Fibroblast alignment and matrix remodeling induced by a stiffness gradient in a skin-derived extracellular matrix hydrogel.

Large skin injuries heal as scars. Stiffness gradually increases from normal skin to scar tissue (20x higher), due to excessive deposition and crosslinking of extracellular matrix (ECM) mostly produced by (myo)fibroblasts. Using a custom mold, skin-derived ECM hydrogels (dECM) were UV crosslinked after diffusion of ruthenium (Ru) to produce a Ru-dECM gradient hydrogel. The Ru diffusion gradient equates to a stiffness gradient and models physiology of the scarred skin. Crosslinking in Ru-dECM hydrogels results in a 23-fold increase in stiffness from a stiffness similar to that of normal skin. Collagen fiber density increases in a stiffness-dependent fashion while stress relaxation also alters, with one additional Maxwell element necessary for characterizing Ru-dECM. Alignment of fibroblasts encapsulated in hydrogels suggests that the stiffness gradient directs fibroblasts to orientate at ∼45 ° in regions below 120 kPa. In areas above 120 kPa, fibroblasts decrease the stiffness prior to adjusting their orientation. Furthermore, fibroblasts remodel their surrounding ECM in a gradient-dependent fashion, with rearrangement of cell-surrounding ECM in high-stiffness areas, and formation of interlaced collagen bundles in low-stiffness areas. Overall, this study shows that fibroblasts remodel their local environment to generate an optimal ECM mechanical and topographical environment. STATEMENT OF SIGNIFICANCE: This study developed a versatile in vitro model with a gradient stiffness using skin-derived ECM hydrogel with unchanged biochemical environment. Using Ruthenium crosslinking, a 20-fold stiffness increase was achieved as observed in fibrotic skin. The interaction between fibroblasts and matrix depends on changes in the matrix stiffness. The stiffness gradient directed the alignment of fibroblasts with ∼45° in regions with≤ 120 kPa. The cells in regions with the higher stiffness decreased stiffness first and then oriented themselves. Furthermore, fibroblasts remodeled surrounding ECM and regulated its mechanics in a gradient-dependent fashion to reach an optimal condition. Our study highlights the dynamic interplay between cells and surrounding matrix, shedding light on potential mechanisms and strategies to target scar formation and remodeling.

A Review of the Role of Bioreactors for iPSCs-Based Tissue-Engineered Articular Cartilage.

BACKGROUND: Osteoarthritis (OA) is the most common degenerative joint disease without an ultimate treatment. In a search for novel approaches, tissue engineering (TE) has shown great potential to be an effective way for hyaline cartilage regeneration and repair in advanced stages of OA. Recently, induced pluripotent stem cells (iPSCs) have been appointed to be essential stem cells for degenerative disease treatment because they allow a personalized medicine approach. For clinical translation, bioreactors in combination with iPSCs-engineerd cartilage could match patients needs, serve as platform for large-scale patient specific cartilage production, and be a tool for patient OA modelling and drug screening. Furthermore, to minimize in vivo experiments and improve cell differentiation and cartilage extracellular matrix (ECM) deposition, TE combines existing approaches with bioreactors. METHODS: This review summarizes the current understanding of bioreactors and the necessary parameters when they are intended for cartilage TE, focusing on the potential use of iPSCs. RESULTS: Bioreactors intended for cartilage TE must resemble the joint cavity niche. However, recreating human synovial joints is not trivial because the interactions between various stimuli are not entirely understood. CONCLUSION: The use of mechanical and electrical stimulation to differentiate iPSCs, and maintain and test chondrocytes are key stimuli influencing hyaline cartilage homeostasis. Incorporating these stimuli to bioreactors can positively impact cartilage TE approaches and their possibility for posterior translation into the clinics.

Quantum Sensing for Real-Time Monitoring of Drug Efficacy in Synovial Fluid from Arthritis Patients.

