Effects of immobilizing sites of RGD peptides in amphiphilic block copolymers on efficacy of cell adhesion

Surface Modification of PEEKs with Cyclic Peptides to Support Endothelialization and Antithrombogenicity

Synthetic polymers are often utilized in the creation of vascular devices, and need to possess specific qualities to prevent thrombosis. Traditional strategies for this include surface modification of vascular devices through covalent attachment of substrates such as heparin, antiplatelet agents, thrombolytic agents, or hydrophilic polymers. One promising prosthetic material is polyether ether ketone (PEEK), which is utilized in various FDA-approved medical devices, including vascular and endovascular prostheses. We hypothesized that surface modification of biologically inert PEEK can help improve its endothelial cell affinity and reduce its thrombogenic potential. To evaluate this, we developed an effective surface-modification approach with unique cyclic peptides, such as CCHGGVRLYC and CCREDVC. We treated the PEEK surface with ammonia plasma, which introduced amine groups onto the PEEK surface. Subsequently, we were able to conjugate these peptides to the plasma-modified PEEKs. We observed that cyclic CCHGGVRLYC conjugated on prosthetic PEEK not only supported endothelialization, but minimized platelet adhesion and activation. This technology can be potentially applied for in vivo vascular and endovascular protheses to enhance their utility and patency.

Tailored biomedical materials for wound healing

Wound healing is a long-term, multi-stage biological process that mainly includes haemostatic, inflammatory, proliferative and tissue remodelling phases. Controlling infection and inflammation and promoting tissue regeneration can contribute well to wound healing. Smart biomaterials offer significant advantages in wound healing because of their ability to control wound healing in time and space. Understanding how biomaterials are designed for different stages of wound healing will facilitate future personalized material tailoring for different wounds, making them beneficial for wound therapy. This review summarizes the design approaches of biomaterials in the field of anti-inflammatory, antimicrobial and tissue regeneration, highlights the advanced precise control achieved by biomaterials in different stages of wound healing and outlines the clinical and practical applications of biomaterials in wound healing.

Synthesis of Functionalized Triblock Copolyesters Derived from Lactic Acid and Macrolactones for Bone Tissue Regeneration

Synthetic and functional grafts are a great alternative to conventional grafts. They can provide a physical support and the precise signaling for cells to heal damaged tissues. In this study, a novel RGD peptide end-functionalized poly(ethylene glycol)-b-poly(lactic acid)-b-poly(globalide)-b-poly(lactic acid)-b-poly(ethylene glycol) (RGD-PEG-PLA-PGl-PLA-PEG-RGD) is synthetized and used to prepare functional scaffolds. The PGl inner block is obtained by enzymatic ring-opening polymerization of globalide. The outer PLA blocks are obtained by ring-opening polymerization of both, l-lactide or a racemic mixture, initiated by the α-ω-telechelic polymacrolactone. The presence of PGl inner block enhances the toughness of PLA-based scaffolds, with an increase of the elongation at break up to 300% when the longer block of PGl is used. PLA-PGl-PLA copolymer is coupled with α-ω-telechelic PEG diacids by esterification reaction. PEGylation provides hydrophilic scaffolds as the contact angle is reduced from 114° to 74.8°. That difference improves the contact between the scaffolds and the culture media. Moreover, the scaffolds are functionalized with RGD peptides at the surface significantly enhancing the adhesion and proliferation of bone marrow-derived primary mesenchymal stem cells and MC3T3-E1 cell lines in vitro. These results place this multifunctional polymer as a great candidate for the preparation of temporary grafts.

Site specific interactions of amino acids with (ZnO)12 cluster: Density functional approach

The Stability and electronic properties of bio-hybrid molecules are investigated in the framework of the first-principles density functional theory. The site-specific interactions between (ZnO)₁₂ nano-cluster and arginine/aspartic acid are investigated. There are partially ionic and covalent bonds between the interacting atoms, higher binding energy 8.86 eV is observed at -COOH site of arginine, and 7.60 eV at -CN site of aspartic acid during the interaction with a nano-cluster. Higher HOMO-LUMO gap 4.3 eV is found in arginine, and smaller 2.6 eV in a cluster, it becomes zero with -COOH site of arginine, and 0.8 eV at -CN site of aspartic acid during the formation of bio-hybrids, i.e. highly stable amino acids arg/asp-nano-cluster (ZnO)₁₂ bio-hybrids are formed with small forbidden energy-gap. This study will support in the formation of drugs which will improve the response in wound healing, immune functioning in burn injuries, and in the treatment of bone dysfunction.HighlightsThe binding energy is higher in a bio-hybrid at -COOH site of Arg, and -CN site of Asp.HOMO-LUMO gap is higher in a pristine Arg (4.3 eV), smaller in a cluster (2.6 eV), zero gap in a bio-hybrid with -COOH site of Arg, smaller 0.8 eV at -CN site of Asp.Higher binding energy is found with the small forbidden energy-gap of bio-hybrid molecules.This study will support in the formation of drugs which will improve the response in wound healing, immune functioning in burn injuries, and in the treatment of bone dysfunction.Communicated by Ramaswamy H. Sarma.

