“Click” chemistry in polymeric scaffolds: Bioactive materials for tissue engineering

Poly(2-isopropenyl-2-oxazoline) – a structural analogue to poly(vinyl azlactone) with Orthogonal Reactivity

A modular copolymer platform based on two oxazole derivatives is presented. Post-polymerisation modifications revealed the potential to selectively modify the individual side groups, providing access to functional copolymer libraries in the future.

S,S-Tetrazine-Based Hydrogels with Visible Light Cleavable Properties for On-Demand Anticancer Drug Delivery

Photocleavable hydrogels are of great importance in the field of controlled drug delivery, stem cell fate regulation, surface patterning, and intelligent devices. However, the development of novel photocleavable gel systems by visible light is usually met with challenges such as the lack of efficient and tunable photocleavable groups and reactions. Herein, we reported the facile fabrication of a new type of photocleavable hydrogels by the direct gelation of 4-arm thiol-terminated polyethylene glycol with 3,6-dichloro-1,2,4,5-tetrazine via the formation of S,S-tetrazine linkages. The prepared hydrogels underwent efficient degradation upon irradiation by ultraviolet or green light, and the degradation kinetics could be significantly promoted by hydrogen peroxide. Correspondingly, the hydrogels loaded with calcium peroxide microparticles or glucose oxidase/catalase enzymes enabled the precise and efficient in vivo photocontrol of gel degradation and drug release for cancer treatment. This work offers a promising and facile strategy towards the fabrication of visible light cleavable hydrogels with tunable and on-demand drug release properties.

Pyridyl disulfide-based thiol–disulfide exchange reaction: shaping the design of redox-responsive polymeric materials

This review provides an overview of synthetic approaches utilized to incorporate the thiol-reactive pyridyl-disulfide motif into various polymeric materials, and briefly highlights its utilization to obtain functional materials.

Fabrication of injectable hydrogels via bio-orthogonal chemistry for tissue engineering

Injectable hydrogels via bio-orthogonal chemistry.

Adjustable and ultrafast light-cured hyaluronic acid hydrogel: promoting biocompatibility and cell growth

Bio-sourced hydrogels are attractive materials for diagnosing, repairing and improving the function of human tissues and organs.

Electrospun Poly (Aspartic Acid)-Modified Zein Nanofibers for Promoting Bone Regeneration

Background

Critical-sized bone defects raise great challenges. Zein is of interest for bone regeneration, but it has limited ability to stimulate cell proliferation. In this regard, a poly (aspartic acid) (PAsp)-zein hybrid is promising, as PAsp can promote rat bone marrow stromal cell (rBMSCs) proliferation and osteogenic differentiation. This research aimed to develop electrospun PAsp-modified zein nanofibers to realize critical-sized bone defects repair.

Methods

Three groups of PAsp-modified zein nanofibers were prepared, they were PAsp grafting percentages of 0% (zein), 5.32% (ZPAA-1), and 7.63% (ZPAA-2). Using rBMSCs as in vitro cell model and SD rats as in vivo animal model, fluorescence staining, SEM, CCK-8, ALP, ARS staining, μCT and histological analysis were performed to verify the biological and osteogenic activities for PAsp-modified zein nanofibers.

Results

As the Asp content increased from 0% to 7.63%, the water contact angle decreased from 129.8 ± 2.3° to 105.5 ± 2.5°. SEM, fluorescence staining and CCK-8 assay showed that ZPAA-2 nanofibers had a superior effect on rBMSCs spreading and proliferation than did zein and ZPAA-1 nanofibers, ALP activity and ARS staining showed that ZPAA-2 can improve rBMSCs osteogenic differentiation. In vivo osteogenic activities was evaluated by μCT analysis, HE, Masson and immunohistochemical staining, indicating accelerated bone formation in ZPAA-2 SD rats after 4 and 8 weeks treatment, with a rank order of ZPAA-2 > ZPAA-1 > zein group. Moreover, the semiquantitative results of the Masson staining revealed that the maturity of the new bone was higher in the ZPAA-2 group than in the other groups.

Conclusion

Electrospun PAsp-modified zein can provide a suitable microenvironment for osteogenic differentiation of rBMSCs, as well as for bone regeneration; the optimal membrane appears to have a PAsp grafting percentage of 7.63%.

