Xiaodong Cao

An injectable hyaluronic acid/PEG hydrogel for cartilage tissue engineering formed by integrating enzymatic crosslinking and Diels–Alder “click chemistry”

The application of enzymatic crosslinking and Diels–Alder (DA) click chemistry for hydrogel formation has recently bloomed, because of the efficient chemical bonding and the mild biological reaction conditions. In this study, an injectable hyaluronic acid/PEG (HA/PEG) hydrogel was successfully fabricated for the first time through integrating two cross-linking processes, including firstly enzymatic crosslinking and subsequent DA click chemistry. The enzymatic crosslinking resulted in a fast gelation of HA/PEG in 5 min, leading to the formation of an injectable material. In addition, the DA click reaction crosslinking made a hydrogel that has outstanding shape memory and anti-fatigue properties. The storage modulus and breakage strength of the hydrogels were close to 27 kPa and 109.4 kPa, respectively. The compressive strain could reach up to 81.9%. After 10 cycles of a loading and unloading test, the hydrogel still could be loaded by 80 kPa for 1 min and the corresponding deformation could be completely recovered in 1 min after unloading. The ATDC-5 cells were capsulated into the hydrogel bulk in situ and showed high metabolic viability and proliferation. All of these results suggest that the HA/PEG injectable hydrogel formed by integrating the two cross-linking processes has a great potential in cartilage tissue engineering.

An interpenetrating HA/G/CS biomimic hydrogel via Diels-Alder click chemistry for cartilage tissue engineering

In order to mimic the natural cartilage extracellular matrix, a novel biological degradable interpenetrating network hydrogel was synthesized from the gelatin (G), hyaluronic acid (HA) and chondroitin sulfate (CS) by Diels-Alder click chemistry. HA was modified with furylamine and G was modified with furancarboxylic acid respectively. (1)H NMR spectra and elemental analysis showed that the substitution degrees of HA-furan and G-furan were 71.5% and 44.5%. Then the hydrogels were finally synthesized by cross-linking furan-modified HA and G derivatives with dimaleimide poly(ethylene glycol) (MAL-PEG-MAL). The mechanical and degradation properties of the hydrogels could be tuned simply through varying the molar ratio between furan and maleimide. Rheological, mechanical and degradation studies demonstrated that the Diels-Alder click chemistry is an efficient method for preparing high performance biological interpenetrating hydrogels. This biomimic hydrogel with improved mechanical properties could have great potential applications in cartilage tissue engineering.

Preparation and properties of carboxylated styrene-butadiene rubber/cellulose nanocrystals composites.

A series of carboxylated styrene-butadiene rubber (XSBR)/cellulose nanocrystals (CNs) latex composites were successfully prepared. The vulcanization process, morphology, dynamic viscoelastic behavior, dynamic mechanical property, thermal and mechanical performance of the XSBR/CNs composites were investigated in detail. The results revealed that CNs were dispersed uniformly in the XSBR matrix and formed a strong filler-filler network. The dynamic mechanical analysis (DMA) showed that the glass transition temperature (T(g)) of XSBR matrix was shifted from 48.45 to 50.64 °C with 3 phr CNs, but decreased from 50.64 to 46.28 °C when further increasing CNs content up to 15 phr. The composites exhibited a significant enhancement in tensile strength (from 16.9 to 24.1 MPa) and tear strength (from 43.5 to 65.2 MPa) with loading CNs from 0 to 15 phr. In addition, the thermo-gravimetric analysis (TGA) showed that the temperature at 5% weight loss of the XSBR/CNs composites decreased slightly with an increase of the CNs content.

Diels–Alder crosslinked HA/PEG hydrogels with high elasticity and fatigue resistance for cell encapsulation and articular cartilage tissue repair

The rapid restoration or regeneration of cartilage tissue biomechanical function remains a challenge, especially the replication of structural and mechanical properties using novel scaffold designs. A new class of cross-linked hydrogels with significantly improved mechanical properties has been synthesized by the Diels–Alder (DA) click reaction, which is widely used in drug delivery, sensor technology, and tissue engineering. However, the long gelation time of DA formed hydrogel is a big obstacle for cell encapsulation and restricts its application in the cytobiology field. In this research, a novel biological hydrogel was synthesized from hyaluronic acid (HA) and PEG by DA “click” chemistry. By simply tuning the furyl-to-maleimide molar ratio and the substitution degree of the furyl group, the value of the compressive modulus was controlled from 4.86 ± 0.42 kPa to 75.90 ± 5.43 kPa and the gelation time could be tuned from 412 min to 51 min at 37 °C. Moreover, the DA formed hydrogel was utilized to investigate the cell encapsulation viability and the influence of gelation time on encapsulated cell survival, and the results showed that a gelation time of about 1 h was suitable for cell viability, proliferation and chondrogenesis. Meanwhile, the HA/PEG hydrogel showed outstanding load-bearing and shape recovery properties even after 2000 loading cycles, mimicking the mechanical properties and behavior of articular cartilage. Therefore, the DA crosslinked HA/PEG hydrogel, with good mechanical properties and short gelation time, has significant potential applications in cartilage tissue engineering.