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.

Intelligent Paper-Free Sprayable Skin Mask Based on an In Situ Formed Janus Hydrogel of an Environmentally Friendly Polymer

Traditional skin care masks usually use a piece of paper to hold the aqueous essences, which are not environmentally friendly and not easy to use. While a paper-free mask is desired, it is faced with a dilemma of moisture holding and rapid release of encapsulated bioactive substances. Herein, a paper-free sprayable skin mask is designed from an intelligent material-a thermogel which undergoes sol-gel-suspension transitions upon heating-to solve this dilemma. A synthesized block copolymer of poly(ethylene glycol) and poly(lactide-co-glycolide) with appropriate ratios can be dissolved in water, and thus easily mixed with a biological substance. The mixture is sprayable. After spraying, a Janus film is formed in situ with a physical gel on the outside and a suspension on the inside facing skin. Thus, both moisture holding and rapid release are achieved. Such a thermogel composed of biodegradable amphiphilic block copolymers loaded with nicotinamide as a skin mask is verified to reduce pigmentation on a 3D pigmented reconstructed epidermis model and further in a clinical study. This work might be stimulating for investigations and applications of biodegradable and intelligent soft matter in the fields of drug delivery and regenerative medicine.

Versatility of unsaturated polyesters from electrospun macrolactones: RGD immobilization to increase cell attachment

Poly(globalide) (PGl), an aliphatic polyester derived from unsaturated macrocylic lactone, can be cross-linked during electrospinning and drug-loaded for regenerative medicine applications. However, it lacks intrinsic recognition sites for cell adhesion and proliferation. In order to improve their cell adhesiveness, and therefore their therapeutic potential, we aimed to functionalize electrospun PGl fibers with RGD sequence generating a biomimetic scaffold. First, an amine compound was attached to the surface double bonds of the PGl fibers. Subsequently, the amino groups were coupled with RGD sequences. X-ray photoelectron spectroscopy (XPS) analysis confirmed the functionalization. The obtained fibers were more hydrophilic, as observed by contact angle analysis, and presented smaller Young's modulus, although similar tensile strength compared with non-functionalized cross-linked fibers. In addition, the functionalization process did not significantly alter fibers morphology, as observed by scanning electron microscopy (SEM). Finally, in vitro analysis evidenced the increase in human mesenchymal stromal cells (hMSC) adhesion (9.88 times higher DNA content after 1 day of culture) and proliferation (3.57 times higher DNA content after 8 days of culture) compared with non-functionalized non-cross-linked fibers. This is the first report demonstrating the functionalization of PGl fibers with RGD sequence, improving PGl therapeutic potential and further corroborating the use of this highly versatile material toward regenerative medicine applications.

A Dual-sensitive Hydrogel Based on Poly(Lactide-co-Glycolide)-Polyethylene Glycol-Poly(Lactide-co-Glycolide) Block Copolymers for 3D Printing

The thermo-sensitive hydrogel formed by triblock copolymers of polyethylene glycols and aliphatic polyesters serves as a promising candidate for bioink due to its excellent biodegradability and biocompatibility. However, the thermo-crosslinking alone cannot achieve a robust hydrogel to support the 3D printed constructs without collapse. Herein, a photo-crosslinkable group was introduced into the triblock copolymers to achieve a dual-sensitive hydrogel. A triblock copolymer poly(lactide-co-glycolide)-polyethylene glycol-poly(lactide-co-glycolide) decorated with acrylate group in the chain end was prepared. The obtained aqueous solutions of the copolymers could transform into hydrogels with excellent shear thinning properties and rapid elastic recovery properties spontaneously on the increase of temperature. The resulted thermogels also allowed for photo-crosslinking by exposure to ultraviolet radiation, with storage modulus dramatically increased to stable the printed constructs. Through a two-step crosslinking strategy, complicated tissue-like constructs with high shape fidelity can be printed using the dual-sensitive inks. Moreover, the mechanical strength, swelling ratio, and printability of the hydrogels can be tuned by varying the substitution rate of the acrylate group without compromising the inks' extrudability. We expect that the dual-sensitive hydrogels may be used as bioinks to print large constructs for applications in tissue engineering.

