Enlargement, Reduction, and Even Reversal of Relative Migration Speeds of Endothelial and Smooth Muscle Cells on Biomaterials Simply by Adjusting RGD Nanospacing

Elasticity Modification of Biomaterials Used in 3D Printing with an Elastin-Silk-like Recombinant Protein

The recombinant structural protein described in this study was designed based on sequences derived from elastin and silk. Silk-elastin hybrid copolymers are characterized by high solubility while maintaining high product flexibility. The phase transition temperature from aqueous solution to hydrogel, as well as other physicochemical and mechanical properties of such particles, can differ significantly depending on the number of sequence repeats. We present a preliminary characterization of the EJ17zipR protein obtained in high yield in a prokaryotic expression system and efficiently purified via a multistep process. Its addition significantly improves biomaterial's rheological and mechanical properties, especially elasticity. As a result, EJ17zipR appears to be a promising component for bioinks designed to print spatially complex structures that positively influence both shape retention and the internal transport of body fluids. The results of biological studies indicate that the addition of the studied protein creates a favorable microenvironment for cell adhesion, growth, and migration.

Characterization of a Chimeric Resilin-Elastin Structural Protein Dedicated to 3D Bioprinting as a Bioink Component

In this study we propose to use for bioprinting a bioink enriched with a recombinant RE15mR protein with a molecular weight of 26 kDa, containing functional sequences derived from resilin and elastin. The resulting protein also contains RGD sequences in its structure, as well as a metalloproteinase cleavage site, allowing positive interaction with the cells seeded on the construct and remodeling the structure of this protein in situ. The described protein is produced in a prokaryotic expression system using an E. coli bacterial strain and purified by a process using a unique combination of known methods not previously used for recombinant elastin-like proteins. The positive effect of RE15mR on the mechanical, physico-chemical, and biological properties of the print is shown in the attached results. The addition of RE15mR to the bioink resulted in improved mechanical and physicochemical properties and promoted the habitation of the prints by cells of the L-929 line.

Nanotexture and crystal phase regulation for synergistic enhancement in re-endothelialization on medical pure titanium surface

Re-endothelialization has been recognized as a promising strategy to address the tissue hyperplasia and subsequent restenosis which are major complications associated with vascular implant/interventional titanium devices. However, the uncontrollable over-proliferation of smooth muscle cells (SMCs) limits the clinical application of numerous modified strategies. Herein, a novel modified strategy involving with a two-step anodic oxidation and annealing treatment was proposed to achieve rapid re-endothelialization function regulated by regular honeycomb nanotexture and specific anatase phase on the titanium surface. Theoretical calculation revealed that the presence of nanotexture reduced the polar component of surface energy, while the generation of anatase significantly enhanced the polar component and total surface energy. Meanwhile, the modified surface with regular nanotexture and anatase phase produced positive effect on the expression of CD31, VE-Cadherin and down-regulated α-SMA proteins expression, indicating excellent capacity of pro-endothelial regeneration and inhibition of SMCs proliferation and migration. One-month in vivo implantation in rabbit carotid arteries further confirmed that modified tube implant surface effectively accelerated confluent endothelial monolayer formation and promoted native-like endothelium tissue regeneration. By contrast, original titanium tube implant induced a disorganized tissue proliferation in the lumen with a high risk of restenosis. Collectively, this study opens us an alternative route to achieve the function that selectively promotes endothelial cells (ECs) growth and suppresses SMCs on the medical titanium surface, which has a great potential in facilitating re-endothelialization on the surface of blood-contacting titanium implant.