Diamond-based T1 relaxometry is a new technique that allows nanoscale magnetic resonance measurements. Here we present its first application in patient samples. More specifically, we demonstrate that relaxometry can determine the free radical load in samples from arthritis patients. We found that we can clearly differentiate between osteoarthritis and rheumatoid arthritis patients in both the synovial fluid itself and cells derived from it. Furthermore, we tested how synovial fluid and its cells respond to piroxicam, a common nonsteroidal anti-inflammatory drug (NSAID). It is known that this drug leads to a reduction in reactive oxygen species production in fibroblast-like synoviocytes (FLS). Here, we investigated the formation of free radicals specifically. While FLS from osteoarthritis patients showed a drastic decrease in the free radical load, cells from rheumatoid arthritis retained a similar radical load after treatment. This offers a possible explanation for why piroxicam is more beneficial for patients with osteoarthritis than those with rheumatoid arthritis.

Viscoelastic properties of plasma-agarose hydrogels dictate favorable fibroblast responses for skin tissue engineering applications.

Dermal wound healing relies on the properties of the extracellular matrix (ECM). Thus, hydrogels that replicate skin ECM have reached clinical application. After a dermal injury, a transient, biodegradable fibrin clot is instrumental in wound healing. Human plasma, and its main constituent, fibrin would make a suitable biomaterial for improving wound healing and processed as hydrogels albeit with limited mechanical strength. To overcome this, plasma-agarose (PA) composite hydrogels have been developed and used to prepare diverse bioengineered tissues. To date, little is known about the influence of variable agarose concentrations on the viscoelastic properties of PA hydrogels and their correlation to cell biology. This study reports the characterization of the viscoelastic properties of different concentrations of agarose in PA hydrogels: 0 %, 0.5 %, 1 %, 1.5 %, and 2 % (w/v), and their influence on the cell number and mitochondrial activity of human dermal fibroblasts. Results show that agarose addition increased the stiffness, relaxation time constants 1 (τ1) and 2 (τ2), and fiber diameter, whereas the porosity decreased. Changes in cell metabolism occurred at the early stages of culturing and correlated to the displacement of fast (τ1) and intermediate (τ2) Maxwell elements. Fibroblasts seeded in low PA concentrations spread faster during 14 d than cells cultured in higher agarose concentrations. Collectively, these results confirm that PA viscoelasticity and hydrogel architecture strongly influenced cell behavior. Therefore, viscoelasticity is a key parameter in the design of PA-based implants.

Differential roles for lysyl oxidase (like), family members in chronic obstructive pulmonary disease; from gene and protein expression to function.

Chronic obstructive pulmonary disease (COPD) is characterized by long-term airflow obstruction with cigarette smoke as a key risk factor. Extracellular matrix (ECM) alterations in COPD may lead to small airway wall fibrosis. Altered collagen cross-linking, potentially mediated by the lysyl oxidase (LO) family of enzymes (LOX, LOXL1-4), orchestrates disturbed ECM homeostasis. In this study, we investigated the effects of smoking status and presence and severity of COPD on LOs gene and protein expression in the airways and the impact of LOs inhibition on airway contraction in an ex vivo mouse model. We used gene expression data from bronchial brushings, airway smooth muscle (ASM) cells in vitro and immunohistochemistry in lung tissue to assess smoke- and COPD-associated differences in LOs gene and protein expression in the small airways. We found higher LOX expression in current- compared to ex-smokers and higher LOXL1 expression in COPD compared to non-COPD patients. LOX and LOXL2 expression were upregulated in COPD ASM cells treated with cigarette smoke extract. LOXL1 and LOXL2 protein levels were higher in small airways from current- compared to non-smokers. In COPD patients, higher LOXL1 and lower LOX protein levels were observed, but no differences for LOXL2, LOXL3, and LOXL4 protein were detected in small airways. Inhibiting LOs activity increased airway contraction in murine lung slices. COPD-associated changes in LOs, in particular LOX and LOXL1, may be related to smoking and contribute to impaired airway function, providing potential novel targets for preventing or treating small airways changes in COPD.

