Tough Bonding of PVA Hydrogel-on-Textured Titanium Alloy with Varying Texture Densities in Swollen State.

Cartilage defects in large joints are a common occurrence in numerous degenerative diseases, especially in osteoarthritis. The hydrogel-on-metal composite has emerged as a potential candidate material, as hydrogels, to some extent, replicate the composition of human articular cartilage consisting of collagen fibers and proteoglycans. However, achieving tough bonding between the hydrogel and titanium alloy remains a significant challenge due to the swelling of the hydrogel in a liquid medium. This swelling results in reduced interfacial toughness between the hydrogel and titanium alloy, limiting its potential clinical applications. Herein, our approach aimed to achieve durable bonding between a hydrogel and a titanium alloy composite in a swollen state by modifying the surface texture of the titanium alloy. Various textures, including circular and triangular patterns, with dimple densities ranging from 10 to 40%, were created on the surface of the titanium alloy. Subsequently, poly(vinyl alcohol) (PVA) hydrogel was deposited onto the textured titanium alloy using a casting-drying method. Our findings revealed that PVA hydrogel on the textured titanium alloy with a 30% texture density exhibited the highest interfacial toughness in the swollen state, measuring at 1300 J m-2 after reaching equilibrium swelling in deionized water, which is a more than 2-fold increase compared to the hydrogel on a smooth substrate. Furthermore, we conducted an analysis of the morphologies of the detached hydrogel from the textured titanium alloy after various swelling durations. The results indicated that interfacial toughness could be enhanced through mechanical interlocking, facilitated by the expanded volume of the hydrogel protrusions as the swelling time increased. Collectively, our study demonstrates the feasibility of achieving tough bonding between a hydrogel and a metal substrate in a liquid environment. This research opens up promising avenues for designing soft/hard heterogeneous materials with strong adhesive properties.

Improved Interfacial Interactions of Dip Coatings by In Situ Introducing Silica to Enhance Corrosion Resistance and Metal Bonding Strength.

Corrosion is an irreversible phenomenon in nature that has been a major source of metal degradation. We herein provide a unique approach for embedding nanoparticles into epoxy resins via hydrogen bonding adsorption of in situ hydrophilic silica. Based on this adsorption action, a super-anticorrosive epoxy-based Teflon (MEP-PTFE) coating for usage on metals such as aluminum alloys was developed utilizing one-step dip coating, with promising engineering and public applications. It should be noted that the binding strength between the resultant MEP-PTFE coating and the substrate was 13.5 N. This coating had an impedance modulus of over 8 × 109 Ω·cm2 at 0.01 Hz and an impressive corrosion inhibition efficiency of 99.999%. The anticorrosion barrier from the diffusion control to the charge transfer control was revealed for the future good design of resin matrix coatings with excellent corrosion resistance.

Superhydrophobic Surface with Stepwise Multilayered Micro- and Nanostructure and an Investigation of Its Corrosion Resistance.

We develop a fluorine-free preparation of the superhydrophobic surface on an aluminum alloy with anticorrosion performance and mechanical robustness. The surface morphology, chemical composition, and water repellency were determined with SEM, CLSM, EDS, FT-IR, TG, and contact-angle measurements, respectively. The aluminum matrix superhydrophobic surface (STA-PDMS-ZnO sample) was able to display excellent repellency to water with a WCA of 152° and a WSA of 2°. The outstanding superhydrophobicity on the as-prepared surface was greatly related to the construction of stepwise multilayered micro- and nanostructure within the superhydrophobic surface. Because of the special surface structure, the mechanical robustness and corrosion resistance of the STA-PDMS-ZnO sample were improved. Notably, the anticorrosion mechanism by air pockets was explained by the comparison of two superhydrophobic surfaces prepared with the same low-surface-energy chemicals. The superhydrophobic surface with a multilayered micro- and nanostructure (STA-PDMS-ZnO sample) showed greater corrosion resistance than the surface coated by superhydrophobic modification (control sample). This is because of the entrapments of numerous air pockets within the aluminum matrix superhydrophobic surface, thus strengthening the corrosion resistance. On the basis of the results, the multidimensional superhydrophobic surface is promising for having a good application future in the field of metal corrosion protection.

Lyophobic slippery surfaces on smooth/hierarchical structured substrates and investigations of their dynamic liquid repellency.

