Autologous Skin Grafts, versus Tissue-engineered Skin Constructs: A Systematic Review and Meta-analysis.

For over 100 years, autologous skin grafts have remained the gold standard for the reconstruction of wounds but are limited in availability. Acellular tissue-engineered skin constructs (acellular TCs) and cellular tissue-engineered skin constructs (cellular TCs) may address these limitations. This systematic review and meta-analysis compare outcomes between them. Methods: A systematic review was conducted using PRISMA guidelines, querying MEDLINE, Embase, Web of Science, and Cochrane to assess graft incorporation, failure, and wound healing. Case reports/series, reviews, in vitro/in vivo work, non-English articles or articles without full text were excluded. Results: Sixty-six articles encompassing 4076 patients were included. No significant differences were found between graft failure rates (P = 0.07) and mean difference of percent reepithelialization (p = 0.92) when split-thickness skin grafts were applied alone versus co-grafted with acellular TCs. Similar mean Vancouver Scar Scale was found for these two groups (p = 0.09). Twenty-one studies used at least one cellular TC. Weighted averages from pooled results did not reveal statistically significant differences in mean reepithelialization or failure rates for epidermal cellular TCs compared with split-thickness skin grafts (p = 0.55). Conclusions: This systematic review is the first to illustrate comparable functional and wound healing outcomes between split-thickness skin grafts alone and those co-grafted with acellular TCs. The use of cellular TCs seems promising from preliminary findings. However, these results are limited in clinical applicability due to the heterogeneity of study data, and further level 1 evidence is required to determine the safety and efficacy of these constructs.

Enhancement of acellular biomineralization, dental pulp stem cell migration, and differentiation by hybrid fibrin gelatin scaffolds.

OBJECTIVE: The current in vitro study aims to evaluate cross-linked hydrogels with and without the addition of fibrin that could potentially be used in endodontic regeneration as a scaffold material. METHODS: Synthesis of gelatin/fibrin scaffold, and performing nanoscale characterization using cryo-electron microscopy, dynamic rheology, and XRF for structure property relations; plating dental pulp stem cells and determining mineralization, migration, and differentiation using rt-PCR, XRF, and Raman spectroscopy. RESULTS: Cryo electron imaging shows gelatin and fibrin, when gelled separately to form classical rectangular cross-linked networks, where the modulus scales inversely with the cube root of the mesh size. When gelled together, a network with a fundamentally different structure is formed, which has higher ductility and when placed as a scaffold in osteogenic media, produces twice the mineral content. Immunofluorescence, RT-PCR and Rahman Spectroscopy indicate that the hybrid gel enhances cell migration, induces odontogenic differentiation of dental pulp stem cells, and promotes formation of dentin. SIGNIFICANCE: The mechanical properties of the hybrid gel scaffold enhance in-migration of stem cells and subsequent differentiation, which are critical for regenerative procedures. Under acellular conditions, placement of the hybrid gel enhances biomineralization, which would strengthen the root if used as a scaffold for endodontic regeneration. Our in vitro findings are consistent with previous in vivo studies which show improved mineralization when bleeding is induced into the canal, given that fibrin is a primary component in blood clotting. Therefore, insertion of the hybrid gelatin-fibrin scaffold could enable more reproducible and consistent outcomes if used for regenerative endodontic treatment (RET).

Non-cytotoxic Root Canal Dressing with Improved Antimicrobial Efficacy.

INTRODUCTION: Recurrent endodontic infections are primarily caused by Enterococcus faecalis and are more challenging to treat, compared with primary infection of the root canal system. Calcium hydroxide (CH) is used as an interappointment dressing in endodontics despite its inefficacy against E. faecalis and other pathogens. To improve antimicrobial properties and limit cytotoxicity of CH, we added salicylic acid to CH (CASA) to disinfect the canal. CASA overcomes the main pathogen responsible for recurrent endodontic infections. The aim of this study was to evaluate the antimicrobial activity of CASA and its cytotoxicity against dental pulp stem cells (DPSCs) and its effect on the differentiation potential of DPSCs. METHODS: Mature E. faecalis biofilm cultured on dentin chips was exposed to CASA and studied using confocal laser scanning microscopy. The dose-dependency of CASA was also studied using the liquid suspension test. The cytotoxicity was tested against DPSCs, and its effect on the expression of osteocalcin and alkaline phosphatase was studied. RESULTS: CASA produced larger zones of inhibition than CH for all species tested and demonstrated superior efficacy than CH against E. faecalis biofilm. Cytotoxicity studies indicated DPSC's high tolerance for CASA; addition of CASA to DPSCs was observed to increase the expression of biological markers related to mineralization. CONCLUSIONS: CASA was proved to have superior antibacterial efficacy against E. faecalis when compared with CH. It also increased the expression of some DPSC differentiation markers involved in mineralization.

