Fibronectin immobilization using water-soluble carbodiimide on poly-L-lactic acid for enhancing initial fibroblast attachment

Cellulose-based bioabsorbable and antibiotic coated surgical staple with bioinspired design for efficient wound closure

The quest to design a flawless wound closure system began long ago and is still underway. Introducing surgical staples is one of the most significant breakthroughs in this effort. In this work, we developed a biodegradable surgical staple to meet the optimal wound closure system criteria and other clinical requirements, such as radiography compatibility and secondary infection prevention. To meet these requirements, a naturally derived cellulose acetate (CA) fiber-reinforced poly-(l-lactic acid) (PLLA) composite was synthesized, and its physicochemical properties were determined using several characterizations such as Fourier-transform infrared spectroscopy (FTIR), Differential scanning calorimetry (DSC) and Universal testing machine (UTM), etc. Taking cues from the Mantis's foreleg, a novel staple design was implemented and verified using Finite Element Analysis (FEA). The CA + PLLA staples were fabricated using melt-casted/3D-printing processes. The staples exhibited excellent biodegradation in both wound and physiological microenvironments with sufficient puncturing strength and later closed the wound's edges mechanically. In addition, the CA + PLLA staples also exhibit metal-like ductility properties to withstand horizontal skin tensions during the healing process. Further, the staples are coated with an antibiotic to combat infections effectively to provide better healing.

Uni-Directionally Oriented Fibro-Porous PLLA/Fibrin Bio-Hybrid Scaffold: Mechano-Morphological and Cell Studies

In this study, we report a biohybrid oriented fibrous scaffold based on nanofibers of poly(l-lactic acid) (PLLA)/fibrin produced by electrospinning and subsequent post-treatment. Induced hydrolytic degradation of the fibers in 0.25 M NaOH solution for various time periods followed by the immobilization of fibrin on the hydrolyzed fiber surfaces was shown to significantly affect the mechanical properties, with the tensile strength (40.6 MPa ± 1.3) and strain at failure (38% ± 4.5) attaining a value within the range of human ligaments and ligament-replacement grafts. Unidirectional electrospinning with a mandrel rotational velocity of 26.4 m/s produced highly aligned fibers with an average diameter of 760 ± 96 nm. After a 20-min hydrolysis treatment in NaOH solution, this was further reduced to an average of 457 ± 89 nm, which is within the range of collagen bundles found in ligament tissue. Based on the results presented herein, the authors hypothesize that a combination of fiber orientation/alignment and immobilization of fibrin can result in the mechanical and morphological modification of PLLA tissue scaffolds for ligament-replacement grafts. Further, it was found that treatment with NaOH enhanced the osteogenic differentiation of hMSCs and the additional inclusion of fibrin further enhanced osteogenic differentiation, as demonstrated by decreased proliferative rates and increased ALP activity.

Magnetic Vortex Nanodiscs Enable Remote Magnetomechanical Neural Stimulation

Magnetic nanomaterials in magnetic fields can serve as versatile transducers for remote interrogation of cell functions. In this study, we leveraged the transition from vortex to in-plane magnetization in iron oxide nanodiscs to modulate the activity of mechanosensory cells. When a vortex configuration of spins is present in magnetic nanomaterials, it enables rapid control over their magnetization direction and magnitude. The vortex configuration manifests in near zero net magnetic moment in the absence of a magnetic field, affording greater colloidal stability of magnetic nanomaterials in suspensions. Together, these properties invite the application of magnetic vortex particles as transducers of externally applied minimally invasive magnetic stimuli in biological systems. Using magnetic modeling and electron holography, we predict and experimentally demonstrate magnetic vortex states in an array of colloidally synthesized magnetite nanodiscs 98-226 nm in diameter. The magnetic nanodiscs applied as transducers of torque for remote control of mechanosensory neurons demonstrated the ability to trigger Ca²⁺ influx in weak (≤28 mT), slowly varying (≤5 Hz) magnetic fields. The extent of cellular response was determined by the magnetic nanodisc volume and magnetic field conditions. Magnetomechanical activation of a mechanosensitive cation channel TRPV4 (transient receptor potential vanilloid family member 4) exogenously expressed in the nonmechanosensitive HEK293 cells corroborated that the stimulation is mediated by mechanosensitive ion channels. With their large magnetic torques and colloidal stability, magnetic vortex particles may facilitate basic studies of mechanoreception and its applications to control electroactive cells with remote magnetic stimuli.