Slippery surfaces were prepared by infusing lubricant into smooth or hierarchical-structured superhydrophobic surfaces (SHS) to compare different surface-free energies. The surfaces obtained showed good repellency towards liquids with various values of surface tension/molecular polarity/viscosity, including hexane, tetradecane, water, ethylene glycol and viscous engine oil. The lyophobicity could be realized on a relatively smooth surface, indicating that the first principle of preparing a lyophobic slippery surface is to perform a low surface-free energy modification. The dynamic liquid repellency was also studied: the sliding speeds of different liquids on lubricant infused SHS showed a negative correlation to their kinematic viscosity values, and a higher surface roughness was favorable for dynamic wettability, whereas for the smooth slippery surface, the travelling speeds showed randomness.

Poly(glycerol) Used for Constructing Mixed Polymeric Micelles as T1 MRI Contrast Agent for Tumor-Targeted Imaging.

There was much interest in the development of nanoscale delivery vehicles based on polymeric micelles to realize the diagnostic and therapeutic applications in biomedicine. Here, with the purpose of constructing a micellar magnetic resonance imaging (MRI) contrast agent (CA) with well biocompatibility and targeting specificity, two types of amphiphilic diblock polymers, mPEG-PG(DOTA(Gd))-b-PCL and FA-PEG-b-PCL, were synthesized to form mixed micelles by coassembly. The nanostructure of the resulting micellar system consisted of poly(caprolactone) (PCL) as core and poly(glycerol) (PG) and poly(ethylene glycol) (PEG) as shell, simultaneously modified with DOTA(Gd) chelates and folic acid (FA), which afforded functions of MRI contrast enhancement and tumor targeting. The mixed micelles in aqueous solution presented a hydrodynamic diameter of about 85 nm. Additionally, this mixed micelles exhibited higher r1 relaxivity (14.01 mM-1 S1-) compared with commercial Magnevist (3.95 mM-1 S1-) and showed negligible cytotoxicity estimated by WST assay. In vitro and in vivo MRI experiments revealed excellent targeting specificity to tumor cells and tissue. Furthermore, considerably enhanced signal intensity and prominent positive contrast effect were achieved at tumor region after tumor-bearing mice were intravenously injected with the mixed micelles. These preliminary results indicated the potential of the mixed micelle as T1 MRI CA for tumor-targeted imaging.

In vitro drug release and cartilage interface lubrication properties of biomimetic polymers.

Osteoarthritis is a degenerative disease that is widely found in the elderly population, with a trend towards a younger age group in recent years. In the early stages of arthritis, patients are treated with hyaluronic acid injections and anti-inflammatory drugs. However, it has been found that hyaluronic acid can only play a supportive role and does not have a lubricating effect, and due to the absence of blood vessels, nerves, and lymphatic vessels in the articular cartilage, the oral anti-inflammatory drugs cannot reach the interface of the inflammatory joints adequately, and the drug utilisation rate is low. Herein, we designed and prepared a brush-like bionic lubricant for joint lubrication and drug loading. The poly(2-methyl-2-oxazoline) branched chain was grafted onto the hyaluronic acid main chain by ring-opening polymerisation and graft polymerisation to form a brush-like bionic lubricin containing multiple hydrophilic groups, which was self-assembled to encapsulate the drug by using its multi-branched special structure for drug loading. The friction behaviour tests on the articular cartilage surface showed that the prepared bionic lubricin has excellent lubrication effect, with a minimum friction coefficient of 0.036 close to the lubrication effect of natural synovial fluid, which is mainly due to the hydrophilic groups on its molecular chain that can adsorb the water molecules and form a hydration layer at the cartilage interface, which plays the role of hydration lubrication. In addition, in vitro drug release studies showed that the synthesised drug-loading biomimetic lubricin had a certain drug release capacity, and the maximum drug release rate could reach 77.8 % at 72 h. The synthesis of this bionic lubricant with dual functions of lubrication and drug release provides a new idea for the treatment of osteoarthritis.

Biotribological properties of UHMWPE grafted with AA under lubrication as artificial joint.