An in vitro model of fibrosis using crosslinked native extracellular matrix-derived hydrogels to modulate biomechanics without changing composition.

Extracellular matrix (ECM) is a dynamic network of proteins, proteoglycans and glycosaminoglycans, providing structure to the tissue and biochemical and biomechanical instructions to the resident cells. In fibrosis, the composition and the organization of the ECM are altered, and these changes influence cellular behaviour. Biochemical (i. e. protein composition) and biomechanical changes in ECM take place simultaneously in vivo. Investigating these changes individually in vitro to examine their (patho)physiological effects has been difficult. In this study, we generated an in vitro model to reflect the altered mechanics of a fibrotic microenvironment through applying fibre crosslinking via ruthenium/sodium persulfate crosslinking on native lung ECM-derived hydrogels. Crosslinking of the hydrogels without changing the biochemical composition of the ECM resulted in increased stiffness and decreased viscoelastic stress relaxation. The altered stress relaxation behaviour was explained using a generalized Maxwell model. Fibre analysis of the hydrogels showed that crosslinked hydrogels had a higher percentage of matrix with a high density and a shorter average fibre length. Fibroblasts seeded on ruthenium-crosslinked lung ECM-derived hydrogels showed myofibroblastic differentiation with a loss of spindle-like morphology together with greater α-smooth muscle actin (α-SMA) expression, increased nuclear area and circularity without any decrease in the viability, compared with the fibroblasts seeded on the native lung-derived ECM hydrogels. In summary, ruthenium crosslinking of native ECM-derived hydrogels provides an exciting opportunity to alter the biomechanical properties of the ECM-derived hydrogels while maintaining the protein composition of the ECM to study the influence of mechanics during fibrotic lung diseases. STATEMENT OF SIGNIFICANCE: Fibrotic lung disease is characterized by changes in composition and excessive deposition of extracellular matrix (ECM). ECM fibre structure also changes due to crosslinking, which results in mechanical changes. Separating the changes in composition and mechanical properties has been difficult to date. In this study, we developed an in vitro model that allows alteration of the mechanical changes alone by applying fibre crosslinking in native lung ECM-derived hydrogels. Characterisations of the crosslinked hydrogels indicated the model mimicked mechanical properties of fibrotic lung tissue and reflected altered fibre organisation. This ECM-based fibrosis model provides a method to preserve the native protein composition while altering the mechanical properties providing an important tool, not only for lung but also other organ fibrosis.

Dopamine-conjugated hyaluronic acid delivered via intra-articular injection provides articular cartilage lubrication and protection.

Due to its high molecular weight and viscosity, hyaluronic acid (HA) is widely used for viscosupplementation to provide joint pain relief in osteoarthritis. However, this benefit is temporary due to poor adhesion of HA on articular surfaces. In this study, we therefore conjugated HA with dopamine to form HADN, which made the HA adhesive while retaining its viscosity enhancement capacity. We hypothesized that HADN could enhance cartilage lubrication through adsorption onto the exposed collagen type II network and repair the lamina splendens. HADN was synthesized by carbodiimide chemistry between hyaluronic acid and dopamine. Analysis of Magnetic Resonance (NMR) and Ultraviolet spectrophotometry (Uv-vis) showed that HADN was successfully synthesized. Adsorption of HADN on collagen was demonstrated using Quartz crystal microbalance with dissipation (QCM-D). Ex vivo tribological tests including measurement of coefficient of friction (COF), dynamic creep, in stance (40 N) and swing (4 N) phases of gait cycle indicated adequate protection of cartilage by HADN with higher lubrication compared to HA alone. HADN solution at the cartilage-glass sliding interface not only retains the same viscosity as HA and provides fluid film lubrication, but also ensures better boundary lubrication through adsorption. To confirm the cartilage surface protection of HADN, we visualized cartilage wear using optical coherence tomography (OCT) and atomic force microscopy (AFM).