Injectable Thermogel Generated by the "Block Blend" Strategy as a Biomaterial for Endoscopic Submucosal Dissection

Endoscopic submucosal dissection is an established method for the removal of early cancers and large lesions from the gastrointestinal tract but is faced with the risk of perforation. To decrease this risk, a submucosal fluid cushion (SFC) is needed clinically by submucosal injection of saline and so on to lift and separate the lesion from the muscular layer. Some materials have been tried as the SFC so far with disadvantages. Here, we proposed a thermogel generated by the "block blend" strategy as an SFC. This system was composed of two amphiphilic block copolymers in water, so it was called a "block blend". We synthesized two non-thermogellable copolymers poly(d,l-lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(d,l-lactide-co-glycolide) and blended them in water to achieve a sol-gel transition upon heating in both pure water and physiological saline. We explored the internal structure of the resultant thermogel with transmission electron microscopy, three-dimensional light scattering, ¹³C NMR, fluorescence resonance energy transfer, and rheological measurements, which indicated a percolated micelle network. The biosafety of the synthesized copolymer was preliminarily confirmed in vitro. The main necessary functions as an SFC, namely, injectability of a sol and the maintained mucosal elevation as a gel after injection, were verified ex vivo. This study has revealed the internal structure of the block blend thermogel and illustrated its potential application as a biomaterial. This work might be stimulating for investigations and applications of intelligent materials with both injectability and thermogellability of tunable phase-transition temperatures.

Exploration of possible cell chirality using material techniques of surface patterning

Consistent left-right (LR) asymmetry or chirality is critical for embryonic development and function maintenance. While chirality on either molecular or organism level has been well established, that on the cellular level has remained an open question for a long time. Although it remains unclear whether chirality exists universally on the cellular level, valuable efforts have recently been made to explore this fundamental topic pertinent to both cell biology and biomaterial science. The development of material fabrication techniques, surface patterning, in particular, has afforded a unique platform to study cell-material interactions. By using patterning techniques, chirality on the cellular level has been examined for cell clusters and single cells in vitro in well-designed experiments. In this review, we first introduce typical fabrication techniques of surface patterning suitable for cell studies and then summarize the main aspects of preliminary evidence of cell chirality on patterned surfaces to date. We finally indicate the limitations of the studies conducted thus far and describe the perspectives of future research in this challenging field. STATEMENT OF SIGNIFICANCE: While both biomacromolecules and organisms can exhibit chirality, it is not yet conclusive whether a cell has left-right (LR) asymmetry. It is important yet challenging to study and reveal the possible existence of cell chirality. By using the technique of surface patterning, the recent decade has witnessed progress in the exploration of possible cell chirality within cell clusters and single cells. Herein, some important preliminary evidence of cell chirality is collected and analyzed. The open questions and perspectives are also described to promote further investigations of cell chirality in biomaterials.

Dual-functional alginate crosslinker: Independent control of crosslinking density and cell adhesive properties of hydrogels via separate conjugation pathways

Alginate is an abundant natural polysaccharide widely utilized in various biomedical applications. Alginate also possesses numerous hydroxyl and carboxylate functional groups that allow chemical modifications to introduce different functionalities. However, it is difficult to apply various chemical reactions to alginate due to limited solubility in organic solvents. Herein, functional moieties for radical polymerization and cell adhesion were separately conjugated to hydroxyl and carboxylate groups of alginate, respectively, in order to independently control the crosslinking density and cell adhesive properties of hydrogels. Sodium counterions of alginate are first substituted with tetrabutylammonium ions to facilitate the dissolution in an organic solvent, followed by in situ conjugations of (1) cell adhesion molecules (CAM) via carbodiimide-mediated amide formation and (2) methacrylate via ring-opening nucleophilic reaction. The resulting CAM-linked methacrylic alginate was able to not only crosslink different monomers to form hydrogels with varying mechanical properties, but also induce stable cell adhesion to the hydrogels.

Effect of RGD content in poly(ethylene glycol)-crosslinked poly(methyl vinyl ether-alt-maleic acid) hydrogels on the expansion of ovarian cancer stem-like cells

The extracellular matrix (ECM) affects cell behaviors, such as survival, proliferation, motility, invasion, and differentiation. The arginine-glycine-aspartic acid (RGD) sequence is present in several ECM proteins, such as fibronectin, collagen type I, fibrinogen, laminin, vitronectin, and osteopontin. It is very critical to develop ECM-like substrates with well-controlled features for the investigation of influence of RGD on the behavior of tumor cells. In this study, poly(ethylene glycol) (PEG)-crosslinked poly(methyl vinyl ether-alt-maleic acid) (P(MVE-alt-MA)) hydrogels (PEMM) with different RGD contents were synthesized, fully characterized, and established as in vitro culture platforms to investigate the effects of RGD content on cancer stem cell (CSC) enrichment. The morphology, proliferation, and viability of SK-OV-3 ovarian cancer cells cultured on hydrogels with different RGD contents, the expression of CSC markers and malignant signaling pathway-related genes, and drug resistance were systematically evaluated. The cell aggregates formed on the hydrogel surface with a lower RGD content acquired certain CSC-like properties, thus drug resistance was enhanced. In contrast, the drug sensitivity of cells on the higher RGD content surface increased because of less CSC-like properties. However, the presence of RGD in the stiff hydrogels (PEMM2) had less effect on the stemness expression than did its presence in the soft hydrogels (PEMM1). The results suggest that RGD content and matrix stiffness can lead to synergetic effects on the expression of cancer cell stemness and the epithelial-mesenchymal transition (EMT), interleukin-6 (IL-6), and Wnt pathways.

