Rafting-Enabled Recovery Avoids Recrystallization in 3D-Printing-Repaired Single-Crystal Superalloys.

The repair of damaged Ni-based superalloy single-crystal turbine blades has been a long-standing challenge. Additive manufacturing by an electron beam is promising to this end, but there is a formidable obstacle: either the residual stress and γ/γ  ' microstructure in the single-crystalline fusion zone after e-beam melting are unacceptable (e.g., prone to cracking), or, after solutionizing heat treatment, recrystallization occurs, bringing forth new grains that degrade the high-temperature creep properties. Here, a post-3D printing recovery protocol is designed that eliminates the driving force for recrystallization, namely, the stored energy associated with the high retained dislocation density, prior to standard solution treatment and aging. The post-electron-beam-melting, pre-solutionizing recovery via sub-solvus annealing is rendered possible by the rafting (i.e., directional coarsening) of γ  ' particles that facilitates dislocation rearrangement and annihilation. The rafted microstructure is removed in subsequent solution treatment, leaving behind a damage-free and residual-stress-free single crystal with uniform γ  ' precipitates indistinguishable from the rest of the turbine blade. This discovery offers a practical means to keep 3D-printed single crystals from cracking due to unrelieved residual stress, or stress-relieved but recrystallizing into a polycrystalline microstructure, paving the way for additive manufacturing to repair, restore, and reshape any superalloy single-crystal product.

Correction: Anti-biofouling ability and cytocompatibility of the zwitterionic brushes-modified cellulose membrane.

Correction for 'Anti-biofouling ability and cytocompatibility of the zwitterionic brushes-modified cellulose membrane' by Pingsheng Liu et al., J. Mater. Chem. B, 2014, 2, 7222-7231.

Anti-biofouling ability and cytocompatibility of the zwitterionic brushes-modified cellulose membrane.

Blood compatibility and cytocompatibility are key requirements of blood-contacting biomaterials for biomedical applications. Here, we showed the general zwitterionic surface modification of cellulose membrane (CM) substrates, via surface-initiated atom transfer radical polymerization (SI-ATRP), to enhance the anti-biofouling ability without compromising the cytocompatibility of the substrates. Robust X-ray photoelectron spectroscopy (XPS) characterization revealed the successful construction of three zwitterionic brushes, which significantly increased the hydrophilicity of the CM substrates. The zwitterionic brushes-modified CM substrates can significantly reduce the non-specific adsorption of proteins, platelet adhesion and cell attachment, indicating a generally and significantly improved anti-biofouling ability, which is comparable to that of the benchmark anti-fouling poly(ethylene glycol) (PEG) surface. Inspired by the varied in situ cell morphology observed on different substrates, we further investigated the cytocompatibility of the zwitterionic coatings and showed the general cytocompatibility of zwitterionic brush-modified CM surfaces based on both 2D (cell cultured with zwitterionic surfaces) and 3D cell cultures (cell encapsulation in zwitterionic hydrogels). This work provides a promising general approach to enhancing the blood compatibility of cellulose-based materials without compromising their cytocompatibility. The cytocompatibility observation may enrich the perceptions of the zwitterionic modification of substrates and may be beneficial for the in vivo applications of zwitterionic materials.

Facile surface modification of silicone rubber with zwitterionic polymers for improving blood compatibility.

A facile approach to modify silicone rubber (SR) membrane for improving the blood compatibility was investigated. The hydrophobic SR surface was firstly activated by air plasma, after which an initiator was immobilized on the activated surface for atom transfer radical polymerization (ATRP). Three zwitterionic polymers were then grafted from SR membrane via surface-initiated atom transfer radical polymerization (SI-ATRP). The surface composition, wettability, and morphology of the membranes before and after modification were characterized by X-ray photoelectron spectroscopy (XPS), static water contact angle (WCA) measurement, and atomic force microscopy (AFM). Results showed that zwitterionic polymers were successfully grafted from SR surfaces, which remarkably improved the wettability of the SR surface. The blood compatibility of the membranes was evaluated by protein adsorption and platelet adhesion tests in vitro. As observed, all the zwitterionic polymer modified surfaces have improved resistance to nonspecific protein adsorption and have excellent resistance to platelet adhesion, showing significantly improved blood compatibility. This work should inspire many creative uses of SR based materials for biomedical applications such as vessel, catheter, and microfluidics.

Synthesis and one-pot tethering of hydroxyl-capped phosphorylcholine onto cellulose membrane for improving hemocompatibility and antibiofouling property.

Tethering of biomimetic phosphorylcholine derivative onto the surface of biomedical devices is an effective method for improving hemocompatibility and antibiofouling property. Herein, series of novel hydroxyl-capped phosphorylcholines (HOPC) with different carbon spacer lengths were first synthesized and characterized with element analysis (EA), Fourier transform infrared spectroscopy(FTIR), and nuclear magnetic resonance spectroscopy (NMR). Then, HOPC (n=5, 2a) was one-pot tethered onto cellulose membrane with hexamethylene diisocyanate (HDI) as a coupling agent. The existence of phosphorylcholine was demonstrated by water contact angle measurement, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The hemocompatibility and antibiofouling property were evaluated by hemolytic test, platelet adhesion, protein adsorption, and Escherichia coli adhesion test. The results showed that cellulose membranes tethered with HOPC exhibited excellent hemocompatibility featured by low platelet adhesion and fibrinogen adsorption as well as antibiofouling property with bacterial adhesion resistance.

