Immunoblot analysis of proteins associated with self-assembled monolayer surfaces of defined chemistries

The role of dendritic cells in the immunomodulation to implanted biomaterials

Considering the substantial role played by dendritic cells (DCs) in the immune system to bridge innate and adaptive immunity, studies on DC-mediated immunity toward biomaterials principally center on their adjuvant effects in facilitating the adaptive immunity of codelivered antigens. However, the effect of the intrinsic properties of biomaterials on dendritic cells has not been clarified. Recently, researchers have begun to investigate and found that biomaterials that are nonadjuvant could also regulate the immune function of DCs and thus affect subsequent tissue regeneration. In the case of proteins adsorbed onto biomaterial surfaces, their intrinsic properties can direct their orientation and conformation, forming “biomaterial-associated molecular patterns (BAMPs)”. Thus, in this review, we focused on the intrinsic physiochemical properties of biomaterials in the absence of antigens that affect DC immune function and summarized the underlying signaling pathways. Moreover, we preliminarily clarified the specific composition of BAMPs and the interplay between some key molecules and DCs, such as heat shock proteins (HSPs) and high mobility group box 1 (HMGB1). This review provides a new direction for future biomaterial design, through which modulation of host immune responses is applicable to tissue engineering and immunotherapy.

3D bioactive composite scaffolds for bone tissue engineering

Bone is the second most commonly transplanted tissue worldwide, with over four million operations using bone grafts or bone substitute materials annually to treat bone defects. However, significant limitations affect current treatment options and clinical demand for bone grafts continues to rise due to conditions such as trauma, cancer, infection and arthritis. Developing bioactive three-dimensional (3D) scaffolds to support bone regeneration has therefore become a key area of focus within bone tissue engineering (BTE). A variety of materials and manufacturing methods including 3D printing have been used to create novel alternatives to traditional bone grafts. However, individual groups of materials including polymers, ceramics and hydrogels have been unable to fully replicate the properties of bone when used alone. Favourable material properties can be combined and bioactivity improved when groups of materials are used together in composite 3D scaffolds. This review will therefore consider the ideal properties of bioactive composite 3D scaffolds and examine recent use of polymers, hydrogels, metals, ceramics and bio-glasses in BTE. Scaffold fabrication methodology, mechanical performance, biocompatibility, bioactivity, and potential clinical translations will be discussed.

Protein adsorption steers blood contact activation on engineered cobalt chromium alloy oxide layers

Biomaterials upon implantation are immediately covered by blood proteins which direct the subsequent blood activation. These early events determine the following cascade of biological reactions and consequently the long-term success of implants. The ability to modulate surface properties of biomaterials is therefore of considerable clinical significance. Goal of this study was an in-depth understanding of the biological response to cobalt chromium stent alloys with engineered surface oxide layers, which showed altered body reactions in vivo. We analyzed in vitro the biological events following initial blood contact on engineered cobalt chromium surfaces featuring said oxide layers. Surface-specific blood reactions were confirmed by scanning electron microscopy and the adsorbed protein layers were characterized by mass spectrometry. This powerful proteomics tool allowed the identification and quantification of over hundred surface-adhering proteins. Proteins associated with the coagulation cascade, platelet adhesion and neutrophil function correlated with the various blood surface activations observed. Furthermore, results of pre-coated surfaces with defined fibrinogen-albumin mixtures suggest that neutrophil adhesion was controlled by fibrinogen orientation and conformation rather than quantity. This study highlights the importance of controlling the biological response in the complex protein-implant surface interactions and the potential of the surface modifications to improve the clinical performance of medical implants.

STATEMENT OF SIGNIFICANCE

The blood contact activation of CoCr alloys is determined by their surface oxide layer properties. Modifications of the oxide layer affected the total amount of adsorbed proteins and the composition of the adsorbed protein layer. Additionally fibrinogen coatings mediated the surface-dependent neutrophil adhesion in a concentration-independent manner, indicating the influence of conformation and/or orientation of the adsorbed protein. Despite the complexity of protein-implant interactions, this study highlights the importance of understanding and controlling mechanisms of protein adhesion in order to improve and steer the performance of medical implants. It shows that modification of the surface oxide layer is a very attractive strategy to directly functionalize metallic implant surfaces and optimize their blood interaction for the desired orthopedic or cardiovascular applications.