Surface Modification of 3D Printed PLA/Halloysite Composite Scaffolds with Antibacterial and Osteogenic Capabilities

Three-dimensional (3D) printing techniques have received considerable focus in the area of bone engineering due to its precise control in the fabrication of complex structures with customizable shapes, internal and external architectures, mechanical strength, and bioactivity. In this study, we design a new composition biomaterial consisting of polylactic acid (PLA), and halloysite nanotubes (HNTs) loaded with zinc nanoparticles (PLA+H+Zn). The hydrophobic surface of the 3D printed scaffold was coated with two layers of fetal bovine serum (FBS) on the sides and one layer of NaOH in the middle. Additionally, a layer of gentamicin was coated on the outermost layer against bacterial infection. Scaffolds were cultured in standard cell culture medium without the addition of osteogenic medium. This surface modification strategy improved material hydrophilicity and enhanced cell adhesion. Pre-osteoblasts cultured on these scaffolds differentiated into osteoblasts and proceeded to produce a type I collagen matrix and subsequent calcium deposition. The 3D printed scaffolds formed from this composition possessed high mechanical strength and showed an osteoinductive potential. Furthermore, the external coating of antibiotics not only preserved the previous osteogenic properties of the 3D scaffold but also significantly reduced bacterial growth. Our surface modification model enabled the fabrication of a material surface that was hydrophilic and antibacterial, simultaneously, with an osteogenic property. The designed PLA+H+Zn may be a viable candidate for the fabrication of customized bone implants.

Correlation between Surface Properties of Polystyrene and Polylactide Materials and Fibroblast and Osteoblast Cell Line Behavior: A Critical Overview of the Literature

Bone reconstruction remains an important challenge today in several clinical situations, notably regarding the control of the competition occurring during proliferation of osteoblasts and fibroblasts. Polystyrene and polylactide are reference materials in the biomedical field. Therefore, it could be expected from the literature that clear correlations have been already established between the behavior of fibroblasts or osteoblasts and the surface characteristics of these materials. After an extensive analysis of the literature, although general trends could be established, our critical review has highlighted the need to develop a more in-depth analysis of the surface properties of these materials. Moreover, the large variation noticed in the experimental conditions used for in vitro animal cell studies impairs comparison between studies. From our comprehensive review on this topic, we have suggested several parameters that would be valuable to standardize to integrate the data from the literature and improve our knowledge on the cell-material interactions.

XPS Modeling of Immobilized Recombinant Angiogenin and Apoliprotein A1 on Biodegradable Nanofibers

The immobilization of viable proteins is an important step in engineering efficient scaffolds for regenerative medicine. For example, angiogenin, a vascular growth factor, can be considered a neurotrophic factor, influencing the neurogenesis, viability, and migration of neurons. Angiogenin shows an exceptional combination of angiogenic, neurotrophic, neuroprotective, antibacterial, and antioxidant activities. Therefore, this protein is a promising molecule that can be immobilized on carriers used for tissue engineering, particularly for diseases that are complicated by neurotrophic and vascular disorders. Another highly important and viable protein is apoliprotein A1. Nevertheless, the immobilization of these proteins onto promising biodegradable nanofibers has not been tested before. In this work, we carefully studied the immobilization of human recombinant angiogenin and apoliprotein A1 onto plasma-coated nanofibers. We developed a new methodology for the quantification of the protein density of these proteins using X-ray photoelectron spectroscopy (XPS) and modeled the XPS data for angiogenin and apoliprotein A1 (Apo-A1). These findings were also confirmed by the analysis of immobilized Apo-A1 using fluorescent microscopy. The presented methodology was validated by the analysis of fibronectin on the surface of plasma-coated poly(ε-caprolactone) (PCL) nanofibers. This methodology can be expanded for other proteins and it should help to quantify the density of proteins on surfaces using routine XPS data treatment.