Modeling of the thermal properties of SARS-CoV-2 S-protein.

We calculate the thermal and conformational states of the spike glycoprotein (S-protein) of SARS-CoV-2 at seven temperatures ranging from 3°C to 95°C by all-atom molecular dynamics (MD) µs-scale simulations with the objectives to understand the structural variations on the temperatures and to determine the potential phase transition while trying to correlate such findings of the S-protein with the observed properties of the SARS-CoV2. Our simulations revealed the following thermal properties of the S-protein: 1) It is structurally stable at 3°C, agreeing with observations that the virus stays active for more than two weeks in the cold supply chain; 2) Its structure varies more significantly at temperature values of 60°C-80°C; 3) The sharpest structural variations occur near 60°C, signaling a plausible critical temperature nearby; 4) The maximum deviation of the receptor-binding domain at 37°C, corroborating the anecdotal observations that the virus is most infective at 37°C; 5) The in silico data agree with reported experiments of the SARS-CoV-2 survival times from weeks to seconds by our clustering approach analysis. Our MD simulations at µs scales demonstrated the S-protein's thermodynamics of the critical states at around 60°C, and the stable and denatured states for temperatures below and above this value, respectively.

Efficacy of hypochlorous acid (HOCl) fog in sanitizing surfaces against Enterococcus faecalis.

BACKGROUND: Fogging is an efficient method when disinfection of large areas is desired. METHODS: Two methods of ultrasonic fogging, pulsed and continuous, were compared on bacteria dried on either aluminum or polystyrene surfaces. We characterized commercial and home-made hypochlorous acid (HOCl) with respect to storage and means of production. RESULTS: We found that the initial chlorine concentration of the commercial solution was approximately 550 ppm, and when stored open under ambient conditions, the chlorine content decreased at a rate of 30% every 100 days. The HOCl produced using the home synthesizers had a maximum chlorine content of 257.6 ppm which decayed by 65% after 100 days. A second synthesizer produced a liquid with high chlorine content and pH, 750ppm and pH = 8.55. The anti-bacterial efficacy was probed using Enterococcus faecalis, a persistent source of infection in public and clinical spaces. Time course studies determined that E. faecalis could survive dry on surfaces for more than 12 weeks, but was easily eliminated in half the fogging time. CONCLUSIONS: The most effective mode of application was determined to be continuous fogging where a 6.59 log reduction was established in vertical geometry. The optimal pulsed fogging protocol produced a similar reduction, but required nearly 5 times as long. The home synthesized versions yielded much lower log bacterial reductions. No significant differences in outcome were determined between polymer or metal surfaces.

In Vitro Toxicity of Bone Graft Materials to Human Mineralizing Cells.

Bone graft materials from synthetic, bovine, and human sources were analyzed and tested for in vitro cytotoxicity on dental pulp stem cells (DPSCs) and osteosarcoma cells (Saos-2). Raman spectroscopy indicated significant amounts of collagen only in human bone-derived materials, where the mineral to protein ratio was 3.55 ± 0.45, consistent with bone. X-ray fluorescence revealed tungsten (W) concentrations of 463 ± 73, 400 ± 77, and 92 ± 42 ppm in synthetic, bovine, and human bone chips, respectively. When these chips were added to DPSCs on tissue culture plastic, the doubling times after two days were the same as the controls, 16.5 ± 0.5 h. Those cultured with synthetic or bovine chips were 96.5 ± 8.1 and 25.2 ± 1.4 h, respectively. Saos-2 was more sensitive. During the first two days with allogeneic or bovine graft materials, cell numbers declined. When DPSC were cultured on collagen, allogeneic and bovine bone chips did not increase doubling times. We propose cytotoxicity was associated with tungsten, where only the concentration in human bone chips was below 184 ppm, the value reported as cytotoxic in vitro. Cells on collagen were resistant to bone chips, possibly due to tungsten adsorption by collagen.