Surface Engineering of Cardiovascular Devices for Improved Hemocompatibility and Rapid Endothelialization

Cardiovascular devices have been widely applied in the clinical treatment of cardiovascular diseases. However, poor hemocompatibility and slow endothelialization on their surface still exist. Numerous surface engineering strategies have mainly sought to modify the device surface through physical, chemical, and biological approaches to improve surface hemocompatibility and endothelialization. The alteration of physical characteristics and pattern topographies brings some hopeful outcomes and plays a notable role in this respect. The chemical and biological approaches can provide potential signs of success in the endothelialization of vascular device surfaces. They usually involve therapeutic drugs, specific peptides, adhesive proteins, antibodies, growth factors and nitric oxide (NO) donors. The gene engineering can enhance the proliferation, growth, and migration of vascular cells, thus boosting the endothelialization. In this review, the surface engineering strategies are highlighted and summarized to improve hemocompatibility and rapid endothelialization on the cardiovascular devices. The potential outlook is also briefly discussed to help guide endothelialization strategies and inspire further innovations. It is hoped that this review can assist with the surface engineering of cardiovascular devices and promote future advancements in this emerging research field.

Enhanced and Prolonged Activity of Enzymes Adsorbed on TEMPO-Oxidized Cellulose Nanofibers

2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibers (TOCNs) have a width of about 4 nm and a very large specific surface area. TOCN is a negatively charged bionanomaterial having carboxy groups on the surface and promising physical properties. In particular, TOCN can be used as an adsorbent for biomolecules for biotechnological applications, but the adsorption behavior of biomolecules on the TOCN surface requires investigation. Thus, in this study, we investigated the adsorption behavior of pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) on TOCN and evaluated the activity, structure, and long-term stability of the adsorbed enzyme. Transmission electron microscopy observation revealed that the enzyme was aligned and adsorbed on the TOCNs, and circular dichroism measurements were used to determine the structure of the enzyme adsorbed on TOCN. Interestingly, the adsorbed enzyme showed higher activity after adsorption, resulting in long-term retention of enzyme activity, probably because the stability of PQQ-GDH was improved by adsorption. These results suggest that TOCN is an excellent biomolecule immobilization material. Our results can be used for the development of biomaterials using TOCN as a scaffold for the adsorption of enzymes with increased stability and activity.

Effects of Microstripe Geometry on Guided Cell Migration

Cell migration on material surfaces is a fundament issue in the fields of biomaterials, cell biology, tissue engineering, regenerative medicine, etc. Herein, we aim to guide cell migration by flat microstripes with significant contrast of cell adhesion and varied geometric features of the adhesive stripes. To this end, we designed and fabricated cell-adhesive arginine-glycine-aspartate (RGD) microstripes on the nonfouling poly(ethylene glycol) (PEG) background and examined the microstripe-guided adhesion and migration of a few cell types. The migration of cell clusters adhering on the RGD regions was found to be significantly affected by the widths and arc radiuses of the guided microstripes. The cells migrated fastest on the straight microstripes with width of about 20 μm, which we defined as single file confined migration (SFCM). We also checked the possible left-right asymmetric bias of cell migration guided by combinatory microstripes with alternative wavy and quasi-straight stripes under a given width, and found that the velocity of CCW (counter clockwise) migration was higher than that of CW (clockwise) migration for primary rat mesenchymal stem cells (rMSCs), whereas no left-right asymmetric bias was observed for NIH3T3 (mouse embryonic fibroblast cell line) and Hela (human cervix epithelial carcinoma cell line) cells. Comparison of migration of cells on the nanotopological stripe and smooth surfaces further confirmed the importance of cell orientation coherence for guided cell migration and strengthened the superiority of SFCM.

Peptide-Based Therapeutics for Oncology

The development of peptide-based drugs, which are usually synthetic analogues of endogenous peptides, is currently one of the most topical directions in drug development. Among them, antitumor peptide-based drugs are of great interest. Anticancer peptides can be classified into three main groups based on their mechanism of action: inhibitory, necrosis-inducing and pro-apoptotic peptides. As an antitumor therapy, peptides are considered to have at least the same efficacy as chemotherapy or surgical treatment, but offer advantages in terms of safety and tolerability, given that chemotherapy is usually characterized by severe adverse effects, and surgery carries additional risks for patients. Short peptides have a number of benefits over other molecules. First, compared with full-length proteins and antibodies, short peptides are less immunogenic, more stable ex-vivo (prolonged storage at room temperature), and have better tumor or organ permeability. Moreover, the production of such short peptide-based drugs is more cost effective. Second, in comparison with small organic molecules, peptides have higher efficacy and specificity. Finally, due to the fact that the main products of peptide metabolism are amino acids, these drugs are usually characterized by lower toxicity. Short peptides have a highly selective mechanism of action, thereby demonstrating low toxicity. Furthermore, with the addition of different stabilizing structural modifications, as well as novel drug delivery systems, the peptide-based drugs are proving to be promising therapeutics for cancer mono- or polytherapy. However, challenges remain including that endogenous and synthetic peptide molecules can be oncogenic. Therefore, it is important to investigate whether peptides contribute to tumor growth. In order to answer such questions, numerous preclinical and clinical studies of peptide-based therapeutics are currently being conducted.