Immobilization of BMP-2-derived peptides on 3D-printed porous scaffolds for enhanced osteogenesis

Three-dimensional (3D) printing technologies open up new perspectives for customizing the external shape and internal architecture of bone scaffolds. In this study, an oligopeptide (SSVPT, Ser-Ser-Val-Pro-Thr) derived from bone morphogenetic protein 2 was conjugated with a dopamine coating on a 3D-printed poly(lactic acid) (PLA) scaffold to enhance osteogenesis. Cell experiments in vitro showed that the scaffold was highly osteoconductive to the adhesion and proliferation of rat marrow mesenchymal stem cells (MSCs). In addition, RT-PCR analysis showed that the scaffold was able to promote the expression of osteogenesis-related genes, such as alkaline phosphatase (ALP), runt-related transcription factor 2 (RUNX2), osteocalcin (OCN) and osteopontin (OPN). Images of the micro-CT 3D reconstruction from the rat cranial bone defect model showed that bone regeneration patterns occurred from one side edge towards the center of the area implanted with the prepared biomimetic peptide hydrogels, demonstrating significantly accelerated bone regeneration. This work will provide a basis to explore the application potential of bioactive scaffolds further.

A redox-responsive hyaluronic acid-based hydrogel for chronic wound management

Polymer-based hydrogels have been widely applied for chronic wound therapeutics, due to their well-acclaimed wound exudate management capability. At the same time, there is still an unmet clinical need for simple wound diagnostic tools to assist clinical decision-making at the point of care and deliver on the vision of patient-personalised wound management. To explore this challenge, we present a one-step synthetic strategy to realise a redox-responsive, hyaluronic acid (HA)-based hydrogel that is sensitive to wound environment-related variations in glutathione (GSH) concentration. By selecting aminoethyl disulfide (AED) as a GSH-sensitive crosslinker and considering GSH concentration variations in active and non-self-healing wounds, we investigated the impact of GSH-induced AED cleavage on hydrogel dimensions, aiming to build GSH-size relationships for potential point-of-care wound diagnosis. The hydrogel was also found to be non-cytotoxic and aided L929 fibroblast growth and proliferation over seven days in vitro. Such a material offers a very low-cost tool for the visual detection of a target analyte that varies dependent on the status of the cells and tissues (wound detection), and may be further exploited as an implant for fibroblast growth and tissue regeneration (wound repair).

Small extracellular vesicle loading systems in cancer therapy: Current status and the way forward

Systemic chemotherapy is a conventional and important strategy for inhibition of cancer progression, but it is usually accompanied by various adverse effects. Targeting drug delivery systems, effective tools to avoid the adverse effects of chemotherapy, have been intensively studied and developed. Recently, the emerging application of exosomes and exosome-mimics (small extracellular vesicles [sEVs]) in targeted drug delivery and therapeutics has been widely appreciated. The sEVs-based delivery system comprises three basic components: vesicles, cargoes and surface decorations. In this article, we review the current status, existing challenges and future directions in this field from the following aspects: selection and production of vesicles; cargoes and methods to load them into vesicles; modifications to the surfaces of vesicles; as well as ways to prolong the half-life of sEVs in the circulation. Existing and emerging data indicate that sEVs are promising nanocarriers for clinical use, but additional efforts are needed to translate research findings into therapeutic products.

The CuAAC: Principles, Homogeneous and Heterogeneous Catalysts, and Novel Developments and Applications

The copper-catalyzed azide/alkyne cycloaddition reaction (CuAAC) has emerged as the most useful "click" chemistry. Polymer science has profited enormously from CuAAC by its simplicity, ease, scope, applicability and efficiency. Basic principles of the CuAAC are reviewed with a focus on homogeneous and heterogeneous catalysts, ligands, anchimeric assistance, and basic chemical principles. Recent developments of ligand design and acceleration are discussed.

In situ-forming, mechanically resilient hydrogels for cell delivery

Injectable, in situ-forming hydrogels can improve cell delivery in tissue engineering applications by facilitating minimally invasive delivery to irregular defect sites and improving cell retention and survival. Tissues targeted for cell delivery often undergo diverse mechanical loading including high stress, high strain, and repetitive loading conditions. This review focuses on the development of hydrogel systems that meet the requirements of mechanical resiliency, cytocompatibility, and injectability for such applications. First, we describe the most important design considerations for maintaining the viability and function of encapsulated cells, for reproducing the target tissue morphology, and for achieving degradation profiles that facilitate tissue replacement. Models describing the relationships between hydrogel structure and mechanical properties are described, focusing on design principles necessary for producing mechanically resilient hydrogels. The advantages and limitations of current strategies for preparing cytocompatible, injectable, and mechanically resilient hydrogels are reviewed, including double networks, nanocomposites, and high molecular weight amphiphilic copolymer networks. Finally, challenges and opportunities are outlined to guide future research in this developing field.