Engineering functional skin constructs: A quantitative comparison of three-dimensional bioprinting with traditional methods.

Tissue engineering has been successful in reproducing human skin equivalents while incorporating new approaches such as three-dimensional (3D) bioprinting. The latter method offers a plethora of advantages including increased production scale, ability to incorporate multiple cell types and printing on demand. However, the quality of printed skin equivalents compared to those developed manually has never been assessed. To leverage the benefits of this method, it is imperative that 3D-printed skin should be structurally and functionally similar to real human skin. Here, we developed four bilayered human skin epidermal-dermal equivalents: non-printed dermis and epidermis (NN), printed dermis and epidermis (PP), printed epidermis and non-printed dermis (PN), and non-printed epidermis and printed dermis (NP). The effects of printing induced shear stress [0.025 kPa (epidermis); 0.049 kPa (dermis)] were characterized both at the cellular and at the tissue level. At cellular level, no statistically significant differences in keratinocyte colony-forming efficiency (CFE) (p = 0.1641) were observed. In the case of fibroblasts, no significant differences in the cell alignment index (p < 0.1717) and their ability to contract collagen gel (p = 0.851) were detected. At the tissue levels, all the four skin equivalents were characterized using histological and immunohistochemical analysis with no significant differences found in either epidermal basal cell count, thickness of viable epidermis, and relative intensity of filaggrin and claudin-1. Our results demonstrated that 3D printing can achieve the same high-quality skin constructs as have been developed traditionally, thus opening new avenues for numerous high-throughput industrial and clinical applications.

Synthesis of an Effective Flame-Retardant Hydrogel for Skin Protection Using Xanthan Gum and Resorcinol Bis(diphenyl phosphate)-Coated Starch.

We report on the production of a flame-resistant xanthan gum (XG)-based hydrogel formulation, which could be directly applied onto the skin for protection against burning projectiles. The hydrogel cream represents an efficient use of XG and starch, both of which are biodegradable, reusable natural materials and are also GRAS-certified. The flame-retardant agent resorcinol bis(diphenyl phosphate) (RDP) was shown to be nontoxic to cells in vitro when adsorbed directly onto the starch delivery vehicle. Three hydrogel formulations were studied, the pure XG hydrogel, commercial FireIce hydrogel, and RDP-XG/RDP-starch hydrogel. After application of a direct flame for 150 s, the RDP-XG/RDP-starch hydrogel produced a thick char layer, which was easily removed, showing undamaged chicken skin and tissue underneath. In contrast, complete burning of skin and tissue was observed on untreated control samples and those covered with FireIce and pure XG hydrogels. The thermal protective performance test was also performed, where the heat transfer was measured as a function of time for all three hydrogels. The RDP-XG/RDP-starch hydrogel was able to prolong the protection time before obtaining a second-degree burn for 103 s, which is double that for FireIce and triple that for the pure XG hydrogel. The model proposed involves endothermic reactions, producing char and burning "cold", as opposed to simply relying on the adsorbed water in the hydrogel for burn protection.

Combination of 3D Printing and ALD for Dentin Fabrication from Dental Pulp Stem Cell Culture.

A combination of fused deposition modeling printing with atomic layer deposition (ALD) of titania was designed to achieve templated biomineralization and terminal odontogenic differentiation of dental pulp stem cells on three-dimensional (3D) printed polylactic acid (PLA) scaffolds. In the absence of the ALD-deposited titania coating, we had previously shown that both plating efficiency and differentiation are adversely impacted when scaffolds are produced by 3D printing rather than traditional polymer molding. These differences were removed when both printed and molded structures were coated with ALD of titania, which improved the outcomes regardless of the manufacturing method. In this case, on all titania-coated substrates, the plating efficiency increased, copious mineral deposition was observed, and RT-PCR indicated a significant upregulation of osteocalcin, a gene associated with mineral deposition. The influence of additional coatings of collagen, gelatin, or fibronectin on the ALD titania-coated and uncoated PLA-printed and molded scaffolds was also investigated. Upregulation of the odontogenic late-stage differentiation sibling protein, dentin sialoprotein, was observed on the collagen ALD-titania-coated scaffolds and to a lesser extent on the gelatin ALD-titania-coated scaffolds.