Investigation of nanotopography on SOCE mediated cell migration via live-cell : Imaging on opaque implant surface

The exploration of cell response to nanotopography has attracted considerable attentions for years. This article focuses on the influence of nanotopography on the intracellular Ca2+ dynamics, the most ubiquitous but ignored second messenger. The classic titanium nanotubes (NT) were fabricated by anodization to formulate nanoporous surfaces. Firstly, the store operative calcium entry (SOCE) in endoplasmic reticulum (ER) and functional Ca2+ release-activated Ca2+ (CRAC) channels were significantly enhanced on NT surfaces that revealed by live-cell Ca2+ imaging and fluorescence resonance energy transfer (FRET) identification of orai1-stim1 connection. To investigate the potential implication of Ca2+ elevation, the dynamic cell migration trajectory was monitored by a self-made holder, which could not only be suitable for the opaque implant surface but also guarantee the focus fields identical during samples shifting. The cell migration on NT surface was more vigorous and rapid, which was correlated with higher focal adhesion proteins expression, Ca2+-dependent calpain activity and stim1 level. In conclusion, this study has confirmed the novel ER Ca2+ hemostasis pathway on nanosurfaces and its crucial role in cell migration regulation, which may help for more biofavorable implant surface design.

Achieving Long-Acting Local Analgesia Using an Intelligent Hydrogel Encapsulated with Drug and pH Regulator

Local anesthetics are important for the treatment of postoperative pain. Since a single injection of the solution of a drug such as bupivacaine (BUP) works only for a few hours, it is much required to develop a long-term injectable formulation that maintains its efficacy for more than 1 day. Herein, an intelligent copolymer hydrogel loaded with BUP microcrystals was invented. The biodegradable block copolymer was synthesized by us and composed of a central hydrophilic poly(ethylene glycol) (PEG) block and two hydrophobic poly(lactide-co-glycolide) (PLGA) blocks. The aqueous system of the amphiphilic copolymer underwent a sol-gel transition between room temperature and body temperature and, thus, physically gelled after injection. Considering the decrease of solubility of BUP with the increase of pH and the internal acidic environment due to the hydrolysis of PLGA, calcium carbonate (CaCO3) powder was introduced as a pH regulator. Then, the internal pH was found to be nearly neutral and many BUP microcrystals were dispersed in the gel network. In this way, BUP had achieved a sustained release out of the thermogel. The maximum possible effect (MPE) in a rat sciatic nerve blockade model was used to describe the sensory blockade effect. In vivo analgesic effects evaluated with a hot plate experiment of rats demonstrated that the thermogel encapsulated with BUP microcrystal and CaCO3 powder significantly prolonged analgesia up to 44 h, the duration time with respect to 50% MPE. The intramuscularly injected implant exhibited biocompatibility in histological analyses. Besides, the untreated leg of the rats was not influenced by the treated leg, indicating no obvious systematic anesthesia of this hydrogel formulation. Such an intelligent and composite formulation represents a potential strategy for long-acting analgesia therapy.

Promoting neurite outgrowth and neural stem cell migration using aligned nanofibers decorated with protrusions and galectin-1 coating

Biomaterials integrated with both topological cues and biological modifications are urgently needed in regenerative medicine. Here, aligned nanofibrous scaffolds decorated with nanoscale SiO2 protrusions and galectin-1 coating are reported. Prospects in neurite outgrowth and neural stem cell migration are discussed for suitable use in neural tissue engineering.

Development of Mesoporous Silica Nanoparticle-Based Films with Tunable Arginine-Glycine-Aspartate Peptide Global Density and Clustering Levels to Study Stem Cell Adhesion and Differentiation

Stem cell adhesion is mediated via the binding of integrin receptors to adhesion motifs present in the extracellular matrix (ECM). The spatial organization of adhesion ligands plays an important role in stem cell integrin-mediated adhesion. In this study, we developed a series of biointerfaces using arginine-glycine-aspartate (RGD)-functionalized mesoporous silica nanoparticles (MSN-RGD) to study the effect of RGD adhesion ligand global density (ligand coverage over the surface), spacing, and RGD clustering levels on stem cell adhesion and differentiation. To prepare the biointerface, MSNs were chemically functionalized with RGD peptides via an antifouling poly(ethylene glycol) (PEG) linker. The RGD surface functionalization ratio could be controlled to create MSNs with high and low RGD ligand clustering levels. MSN films with varying RGD global densities could be created by blending different ratios of MSN-RGD and non-RGD-functionalized MSNs together. A computational simulation study was performed to analyze nanoparticle distribution and RGD spacing on the resulting surfaces to determine experimental conditions. Enhanced cell adhesion and spreading were observed when RGD global density increased from 1.06 to 5.32 nmol cm-2 using highly clustered RGD-MSN-based films. Higher RGD ligand clustering levels led to larger cell spreading and increased formation of focal adhesions. Moreover, a higher RGD ligand clustering level promoted the expression of alkaline phosphatase in hMSCs. Overall, these findings indicate that both RGD global density and clustering levels are crucial variables in regulating stem cell behaviors. This study provides important information about ligand-integrin interactions, which could be implemented into biomaterial design to achieve optimal performance of adhesive functional peptides.