Thin-layer matrix sublimation with vapor-sorption induced co-crystallization for sensitive and reproducible SAMDI-TOF MS analysis of protein biosensors

Coupling immunoassays on self-assembled monolayers (SAMs) to matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) provides improved assay selectivity compared with traditional photometric detection techniques. We show that thin-layer-transfer (TLT) of α-cyano-4-hydroxycinnaminic acid (CHCA) MALDI matrix via vacuum sublimation followed by organic solvent-based vapor-sorption induced co-crystallization (VIC) results in unique matrix/analyte co-crystallization tendencies that optimizes assay reproducibility and sensitivity. Unique matrix crystal morphologies resulted from VIC solvent vapors, indicating nucleation and crystal growth characteristics depend upon VIC parameters. We observed that CHCA microcrystals generated by methanol VIC resulted in >10× better sensitivity, increased analyte charging, and improved precision compared with dried droplet measurements. The uniformity of matrix/analyte co-crystallization across planar immunoassays directed at intact proteins yielded low spectral variation for single shot replicates (18.5 % relative standard deviation, RSD) and signal averaged spectra (<10 % RSD). We envision that TLT and VIC for MALDI-TOF will enable high-throughput, reproducible array-based immunoassays for protein molecular diagnostic assays in diverse biochemical and clinical applications.

Time-dependent conformational changes in adsorbed albumin and its effect on platelet adhesion

Recent studies have shown that platelets can adhere to adsorbed albumin (Alb) through a receptor-mediated mechanism, but only if the Alb undergoes more than a critical degree of adsorption-induced unfolding. The objectives of this research were to investigate whether Alb that was initially adsorbed in a manner that induced unfolding that was less than this critical level would undergo further unfolding with time and, if so, whether this would induce the onset of platelet adhesion once this critical level was exceeded. To address these questions, CD spectropolarimetry was used to monitor the structure of Alb on OH- and CH(3)-functionalized alkanethiol self-assembled monolayer surfaces, with the Alb initially adsorbed under conditions resulting in degrees of unfolding that were below this critical level, and then the adsorbed Alb layers were aged over 6 months in sterile physiological saline at 37 °C. Platelet adhesion to Alb was quantified at selected time points via a lactate dehydrogenase (LDH) assay. The results indicate that an adsorbed Alb layer does undergo further structural changes with increasing residence time and supports platelet adhesion once it unfolds beyond the previously determined critical level. These results may be relevant to the clinically observed problem of the onset of late-thrombosis, which occurs on cardiovascular implants such as drug-eluting stents.

Modification of polyurethane surface with an antithrombin-heparin complex for blood contact: influence of molecular weight of polyethylene oxide used as a linker/spacer

Polyurethane (PU) was modified using isocyanate chemistry to graft polyethylene oxide (PEO) of various molecular weights (range 300-4600). An antithrombin-heparin (ATH) covalent complex was subsequently attached to the free PEO chain ends, which had been functionalized with N-hydroxysuccinimide (NHS) groups. Surfaces were characterized by water contact angle and X-ray photoelectron spectroscopy (XPS) to confirm the modifications. Adsorption of fibrinogen from buffer was found to decrease by ~80% for the PEO-modified surfaces compared to the unmodified PU. The surfaces with ATH attached to the distal chain end of the grafted PEO were equally protein resistant, and when the data were normalized to the ATH surface density, PEO in the lower MW range showed greater protein resistance. Western blots of proteins eluted from the surfaces after plasma contact confirmed these trends. The uptake of ATH on the PEO-modified surfaces was greatest for the PEO of lower MW (300 and 600), and antithrombin binding from plasma (an indicator of heparin anticoagulant activity) was highest for these same surfaces. The PEO-ATH- and PEO-modified surfaces also showed low platelet adhesion from flowing whole blood. It is concluded that for the PEO-ATH surfaces, PEO in the low MW range, specifically MW 600, may be optimal for achieving an appropriate balance between resistance to nonspecific protein adsorption and the ability to take up ATH and bind antithrombin in subsequent blood contact.