Enhanced osteoconductivity on electrically charged titanium implants treated by physicochemical surface modifications methods.

Biomimetic design is a key tenet of orthopedic device technology, and in particular the development of responsive surfaces that promote ion exchange with interfacing tissues, facilitating the ionic events that occur naturally during bone repair, hold promise in orthopedic fixation strategies. Non-bioactive nanostructured titanium implants treated by shot-blasting and acid-etching (AE) induced higher bone implant contact (BIC=52% and 65%) compared to shot-blasted treated (SB) implants (BIC=46% and 47%) at weeks 4 and 8, respectively. However, bioactive charged implants produced by plasma (PL) or thermochemical (BIO) processes exhibited enhanced osteoconductivity through specific ionic surface-tissue exchange (PL, BIC= 69% and 77% and BIO, BIC= 85% and 87% at weeks 4 and 8 respectively). Furthermore, bioactive surfaces (PL and BIO) showed functional mechanical stability (resonance frequency analyses) as early as 4 weeks post implantation via increased total bone area (BAT=56% and 59%) ingrowth compared to SB (BAT=35%) and AE (BAT=35%) surfaces.

Attenuated Glial Reactivity on Topographically Functionalized Poly(3,4-Ethylenedioxythiophene):P-Toluene Sulfonate (PEDOT:PTS) Neuroelectrodes Fabricated by Microimprint Lithography.

Following implantation, neuroelectrode functionality is susceptible to deterioration via reactive host cell response and glial scar-induced encapsulation. Within the neuroengineering community, there is a consensus that the induction of selective adhesion and regulated cellular interaction at the tissue-electrode interface can significantly enhance device interfacing and functionality in vivo. In particular, topographical modification holds promise for the development of functionalized neural interfaces to mediate initial cell adhesion and the subsequent evolution of gliosis, minimizing the onset of a proinflammatory glial phenotype, to provide long-term stability. Herein, a low-temperature microimprint-lithography technique for the development of micro-topographically functionalized neuroelectrode interfaces in electrodeposited poly(3,4-ethylenedioxythiophene):p-toluene sulfonate (PEDOT:PTS) is described and assessed in vitro. Platinum (Pt) microelectrodes are subjected to electrodeposition of a PEDOT:PTS microcoating, which is subsequently topographically functionalized with an ordered array of micropits, inducing a significant reduction in electrode electrical impedance and an increase in charge storage capacity. Furthermore, topographically functionalized electrodes reduce the adhesion of reactive astrocytes in vitro, evident from morphological changes in cell area, focal adhesion formation, and the synthesis of proinflammatory cytokines and chemokine factors. This study contributes to the understanding of gliosis in complex primary mixed cell cultures, and describes the role of micro-topographically modified neural interfaces in the development of stable microelectrode interfaces.

Effects of Polydopamine Functionalization on Boron Nitride Nanotube Dispersion and Cytocompatibility.

Boron nitride nanotubes (BNNTs) have unique physical properties, of value in biomedical applications; however, their dispersion and functionalization represent a critical challenge in their successful employment as biomaterials. In the present study, we report a process for the efficient disentanglement of BNNTs via a dual surfactant/polydopamine (PD) process. High-resolution transmission electron microscopy (HR-TEM) indicated that individual BNNTs become coated with a uniform PD nanocoating, which significantly enhanced dispersion of BNNTs in aqueous solutions. Furthermore, the cytocompatibility of PD-coated BNNTs was assessed in vitro with cultured human osteoblasts (HOBs) at concentrations of 1, 10, and 30 µg/mL and over three time-points (24, 48, and 72 h). In this study it was demonstrated that PD-functionalized BNNTs become individually localized within the cytoplasm by endosomal escape and that concentrations of up to 30 µg/mL of PD-BNNTs were cytocompatible in HOBs cells following 72 h of exposure.

Advances in surfaces and osseointegration in implantology. Biomimetic surfaces.