Atmospheric pressure cold plasma versus wet-chemical surface treatments for carboxyl functionalization of polylactic acid: A first step toward covalent immobilization of bioactive molecules

The use of polylactic acid (PLA) has attracted growing interest, particularly in recent years, for biomedical applications because of its mechanical properties, biocompatibility, and biodegradability. Despite this, features such as surface hydrophobicity and the absence of suitable functional groups for covalent immobilization of bioactive molecules, make it challenging to endow PLA-based medical devices with additional features and thus broaden their range of applicability. In the present study, we demonstrate the suitability of atmospheric pressure dielectric barrier discharges operating in the Townsend regime as a promising alternative to other surface treatments, such as diazonium and alkali hydrolytic treatments, for carboxyl functionalization of PLA. Chemical changes in PLA surfaces are evaluated by contact angle measurements and by X-ray photoelectron spectroscopy while physical changes are investigated by scanning electron microscopy and atomic force microscopy. The amount of carboxyl groups generated on PLA surfaces is assessed by toluidine blue O assay and substantiated by grafting, through carboxyl groups, a fluorescent probe containing amino functionalities. All of the surface treatments have proven to be very effective in generating carboxylic groups on the PLA surface. Nevertheless, plasma treatment is shown to not degrade the PLA surface, in sharp contrast with diazonium and alkali hydrolytic treatments.

Adding Functions to Biomaterial Surfaces through Protein Incorporation

The concept of biomaterials has evolved from one of inert mechanical supports with a long-term, biologically inactive role in the body into complex matrices that exhibit selective cell binding, promote proliferation and matrix production, and may ultimately become replaced by newly generated tissues in vivo. Functionalization of material surfaces with biomolecules is critical to their ability to evade immunorecognition, interact productively with surrounding tissues and extracellular matrix, and avoid bacterial colonization. Antibody molecules and their derived fragments are commonly immobilized on materials to mediate coating with specific cell types in fields such as stent endothelialization and drug delivery. The incorporation of growth factors into biomaterials has found application in promoting and accelerating bone formation in osteogenerative and related applications. Peptides and extracellular matrix proteins can impart biomolecule- and cell-specificities to materials while antimicrobial peptides have found roles in preventing biofilm formation on devices and implants. In this progress report, we detail developments in the use of diverse proteins and peptides to modify the surfaces of hard biomaterials in vivo and in vitro. Chemical approaches to immobilizing active biomolecules are presented, as well as platform technologies for isolation or generation of natural or synthetic molecules suitable for biomaterial functionalization.

Biofunctionalization of polymeric surfaces

Most of the synthetic polymeric biomaterials used for biomedical applications lack of functional groups able to specifically instruct cells to unlock their potential for tissue regeneration. Surface modification strategies are able to overcome this limitation by introducing bioactive cues. In this study, several functionalization approaches are analyzed. Wet chemical methods such as controlled hydrolysis of polyesters followed by biomolecules grafting by carbodiimide chemistry are simple and versatile approaches, able to succesfully improve the bioactivity of devices with virtually any architecture. Grafting of short peptides, extracellular matrix proteins (ECM) or engineered protein-like recombinamers are promising techniques to improve cell adhesion to biomaterials, including polylactic acid (PLA) and its derivatives. ECM molecules and recombinamers can present more effectively bioactive signals, even in presence of competing, nonadhesive serum proteins. Besides adhesion, surface modifications intended to improve cell attachment, play a role on other cell responses, such as migratory potential. Collagen coating were shown to enhance the expression of the migratory receptor CXCR4 in mesenchymal stromal cells, when compared to short RGD peptides, while the modality of functionalization (covalent vs. physisorbed) tuned the rate of cell migration from PLA-based microcarriers. This multiple effects have to be taken into account when designing biomaterials for cell delivery and tissue engineering. Furthermore, as we aim to recapitulate in vitro the complexity of native tissues, alternative strategies based on the generation of decellularized polymer scaffold rich in cell-deposited ECM are proposed.