Copolymer coatings consisting of 2-methacryloyloxyethyl phosphorylcholine and 3-methacryloxypropyl trimethoxysilane via ATRP to improve cellulose biocompatibility.

AB diblock copolymers comprised of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and poly(3-methacryloxypropyl trimethoxysilane) (PMTSi) segments, which are used for biocompatible coatings, were investigated. Block copolymers with various compositions were synthesized by atomic transfer radical polymerization (ATRP). The obtained copolymers were dissolved in an ethanol solution, and dynamic light scattering showed that all block copolymers were capable of existing as micelles. After a convenient "one-step" reaction, the cellulose membranes could be covalently modified by these copolymers with stable chemical bonds (C-O-Si and Si-O-Si). Block copolymers with different PMPC chain length were applied to surface modification to find the most suitable copolymer. The functional MPC density can be controlled by adjusting the ratio of the two monomers (MPC and MTSi), which also affect surface properties, including the surface contact angle, surface morphology, and number of functional PC groups. The low-fouling properties were measured by protein adsorption, platelet adhesion and activation, and cell adhesion. Protein adsorption of bovine serum albumin (BSA), fibrinogen, and human plasma were also tested and a moderate monomer composite was attained. The protein adsorption behavior on the novel interfaces depends both on MPC density and PMPC chain length. Platelet adhesion and activation were reduced on all the modified surfaces. The adhesion of Human Embryonic Kidney 293 (293T) cells on the coated surfaces also decreased.

Grafting of zwitterion from cellulose membranes via ATRP for improving blood compatibility.

A p-vinylbenzyl sulfobetaine was grafted from cellulose membrane (CM) using surface-initiated atom transfer radical polymerization for blood compatibility improvement. Surface structure, wettability, morphology, and thermal stability of the CM substrates before and after modification were characterized by attenuated total reflectance Fourier transform infrared spectra, X-ray photoelectron spectroscopy measurement, water contact angle measurement, atomic force microscopy, and thermogravimetric analysis, respectively. The results showed that zwitterionic brushes were successfully fabricated on the CM surfaces, and the content of the grafted layer increased gradually with the polymerization time. The blood compatibility of the CM substrates was evaluated by protein adsorption tests and platelet adhesion tests in vitro. It was found that all the CMs functionalized with zwitterionic brush showed improved resistance to nonspecific protein adsorption and platelet adhesion, even though the grafting polymerization was conducted for several minutes.

Enhanced blood compatibility of polyurethane functionalized with sulfobetaine.

The purpose of this work is to develop a biocompatible polyurethane surface by the tailoring of sulfobetaine. The polyurethane film was first grafted polymerization with acrylic acid by ozonization, followed by immobilizing sulfobetaine via two routes: (i) synthesize primary amine group terminated sulfobetaine and then couple onto the surface of polyurethane using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC); (ii) couple the primary amine group terminated tertiary amine onto the surface of polyurethane primarily using EDC and then form sulfobetaine through a ring-opening reaction between tertiary amine and 1,3-propanesultone (PS). The reaction process was monitored with attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). The blood compatibility was evaluated by a hemolytic test and platelet-rich plasma (PRP) adhesion experiment. Little hemolysis took place on the surface of polyurethane grafted with sulfobetaine. Platelets adhering on the surface of grafted polyurethane decreased greatly as compared to the original after 1 and 3h of incubation with PRP.

Platelet adhesion and protein adsorption on silicone rubber surface by ozone-induced grafted polymerization with carboxybetaine monomer.

Platelet adhesion and protein adsorption on the silicone rubber film grafted with N,N'-dimethyl-N-methacryloyloxyethyl-N-(2-carboxyethyl) ammonium (DMMCA) was studied. The grafting was carried out by means of ozone-induced method and was confirmed by ATR-FTIR and XPS investigations. The grafted films possessed relatively hydrophilic surface revealed by contact angle measurement. The blood compatibility of the grafted film was evaluated in vitro by platelet adhesion in platelet-rich plasma (PRP) and protein absorption in bovine fibrinogen (BFG) using silicone film as the reference. No substantial platelet adhesion was observed for the grafted films incubated in PRP for 60 and 180 min. The protein absorption was also significantly reduced after incubated in bovine fibrinogen for 60 min. Both the results indicated that the blood compatibility of silicone rubber was greatly improved by ozone-induced grafting of carboxybetaine zwitterionic polymer onto its surface.

Chemical graft polymerization of sulfobetaine monomer on polyurethane surface for reduction in platelet adhesion.