Dual Interactions of Amphiphilic Gelatin Copolymer and Nanocurcumin Improving the Delivery Efficiency of the Nanogels

Herein, a new process to manufacture multicore micelles nanoparticles reinforced with co-assembly via hydrophobic interaction and electrostatic interaction under the help of ultrasonication was developed. The precise co-assembly between negative/hydrophobic drug and positive charged amphiphilic copolymer based pluronic platform allows the formation of complex micelles structures as the multicore motif with predefined functions. In this study, curcumin was selected as a drug model while positively charged copolymer was based on a pluronic-conjugated gelatin with different hydrophobicity length of Pluronic F87 and Pluronic F127. Under impact of dual hydrophobic and electrostatic interactions, the nCur-encapsulated core-shell micelles formed ranging from 40 nm to 70 nm and 40-100 nm by transmission electron microscopy (TEM) and Dynamic Light Scattering (DLS), respectively. It is found that the structures emerged depended on the relative lengths of the hydrophobic blocks in pluronic. Regarding g2(τ) behavior from DLS measurement, the nanogels showed a high stability in spherical form. Surprisingly, the release profiles showed a sustainable behavior of Cur from this system for drug delivery approaches. In vitro study exhibited that nCur-encapsulated complex micelles increased inhibitory activity against cancer cells growth with IC50 is 4.02 ± 0.11 mg/L (10.92 ± 0.3 µM) which is higher than of free curcumin at 9.40 ± 0.17 mg/L (25.54 ± 0.18 µM). The results obtained can provide the new method to generate the hierarchical assembly of copolymers with incorporated loading with the same property.

Silver nanoparticle@DNA tetrahedron-based colorimetric detection of HIV-related DNA with cascade strand displacement amplification

DNA tetrahedron-modified silver nanoparticles (AgNPs) were achieved via amino-silver chemistry for the first time and were applied as a colorimetric biosensor for detecting HIV-related DNA. Target DNA initiated strand displacement polymerization and nicking endonuclease-aided cycles were involved to link DNA tetrahedron-modified AgNPs, reporting colorimetric responses. This developed method showed excellent specificity and sensitivity. A wide linear range from 1 to 15 000 nM was achieved with a limit of detection of 0.84 nM. Moreover, it was successfully applied to determine DNA in blood serum samples.

Rapid conjugation of nanoparticles, proteins and siRNAs to microbubbles by strain-promoted click chemistry for ultrasound imaging and drug delivery

A new strategy using catalyst-free strain-promoted alkyne-azide cycloaddition (SPAAC) "click" chemistry for the ligation of anti-cancer drug-loaded nanoparticles, functionalized proteins, and siRNA conjugated micelles to microbubbles (MB) was established. The results showed fast ligation within 5 min without sacrificing microbubble size and density. The ultrasound test showed good imaging abilities of the microbubbles after functionalization. This microbubble-therapeutic SPAAC "click" conjugation developed in the current study involves no toxic catalyst or initiator, has ultra-fast reaction speed, and is versatile for the ligation of various anti-cancer or therapeutic agents to microbubbles. These advantages render the SPAAC click strategy promising for broad applications in ultrasound-guided imaging and therapeutic delivery.

Functionalization of PLLA with Polymer Brushes to Trigger the Assembly of Fibronectin into Nanonetworks

Poly-l-lactic acid (PLLA) has been used as a biodegradable polymer for many years; the key characteristics of this polymer make it a versatile and useful resource for regenerative medicine. However, it is not inherently bioactive. Thus, here, a novel process is presented to functionalize PLLA surfaces with poly(ethyl acrylate) (PEA) brushes to provide biological functionality through PEA's ability to induce spontaneous organization of the extracellular matrix component fibronectin (FN) into physiological-like nanofibrils. This process allows control of surface biofunctionality while maintaining PLLA bulk properties (i.e., degradation profile, mechanical strength). The new approach is based on surface-initiated atomic transfer radical polymerization, which achieves a molecularly thin coating of PEA on top of the underlying PLLA. Beside surface characterization via atomic force microscopy, X-ray photoelectron spectroscopy and water contact angle to measure PEA grafting, the biological activity of this surface modification is investigated. PEA brushes trigger FN organization into nanofibrils, which retain their ability to enhance adhesion and differentiation of C2C12 cells. The results demonstrate the potential of this technology to engineer controlled microenvironments to tune cell fate via biologically active surface modification of an otherwise bioinert biodegradable polymer, gaining wide use in tissue engineering applications.