Local administration of calcitriol positively influences bone remodeling and maturation during restoration of mandibular bone defects in rats

The aim of this study was to investigate the influence of calcitriol on osteoinduction following local administration into mandibular bone defects. Calcitriol-loaded absorbable collagen membrane scaffolds were prepared using the polydopamine coating method and characterized by scanning electron microscopy. Composite scaffolds were implanted into rat mandibular bone defects in the following groups: no graft material (control), bare collagen membrane (CM group), collagen membrane bearing polydopamine coating (DOP/CM group), and collagen membrane bearing polydopamine coating absorbed with calcitriol (CAL/DOP/CM group). At 1, 2, 4 and 8weeks post-surgery, the osteogenic potential of calcitriol was examined by histological and immunohistochemical methods. Following in vivo implantation, calcitriol-loaded composite scaffolds underwent rapid degradation with pronounced replacement by new bone and induced reunion of the bone marrow cavity. Calcitriol showed strong potential in inhibiting osteoclastogenesis and promotion of osteogenic differentiation at weeks 1, and 2. Furthermore, statistical analysis revealed that the newly formed bone volume in the CAL/DOP/CM group was significantly higher than other groups at weeks 1, and 2. At weeks 4, and 8, the CAL/DOP/CM group showed more mineralized bone and uniform collagen structure. These data suggest that local administration of calcitriol is promising in promoting osteogenesis and mineralization for restoration of mandibular bone defects.

Effect of structure, topography and chemistry on fibroblast adhesion and morphology

Surface biofunctionalisation of many biodegradable polymers is one of the used strategies to improve the biological activity of such materials. In this work, the introduction of collagen type I over the surface of a biodegradable polymer (poly lactic acid) processed in the forms of films and fibers leads to an enhancing of the cellular adhesion of human dermal fibroblast when compared to unmodified polymer and biomolecule-physisorbed polymer surface. The change of topography of the material does not affect the cellular adhesion but results in a higher proliferation of the fibroblast cultured over the fibers. Moreover, the difference of topography governs the cellular morphology, i.e. cells adopt a more stretched conformation where cultured over the films while a more elongated with lower area morphology are obtained for the cells grown over the fibers. This study is relevant for designing and modifying different biodegradable polymers for their use as scaffolds for different applications in the field of Tissue Engineering and Regenerative Medicine.

Surface Entrapment of Fibronectin on Electrospun PLGA Scaffolds for Periodontal Tissue Engineering

Nowadays, the challenge in the tissue engineering field consists in the development of biomaterials designed to regenerate ad integrum damaged tissues. Despite the current use of bioresorbable polyesters such as poly(l-lactide) (PLA), poly(d,l-lactide-co-glycolide) (PLGA), and poly-ɛ-caprolactone in soft tissue regeneration researches, their hydrophobic properties negatively influence the cell adhesion. Here, to overcome it, we have developed a fibronectin (FN)-functionalized electrospun PLGA scaffold for periodontal ligament regeneration. Functionalization of electrospun PLGA scaffolds was performed by alkaline hydrolysis (0.1 or 0.01 M NaOH). Then, hydrolyzed scaffolds were coated by simple deposition of an FN layer (10 μg/mL). FN coating was evidenced by X-ray photoelectron analysis. A decrease of contact angle and greater cell adhesion to hydrolyzed, FN-coated PLGA scaffolds were noticed. Suitable degradation behavior without pH variations was observed for all samples up to 28 days. All treated materials presented strong shrinkage, fiber orientation loss, and collapsed fibers. However, functionalization process using 0.01 M NaOH concentration resulted in unchanged scaffold porosity, preserved chemical composition, and similar mechanical properties compared with untreated scaffolds. The proposed simplified method to functionalize electrospun PLGA fibers is an efficient route to make polyester scaffolds more biocompatible and shows potential for tissue engineering.

A layer-by-layer approach to natural polymer-derived bioactive coatings on magnesium alloys

The development of polyelectrolyte multilayered coatings on magnesium alloy substrates that can be used for controlled delivery of growth factors and required biomolecules from the surface of these degradable implants could have a significant impact in the field of bone tissue regeneration. The current work reports on the fabrication of multilayered coatings of alginate and poly-L-lysine on alkaline- and fluoride-pretreated AZ31 substrates using a layer-by-layer (LbL) technique under physiological conditions. Furthermore, these coatings were surface functionalized by chemical cross-linking and fibronectin immobilization, and the resultant changes in surface properties have been shown to influence the cellular activity of these multilayered films. The physicochemical characteristics of these coated substrates have been investigated using attenuated total reflectance Fourier transform infrared spectroscopy, atomic force microscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Cytocompatibility studies using MC3T3-E1 osteoblasts show that the fluoride-pretreated, cross-linked and fibronectin-immobilized LbL-coated substrates are more bioactive and less cytotoxic than the hydroxide-pretreated, cross-linked and fibronectin-immobilized LbL-coated samples. The in vitro degradation results show that the multilayered coatings of these natural polysaccharide- and synthetic polyamino acid-based polyelectrolytes do not alter the degradation kinetics of the substrates; however, the pretreatment conditions have a significant impact on the overall coating degradation behavior. These preliminary results collectively show the potential use of LbL coatings on magnesium-based degradable scaffolds to improve their surface bioactivity.