Osteolysis caused by wear particles from polyethylene in the artificial hip joints is a serious issue. In order to endow the low friction and wear of the bearing surface of ultra-high molecular weight polyethylene (UHMWPE) artificial joint for a longer term, hydrophilic acrylic acid (AA) was grafted on UHMWPE powders with the method of ultraviolet irradiation and then the modified powders were hot pressed. The tribological properties of modified UHMWPE sliding against CoCrMo metallic plate on reciprocating tribometer under calf serum, saline and distilled water lubrication during a long-term friction were investigated. The measurement of Fourier-transform infrared spectroscopy indicates that AA is successfully grafted on the surface of UHMWPE powders by photo-induced graft polymerization. Contact angles of UHMWPE are decreased from 83° to 35° by grafting and the surface wettability is effectively improved. The tensile strength of modified sample decreases. The friction coefficient and wear rate of UHMWPE-g-PAA under calf serum, saline and distilled water lubrication are lower than that of untreated UHMWPE. With the increase of grafting ratio, the wear rate of UHMWPE-g-PAA decreases firstly and then increases. The modified UHMWPE with grafting ratio of 3.5 % has the lowest wear rate, which is just quarter of the untreated UHMWPE. The hydrated PAA polymer brushes enclosed in the UHMWPE bulk material provide continuous lubrication during long term sliding.

A lubricant and adhesive hydrogel cross-linked from hyaluronic acid and chitosan for articular cartilage regeneration.

Trauma-induced articular cartilage damages are common in clinical practice. Hydrogels have been used to fill the cartilage defects and act as extracellular matrices for cell migration and tissue regeneration. Lubrication and stability of the filler materials are essential to achieve a satisfying healing effect in cartilage regeneration. However, conventional hydrogels failed to provide a lubricous effect, or could not anchor to the wound to maintain a stable curing effect. Herein, we fabricated dually cross-linked hydrogels using oxidized hyaluronic acid (OHA) and N-(2-hydroxypropyl)-3-trimethylammonium chitosan chloride (HTCC) methacrylate (HTCCMA). The OHA/HTCCMA hydrogels, which were dynamically cross-linked and then covalently cross-linked by photo-irradiation, showed appropriate rheological properties and self-healing capability. The hydrogels exhibited moderate and stable tissue adhesion property due to formation of dynamic covalent bonds with the cartilage surface. The coefficient of friction values were 0.065 and 0.078 for the dynamically cross-linked and double-cross-linked hydrogels, respectively, demonstrating superior lubrication. In vitro studies showed that the hydrogels had good antibacterial ability and promoted cell proliferation. In vivo studies confirmed that the hydrogels were biocompatible and biodegradable, and exhibited a robust regenerating ability for articular cartilage. This lubricant-adhesive hydrogel is expected to be promising for the treatment of joint injuries as well as regeneration.

Injectable nanohybrid scaffold for biopharmaceuticals delivery and soft tissue engineering.

An injectable nanofibrous hydrogel scaffold integrated with growth factors (GFs) loaded polysaccharide nanoparticles was developed that specifically allows for targeted adipose-derived stem cells (ASCs) encapsulation and soft tissue engineering. The nanofibrous hydrogel was produced via biological conjugation of biotin-terminated star-shaped poly(ethylene glycol) (PEG-Biotin) and streptavidin-functionalized hyaluronic acid (HA-Streptavidin). The polysaccharide nanoparticles were noncovalently assembled via electrostatic interactions between low-molecular-weight heparin (LMWH) and N,N,N-trimethylchitosan chloride (TMC). Vascular endothelial growth factor (VEGF) was entrapped in the LMWH/TMC nanoparticles by affinity interactions with LMWH.

A tannic acid-reinforced PEEK-hydrogel composite material with good biotribological and self-healing properties for artificial joints.

Polyetheretherketone (PEEK) is widely considered as a promising material for joint implants but it still has limitations involving high friction and wear. To mimic the cartilage-subchondral bone structure in natural joints, a polyvinyl alcohol (PVA) hydrogel layer was fabricated on the PEEK substrate to provide a lubrication mechanism. In addition, tannic acid was applied to form dynamic hydrogen bonds with PVA molecules, for the purpose of strengthening the hydrogel layer and endowing it with self-healing ability. Our experimental results demonstrated that the prepared PEEK-hydrogel composite exhibited good biotribological performance with a low average friction coefficient around 0.06 and little wear after the friction test. It also could repair the scratch made by a blade spontaneously at room temperature taking advantage of the reversibility of the hydrogen bonds. The influence of the properties of the PVA hydrogel and the concentration of tannic acid on the frictional and self-healing behavior of the composite structure was investigated and the internal mechanism was discussed. This work presents a facile method to fabricate a PEEK-hydrogel composite possessing outstanding tribological properties and self-healing capacity simultaneously, hopefully promoting its potential in producing artificial joints.

Silver/Polypyrrole-Functionalized Polyurethane Foam Embedded Phase Change Materials for Thermal Energy Harvesting.