Quantification of azide groups on a material surface and a biomolecule using a clickable and cleavable fluorescent compound

We propose a novel method for quantifying azide groups on a solid surface and a protein.

Recent advances in stimuli-responsive polymeric micelles via click chemistry

Stimuli-responsive polymeric micelles via click chemistry are divided into six major sections (temperature, light, ultrasound, pH, enzymes, and redox).

Adequate Reducing Conditions Enable Conjugation of Oxidized Peptides to Polymers by One-Pot Thiol Click Chemistry

Thiol(-click) chemistry has been extensively investigated to conjugate (bio)molecules to polymers. Handling of cysteine-containing molecules may however be cumbersome, especially in the case of fast-oxidizing coiled-coil-forming peptides. In the present study, we investigated the practicality of a one-pot process to concomitantly reduce and conjugate an oxidized peptide to a polymer. Three thiol-based conjugation chemistries (vinyl sulfone (VS), maleimide, and pyridyldithiol) were assayed along with three reducing agents (tris(2-carboxyethyl)phosphine (TCEP), dithiothreitol, and β-mercaptoethanol). Seven out of the nine possible combinations significantly enhanced the conjugation yield, provided that an adequate concentration of reductant was used. Among them, the coincubation of an oxidized peptide with TCEP and a VS-modified polymer displayed the highest level of conjugation. Our results also provide insights into two topics that currently lack consensus: TCEP is stable in 10 mM phosphate buffered saline and it reacts with thiol-alkylating agents at submillimolar concentrations, and thus should be carefully used in order to avoid interference with thiol-based conjugation reactions.

Click Chemistry-Based Injectable Hydrogels and Bioprinting Inks for Tissue Engineering Applications

BACKGROUND

The tissue engineering and regenerative medicine approach require biomaterials which are biocompatible, easily reproducible in less time, biodegradable and should be able to generate complex three-dimensional (3D) structures to mimic the native tissue structures. Click chemistry offers the much-needed multifunctional hydrogel materials which are interesting biomaterials for the tissue engineering and bioprinting inks applications owing to their excellent ability to form hydrogels with printability instantly and to retain the live cells in their 3D network without losing the mechanical integrity even under swollen state.

METHODS

In this review, we present the recent developments of in situ hydrogel in the field of click chemistry reported for the tissue engineering and 3D bioinks applications, by mainly covering the diverse types of click chemistry methods such as Diels-Alder reaction, strain-promoted azide-alkyne cycloaddition reactions, thiol-ene reactions, oxime reactions and other interrelated reactions, excluding enzyme-based reactions.

RESULTS

The click chemistry-based hydrogels are formed spontaneously on mixing of reactive compounds and can encapsulate live cells with high viability for a long time. The recent works reported by combining the advantages of click chemistry and 3D bioprinting technology have shown to produce 3D tissue constructs with high resolution using biocompatible hydrogels as bioinks and in situ injectable forms.

CONCLUSION

Interestingly, the emergence of click chemistry reactions in bioink synthesis for 3D bioprinting have shown the massive potential of these reaction methods in creating 3D tissue constructs. However, the limitations and challenges involved in the click chemistry reactions should be analyzed and bettered to be applied to tissue engineering and 3D bioinks. The future scope of these materials is promising, including their applications in in situ 3D bioprinting for tissue or organ regeneration.

Poly(vinyl alcohol) electrospun nanofibers containing antimicrobial Rhodomyrtus tomentosa extract

Electrospun nanofibers were prepared from Rhodomyrtus tomentosa extract and poly(vinyl alcohol). The antimicrobial effect was assessed against two Gram-negative bacterial strains ( Escherichia coli, Pseudomonas aeruginosa) and two Gram-positive bacterial strains ( Bacillus subtilis, Enterococcus faecalis) by paper disc diffusion method. Ethyl acetate extract of R. tomentosa was selected for fabrication of nanofibers because it shows the most active antimicrobial activity with zone of inhibition ranging from 9.33 ± 0.21 to 13.67 ± 0.32 mm. The presence of high abundance of myricetin and rhodomyrtone might contribute to the antibiotic activity against all tested bacterial strains. The average diameter of the R. tomentosa extract/poly(vinyl alcohol) nanofibers increased from 120.4 to 214.8 nm with increasing concentration of R. tomentosa extract from 0.5% to 2.5%. The antimicrobial activity of R. tomentosa extract/poly(vinyl alcohol) nanofibers was relatively higher at concentration of the extract (1.5% and 2.5%) against all test organisms with a clear zone of inhibition 7–12 mm. The results demonstrated that R. tomentosa extract/poly(vinyl alcohol) electrospun nanofibers are an interesting platform for delivery of bioactive compounds as wound dressing or other strategies for combating bacterial infections.