The present work is a revision of the processes occurring in osseointegration of titanium dental implants according to different types of surfaces -namely, polished surfaces, rough surfaces obtained from subtraction methods, as well as the new hydroxyapatite biomimetic surfaces obtained from thermochemical processes. Hydroxyapatite's high plasma-projection temperatures have proven to prevent the formation of crystalline apatite on the titanium dental implant, but lead to the formation of amorphous calcium phosphate (i.e., with no crystal structure) instead. This layer produce some osseointegration yet the calcium phosphate layer will eventually dissolve and leave a gap between the bone and the dental implant, thus leading to osseointegration failure due to bacterial colonization. A new surface -recently obtained by thermochemical processes- produces, by crystallization, a layer of apatite with the same mineral content as human bone that is chemically bonded to the titanium surface. Osseointegration speed was tested by means of minipigs, showing bone formation after 3 to 4 weeks, with the security that a dental implant can be loaded. This surface can be an excellent candidate for immediate or early loading procedures.

Adhesive peptide and polymer density modulate 3D cell traction forces within synthetic hydrogels.

Cell-extracellular matrix forces provide pivotal signals regulating diverse physiological and pathological processes. Although mechanobiology has been widely studied in two-dimensional configurations, limited research has been conducted in three-dimensional (3D) systems due to the complex nature of mechanics and cellular behaviors. In this study, we established a platform integrating a well-defined synthetic hydrogel system (PEG-4MAL) with 3D traction force microscopy (TFM) methodologies to evaluate deformation and force responses within synthetic microenvironments, providing insights that are not tractable using biological matrices because of the interdependence of biochemical and biophysical properties and complex mechanics. We dissected the contributions of adhesive peptide density and polymer density, which determines hydrogel stiffness, to 3D force generation for fibroblasts. A critical threshold of adhesive peptide density at a constant matrix elasticity is required for cells to generate 3D forces. Furthermore, matrix displacements and strains decreased with matrix stiffness whereas stresses, and tractions increased with matrix stiffness until reaching constant values at higher stiffness values. Finally, Rho-kinase-dependent contractility and vinculin expression are required to generate significant 3D forces in both collagen and synthetic hydrogels. This research establishes a tunable platform for the study of mechanobiology and provides new insights into how cells sense and transmit forces in 3D.

Analyzing immune response to engineered hydrogels by hierarchical clustering of inflammatory cell subsets.

Understanding the immune response to hydrogel implantation is critical for the design of immunomodulatory biomaterials. To study the progression of inflammation around poly(ethylene glycol) hydrogels presenting Arg-Gly-Asp (RGD) peptides and vascular endothelial growth factor, we used temporal analysis of high-dimensional flow cytometry data paired with intravital imaging, immunohistochemistry, and multiplexed proteomic profiling. RGD-presenting hydrogels created a reparative microenvironment promoting CD206+ cellular infiltration and revascularization in wounded dorsal skin tissue. Unbiased clustering algorithms (SPADE) revealed significant phenotypic transition shifts as a function of the cell-adhesion hydrogel properties. SPADE identified an intermediate macrophage subset functionally regulating in vivo cytokine secretion that was preferentially recruited for RGD-presenting hydrogels, whereas dendritic cell subsets were preferentially recruited to RDG-presenting hydrogels. Last, RGD-presenting hydrogels controlled macrophage functional cytokine secretion to direct polarization and vascularization. Our studies show that unbiased clustering of single-cell data provides unbiased insights into the underlying immune response to engineered materials.

In vitro analysis of a physiological strain sensor formulated from a PEDOT:PSS functionalized carbon nanotube-poly(glycerol sebacate urethane) composite.

Biodegradable strain sensors able to undergo controlled degradation following implantation have recently received significant interest as novel approaches to detect pathological tissue swelling or non-physiological stresses. In this study, the physicomechanical, electrochemical and active pressure sensing behavior of an electrically conductive and biodegradable poly(glycerol sebacate urethane) (PGSU) composite, reinforced with poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) functionalized carbon nanotubes (CNTs), was evaluated in vitro. Analysis of these PGSU-CNTs composites demonstrated that the incorporation of functionalized CNTs into a biodegradable elastomer resulted in enhanced mechanical strength, conductivity and tailored matrix biodegradation. PGSU-CNT composites were subsequently formulated into flexible and active pressure sensors which demonstrated optimal sensitivity to applied 1% uniaxial tensile strains. Finally, cytocompatibility analysis a with primary neural culture confirmed that PGSU-CNT composites exhibited low cytotoxicity, and supported neuron adhesion, viability, and proliferation in vitro.

Antioxidant functionalized polymer capsules to prevent oxidative stress.