Conversion of solar energy into thermal energy stored in phase change materials (PCMs) can effectively relieve the energy dilemma and improve energy utilization efficiency. However, facile fabrication of form-stable PCMs (FSPCMs) to achieve simultaneously energetic solar-thermal, conversion and storage remains a formidable challenge. Herein, we report a desirable solar-thermal energy conversion and storage system that utilizes paraffin (PW) as energy-storage units, the silver/polypyrrole-functionalized polyurethane (PU) foam as the cage and energy conversion platform to restrain the fluidity of the melting paraffin and achieve high solar-thermal energy conversion efficiency (93.7%) simultaneously. The obtained FSPCMs possess high thermal energy storage density (187.4 J/g) and an excellent leak-proof property. In addition, 200 accelerated solar-thermal energy conversion-cycling tests demonstrated that the resultant FSPCMs had excellent cycling durability and reversible solar-thermal energy conversion ability, which offered a potential possibility in the field of solar energy utilization technology.

Multilayers of poly(ethyleneimine)/poly(acrylic acid) coatings on Ti6Al4V acting as lubricated polymer-bearing interface.

To achieve an efficient lubricated interface on titanium alloy (Ti6Al4V) alloy, polyelectrolyte multilayer (PEM) polymer coatings, based on poly(ethyleneimine)/poly(acrylic acid) (PEI/PAA), were fabricated on the surface of Ti6Al4V alloy substrates using the layer-by-layer (LbL) assembly technique. Their composition and morphology were confirmed by Fourier-transform infrared/attenuated total reflectance (FTIR/ATR) spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. The tribological properties were investigated by a ball-on-disk rotating tribometer using deionized water, saline, and calf serum. The results exhibit that (PEI/PAA)*n coatings have the internal cross-linked network and porous structure on the surface. The surface of PEI/PAA coatings-modified Ti6Al4V shows the sufficient wettability. The polymer-bearing interface of (PEI/PAA)*10 exhibits a low friction coefficient, 0.059, for 2 hr, and represents an 88% decline compared with bare Ti6Al4V. Moreover, the wear track on the polymer-bearing interface is superlow. There is no obvious wear volume, which indicates effective wear resistance. The hydrated layer, the cross-linked network structure, and the porous structure of PEM coatings are the main factors for efficient tribological properties. The multilayer PEI/PAA coating shows the potential uses of developing the lubricated-bearing interface on Ti6Al4V alloy.

Bio-inspired surface modification of PEEK through the dual cross-linked hydrogel layers.

The biocompatible high-performance material PEEK (polyetheretherketone) is an attractive implant material, however, its hydrophobicity and high friction coefficients severely hinder its biomedical applications. Thus, it is inferred from the recent advances in surface modification technology, achieving the biomimetic natural joint lubrication systems on PEEK still remains a challenge. In view of the above, herein we proposed a novel two-step strategy to fabricate a "soft (dual cross-linked hydrogel) layer-hard (PEEK) substrate" texture that mimics the structure and function of soft cartilage on the hard basal bone in joints. At first, a layer of acrylic acid-co-acryl amide (AA-AM) hydrogel is anchored to the PEEK substrate through UV-initiated polymerization. In the second step, hydrogel coated PEEK substrate is immersed in ferric nitrate solution to create the secondary cross-linkage between Fe3+ and -COOH groups in the hydrogel. As a result, the consequential top-coat hydrogel layer not only transforms the surface wettability (hydrophobic to hydrophilic) but also provides scratch resistance to the underlying PEEK substrate. The modified specimens display low friction coefficients in water under different load conditions. In addition, the obtained surface exhibits a certain self-repairing ability due to its unique physically reversible network structure. Therefore, this work provides a promising strategy for broadening the use of PEEK in orthopedic implants.

Doubly crosslinked biodegradable hydrogels based on gellan gum and chitosan for drug delivery and wound dressing.

