydrophobic Cur were dramatically improved. Because the multiple interactions between the two drugs and the hydrogel lead to different release profiles for Cur and Dox, the dual-drug loaded hydrogel presented superior long-term sustained antitumor efficacy compared with the free drug and the Dox single-loaded hydrogel. The dual-drug loaded hydrogel exhibited an enhanced therapeutic effect and a reversal of multiple drug resistance (MDR) to Dox. Moreover, by investigating the mechanism of the thixotropicity of our hydrogel, we concluded that this property results from the slipping and deformation of ß-sheet enriched domains as well as the destruction/reconstruction of weak crosslinks.

Bandgap Engineered Polypyrrole-Polydopamine Hybrid with Intrinsic Raman and Photoacoustic Imaging Contrasts.

Intrinsically multimodal nanomaterials have revealed their great potential as a new class of contrast agents. We herein report a bandgap engineering strategy to develop an intrinsically Raman-photoacoustic (PA) active probe that is based on semiconducting conjugated polymers. This dual modal probe is prepared by doping a semiconducting conjugated polymer with polydopamine (PDA) through a one-pot reaction. When applied in the polypyrrole (PPy), this strategy can enhance Raman scattering and the PA amplitude of PPy-PDA hybrid by 3.2 and 2.4 times, respectively, so that both signals can be further applied in bioimaging. In the hybrid, such a dual-enhancement effect is achieved by infusing these two macromolecules at the nanoscale to reduce the optical bandgap energy. This work not only introduces a dual modal contrast agent but also provides a new method of manipulating semiconducting polymer's inherent optical features for bioimaging.

Preparation of on-plate immobilized metal ion affinity chromatography platform via dopamine chemistry for highly selective isolation of phosphopeptides with matrix assisted laser desorption/ionization mass spectrometry analysis.

In this study, a novel on-plate IMAC technique was developed for highly selective enrichment and isolation of phosphopeptides with high-throughput MALDI-TOF-MS analysis. At first, a MALDI plate was coated with polydopamine (PDA), and then Ti(4+) was immobilized on the PDA-coated plate. The obtained IMAC plate was successfully applied to the highly selective enrichment and isolation of phosphopeptides in protein digests and human serum. Because of no loss of samples, the on-plate IMAC platform exhibits excellent selectivity and sensitivity in the selective enrichment and isolation of phosphopeptides, which provides a potential technique for high selectivity in the detection of low-abundance phosphopeptides in biological samples.