Lectin-Functionalized Polyethylene Glycol for Relief of Mucosal Dryness.

The importance of lubrication between oral surfaces provided by the salivary film is most acutely apparent when it is disrupted, a prevalent consequence of salivary gland hypofunction experienced with aging, a symptom of certain diseases, or a side effect of some medical interventions. Sufferers report difficulty with speech and oral food processing and collectively is detrimental to quality of life. Polyethylene glycol (PEG) is widely employed as a successful biocompatible boundary lubricant in engineering and biomedical applications. It is hypothesized that the immobilization of PEG to biological materials such as oral epithelial cells and tissue can mimic the salivary film and provide durable relief from the symptoms of mucosal dryness. To do so, PEG is functionalized with a sugar binding lectin (wheat germ agglutinin) to enhance epithelial adhesion through lectin-sugar interactions. Retention and lubricity are characterized on an ex vivo oral tissue tribology rig. WGA-PEG coats and retains on mucin films, oral epithelial cells, and porcine tongue tissue, and offers sustained reduction in coefficient of friction (COF). WGA-PEG could be developed into a useful topical treatment for reducing oral friction and the perception of dry mouth.

Nonviral Expression of LL-37 in a Human Skin Equivalent to Prevent Infection in Skin Wounds.

Inefficient autologous tissue recovery in skin wounds increases the susceptibility of patients to infections caused by multidrug resistant microorganisms, resulting in a high mortality rate. Genetic modification of skin cells has become an important field of study because it could lead to the construction of more functional skin grafts, through the overexpression of antimicrobial peptides that would prevent early contamination and infection with bacteria. In this study, we produce and evaluate human skin equivalents (HSEs) containing transfected human primary fibroblasts and keratinocytes by polyplexes to express the antimicrobial peptide LL-37. The effect of LL-37 on the metabolic activity of normal HSEs was evaluated before the construction of the transfected HSEs, and the antimicrobial efficacy against Pseudomonas aeruginosa and Staphylococcus aureus was evaluated. Subsequently, the levels of LL-37 in the culture supernatants of transfected HSEs, as well as the local expression, were determined. It was found that LL-37 treatment significantly promoted the cellular proliferation of HSEs. Furthermore, HSEs that express elevated levels of LL-37 were shown to possess histological characteristics close to the normal skin and display enhanced antimicrobial activity against S. aureus in vitro. These findings demonstrate that HSEs expressing LL-37 through nonviral modification of skin cells are a promising approach for the prevention of bacterial colonization in wounds.

Lubricating properties of chewing stimulated whole saliva from patients suffering from xerostomia.

OBJECTIVES: The study aimed to quantify the lubricating properties of chewing stimulated whole saliva from healthy controls (n = 22), from patients suffering from primary Sjögren's syndrome (n = 37) and from patients undergoing head-and-neck radiotherapy (n = 34). MATERIALS AND METHODS: All participants had to complete the Xerostomia Inventory questionnaire to score dry mouth sensation. Lubrication was measured using an ex vivo tongue-enamel friction system in terms of Relief and Relief period. MUC5b and total protein concentrations of the saliva samples were measured by an enzyme-linked immunosorbent assay and a bicinchoninic acid assay, respectively. RESULTS: Relief of Sjögren's patients' saliva and post-irradiation patients' saliva was similar compared with healthy controls, but saliva from post-irradiation patients lubricated significantly better than saliva from Sjögren's patients. The Relief period was similar between the three groups. The Relief and Relief period were higher for saliva samples post-irradiation compared to pre-irradiation. MUC5b and total protein concentrations were comparable in all groups. MUC5b and total protein output were significantly lower in patients subjected to radiotherapy compared to saliva from healthy controls and pre-irradiation patients. MUC5b concentrations positively correlated with lubricating properties of post-irradiation patient saliva. CONCLUSIONS: The lubricating properties of patient saliva were not any worse than healthy controls. Lower flow rate leads to lower availability of saliva in the oral cavity and decreases the overall output of protein and MUC5b, which might result in an insufficient replenishing of the mucosal salivary film. CLINICAL RELEVANCE: An insufficient replenishing might underlie the sensation of a dry mouth and loss of oral function.