Surface modification is an effective way to improve the hemocompatibility and remain bulk properties of biomaterials. Recently, polymer tailored with zwitterions was found having good blood compatibility. In this study, the zwitterionic monomer of sulfobetaine was graft polymerized onto polyurethane (PU) surface in a three-step heterogenous system through the vinyl bonds of acrylic acid (AA) or hydroxyethyl methacrylate (HEMA), which was immobilized with hexamethylene diisocyanate (HDI) beforehand. First, PU was activated with isocyanate groups using HDI as coupling agent. Second, AA or HEMA was introduced through reaction of AA or HEMA with NCO groups bonded on PU surface. Last, zwitterionic monomer of sulfobetain was graft polymerized with vinyl group of AA or HEMA using AIBN as polymerization initiator. The reaction process was monitored with ATR-IR spectra and XPS spectra. Variation of graft yield with temperature and monomer feed concentration was investigated and feasible conditions were optimized. The wettability of films was investigated by water contact angle measurement and water absorbance. Platelet adhesion experiment was conducted as a preliminary test to confirm the improved blood compatibility of PU. The number of platelets adhering to PU decreased greatly comparing with the originals after 1 and 3 h of contact with human plate-rich plasma (PRP).

Polyurethane vascular catheter surface grafted with zwitterionic sulfobetaine monomer activated by ozone.

Polyurethane (PU) is a conventional biomedical material with favorable biocompatibility and excellent mechanical properties and widely used in making vascular catheter, but its antithrombogenic property is not good enough to make it as a more demanding applicable biomaterial. Surface modification is an effective way to improve the hemocompatibility for biomaterials. The purpose of present study was to use ozonization method to modify the surface of PU vascular catheter slice to improve its antithrombogenicity by grafting N,N-dimethyl-N-methacryloxyethyl-N-(3-sulfopropyl) ammonium (DMMSA), a zwitterionic sulfobetaine monomer. PU vascular catheter (PUVC) grafted with DMMSA (PUVC-g-PDMMSA) was characterized by ATR-FTIR and XPS. ATR-FTIR and XPS investigation confirmed the graft polymerization. The blood compatibility of the grafted films was evaluated by platelet rich plasma (PRP) platelet adhesion study and scanning electron microscopy (SEM) was used to observe the morphology of platelet using PU vascular catheter (PUVC) as the reference. No platelet adhesion was observed for the grafted PUVC slice incubated with PRP at 37 degrees C for 120 min. It is significant that this new zwitterionic sulfobetaine grafted PUVC have improved antithrobogenicity. It is effective that the inner surface of vascular catheter with inner diameter in only 3mm can be grafted with PDMMSA by using ozonization method.

Various approaches to modify biomaterial surfaces for improving hemocompatibility.

In this paper, the mechanism of thrombus formation on the surface of polymeric materials and the various approaches of modifying biomaterial surfaces to improve their hemocompatibility are reviewed. Moreover, the blood compatibility of the cellulose membrane grafted with O-butyrylchitosan (OBCS) by using a radiation grafting technique was studied. Surface analysis of grafted cellulose membrane was verified by attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and electron spectroscopy for chemical analysis (ESCA), which confirmed that OBCS was successfully grafted onto the cellulose membrane surfaces. Blood compatibility of the grafted cellulose membranes was evaluated by platelet rich plasma (PRP) contacting experiments and protein adsorption experiments using blank cellulose membranes as the control. The blood compatibility of OBCS grafted cellulose membranes is better than that of blank cellulose membranes. These results suggest that the photocrosslinkable chitosan developed here has the potential of serving in blood-contacting applications in medical use.

Platelet adhesive resistance of segmented polyurethane film surface-grafted with vinyl benzyl sulfo monomer of ammonium zwitterions.

Platelet from human plasma adhered on the segmented poly(ether urethane) (SPEU) film grafted with N,N-dimethyl-N-(p-vinylbenyl)-N-(3-sulfopropyl) ammonium (DMVSA) was studied. SPEU films were hydroxylated by potassium peroxosulfate (KPS) and then grafted with DMVSA using ceric ammonium nitrate (CAN) as initiator. The mixing time of hydroxylated SPEU/CAN and the monomer concentration effect on graft polymerization yield were determined by ATR-FTIR. Surface analysis of the grafted films by ATR-FTIR and ESCA confirmed that DMVSA was successfully grafted onto the SPEU film surface. The grafted film possessed a relatively hydrophilic surface, as revealed by water contact angle measurement. The improved blood compatibility of the grafted films was preliminarily evaluated by a platelet-rich plasma adhesion study and scanning electron microscopy, using original SPEU and hydroxylated SPEU films as the controls. The results showed that platelet attachment was decreased greatly on the segmented polyurethane films grafted with DMVSA. This kind of new biomaterials grafted with sulfo ammonium zwitterionic monomers might have potential for biomedical applications.

[Attachment and growth of cultured fibroblast cells on chitosan/PHEA-blended hydrogels].

The chitosan/PHEA-blended hydrogels were prepared from PHEA and chitosan in various blend ratios. The water contents of the hydrogels were in the range of 50%-80% (wt). The attachment and growth of fibroblast cells(L929) on the hydrogels were studied. The results indicated the PHEA content in hydrogels has great effect on cell attachment but has little effect on the growth of L929 cells.