Cellulose nanocrystals reinforced foamed nitrile rubber nanocomposites

Research on foamed nitrile rubber (NBR)/cellulose nanocrystals (CNs) nanocomposites is rarely found in the literatures. In this paper, CNs suspension and NBR latex was mixed to prepared the foamed NBR/CNs nanocomposites. We found that the CNs mainly located in the cell walls, effectively reinforcing the foamed NBR. The strong interaction between the CNs and NBR matrix restricted the mobility of NBR chains surrounding the CNs, hence increasing the crosslink density of the NBR matrix. CNs exhibited excellent reinforcement on the foamed NBR: a remarkable increase nearly 76% in the tensile strength of the foamed nanocomposites was achieved with a load of only 15 phr CNs. Enhanced mechanical properties make the foamed NBR/CNs nanocomposites a promising damping material for industrial applications with a potential to reduce the petroleum consumption.

Micropatterned TiO2 nanotubes: fabrication, characterization and in vitro protein/cell responses

Effective bone repair and reconstruction after the implantation of Ti-based materials requires the provision of topological cues on the materials surface to promote specific biological responses from the surrounding environment. This is often realized by surface modification. In this paper, micropatterned TiO2 nanotubes are fabricated on a Ti surface via a combination of photolithography and electrochemical anodization, by which micro- and nano-scale geometry can be controlled. The preparation conditions are optimized and the interaction between the micropatterning (via photolithography) and nanopatterning (via electrochemical anodization) processes is investigated in detail. The resulting materials are then used for protein adsorption and a cell adhesion test. It is found that protein adsorption and cell adhesion can trace the topological cues by presenting high selectivity between the micropatterned TiO2 nanotubes and the Ti surface. We hope our study can benefit the research of Ti-based repairing materials, especially for those which need to manipulate protein adsorption and cell adhesion behavior.

A hydrogel actuator with flexible folding deformation and shape programming via using sodium carboxymethyl cellulose and acrylic acid

Hydrogel actuator is an intelligent material, which can work as artificial muscle. However, most present hydrogel actuators, due to the inferior mechanical property and uncontrolled folding property, have always resulted in slipping off or the failure of grasping an object with specific shape and required weight. In order to solve this problem, here a tough hydrogel actuator with programmable folding deformation has been prepared by combining the selective implanting method and ionic coordination. The shape and folding angle (from 0 to 180 o) of hydrogel actuator can be precisely controlled by altering the location and size of the implanting parts that seems like the joints of finger. The ionic coordination is not only the force to trigger the folding of hydrogel, but also utilized to reinforce the mechanical property. We believed the superior mechanical and shape-programmable property can endow the hydrogel actuator with great application prospect in soft machine.

Polymyxin B immobilized on cross-linked cellulose microspheres for endotoxin adsorption.

Cross-linked cellulose microspheres (CL-CMs) were successfully prepared by inverse crosslinking suspension method. NaOH/urea aqueous solution was used as solvent to dissolve cellulose at low temperature. The microspheres presented good spherical shape and monodispersity, which were applied to synthesize endotoxin adsorbent with polymyxin B (PMB) as ligand. The adsorbent showed good adsorption capability on endotoxin in physiologic saline solution and the maximum adsorption capacity was 3605 EU/g (1 EU=100 pg). It was worth noting that more than 70% of endotoxin could be effectively removed from the human plasma with the initial concentration of endotoxin ranged from 1 EU/mL to 5 EU/mL. The dynamic adsorption efficiency of endotoxin was 72.3% at the plasma perfusion rate of 300 mL/h with the endotoxin concentration of 4 EU/mL, while the variation of plasma protein before and after adsorption was only 8.9%. It suggests that the PMB immobilized CL-CMs have great potential application in clinical blood purification.