A Review of the Synthesis and Applications of Polymer–Nanoclay Composites

Recent advancements in material technologies have promoted the development of various preparation strategies and applications of novel polymer–nanoclay composites. Innovative synthesis pathways have resulted in novel polymer–nanoclay composites with improved properties, which have been successfully incorporated in diverse fields such as aerospace, automobile, construction, petroleum, biomedical and wastewater treatment. These composites are recognized as promising advanced materials due to their superior properties, such as enhanced density, strength, relatively large surface areas, high elastic modulus, flame retardancy, and thermomechanical/optoelectronic/magnetic properties. The primary focus of this review is to deliver an up-to-date overview of polymer–nanoclay composites along with their synthesis routes and applications. The discussion highlights potential future directions for this emerging field of research.

A Hyaluronic Acid Based Injectable Hydrogel Formed via Photo-Crosslinking Reaction and Thermal-Induced Diels-Alder Reaction for Cartilage Tissue Engineering

A hyaluronic acid (HA) based injectable hydrogel with gradually increasing mechanical properties was synthesized via photo-crosslinking reaction and thermal-induced Diels-Alder (DA) reaction. The injectable hydrogel can quickly gelate within 30 s by photo-crosslinking of HA-furan under the catalysis of lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP). This injectable property is beneficial to keep the encapsulated cell activity and convenient for clinical operation. And the mechanical properties can be control from 4.86 to 10.66 kPa by exposure time. Then, the thermal-induced DA click chemistry further occurs between furan groups and maleimide groups which gradually promoted the crosslinking density of the injectable hydrogel. The mechanical properties of the injectable hydrogel can be promoted to 21 kPa. ATDC-5 cells were successfully encapsulated in the injectable hydrogel and showed good activity. All the results suggested that the injectable hydrogel with gradually increasing mechanical properties formed by photo-crosslinking reaction and thermal-induced DA reaction has a good prospect of application in cartilage tissue engineering.

A biodegradable polyphosphoester-functionalized poly(disulfide) nanocarrier for reduction-triggered intracellular drug delivery

Stimuli-responsive and biodegradable polymeric carriers are of great importance for safe delivery and efficient release of chemotherapeutic agents. In this work, given the unique advantages of poly(disulfide)s and biodegradable polyphosphoesters, we designed and constructed a reduction-sensitive amphiphilic triblock copolymer poly(ethyl ethylene phosphate)-b-poly(disulfide)-b-poly(ethyl ethylene phosphate) (PEEP-PDS-PEEP) by combining thiol-disulfide polycondensation and ring-opening polymerization (ROP). The thiol-disulfide polycondensation between 1,6-hexanedithiol and 2,2'-dithiodipyridine yielded the linear telechelic pyridyl disulfide-terminated poly(disulfide)s, followed by the treatment with 2-mercaptoethanol to quantitatively produce dihydroxyl-terminated poly(disulfide)s, which was used to initiate the ROP reaction of 2-ethoxy-2-oxo-1,3,2-dioxaphospholane, generating ABA-type amphiphilic triblock copolymers. The chemical structures of various polymers were thoroughly characterized and verified using nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, gel permeation chromatography (GPC) and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectroscopy. The resultant amphiphilic PEEP-PDS-PEEP could self-assemble into spherical nanoparticles in aqueous solution as evidenced from dynamic light scattering (DLS) and transmission electron microscopy (TEM) analyses. Hydrophobic anti-tumor drug doxorubicin (DOX) was used to study the encapsulation capacity of nanoparticles, the drug loading content (DLC) and drug loading efficiency (DLE) values were determined to be 11.2% and 31.5%, respectively. In vitro release studies indicated that DOX was released much faster under reductive conditions compared to physiological conditions, confirming their reduction-responsive release behavior owing to the scission of the poly(disulfide) segment and subsequent disintegration of nanoparticles. The cellular uptake study using a live cell imaging system demonstrated that this DOX-loaded nanoparticle can be internalized into HeLa cells and release DOX over time. Methyl thiazolyl tetrazolium (MTT) assay revealed the favorable cytocompatibility of a bare triblock copolymer toward both L929 and HeLa cells, whereas the DOX-loaded copolymer nanoparticles exhibited the lower inhibitory ability against HeLa and HepG2 cell proliferation than free DOX. This finding presents a strategy for the construction of biocompatible and reduction-responsive polymeric drug carriers.