Self-Assembly of Integrin Ligands on the Apical Membrane Inhibits the Migration of Glioma Cells

Malignant brain cancer remains challenging in treatment due to the highly invasive quality of gliomas. Inspired by the upregulated expression of integrin β1 subunits in tumors, we designed and synthesized an integrin-targeting self-assembling ligand based on a laminin-derived peptide that selectively forms nanofibrous microdomains on the apical membrane of glioma cells, inhibiting their migration and invasion.

In vitro evaluation of vascular endothelial cell behaviors on biomimetic vascular basement membranes

Vascular basement membrane (VBM) is a thin layer of fibrous extracellular matrix linking endothelium, and collagen type IV (COL IV) is its main composition. VBM plays a crucial role in anchoring down the endothelium to its loose connective tissue underneath. For vascular grafts, constructing biomimetic VBMs on the luminal surface is thus an effective approach to improve endothelialization in situ. In the present work, three types of polycaprolactone (PCL) membranes were produced and characterized through cell counting kit-8 (CCK-8) assay, adhesion force and elastic modulus test to examine the influence of fiber diameter and membrane composition on vascular endothelial cell (EC) behaviors. The PCL membranes with finer fibers of 54.77 nm (PCL-54) could biomimic the nanotopography of VBMs more efficiently than 544.64 nm (PCL-544), and they were more suitable for Pig iliac endothelium cells (PIECs) adhesion and proliferation, meanwhile, inducing higher elastic modulus and adhesion force of PIECs. On this foundation, we further immobilized COL IV onto PCL-54 (PCL-COL IV) to biomimic VBMs compositionally. Results showed that PIECs on PCL-COL IV exhibited the highest viability and proliferation. Besides, quantitative data indicated that the elastic modulus of the PIECs on PCL-COL IV (4441.00 Pa) was as two times higher than that on PCL-54 (2312.26 Pa), and the adhesion force grew to 1120.99 pN from 673.58 pN of PIECs on PCL-54. In summary, the PCL-COL IV membranes show high similarity with the native VBMs in terms of structure and composition, suggesting a promising potential for surface modification to vascular grafts for improved endothelialization.

Hyaluronan-Based Grafting Strategies for Liver Stem Cell Therapy and Tracking Methods

Cell adhesion is essential for survival, it plays important roles in physiological cell functions, and it is an innovative target in regenerative medicine. Among the molecular interactions and the pathways triggered during cell adhesion, the binding of cluster of differentiation 44 (CD44), a cell-surface glycoprotein involved in cell-cell interactions, to hyaluronic acid (HA), a major component of the extracellular matrix, is a crucial step. Cell therapy has emerged as a promising treatment for advanced liver diseases; however, so far, it has led to low cell engraftment and limited cell repopulation of the target tissue. Currently, different strategies are under investigation to improve cell grafting in the liver, including the use of organic and inorganic biomatrices that mimic the microenvironment of the extracellular matrix. Hyaluronans, major components of stem cell niches, are attractive candidates for coating stem cells since they improve viability, proliferation, and engraftment in damaged livers. In this review, we will discuss the new strategies that have been adopted to improve cell grafting and track cells after transplantation.

An improved synthesis of a cyclopropene-based molecule for the fabrication of bioengineered tissues via copper-free click chemistry

BACKGROUND

Since its introduction in the field of biological imaging, the use of copper-free click chemistry has been extended to produce improved materials for vascular surgery, ophthalmology, environmental, and automotive applications. This wide applicability suggests that larger quantities of the chemical reagents for copper-free click chemistry will be required in the future. However, the large-scale synthesis of such chemicals has been barely investigated. A possible reason is the shortage of reliable synthetic protocols to obtain large quantities of these building blocks. We therefore present in this paper an improved synthetic protocol to obtain a cyclopropene-based carbonate, a key building block for the well-known copper-free click chemistry.

METHOD

Our protocol builds upon an already available method to obtain a cyclopropene-based carbonate. When scaled up, several parameters of this method were changed in order to obtain an improved yield. First, the use of lower temperatures and slower addition rates of the chemicals avoided the formation of detrimental hotspots in the reaction system. Second, the use of less hygroscopic solvents minimized the decomposition of the cyclopropene carbonate. Finally, chromatographic purifications were minimized and improved by using deactivated silica.

RESULTS

We obtained the compound (2-methylcycloprop-2-en-1-yl)methyl (4-nitrophenyl) carbonate, a key building block for copper-free click chemistry, in an unprecedented 60% overall yield on a six-gram scale.