TiO2 nanoparticles synergize with substrate mechanics to improve dental pulp stem cells proliferation and differentiation.

Multiple studies exist on the influence of TiO2 nanoparticle uptake on cell behavior. Yet little is known about the lingering influence of nanoparticles accumulation within the external environment which is particularly important to stem cell differentiation. Herein, dental pulp stem cells were cultured on hard and soft polybutadiene substrates, where 0.1 mg/mL rutile TiO2 nanoparticles were introduced once, 24 h after plating. In the absence of TiO2, the doubling time on soft substrate is significantly longer, while addition of TiO2 decreases it to the same level as on the hard substrate. FACS analysis indicates particle uptake initially at 25% is reduced to 2.5% after 14 days. In the absence of TiO2, no biomineralization on the soft and snowflake-like hydroxyapatite deposits on the hard substrate are shown at week 4. With the addition of TiO2, SEM/EDAX reveals copious mineral deposition templated on large banded collagen fibers on both substrates. The mineral-to-matrix ratios analyzed by Raman spectroscopy are unremarkable in the absence of TiO2. However, with addition of TiO2, the ratios are consistent with native bone on the hard and dentin on the soft substrates. This is further confirmed by RT-PCR, which showed upregulation of markers consistent with osteogenesis and odontogenesis, respectively.

Development of In Vitro Bioengineered Vascular Grafts for Microsurgery and Vascular Surgery Applications.

INTRODUCTION: The use of vascular grafts is continuing to rise due to the increasing prevalence of coronary artery bypass grafting and microvascular flap-based tissue reconstructions. The current options of using native vessels (saphenous vein) or the synthetic grafts (Dacron) have been unable to manage current needs. In this study, we employed an original tissue engineering approach to develop a multi-layered vascular graft that has the potential to address some of the limitations of the existing grafts. MATERIALS AND METHODS: Biomaterials, gelatin and fibrin, were used to develop a two-layered vascular graft. The graft was seeded with endothelial cells and imaged using confocal microscopy. The graft's architecture and its mechanical properties were also characterized using histology, Scanning Electron Microscopy and rheological studies. RESULTS: Our methodology resulted in the development of a vascular graft with precise spatial localization of the two layers. The endothelial cells fully covered the lumen of the developed vascular graft, thus providing a non-thrombogenic surface. The elastic modulus of the biomaterials employed in this graft was found to be 5.186 KPa, paralleling that of internal mammary artery. The burst pressure of this graft was also measured and was found close to that of the saphenous vein (~2000 mm Hg). CONCLUSIONS: We were successfully able to employ a unique method to synthesize a multi-layered vascularized graft having adequate biological and mechanical properties. Studies are ongoing involving implantation of this developed vascular graft in the rat femoral artery and characterization of parameters such as vascular remodeling and patency.

A chip-based potentiometric sensor for a Zika virus diagnostic using 3D surface molecular imprinting.

The latest Zika virus (ZIKV) pandemic caused great international concern from explosively proliferating throughout the Americas. Currently, there is no vaccine to prevent Zika virus infection and available tests rely on antibodies or RNA. Unfortunately, antibody-based detection systems can result in false positive results and RNA-based detection systems are costly, time-consuming, and impractical for testing in remote regions. In this study, a potential point-of-care (POC) diagnostic system was developed using a chip-based potentiometric sensor to detect Zika virus using a 3D molecular imprinting technique. This chip-based potentiometric sensor system was able to detect 10-1 PFU mL-1 ZIKV in a buffered solution under 20 minutes without any sample manipulation. This sensor was tested against Dengue virus at clinical viral loads and showed no sign of cross-reactivity. When tested against human saliva samples containing clinical viral loads, this sensor was able to detect 10 PFU mL-1 ZIKV among the pool of bio-macromolecules. The high sensitivity and high selectivity demonstrated here proved that this lab-on-a-chip diagnostic has the potential to become a POC detection system for rapid and accurate screening of flaviviruses.