Trail Formation Alleviates Excessive Adhesion and Maintains Efficient Neutrophil Migration

Migrating neutrophils are found to leave behind subcellular trails in vivo, but the underlying mechanisms remain unclear. Here, an in vitro cell migration test plus an in vivo observation was applied to monitor neutrophil migration on intercellular cell adhesion molecule-1 (ICAM-1) presenting surfaces. Results indicated that migrating neutrophils left behind long-lasting, chemokine-containing trails. Trail formation tended to alleviate excessive cell adhesion enhanced by the trans-binding antibody and maintain efficient cell migration, which was associated with differential instantaneous edge velocity between the cell front and rear. CD11a and CD11b worked differently in inducing trail formation with polarized distributions on the cell body and uropod. Trail release at the cell rear was attributed to membrane ripping, in which β2-integrin was disrupted from the cell membrane through myosin-mediated rear contraction and integrin-cytoskeleton dissociation, potentiating a specialized strategy of integrin loss and cell deadhesion to maintain efficient migration. Moreover, neutrophil trails left on the substrate served as immune forerunners to recruit dendritic cells. These results provided an insight in elucidating the mechanisms of neutrophil trail formation and deciphering the roles of trail formation in efficient neutrophil migration.

Stereo Coverage and Overall Stiffness of Biomaterial Arrays Underly Parts of Topography Effects on Cell Adhesion

Surface topography is a biophysical factor affecting cell behaviors, yet the underlying cues are still not clear. Herein, we hypothesized that stereo coverage and overall stiffness of biomaterial arrays on the scale of single cells underly parts of topography effects on cell adhesion. We fabricated a series of microarrays (micropillar, micropit, and microtube) of poly(l-lactic acid) (PLLA) using mold casting based on pre-designed templates. The characteristic sizes of array units were less than that of a single cell, and thus, each cell could sense the micropatterns with varied roughness. With human umbilical vein endothelial cells (HUVECs) as the model cell type, we examined spreading areas and cell viabilities on different surfaces. "Stereo coverage" was defined to quantify the actual cell spreading fraction on a topographic surface. Particularly in the case of high micropillars, cells were confirmed not able to touch the bottom and had to partially hang among the micropillars. Then, in our opinion, a cell sensed the overall stiffness combining the bulk stiffness of the raw material and the stiffness of the culture medium. Spreading area and single cell viability were correlated to coverage and topographic feature of the prepared microarrays in particular with the significantly protruded geometry feather. Cell traction forces exerted on micropillars were also discussed. These findings provide new insights into the surface modifications toward biomedical implants.