CONCLUSIONS

Our improved synthetic protocol demonstrates the potential of large-scale production of improved materials using click chemistry, with potential future applications in the fields of molecular imaging, vascular surgery, ophthalmology, and theranostics.

Advances in intracellular delivery through supramolecular self-assembly of oligonucleotides and peptides

Cells utilize natural supramolecular assemblies to maintain homeostasis and biological functions. Naturally inspired modular assembly of biomaterials are now being exploited for understanding or manipulating cell biology for treatment, diagnosis, and detection of diseases. Supramolecular biomaterials, in particular peptides and oligonucleotides, can be precisely tuned to have diverse structural, mechanical, physicochemical and biological properties. These merits of oligonucleotides and peptides as building blocks have given rise to the evolution of numerous nucleic acid- and peptide-based self-assembling nanomaterials for various medical applications, including drug delivery, tissue engineering, regenerative medicine, and immunotherapy. In this review, we provide an extensive overview of the intracellular delivery approaches using supramolecular self-assembly of DNA, RNA, and peptides. Furthermore, we discuss the current challenges related to subcellular delivery and provide future perspectives of the application of supramolecular biomaterials for intracellular delivery in theranostics.

Controlling the Surface Chemistry of a Hydrogel for Spatially Defined Cell Adhesion

A two-step synthesis is described for activating the surface of a fully hydrated hydrogel that is of interest as a possible scaffold for neural regeneration devices. The first step exploits the water content of the hydrogel and the hydrophobicity of the reaction solvent to create a thin oxide layer on the hydrogel surface using a common titanium or zirconium alkoxide. This layer serves as a reactive interface that enables rapid transformation of the hydrophilic, cell-nonadhesive hydrogel into either a highly hydrophobic surface by reaction with an alkylphosphonic acid, or into a cell-adhesive one using a (α,ω-diphosphono)alkane. Physically imprinting a mask ("debossing") into the hydrogel, followed by a two-step surface modification with a phosphonate, allows for patterning its surface to create spatially defined, cell-adhesive regions.

Photo/thermoresponsive ABC triblock copolymer-based ion gels: photoinduced structural transitions

A photo/thermoresponsive ABC triblock copolymer-based ion gel exhibiting photoinduced structural transitions accompanied by significant rheological changes is newly developed. The ABC triblock copolymer comprises an ionic liquid (IL)-phobic A block, an IL-philic B block, and a photo/thermoresponsive C block containing azobenzene moieties. The IL-phobic A block forms a rigid micellar core in an IL over a wide temperature range and the photo/thermoresponsive C block undergoes upper critical solution temperature (UCST)-type phase transition in ILs. In concentrated polymer solution, the ABC triblock copolymer can form a percolated micellar network at low temperatures through aggregation of A and C blocks as physical crosslinks, bridged by IL-philic B blocks. In contrast, the ion gel undergoes structural transition to jammed micelles at high temperatures due to the disassembly of the thermoresponsive C block, resulting in significant softening of the ion gel. Importantly, the temperature dependences of the viscoelastic properties of the ion gel differ drastically depending on photo-irradiation conditions as the photoinduced isomerization of azobenzene moieties in the C block modulates the affinity between the polymer chain and IL. Utilizing this feature, photoinduced softening/hardening of the ion gel is realized at constant temperature. This study provides a promising strategy to control the rheological properties of nonvolatile soft materials via contactless light irradiation that could be exploited in various applications such as photoresponsive soft actuators and photo-healable soft materials.

Recent Progress in the Construction of Functional Artificial Bone by Cytokine-Controlled Strategies

OBJECTIVE

Combining artificial scaffolds with stimulatory factors to reconstruct lost bone tissues is one of the hottest research directions. The purpose of this review was to conduct a retrospective survey on the latest reports on artificial bone fabrication with functional cytokines.

DATA SOURCES

The status of related scientific research from the year 2005 to 2018 was analyzed through the mode of literature retrieval in PubMed and VIP Database. The retrieval words are as follows: "bone tissue engineering," "angiogenesis," "cytokines," "osteogenesis," "biomimetic bone marrow," "sol-gel," "delivery system," and the corresponding Chinese words.

STUDY SELECTION

After reading through the title and abstract for early screening, the full text of relevant studies was evaluated and those not related with this review had been ruled out.

RESULTS

According to the literature retrospective survey, there were three key points for the successful construction of functional artificial bones: (1) the continuous supply of relatively low concentration of cytokines during the required period; (2) the delivery of two or more cytokines essential to the process and ensure the relatively spatial independence to reduce the unnecessary interference; and (3) supporting the early-stage angiogenesis and late-stage osteogenesis, respectively, regulating and balancing the crosslinking of both to avoid the surface ossification that would probably block the osteogenesis inside.

CONCLUSIONS

The synergistic effect of both angiogenic factors and osteogenic factors applied in bone regeneration is a key point in the combined functional artificial bone. Through analysis, comparison, and summary of the current strategies, we proposed that the most promising one is to mimic the natural bone marrow function to facilitate the regeneration process and ensure the efficient repair of large weight-bearing bone defect.