Biopolymer-based hydrogels with sustained drug release capability and antibacterial activity have exhibited great potential in clinical application in drug delivery and wound healing. In this study, a new type of composite wound dressing hydrogel aiming at avoiding wound infection was developed through embedding drug loaded gellan gum microspheres (GMs) into a doubly crosslinked hydrogel, which was constructed by Schiff-base crosslinking of oxidized gellan gum (OG) (pre-crosslinked by calcium ion) and carboxymethyl chitosan (CMCS). The gelation time, swelling index, degradation rate and mechanical properties of the blank hydrogel was optimized by varying the ratios of CMCS/OG (w/w) with fixed OG/calcium (w/w) ratio. The best overall performance of the hydrogel was obtained when CMCS/OG is 16/7 (w/w), with a 139 s gelation time, swelling index remained above 30 after swelling equilibrium, 100.5% degradation rate on the seventh day, and 8.8 KPa compressive modulus. After being embedded with cargo-loaded GMs, the aforementioned performance of the blank hydrogel was improved, and the sustained release of cargoes (antibacterial drugs, tetracycline hydrochloride and silver sulfadiazine) was observed. Moreover, the excellent antibacterial activity of the composite hydrogel was also demonstrated in vitro. These results support the bioactive composite hydrogel can be employed as a promising injectable scaffold for promoting wound regeneration and drug delivery.

Study on compressive mechanical properties of nanohydroxyapatite reinforced poly(vinyl alcohol) gel composites as biomaterial.

Nanohydroxyapatite reinforced poly(vinyl alcohol) (nano-HA/PVA) gel composites has been proposed as a promising biomaterial to replace diseased or damaged articular cartilage. In this paper, nano-HA/PVA gel composites were prepared by in situ synthesis nano-HA particles in PVA solution and accompanied with freeze/thaw method. The influence of nano-HA content, PVA concentration and freeze/thaw cycle times on the compressive mechanical behavior of nano-HA/PVA gel composites were evaluated using mechanical test equipment. The results showed that the compressive mechanical behavior of nano-HA/PVA gel composites was similar to that of natural articular cartilage, which held special viscoelastic characteristics. Both the compressive strength and modulus of the composites improved correspondingly with the rise of freeze/thaw cycle times and PVA concentration. The compressive strength and modulus of nano-HA/PVA gel composites firstly increased and then presented decreasing trend with the rise of nano-HA content. Furthermore, the compressive modulus of the composites improved exponentially with the rise of compressive strain ratio.

Magnetic and self-healing chitosan-alginate hydrogel encapsulated gelatin microspheres via covalent cross-linking for drug delivery.

In order to broaden the abilities of injectable hydrogel scaffolds, a self-healing chitosan/alginate hydrogel encapsulated with magnetic gelatin microspheres (MGMs) was prepared for anti-cancer drug delivery and soft tissue engineering. The hydrogel was formulated by cross-linking carboxyethyl chitosan (CEC) and oxidized alginate (OAlg) via the Schiff-base reaction. To strengthen the mechanical and biological capabilities of hydrogel, MGMs containing 5-fluorouracil (5-Fu) were prepared by an emulsion cross-linking method. In vitro gelation time, swelling ratio, degradation, compressive modulus and rheological behaviors were tested to monitor the effect of MGMs on the CEC-OAlg hydrogel. With a concentration of 30 mg/mL MGMs, the composite hydrogel provided with the suitable performance and showed excellent self-healing ability under physiological condition. Moreover, this composite hydrogel showed the sustained in vitro drug release compared with control MGMs and CEC-OAlg hydrogel. Our results demonstrated that this magnetic and self-healing CEC-OAlg hydrogel scaffold encapsulated MGMs containing 5-Fu was expected to be a platform for drug delivery and soft tissue engineering.

Covalently polysaccharide-based alginate/chitosan hydrogel embedded alginate microspheres for BSA encapsulation and soft tissue engineering.

Hydrogels based scaffolds are very promising materials for a wide range of medical applications including tissue engineering and drug delivery. This study reports a covalently cross-linked composite hydrogel embedded with microspheres basing natural polysaccharides as a protein delivery system for soft tissue engineering. This biodegradable composite hydrogel derived from water-soluble chitosan and alginate derivatives upon mixing, without addition of chemical cross-linking agents. The gelation is attributed to the Schiff-base reaction between amino and aldehyde groups of N-succinyl chitosan (N-Chi) and oxidized alginate (OAlg), respectively. Meanwhile, gel-like microspheres were prepared with a diameter of 2-10 µm by conjugating sodium alginate with Ca2+ in an aqueous emulsion via the emulsion cross-linking technique. Bull Serum Albumin (BSA) was encapsulated into alginate gel microspheres and subsequently incorporated into OAlg/N-Chi hydrogels to produce a composite scaffold. In the current work, gelation rate, morphology, mechanical properties, swelling ratio, in vitro degradation and BSA release of the composite scaffolds were examined. The results show that mechanical and stable properties of gel scaffolds can be significantly improved by embedding alginate microspheres. The alginate microspheres can serve as a filler to toughen the soft OAlg/N-Chi hydrogels. Compressive modulus of composite gel scaffolds containing 0.5 mL volume of microspheres was 57.3 KPa, which was higher than the control hydrogel without microspheres. Moreover, the controlled release of BSA encapsulated within this composite hydrogels showed significantly lower rate when compared with control hydrogel or microspheres alone. These characteristics provide a potential opportunity to use this injectable composite gel scaffold in protein delivery and soft tissue engineering applications.