Cartilage lamina splendens inspired nanostructured coating for biomaterial lubrication.

Biomaterials that are used in biological systems, such as polycarbonate urethane (PCU) knee joint implants and contact lenses, generally lack lubrication. This limits their integration with the body and impedes their function. Here, we propose a nanostructured film based on hydrophilic polysaccharide hyaluronic acid conjugated with dopamine (HADN) and zwitterionic reduced glutathione (Glu), which forms a composite coating (HADN-Glu) to enhance the lubrication between cartilage and PCU. HADN was synthesized by carbodiimide chemistry between hyaluronic acid and dopamine and deposited on PCU surface under mild oxidative conditions. Then, zwitterionic peptide-reduced glutathione was bioconjugated to HADN, forming a lubrication film. Analysis based on X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and wettability indicated that HADN and Glu had grafted successfully onto the PCU surface. Measurements of the coefficient of friction (COF), friction energy dissipation and cartilage roughness indicated that cartilage was effectively protected by the high lubrication of HADN-Glu. Both at low and high applied loads, this effect was likely due to the enhanced boundary lubrication enabled by HADN-Glu on the PCU surface. Moreover, HADN-Glu is highly biocompatible with chondrocyte cells, suggesting that this film will benefit the design of implants where lubrication is needed.

Examining the uptake and bioaccumulation of molybdenum nanoparticles and their effect on antioxidant activities in growing rice seedlings.

The synthesized α-MoO3 and MoS2 NPs had nanosheet and nanoflower-like structures with crystallite size of 21.34 nm and 4.32 nm, respectively. The uptake, bioaccumulation, and impact of these two Mo-NPs were studied in rice (Oryza sativa L) cv. HUR 3022 seedlings exposed to 100, 500, and 1000 ppm concentrations in hydroponics for 10 days in the growth medium. The uptake of α-MoO3 and MoS2 NPs by rice exposed to 100 ppm concentrations of NPs led to the accumulation of 7.32 ppm/4.55 ppm and 1.84 ppm/1.19 ppm in roots/shoots, respectively, as compared to controls. Unlike MoO3, more accumulation of MoS2 in roots reflect less translocation of this NP from roots to shoots. Results suggest tissue-specific distribution of NPs in rice seedlings. The increased growth and elevated protein levels in rice seedlings at 100 ppm concentrations of nanoparticles imply a stimulation in the repair mechanism at low doses indicating hormesis. MoS2 NPs treatments led to increased chlorophyll a levels suggesting it to be non-compromising with photosynthetic process in rice. The high malondialdehyde levels and altered activities of antioxidant enzymes GPX, APX, and CAT in rice seedlings exposed to α-MoO3 or MoS2 NPs indicate oxidative imbalance. Between α-MoO3 and MoS2 NPs, the former shows toxic effects as reflected from the decreased levels of photosynthetic pigments at all concentrations; however, an activation of chloroplast ROS detoxification is evident in the presence of MoS2 NPs. The BCF > 1 for both α-MoO3 and MoS2 NPs and TF of 0.6-2.0 and 0.42-0.65 suggest the latter to be more environmentally safe. In conclusion, a100 ppm MoS2 NPs concentration has low translocation and less accumulation with no significant impact on growth of rice cv. HUR 3022 seedlings and appears to be environmentally safe for future applications.

Molecular and Biomechanical Clues From Cardiac Tissue Decellularized Extracellular Matrix Drive Stromal Cell Plasticity.