Integrin Clustering Matters: A Review of Biomaterials Functionalized with Multivalent Integrin-Binding Ligands to Improve Cell Adhesion, Migration, Differentiation, Angiogenesis, and Biomedical Device Integration

Material systems that exhibit tailored interactions with cells are a cornerstone of biomaterial and tissue engineering technologies. One method of achieving these tailored interactions is to biofunctionalize materials with peptide ligands that bind integrin receptors present on the cell surface. However, cell biology research has illustrated that both integrin binding and integrin clustering are required to achieve a full adhesion response. This biophysical knowledge has motivated researchers to develop material systems biofunctionalized with nanoscale clusters of ligands that promote both integrin occupancy and clustering of the receptors. These materials have improved a wide variety of biological interactions in vitro including cell adhesion, proliferation, migration speed, gene expression, and stem cell differentiation; and improved in vivo outcomes including increased angiogenesis, tissue healing, and biomedical device integration. This review first introduces the techniques that enable the fabrication of these nanopatterned materials, describes the improved biological effects that have been achieved, and lastly discusses the current limitations of the technology and where future advances may occur. Although this technology is still in its nascency, it will undoubtedly play an important role in the future development of biomaterials and tissue engineering scaffolds for both in vitro and in vivo applications.

Bioresorbable polypeptide-based comb-polymers efficiently improves the stability and pharmacokinetics of proteins in vivo

Stimuli-responsive polypeptides are a promising class of biomaterials due to their tunable physicochemical and biological properties. Herein, a series of novel pH- and thermo-responsive block copolymers based on polypeptides were synthesized by ring-opening polymerization of γ-benzyl-l-glutamate-N-carboxyanhydride in the presence of poly(ethylene glycol)-diamine macroinitiator followed by aminolysis. The resulting polypeptide-based triblock copolymer, poly[(2-(dibutylamino)ethyl-l-glutamate)-co-(γ-benzyl-l-glutamate)]-poly(ethylene glycol)-b-poly[(2-(dibutylamino)ethyl-l-glutamate)-co-(γ-benzyl-l-glutamate)] (PNLG-co-PBLG-b-PEG-b-PBLG-co-PNLG), exists as a low viscous sol at low pH and temperature (≤pH 6.4, 25 °C) but it transforms to a soft gel under physiological conditions (pH 7.4 and 37 °C). The physical properties of the polypeptide gel can be tuned by controlling the ratio between hydrophobic PBLG and pH-sensitive PNLG blocks. The polypeptide-based copolymer did not show any noticeable cytotoxicity to fibroblast cells in vitro. It was found that subcutaneous injection of the polypeptide copolymer solution into the dorsal region of Sprague-Dawley (SD) rats formed a gel instantly without major inflammation. The gels were completely biodegraded in six weeks and found to be bioresorbable. Human growth hormone (hGH)-loaded polypeptide-based biodegradable copolymer sols readily formed a viscoelastic gel that inhibited an initial burst and prolonged the hGH release for one week. Overall, due to their bioresorbable and sustained release protein characteristics, polypeptide hydrogels may serve as viable platforms for therapeutic protein delivery and the surface tunable properties of polypeptide hydrogels can be exploited for other potential therapeutic proteins.

Cell proliferation influenced by matrix compliance of gelatin grafted poly(d,l-Lactide) three dimensional scaffolds

Surface and mechanical properties of the biomaterials are determinants of cellular responses. In our previous study, star-shaped poly(d,l-Lactide)-b-gelatin (ss-pLG) was reported for possessing improved cellular adhesion and proliferation. Here, we extended our investigation to establish the cellular compatibility of gelatin-grafted PDLLA with respect to mechanical properties of biological tissues. In this view, linear PDLLA-b-gelatin (l-pLG) was synthesized and tissue-level compatibility of 1-pLG and ss-pLG against fibroblasts (L929), myoblasts (C2C12) and preosteoblasts (MG-63) was examined. The cell proliferation of C2C12 was significantly higher within l-pLG scaffolds, whereas L929 showed intensified growth within ss-pLG scaffolds. The difference in cell proliferation may be attributed to the varying mechanical properties of scaffolds; where the stiffness of l-pLG scaffolds was notably higher than ss-pLG scaffolds, most likely due to the variable levels of gelatin grafting on the backbone of PDLLA. Therefore, gelatin grafting can be used to modulate mechanical property of the scaffolds and this study reveals the significance of the matrix stiffness to produce the successful 3D scaffolds for tissue engineering applications.