Polymeric capsules exhibit significant potential for therapeutic applications as microreactors, where the bio-chemical reactions of interest are efficiently performed in a spatial and time defined manner due to the encapsulation of an active biomolecule (e.g., enzyme) and control over the transfer of reagents and products through the capsular membrane. In this work, catalase loaded polymer capsules functionalized with an external layer of tannic acid (TA) are fabricated via a layer-by-layer approach using calcium carbonate as a sacrificial template. The capsules functionalised with TA exhibit a higher scavenging capacity for hydrogen peroxide and hydroxyl radicals, suggesting that the external layer of TA shows intrinsic antioxidant properties, and represents a valid strategy to increase the overall antioxidant potential of the developed capsules. Additionally, the hydrogen peroxide scavenging capacity of the capsules is enhanced in the presence of the encapsulated catalase. The capsules prevent oxidative stress in an in vitro inflammation model of degenerative disc disease. Moreover, the expression of matrix metalloproteinase-3 (MMP-3), and disintegrin and metalloproteinase with thrombospondin motif-5 (ADAMTS-5), which represents the major proteolytic enzymes in intervertebral disc, are attenuated in the presence of the polymer capsules. This platform technology exhibits potential to reduce oxidative stress, a key modulator in the pathology of a broad range of inflammatory diseases. STATEMENT OF SIGNIFICANCE: Oxidative stress damages important cell structures leading to cellular apoptosis and senescence, for numerous disease pathologies including cancer, neurodegeneration or osteoarthritis. Thus, the development of biomaterials-based systems to control oxidative stress has gained an increasing interest. Herein, polymer capsules loaded with catalase and functionalized with an external layer of tannic acid are fabricated, which can efficiently scavenge important reactive oxygen species (i.e., hydroxyl radicals and hydrogen peroxide) and modulate extracellular matrix activity in an in vitro inflammation model of nucleus pulposus. The present work represents accordingly, an important advance in the development and application of polymer capsules with antioxidant properties for the treatment of oxidative stress, which is applicable for multiple inflammatory disease targets.

Direct Laser Interference Patterning of CoCr Alloy Surfaces to Control Endothelial Cell and Platelet Response for Cardiovascular Applications.

The main drawbacks of cardiovascular bare-metal stents (BMS) are in-stent restenosis and stent thrombosis as a result of an incomplete endothelialization after stent implantation. Nano- and microscale modification of implant surfaces is a strategy to recover the functionality of the artery by stimulating and guiding molecular and biological processes at the implant/tissue interface. In this study, cobalt-chromium (CoCr) alloy surfaces are modified via direct laser interference patterning (DLIP) in order to create linear patterning onto CoCr surfaces with different periodicities (≈3, 10, 20, and 32 µm) and depths (≈20 and 800 nm). Changes in surface topography, chemistry, and wettability are thoroughly characterized before and after modification. Human umbilical vein endothelial cells' adhesion and spreading are similar for all patterned and plain CoCr surfaces. Moreover, high-depth series induce cell elongation, alignment, and migration along the patterned lines. Platelet adhesion and aggregation decrease in all patterned surfaces compared to CoCr control, which is associated with changes in wettability and oxide layer characteristics. Cellular studies provide evidence of the potential of DLIP topographies to foster endothelialization without enhancement of platelet adhesion, which will be of high importance when designing new BMS in the future.

Polyhydroxyalkanoate/carbon nanotube nanocomposites: flexible electrically conducting elastomers for neural applications.

AIM: Medium chain length-polyhydroxyalkanoate/multi-walled carbon nanotube (MWCNTs) nanocomposites with a range of mechanical and electrochemical properties were fabricated via assisted dispersion and solvent casting, and their suitability as neural interface biomaterials was investigated. MATERIALS & METHODS: Mechanical and electrical properties of medium chain length-polyhydroxyalkanoate/MWCNTs nanocomposite films were evaluated by tensile test and electrical impedance spectroscopy, respectively. Primary rat mesencephalic cells were seeded on the composites and quantitative immunostaining of relevant neural biomarkers, and electrical stimulation studies were performed. RESULTS: Incorporation of MWCNTs to the polymeric matrix modulated the mechanical and electrical properties of resulting composites, and promoted differential cell viability, morphology and function as a function of MWCNT concentration. CONCLUSION: This study demonstrates the feasibility of a green thermoplastic MWCNTs nanocomposite for potential use in neural interfacing applications.