Recent advances in regenerative biomaterials

Nowadays, biomaterials have evolved from the inert supports or functional substitutes to the bioactive materials able to trigger or promote the regenerative potential of tissues. The interdisciplinary progress has broadened the definition of 'biomaterials', and a typical new insight is the concept of tissue induction biomaterials. The term 'regenerative biomaterials' and thus the contents of this article are relevant to yet beyond tissue induction biomaterials. This review summarizes the recent progress of medical materials including metals, ceramics, hydrogels, other polymers and bio-derived materials. As the application aspects are concerned, this article introduces regenerative biomaterials for bone and cartilage regeneration, cardiovascular repair, 3D bioprinting, wound healing and medical cosmetology. Cell-biomaterial interactions are highlighted. Since the global pandemic of coronavirus disease 2019, the review particularly mentions biomaterials for public health emergency. In the last section, perspectives are suggested: (i) creation of new materials is the source of innovation; (ii) modification of existing materials is an effective strategy for performance improvement; (iii) biomaterial degradation and tissue regeneration are required to be harmonious with each other; (iv) host responses can significantly influence the clinical outcomes; (v) the long-term outcomes should be paid more attention to; (vi) the noninvasive approaches for monitoring in vivo dynamic evolution are required to be developed; (vii) public health emergencies call for more research and development of biomaterials; and (viii) clinical translation needs to be pushed forward in a full-chain way. In the future, more new insights are expected to be shed into the brilliant field-regenerative biomaterials.

A Polymeric Strategy Empowering Vascular Cell Selectivity and Potential Application Superior to Extracellular Matrix Peptides

Endothelialization of vascular implants plays a vital role in maintaining the long-term vascular patency. In situ endothelialization and re-endothelialization is generally achieved by selectively promoting endothelial cell (EC) adhesion and, meanwhile, suppressing smooth muscle cell (SMC) adhesion. Currently, such EC versus SMC selectivity is achieved and extensively used in vascular-related biomaterials utilizing extracellular-matrix-derived EC-selective peptides, dominantly REDV and YIGSR. Nevertheless, the application of EC-selective peptides is limited due to their easy proteolysis, time-consuming synthesis, and expensiveness. To address these limitations, a polymeric strategy in designing and finding EC-selective biomaterials using amphiphilic β-peptide polymers by tuning serum protein adsorption is reported. The optimal β-peptide polymer displays EC versus SMC selectivity even superior to EC-selective REDV peptide regarding cell adhesion, proliferation, and migration of ECs versus SMCs. Study of the mechanism indicates that surface adsorption of bovine serum albumin, an abundant and anti-adhesive serum protein, plays a critical role in the ECs versus SMCs selectivity of β-peptide polymer. In addition, surface modification of the optimal β-peptide polymer effectively promotes the endothelialization of vascular implants and inhibits intimal hyperplasia. This study provides an alternative strategy in designing and finding EC-selective biomaterials, implying great potential in the vascular-related biomaterial study and application.

RGD Nanoarrays with Nanospacing Gradient Selectively Induce Orientation and Directed Migration of Endothelial and Smooth Muscle Cells

Directed migration of cells through cell-surface interactions is a paramount prerequisite in biomaterial-induced tissue regeneration. However, whether and how the nanoscale spatial gradient of adhesion molecules on a material surface can induce directed migration of cells is not sufficiently known. Herein, we employed block copolymer micelle nanolithography to prepare gold nanoarrays with a nanospacing gradient, which were prepared by continuously changing the dipping velocity. Then, a self-assembly monolayer technique was applied to graft arginine-glycine-aspartate (RGD) peptides on the nanodots and poly(ethylene glycol) (PEG) on the glass background. Since RGD can trigger specific cell adhesion via conjugating with integrin (its receptor in the cell membrane) and PEG can resist protein adsorption and nonspecific cell adhesion, a nanopattern with cell-adhesion contrast and a gradient of RGD nanospacing was eventually prepared. In vitro cell behaviors were examined using endothelial cells (ECs) and smooth muscle cells (SMCs) as a demonstration. We found that SMCs exhibited significant orientation and directed migration along the nanospacing gradient, while ECs exhibited only a weak spontaneously anisotropic migration. The gradient response was also dependent upon the RGD nanospacing ranges, namely, the start and end nanospacings under a given distance and gradient. The different responses of these two cell types to the RGD nanospacing gradient provide new insights for designing cell-selective nanomaterials potentially used in cell screening, wound healing, etc.