Layered Double Hydroxide and Polypeptide Thermogel Nanocomposite System for Chondrogenic Differentiation of Stem Cells

Stem cell therapy for damaged cartilage suffers from low rates of retention, survival, and differentiation into chondrocytes at the target site. To solve these problems, here we propose a two-dimensional/three-dimensional (2D/3D) nanocomposite system. As a new two-dimensional (2D) material, hexagonal layered double hydroxides (LDHs) with a uniform lateral length of 2-3 μm were prepared by a hydrothermal process. Then, tonsil-derived mesenchymal stem cells (TMSCs), arginylglycylaspartic acid-coated LDHs, and kartogenin (KGN) were incorporated into the gel through the thermal-energy-driven gelation of the system. The cells exhibited a tendency to aggregate in the nanocomposite system. In particular, chondrogenic biomarkers of type II collagen and transcription factor SOX 9 significantly increased at both the mRNA and protein levels in the nanocomposite system, compared to the pure thermogel systems. The inorganic 2D materials increased the rigidity of the matrix, slowed down the release of a soluble factor (KGN), and improved cell-material interactions in the gel. The current 2D/3D nanocomposite system of bioactive LDH/thermogel can be a new platform material overcoming drawbacks of hydrogel-based 3D cell culture systems and is eventually expected to be applied as an injectable stem cell therapy.

Thermosensitive hydrogels a versatile concept adapted to vaginal drug delivery

Vaginal drug delivery represents an attractive strategy for local and systemic delivery of drugs otherwise poorly absorbed after oral administration. The rather dense vascular network, mucus permeability and the physiological phenomenon of the uterine first-pass effect can all be exploited for therapeutic benefit. However, several physiological factors such as an acidic pH, constant secretion, and turnover of mucus as well as varying thickness of the vaginal epithelium can impact sustained drug delivery. In recent years, polymers have been designed to tackle challenges mentioned above. In particular, thermosensitive hydrogels hold great promise due to their stability, biocompatibility, adhesion properties and adjustable drug release kinetics. Here, we discuss the physiological and anatomical uniqueness of the vaginal environment and how it impacts the safe and efficient vaginal delivery and also reviewed several thermosensitive hydrogels deemed suitable for vaginal drug delivery by addressing specific characteristics, which are essential to engage the vaginal environment successfully.

Multilayer Choline Phosphate Molecule Modified Surface with Enhanced Cell Adhesion but Resistance to Protein Adsorption

Choline phosphate (CP), which is a new zwitterionic molecule, and has the reverse order of phosphate choline (PC) and could bind to the cell membrane though the unique CP-PC interaction. Here we modified a glass surface with multilayer CP molecules using surface-initiated atom-transfer radical polymerization (SI-ATRP) and the ring-opening method. Polymeric brushes of (dimethylamino)ethyl methacrylate (DMAEMA) were synthesized by SI-ATRP from the glass surface. Then the grafted PDMAEMA brushes were used to introduce CP groups to fabricate the multilayer CP molecule modified surface. The protein adsorption experiment and cell culture test were used to evaluate the biocompatibility of the modified surfaces by using human umbilical veinendothelial cells (HUVECs). The protein adsorption results demonstrated that the multilayer CP molecule decorated surface could prevent the adsorption of fibrinogen and serum protein. The adhesion and proliferation of cells were improved significantly on the multilayer CP molecule modified surface. Therefore, the biocompatibility of the material surface could be improved by the modified multilayer CP molecule, which exhibits great potential for biomedical applications, e.g., scaffolds in tissue engineering.

Tissue-engineered cartilage constructed by a biotin-conjugated anti-CD44 avidin binding technique for the repairing of cartilage defects in the weight-bearing area of knee joints in pigs

OBJECTIVES

The lack of effective treatment for cartilage defects has prompted investigations using tissue engineering techniques for their regeneration and repair. The success of tissue-engineered repair of cartilage may depend on the rapid and efficient adhesion of transplanted cells to a scaffold. Our aim in this study was to repair full-thickness defects in articular cartilage in the weight-bearing area of a porcine model, and to investigate whether the CD44 monoclonal antibody biotin-avidin (CBA) binding technique could provide satisfactory tissue-engineered cartilage.

METHODS

Cartilage defects were created in the load-bearing region of the lateral femoral condyle of mini-type pigs. The defects were repaired with traditional tissue-engineered cartilage, tissue-engineered cartilage constructed with the biotin-avidin (BA) technique, tissue-engineered cartilage constructed with the CBA technique and with autologous cartilage. The biomechanical properties, Western blot assay, histological findings and immunohistochemical staining were explored.

RESULTS

The CBA group showed similar results to the autologous group in biomechanical properties, Moran's criteria, histological tests and Wakitani histological scoring.

CONCLUSIONS

These results suggest that tissue-engineered cartilage constructed using the CBA technique could be used effectively to repair cartilage defects in the weight-bearing area of joints.Cite this article: H. Lin, J. Zhou, L. Cao, H. R. Wang, J. Dong, Z. R. Chen. Tissue-engineered cartilage constructed by a biotin-conjugated anti-CD44 avidin binding technique for the repairing of cartilage defects in the weight-bearing area of knee joints in pigs. Bone Joint Res 2017;6:-295. DOI: 10.1302/2046-3758.65.BJR-2016-0277.