Regulating substrate mechanics to achieve odontogenic differentiation for dental pulp stem cells on TiO2 filled and unfilled polyisoprene.

We have shown that materials other than hydrogels commonly used in tissue engineering can be effective in enabling differentiation of dental pulp stem cells (DPSC). Here we demonstrate that a hydrophobic elastomer, polyisoprene (PI), a component of Gutta-percha, normally used to obturate the tooth canal, can also be used to initiate differentiation of the pulp. We showed that PI substrates without additional coating promote cell adhesion and differentiation, while their moduli can be easily adjusted either by varying the coating thickness or incorporation of inorganic particles. DPSC plated on those PI substrates were shown, using SPM and hysitron indentation, to adjust their moduli to conform to differentially small changes in the substrate modulus. In addition, optical tweezers were used to separately measure the membrane and cytoplasm moduli of DPSC, with and without Rho kinase inhibitor. The results indicated that the changes in modulus were attributed predominantly to changes within the cytoplasm, rather than the cell membrane. CLSM was used to identify cell morphology. Differentiation, as determined by qRT-PCR, of the upregulation of OCN, and COL1α1 as well as biomineralization, characterized by SEM/EDAX, was observed on hard PI substrates in the absence of induction factors, i.e. dexamethasone, with moduli 3-4 MPa, regardless of preparation. SEM showed that even though biomineralization was deposited on both spun cast thin PI and filled thick PI substrates, the minerals were aggregated into large clusters on thin PI, and uniformly distributed on filled thick PI, where it was templated within banded collagen fibers. STATEMENT OF SIGNIFICANCE: This manuscript demonstrates the potential of polyisoprene (PI), an elastomeric polymer, for use in tissue engineering. We show how dental pulp stem cells adjust their moduli continuously to match infinitesimally small changes in substrate mechanics, till a critical threshold is reached when they will differentiate. The lineage of differentiation then becomes a sensitive function of both mechanics and morphology for a given chemical composition. Since PI is a major component of Gutta-percha, the FDA approved material commonly used for obturating the root canal, this work suggests that it can easily be adapted for in vivo use in dental regeneration.

Effect of Graphene on Differentiation and Mineralization of Dental Pulp Stem Cells in Poly(4-vinylpyridine) Matrix in Vitro.

We have investigated the influence of graphene nanoplatelet scaffolds for dental pulp cells (DPSCs) made from poly(4-vinylpyridine) (P4VP) either via spin-casting flat films or electrospinning nano- and microscale fibers. We found that graphene predominated over other factors in promoting differentiation of DPSCs. In the absence of graphene, real-time-polymerase chain reaction (RT-PCR) and energy dispersive X-ray (EDX) analyses indicated that the DPSCs differentiated along odontogenic lineages only on the nano- and microelectrospun scaffolds. Closer scanning electron microscopy (SEM) imaging revealed formation of banded collagen structures, which nucleated on the electrospun fibers in the absence of graphene. Biomineral deposition was templated on these fibers, with mineral to protein ratios similar to dentin. In the microfibers, the graphene was completely encapsulated and appeared to hinder biomineralization. Previously minimal biomineralization and banded collagen were observed on flat spun cast substrates. Addition of graphene appeared to induce nucleation of banded collagen fibers and template biomineral deposition. Addition of graphene did not affect the outcome of the DPSCs cultured on the nanofibers, which biomineralized regardless of graphene inclusion. Based on these results, we hypothesize that direct contact with graphene is the primary factor determining differentiation of the DPSCs. On the flat surface and nanoscale electrospun fibers, the graphene protrudes from the sample enabling direct contact with the extracellular matrix (ECM) and cells, while on the microfibers, the graphene is fully encapsulated within the matrix. TUNA imaging with scanning force microscopy showed enhanced conductivity on fibers with encapsulated graphene, which we hypothesize may change the conformation of adsorbed ECM proteins, affecting DPSCs differentiation.

The influence of roughness on stem cell differentiation using 3D printed polylactic acid scaffolds.