Construction of lubricant composite coating on Ti6Al4V alloy using micro-arc oxidation and grafting hydrophilic polymer.

To improve the tribological properties of Ti6Al4V alloy to realize the application in artificial joints, a novel composite coating was designed and fabricated on its surface through the combination of two different surface modification techniques-micro-arc oxidation (MAO) and grafting hydrophilic polymer. The characterizations of morphologies and composition of MAO layer were examined using scanning electron microscopy (SEM), energy dispersive spectroscope (EDS) and X-ray diffraction (XRD). It was found that a TiO2 layer displaying uniform porous structure formed on the surface based on the optimal MAO parameters of an oxidation voltage of 450 V and an oxidation time of 60 min. After grafting 3-dimethyl(3-(N-methacrylamido)propyl) ammonium propane sulfonate (MPDSAH), Fourier-transform infrared spectroscopy with attenuated total reflection (FT-IR/ATR) and wettability test demonstrated the successful modification. Tribological performance of composite coating-modified Ti6Al4V alloy in water exhibited the low friction coefficient of 0.13 and favorable wear resistance.

Improving surface wettability and lubrication of polyetheretherketone (PEEK) by combining with polyvinyl alcohol (PVA) hydrogel.

Poor surface wettability and relative high friction coefficients of pristine polyetheretherketone (PEEK) have limited its application in orthopedic implants. In this study, inspired by the structure of natural articular cartilage, we presented a novel method to fabricate a "soft-on-hard" structure on the surface of pristine PEEK specimens, which combined a soft polyvinyl alcohol (PVA) hydrogel layer and a three-dimensional porous layer with PEEK substrates. A variety of analytical methods were used to evaluate their properties, our results demonstrated that the hydrogel layer could be seamlessly connected with substrate, and the hydrogel-covered PEEK owned a highly hydrophilic surface, a very low water contact angle of 7° could be obtained. The friction coefficients of untreated and hydrogel-covered PEEK surfaces were measured using a tribometer under water lubrication, due to the presence of the top hydrogel layer and the hard substrate could provide excellent aqueous lubrication and bearing capacity, respectively, the friction coefficient could be reduced from 0.292 to 0.021. In addition, the porous layer under PVA hydrogel layer could work as gel reservoirs, the reserved hydrogel would be released after the surface layer was sheared off, and a regenerable lubrication status was obtained. This work provides a new route for the design of improving the surface wettability and tribological properties of PEEK.

Biodegradable Nanoglobular Magnetic Resonance Imaging Contrast Agent Constructed with Host-Guest Self-Assembly for Tumor-Targeted Imaging.

Gadolinium-based macromolecular magnetic resonance imaging (MRI) contrast agents (CAs) have attracted increasing interest in tumor diagnosis. However, their practical application is potentially limited because the long-term retention of gadolinium ion in vivo will induce toxicity. Here, a nanoglobular MRI contrast agent (CA) PAMAM-PG- g-s-s-DOTA(Gd) + FA was designed and synthesized on the basis of the facile host-guest interaction between ß-cyclodextrin and adamantane, which initiated the self-assembly of poly(glycerol) (PG) separately conjugated with gadolinium chelates by disulfide bonds and folic acid (FA) molecule onto the surface of poly(amidoamine) (PAMAM) dendrimer, finally realizing the biodegradability and targeting specificity. The nanoglobular CA has a higher longitudinal relaxivity ( r1) than commercial gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA), showing a value of 8.39 mM-1 s-1 at 0.5 T, and presents favorable biocompatibility on the observations of cytotoxicity and tissue toxicity. Furthermore, MRI on cells and tumor-bearing mice both demonstrate the obvious targeting specificity, on the basis of which the effective contrast enhancement at tumor location was obtained. In addition, this CA exhibits the ability of cleavage to form free small-molecule gadolinium chelates and can realize minimal gadolinium retention in main organs and tissues after tumor detection. These results suggest that the biodegradable nanoglobular PAMAM-PG- g-s-s-DOTA(Gd) + FA can be a safe and efficient MRI CA for tumor diagnosis.