Decellularized-organ-derived extracellular matrix (dECM) has been used for many years in tissue engineering and regenerative medicine. The manufacturing of hydrogels from dECM allows to make use of the pro-regenerative properties of the ECM and, simultaneously, to shape the material in any necessary way. The objective of the present project was to investigate differences between cardiovascular tissues (left ventricle, mitral valve, and aorta) with respect to generating dECM hydrogels and their interaction with cells in 2D and 3D. The left ventricle, mitral valve, and aorta of porcine hearts were decellularized using a series of detergent treatments (SDS, Triton-X 100 and deoxycholate). Mass spectrometry-based proteomics yielded the ECM proteins composition of the dECM. The dECM was digested with pepsin and resuspended in PBS (pH 7.4). Upon warming to 37°C, the suspension turns into a gel. Hydrogel stiffness was determined for samples with a dECM concentration of 20 mg/mL. Adipose tissue-derived stromal cells (ASC) and a combination of ASC with human pulmonary microvascular endothelial cells (HPMVEC) were cultured, respectively, on and in hydrogels to analyze cellular plasticity in 2D and vascular network formation in 3D. Differentiation of ASC was induced with 10 ng/mL of TGF-ß1 and SM22α used as differentiation marker. 3D vascular network formation was evaluated with confocal microscopy after immunofluorescent staining of PECAM-1. In dECM, the most abundant protein was collagen VI for the left ventricle and mitral valve and elastin for the aorta. The stiffness of the hydrogel derived from the aorta (6,998 ± 895 Pa) was significantly higher than those derived from the left ventricle (3,384 ± 698 Pa) and the mitral valve (3,233 ± 323 Pa) (One-way ANOVA, p = 0.0008). Aorta-derived dECM hydrogel drove non-induced (without TGF-ß1) differentiation, while hydrogels derived from the left ventricle and mitral valve inhibited TGF-ß1-induced differentiation. All hydrogels supported vascular network formation within 7 days of culture, but ventricular dECM hydrogel demonstrated more robust vascular networks, with thicker and longer vascular structures. All the three main cardiovascular tissues, myocardium, valves, and large arteries, could be used to fabricate hydrogels from dECM, and these showed an origin-dependent influence on ASC differentiation and vascular network formation.

Correction to: Dry mouth: saliva substitutes which adsorb and modify existing salivary condition films improve oral lubrication.

After publication of this paper, the authors observed that that figure 6 appears before figure 5.

A bioinspired mucoadhesive restores lubrication of degraded cartilage through reestablishment of lamina splendens.

Adsorbed lubricious films composed of biomacromolecules are natively present at all articulating interfaces in the human body where they provide ultralow friction and maintain normal physiological function. Biolubrication gets impaired due to diseases such as osteoarthritis, in which cartilage damage results from alterations in synovial fluid and lamina splendens composition. Osteoarthritis is treated with hyaluronic acid (HA) orally or via intra-articular injection, but due to the poor adsorption of HA on the cartilage surface in the absence of adhesive molecules, pain relief is temporary. Here, we describe how natural lubrication on degraded cartilage surface can be restored with the help of a bioinspired mucoadhesive biopolymer chitosan catechol (Chi-C). Quartz crystal microbalance was used to mimic the formation of lamina splendens in vitro, known as synovial fluid conditioning films (SyCF), and colloidal probe atomic force microscopy was used to measure their nanoscale frictional properties. Clear evidence of glycoprotein (PRG4) recruitment by Chi-C increased the softness of SyCF, which also improved nanoscale lubrication in vitro, decreasing the friction coefficient from 0.06 to 0.03. At the macroscale, cartilage damage induced by Chondroitinase ABC increased the coefficient of friction (COF) from 0.07 ±â€¯0.04 (healthy tissue) to 0.15 ±â€¯0.03 (after tissue damage) in the presence of synovial fluid after sliding for 50 min. After Chi-C treatment of damaged cartilage, the COF fell to 0.06 ±â€¯0.03, which is comparable to healthy cartilage. Chi-C did not adversely affect the metabolic activity of human chondrocytes. This study provides new key insight into the potential for restoring biolubrication through the use of muco-adhesive molecules.