Research and clinical translation of trilayer stent-graft of expanded polytetrafluoroethylene for interventional treatment of aortic dissection

The aortic dissection (AD) is a life-threatening disease. The transcatheter endovascular aortic repair (EVAR) affords a minimally invasive technique to save lives of these critical patients, and an appropriate stent-graft gets to be the key medical device during an EVAR procedure. Herein, we report a trilayer stent-graft and corresponding delivery system used for the treatment of the AD disease. The stent-graft is made of nitinol stents with an asymmetric Z-wave design and two expanded polytetrafluoroethylene (ePTFE) membranes. Each of inner and outer surfaces of the stent-graft was covered by an ePTFE membrane, and the two membranes were then sintered together. The biological studies of the sintered ePTFE membranes indicated that the stent-graft had excellent cytocompatibility and hemocompatibility in vitro. Both the stent-graft and the delivery system exhibited satisfactory mechanical properties and operability. The safety and efficacy of this stent-graft and the corresponding delivery system were demonstrated in vivo. In 9 canine experiments, the blood vessels of the animals implanted with the stent-grafts were of good patency, and there were no thrombus and obvious stenosis by angiography after implantation for 6 months. Furthermore, all of the 9 clinical cases experienced successful implantation using the stent-graft and its post-release delivery system, and the one-year follow-ups indicated the preliminary safety and efficacy of the trilayer stent-graft with an asymmetric Z-wave design for interventional treatment.

A Facile Composite Strategy to Prepare a Biodegradable Polymer Based Radiopaque Raw Material for "Visualizable" Biomedical Implants

Enabling a biodegradable polymer radiopaque under X-ray is much desired for many medical devices. Physical blending of a present biodegradable polymer and a commercialized medical contrast agent is convenient yet lacks comprehensive fundamental research. Herein, we prepared a biodegradable polymer-based radiopaque raw material by blending poly(l-lactic acid) (PLLA or simply PLA) and iohexol (IHX), where PLA constituted the continuous phase and IHX particles served as the dispersed phase. The strong X-ray adsorption of IHX enabled the composite radiopaque; the hydrolysis of the polyester and the water solubility of the contrast agent enabled the composite biodegradable in an aqueous medium. The idea was confirmed by in vitro characterizations of the resultant composite, in vivo subcutaneous implantation in rats up to 6 months, and the clear visualization of a part of a biodegradable occluder in a Bama piglet under X-ray. We also found that the crystallization of PLA was significantly enhanced in the presence of the solid particles, which should be taken into consideration in the design of an appropriate biomaterial composite because crystallization degree influences the biodegradation rate and mechanical property of a material to a large extent. We further tried to introduce a small amount of poly(vinylpyrrolidone) into the blend of PLA and IHX. Compared to the bicomponent composite, the tricomponent one exhibited decreased modulus and increased elongation at break and tensile strength. This paves more ways for researchers to select appropriate raw materials according to the regenerated tissue and the application site.

“Invisible” orthodontics by polymeric “clear” aligners molded on 3D-printed personalized dental models

The malalignment of teeth is treated classically by metal braces with alloy wires, which has an unfavorable influence on the patients appearance during the treatment. With the development of digitization, computer simulation and three-dimensional (3D) printing technology, herein, a modern treatment was tried using clear polymeric aligners, which were fabricated by molding polyurethane films via thermoforming on the 3D-printed personalized dental models. The key parameters of photocurable 3D printing of dental models and the mechanical properties of the clear aligner film material were examined. The precision of a 3D-printed dental model mainly relied on characteristics of photocurable resin, the resolution of light source and the exposure condition, which determined the eventual shape of the molded clear aligner and thus the orthodontic treatment efficacy. The biocompatibility of the polyurethane film material was confirmed through cytotoxicity and hemolysis tests in vitro. Following a series of 3D-printed personalized dental models and finite element analysis to predict and plan the fabrication and orthodontic processes, corresponding clear aligners were fabricated and applied in animal experiments, which proved the efficacy and biocompatibility in vivo. Clinical treatments of 120 orthodontic cases were finally carried out with success, which highlights the advantage of the clear aligners as an esthetic, compatible and efficient appliance.