With the increase in popularity of 3D printing, an important question arises as to the equivalence between devices manufactured by standard methods vs. those presenting with identical bulk specifications, but manufactured via fused deposition modeling (FDM) printing. Using thermal imaging in conjunction with electron and atomic force microscopy, we demonstrate that large thermal gradients, whose distribution is difficult to predict, are associated with FDM printing and result in incomplete fusion and sharkskin of the printing filament. Even though these features are micro or submicron scale, and hence may not interfere with the intended function of the device, they can have a profound influence if the device comes in contact with living tissue. Dental pulp stem cells were cultured on substrates of identical dimensions, which were either printed or molded from the same PLA stock material. The cultures exhibited significant differences in plating efficiency, migration trajectory, and morphology at early times stemming from attempts by the cells to minimize cytoplasm deformation as they attempt to adhere on the printed surfaces. Even though biomineralization without dexamethasone induction was observed in all cultures at later times, different gene expression patterns were observed on the two surfaces. (Osteogenic markers were upregulated on molded substrates, while odontogenic markers were upregulated on the FDM printed surfaces.) Our results clearly indicate that the method of manufacturing is an important consideration in comparing devices, which come in contact with living tissues.

Templated dentin formation by dental pulp stem cells on banded collagen bundles nucleated on electrospun poly (4-vinyl pyridine) fibers in vitro.

Eventhough it is well established that materials can promote stem cell differentiation, hard tissue formation is a templated process for which little is known regarding the in vitro process. We have found that surface curvature enables self-assembly of triple helical collagen fibrils into banded bundle structures from rat tail and human collagen secreted by dental pulp stem cells. Collagen fibrils were adsorbed at 4 °C on spun cast flat P4VP films and electrospun fibers. Protein adsorption was observed on both surfaces, but large banded bundles with a uniform spacing of approximately 55 nm were present only on the fiber surfaces. SEM/EDS mapping showed that dental pulp stem cells plated on the same surfaces biomineralized copiously only along the electrospun fibers. Raman spectroscopy indicated that despite the presence of adsorbed collagen on the flat surfaces, only the deposits present on the fibrous surface had a protein to hydroxyl apatite ratio similar to natural dentin from human teeth. RT-PCR indicated up regulation of collagen, osteocalcin and dental sialophosphate protein, confirming that odontogenic differentiation is promoted only on the fiber scaffolds. Taken together the results indicate that, in addition to surface chemistry, the supermolecular structure of ECM collagen, which is essential in directing DPSCs differentiation and templating biomineralization, can be modified by the underlying surface morphology. STATEMENT OF SIGNIFICANCE: The past decade has been focused efforts in the use of dental pulp stem cells (DPSC) for dental regeneration. Eventhough the factors required for DPSCs differentiation have been well studied, actual mineral deposition, positively identified as dentin, has not been achieved in vitro. Hard tissue is known to be a templated process in vivo where the mineral to protein ratio is tightly controlled via proteins which aid in collagen conformation and mineral sequestration. Here we show that one can mimic this process in vitro via the combination of materials selection and morphology. The material chemistry is shown to induce genetic upregulation the genes responsible for collagen and osteocalcin, while Raman spectroscopy confirms the translation and adsorption the proteins on the substrate. But, we show that the simple presence of collagen is not enough to template actual biomineral deposition similar to that found in vivo. Mineral deposition is a complicated process templated on collagen bundles and mediated by specific sibling proteins that determine the protein to mineral ratio. Here we show that surface curvature can reduce the barrier to collagen bundle formation, directing DPSC differentiation along odontogenic lineage, and subsequently templating actual dentin, comparable to that found in vivo in human teeth.

The influence of surface chemistry on adsorbed fibrinogen conformation, orientation, fiber formation and platelet adhesion.