Next Generation Salivary Lubrication Enhancer Derived from Recombinant Supercharged Polypeptides for Xerostomia.

Insufficient retention of water in adsorbed salivary conditioning films (SCFs) because of altered saliva secretion can lead to oral dryness (xerostomia). Patients with xerostomia sometimes are given artificial saliva, which often lacks efficacy because of the presence of exogenous molecules with limited lubrication properties. Recombinant supercharged polypeptides (SUPs) improve salivary lubrication by enhancing the functionality of endogenously available salivary proteins, which is in stark contrast to administration of exogenous lubrication enhancers. This novel approach is based on establishing a layered architecture enabled by electrostatic bond formation to stabilize and produce robust SCFs in vitro. Here, we first determined the optimal molecular weight of SUPs to achieve the best lubrication performance employing biophysical and in vitro friction measurements. Next, in an ex vivo tongue-enamel friction system, stimulated whole saliva from patients with Sjögren syndrome was tested to transfer this strategy to a preclinical situation. Out of a library of genetically engineered cationic polypeptides, the variant SUP K108cys that contains 108 positive charges and two cysteine residues at each terminus was identified as the best SUP to restore oral lubrication. Employing this SUP, the duration of lubrication (Relief Period) for SCFs from healthy and patient saliva was significantly extended. For patient saliva, the lubrication duration was increased from 3.8 to 21 min with SUP K108cys treatment. Investigation of the tribochemical mechanism revealed that lubrication enhancement is because of the electrostatic stabilization of SCFs and mucin recruitment, which is accompanied by strong water fixation and reduced water evaporation.

Dry mouth: saliva substitutes which adsorb and modify existing salivary condition films improve oral lubrication.

OBJECTIVES: The aims of this study are to assess different saliva substitutes for their efficacy to lubricate the oral cavity, and to relate this oral lubrication to the ability of saliva substitutes to adsorb on and change the structure of the existing salivary conditioning film (SCF). MATERIALS AND METHODS: Quartz crystal microbalance with dissipation was used to study the capability of saliva substitutes to interact with natural SCF and the ability to change the secondary SCF (S-SCF). A tongue-enamel friction system mimicking xerostomic conditions was used to assess the relief and relief period expected from these substitutes under set circumstances. RESULTS: Saliva Orthana spray, Biotène spray and Gum Hydral gel had an immediate effect on a SCF, increasing its structural softness. BioXtra gel, Biotène gel, Gum Hydral gel and Glandosane spray changed the S-SCF by increasing salivary protein adsorption, while others showed no sign of interaction. With respect to relief, only 2 out of the 16 saliva substitutes tested (Saliva Orthana spray and Gum Hydral gel) performed better than water. Overall, relief period correlated positively to structural softness change, whereas a positive correlation was seen between relief and mass adsorption. CONCLUSIONS: The majority of saliva substitutes did not adsorb on the SCF, thus did not enhance lubrication. Only saliva substitutes containing carrageenan, carboxymethylcellulose, pig gastric mucin, xanthan gum and carbomer performed better in enhancing oral lubrication. CLINICAL RELEVANCE: This objective assessment will help clinicians and patients make better choice of saliva substitutes. This study provides a scientific basis for future improvement in saliva substitutes.

Tribological properties of microporous polydimethylsiloxane (PDMS) surfaces under physiological conditions.