A Gelatin Hydrogel-Containing Nano-Organic PEI⁻Ppy with a Photothermal Responsive Effect for Tissue Engineering Applications

The introduction and designing of functional thermoresponsive hydrogels have been recommended as recent potential therapeutic approaches for biomedical applications. The development of bioactive materials such as thermosensitive gelatin-incorporated nano-organic materials with a porous structure and photothermally triggerable and cell adhesion properties may potentially achieve this goal. This novel class of photothermal hydrogels can provide an advantage of hyperthermia together with a reversibly transformable hydrogel for tissue engineering. Polypyrrole (Ppy) is a bioorganic conducting polymeric substance and has long been used in biomedical applications owing to its brilliant stability, electrically conductive features, and excellent absorbance around the near-infrared (NIR) region. In this study, a cationic photothermal triggerable/guidable gelatin hydrogel containing a polyethylenimine (PEI)⁻Ppy nanocomplex with a porous microstructure was established, and its physicochemical characteristics were studied through dynamic light scattering, scanning electronic microscopy, transmission electron microscopy, an FTIR; and cellular interaction behaviors towards fibroblasts incubated with a test sample were examined via MTT assay and fluorescence microscopy. Photothermal performance was evaluated. Furthermore, the in vivo study was performed on male Wistar rat full thickness excisions model for checking the safety and efficacy of the designed gelatin⁻PEI⁻Ppy nanohydrogel system in wound healing and for other biomedical uses in future. This photothermally sensitive hydrogel system has an NIR-triggerable property that provides local hyperthermic temperature by PEI⁻Ppy nanoparticles for tissue engineering applications. Features of the designed hydrogel may fill other niches, such as being an antibacterial agent, generation of free radicals to further improve wound healing, and remodeling of the promising photothermal therapy for future tissue engineering applications.

Porous Polyethylene Coated with Functionalized Hydroxyapatite Particles as a Bone Reconstruction Material

In this study, porous polyethylene scaffolds were examined as bone substitutes in vitro and in vivo in critical-sized calvarial bone defects in transgenic Sprague-Dawley rats. A microscopic examination revealed that the pores appeared to be interconnected across the material, making them suitable for cell growth. The creep recovery behavior of porous polyethylene at different loads indicated that the creep strain had two main portions. In both portions, strain increased with increased applied load and temperature. In terms of the thermographic behavior of the material, remarkable changes in melting temperature and heat fusion were revealed with increased the heating rates. The tensile strength results showed that the material was sensitive to the strain rate and that there was adequate mechanical strength to support cell growth. The in vitro cell culture results showed that human bone marrow mesenchymal stem cells attached to the porous polyethylene scaffold. Calcium sulfate–hydroxyapatite (CS–HA) coating of the scaffold not only improved attachment but also increased the proliferation of human bone marrow mesenchymal stem cells. In vivo, histological analysis showed that the study groups had active bone remodeling at the border of the defect. Bone regeneration at the border was also evident, which confirmed that the polyethylene acted as an osteoconductive bone graft. Furthermore, bone formation inside the pores of the coated polyethylene was also noted, which would enhance the process of osteointegration.

Design and synthesis study of the thermo-sensitive poly (N-vinylpyrrolidone-b- N, N-diethylacrylamide)

The reversible addition fragmentation chain transfer (RAFT) polymerization method was adopted here to prepare a series of thermo-sensitive copolymers, poly (N,N-diethyl- acrylamide-b-N-vinylpyrrolidone). Their structures, molecular weight distribution and temperature sensitivity performances were characterized by the nuclear magnetic resonance (1HNMR), the gel permeation chromatography (GPC) and the fluorescence spectrophotometer, respectively. It has been identified that the synthesis reaction of the block copolymer was living polymerization. The thermo-sensitivity study suggested that N-vinylpyrrolidone (NVP), played a key role on the lower critical solution temperature (LCST) performance.