Thrombosis is a clear risk when any foreign material is in contact with the bloodstream. Here we propose an immunohistological stain-based model for non-enzymatic clot formation that enables a facile screen for the thrombogenicity of blood-contacting materials. We exposed polymers with different surface chemistries to protease-free human fibrinogen. We observed that on hydrophilic surfaces, fibrinogen is adsorbed via αC regions, while the γ400-411 platelet-binding dodecapeptide on the D region becomes exposed, and fibrinogen fibers do not form. In contrast, fibrinogen is adsorbed on hydrophobic surfaces via the relatively hydrophobic D and E regions, exposing the αC regions while rendering the γ400-411 inaccessible. Fibrinogen adsorbed on hydrophobic surfaces is thus able to recruit other fibrinogen molecules through αC regions and polymerize into large fibrinogen fibers, similar to those formed in vivo in the presence of thrombin. Moreover, the γ400-411 is available only on the large fibers not elsewhere throughout the hydrophobic surface after fibrinogen fiber formation. When these surfaces were exposed to gel-sieved platelets or platelet rich plasma, a uniform monolayer of platelets, which appeared to be activated, was observed on the hydrophilic surfaces. In contrast, large agglomerates of platelets were clustered on fibers on the hydrophobic surfaces, resembling small nucleating thrombi. Endothelial cells were also able to adhere to the monomeric coating of fibrinogen on hydrophobic surfaces. These observations reveal that the extent and type of fibrinogen adsorption, as well as the propensity of adsorbed fibrinogen to bind platelets, may be modulated by careful selection of surface chemistry. STATEMENTS OF SIGNIFICANCE: Thrombosis is a well-known side effect of the introduction of foreign materials into the bloodstream, as might exist in medical devices including but not limited to stents, valves, and intravascular catheters. Despite many reported studies, the body's response to foreign materials in contact with the blood remains poorly understood. Current preventive methods consist of drug eluting coatings on the devices or the systemic administration of standard anticoagulants. Here we present a potential mechanism by which surface chemistry can affects fibrinogen conformation and thus affects platelet adhesion and consequently thrombus formation. Our findings suggest a possible coating which enables endothelial cell adhesion while preventing platelet adhesion.

Correction: Manipulation of cell adhesion and dynamics using RGD functionalized polymers.

Correction for 'Manipulation of cell adhesion and dynamics using RGD functionalized polymers' by Juyi Li et al., J. Mater. Chem. B, 2017, DOI: .

Manipulation of cell adhesion and dynamics using RGD functionalized polymers.

We have successfully synthesized an ABA tri-block co-polymer of poly(methacrylic acid)-block-poly(2-hydroxyethyl methacrylate)-block-poly(methacrylic acid), having Mw = 100k and 272k where we were able to insert RDG or RGD peptide sequences using thiol-acrylate Michael addition. A soft silicone stamp was then used to imprint a 0.4-micron wide grating of the copolymer with a period of 10 microns. The samples were then examined with atomic force microscopy after application of an external electric field and the pattern was observed to stretch by a factor of five. Cells plated onto these substrates showed clear preference for the striped patterns formed under the influence of the external field, and no preferential attachment to the patterns formed in the absence of the field. Cell migration experiments, using the agarose droplet method, performed on spun cast copolymer films showed minimal migration and adhesion on the substrates without peptides or those with only with the RDG peptide, while good adhesion and significant outward migration was observed for cells plated on the copolymers with the RGD sequence. Taken together these results confirmed our hypothesis that a smart biomimetic polymer substrate could be constructed where functional domains could be revealed selectively allowing us to mimic the natural design of engineered tissue constructs.

Differentiation of Dental Pulp Stem Cells on Gutta-Percha Scaffolds.

Advances in treatment of tooth injury have shown that tooth regeneration from the pulp was a viable alternative of root canal therapy. In this study, we demonstrated that Gutta-percha, nanocomposites primarily used for obturation of the canal, are not cytotoxic and can induce differentiation of dental pulp stem cells (DPSC) in the absence of soluble mediators. Flat scaffolds were obtained by spin coating Si wafers with three Gutta-percha compounds: GuttaCore™, ProTaper™, and Lexicon™. The images of annealed surfaces showed that the nanoparticles were encapsulated, forming surfaces with root mean square (RMS) roughness of 136⁻211 nm. Then, by culturing DPSC on these substrates we found that after some initial difficulty in adhesion, confluent tissues were formed after 21 days. Imaging of the polyisoprene (PI) surfaces showed that biomineral deposition only occurred when dexamethasone was present in the media. Spectra obtained from the minerals was consistent with that of hydroxyapatite (HA). In contrast, HA deposition was observed on all Gutta-percha scaffolds regardless of the presence or absence of dexamethasone, implying that surface roughness may be an enabling factor in the differentiation process. These results indicate that Gutta-percha nanocomposites may be good candidates for pulp regeneration therapy.