Textured biomaterials have been extensively used in biomedical engineering to modulate mammalian and bacterial cell adhesion and proliferation, implant integration with human body and infection prevention. However, the tribological implications of texturing under wet physiological conditions have not been well quantified. This study aimed to characterize the tribological properties of micropore-textured polydimethylsiloxane (PDMS) under physiological conditions and investigate the effect of adsorbed lubricious molecules on friction. In this study, untextured and micropore-textured PDMS surfaces were slid against curved smooth glass surfaces under the contact pressures of 10-400 kPa, sliding speeds of 0.1-5 mm/s in aqueous solutions with the viscosity of 1-1000 mPa·s. Reconstituted human whole saliva (RHWS) at pH 7 and porcine gastric mucin (PGM) at both pH 2 and 7 were used as lubricious coatings on PDMS. While the micropore-texturing delayed the transition of lubrication regimes, it increased the coefficient of friction (COF). Although RHWS and PGM coatings decreased the COF significantly, the protein coatings could not help the COF of micropore-textured surfaces getting lower than that of untextured surfaces. The results suggest textured polymeric surfaces could generate larger friction under physiological conditions and lead to a higher chance of inflammation near the implants.

Characterization of the in vitro, ex vivo, and in vivo Efficacy of the Antimicrobial Peptide DPK-060 Used for Topical Treatment.

Antimicrobial peptides, also known as host defense peptides, have recently emerged as a promising new category of therapeutic agents for the treatment of infectious diseases. This study evaluated the preclinical in vitro, ex vivo, and in vivo antimicrobial activity, as well as the potential to cause skin irritation, of human kininogen-derived antimicrobial peptide DPK-060 in different formulations designed for topical delivery. We found that DPK-060 formulated in acetate buffer or poloxamer gel caused a marked reduction of bacterial counts of Staphylococcus aureus in vitro (minimum microbicidal concentration <5 µg/ml). We also found that DPK-060 in poloxamer gel significantly suppressed microbial survival in an ex vivo wound infection model using pig skin and in an in vivo mouse model of surgical site infection (≥99 or ≥94% reduction in bacterial counts was achieved with 1% DPK-060 at 4 h post-treatment, respectively). Encapsulation of DPK-060 in different types of lipid nanocapsules or cubosomes did not improve the bactericidal potential of the peptide under the applied test conditions. No reduction in cell viability was observed in response to administration of DPK-060 in any of the formulations tested. In conclusion, the present study confirms that DPK-060 has the potential to be an effective and safe drug candidate for the topical treatment of microbial infections; however, adsorption of the peptide to nanocarriers failed to show any additional benefits.

Bioactive Silk Coatings Reduce the Adhesion of Staphylococcus aureus while Supporting Growth of Osteoblast-like Cells.

Orthopedic and dental implants are associated with a substantial risk of failure due to biomaterial-associated infections and poor osseointegration. To prevent such outcomes, a coating can be applied on the implant to ideally both reduce the risk of bacterial adhesion and support establishment of osteoblasts. We present a strategy to construct dual-functional silk coatings with such properties. Silk coatings were made from a recombinant partial spider silk protein either alone (silkwt) or fused with a cell-binding motif derived from fibronectin (FN-silk). The biofilm-dispersal enzyme Dispersin B (DspB) and two peptidoglycan degrading endolysins, PlySs2 and SAL-1, were produced recombinantly. A sortase recognition tag (SrtTag) was included to allow site-specific conjugation of each enzyme onto silkwt and FN-silk coatings using an engineered variant of the transpeptidase Sortase A (SrtA*). To evaluate bacterial adhesion on the samples, Staphylococcus aureus was incubated on the coatings and subsequently subjected to live/dead staining. Fluorescence microscopy revealed a reduced number of bacteria on all silk coatings containing enzymes. Moreover, the bacteria were mobile to a higher degree, indicating a negative influence on the bacterial adhesion. The capability to support mammalian cell interactions was assessed by cultivation of the osteosarcoma cell line U-2 OS on dual-functional surfaces, prepared by conjugating the enzymes onto FN-silk coatings. U-2 OS cells could adhere to silk coatings with enzymes and showed high spreading and viability, demonstrating good cell compatibility.