Polydopamine-mediated immobilization of multiple bioactive molecules for the development of functional vascular graft materials

In this study, we introduced a simple method for polydopamine-mediated immobilization of dual bioactive factors for the preparation of functionalized vascular graft materials. Polydopamine was deposited on elastic and biodegradable poly(lactic acid-co-ɛ-caprolactone) (PLCL) films, and a cell adhesive RGD-containing peptide and basic fibroblast growth factor were subsequently immobilized by simple dipping. We used an enzyme-linked immunosorbent assay and fluorescamine assay to confirm that we had stably immobilized bioactive molecules on the polydopamine-coated PLCL film in a reaction time-dependent manner. When human umbilical vein endothelial cells (HUVEC) were cultured on the prepared substrates, the number of adherent cells and proliferation of HUVEC for up to 14 days were greatest on the film immobilized with dual factors. On the other hand, the film immobilized with RGD peptide exhibited the highest migration speed compared to the other groups. The expression of cluster of differentiation 31 and von Willebrand factor, which indicates maturation of endothelial cells, was highly stimulated in the dual factor-immobilized group, and passively adsorbed factors showed a negligible effect. The immobilization of bioactive molecules inspired by polydopamine was successful, and adhesion, migration, proliferation and differentiation of HUVEC were synergistically accelerated by the presence of multiple signaling factors. Collectively, our results have demonstrated that a simple coating with polydopamine enables the immobilization of multiple bioactive molecules for preparation of polymeric functionalized vascular graft materials.

Conjugation of fibronectin onto three-dimensional porous scaffolds for vascular tissue engineering applications

Tissue engineering scaffolds provide the three-dimensional (3-D) geometry and mechanical framework required for regulating cell behavior and facilitating tissue maturation. Unfortunately, most synthetic scaffolds lack the biological recognition motifs required for seeded cell interaction. In order to impart this recognition, synthetic scaffolds should possess appropriate biological functionality. Here, for the first time, we present a comprehensive study of fibronectin (FN) conjugation onto highly porous 3-D poly(carbonate) urethane scaffolds through grafted poly(acrylic acid) spacers on the urethane backbone. Scanning electron microscopy was used to ensure that the porous structures of the scaffolds were preserved throughout the multiple conjugation steps, and Fourier transform infrared spectroscopy was used to monitor the reaction progress. Toluidine blue staining revealed that increasing acrylic acid concentration and grafting time increased the number of poly(acrylic acid) groups incorporated. High resolution X-ray photoelectron spectroscopy studies of the scaffolds demonstrated an increase in nitrogen and sulfur due to FN conjugation. Immunofluorescence microscopy studies showed an even distribution of conjugated FN on the 3-D scaffolds. Cell culture studies using human coronary artery smooth muscle cells demonstrated that FN-conjugated scaffolds had improved cell attachment and infiltration depth compared with scaffolds without FN conjugation and with those scaffolds on which FN was merely adsorbed.

The enhancement of dermal papilla cell aggregation by extracellular matrix proteins through effects on cell-substratum adhesivity and cell motility

Generally, cells tend to aggregate on a substratum with lower cell adhesivity. However, it also leads to compromised cell growth and higher cell loss after seeding. This study is aimed at tackling this dilemma by extracellular matrix (ECM) protein coating of a lower adhesive substratum poly(ethylene-co-vinyl alcohol) (EVAL) that has been shown to facilitate hair follicle dermal papilla (DP) spheroid formation. We found that coating with either fibronectin (Fn), collagen I, or collagen IV yields higher adhesivity and cell growth than that with laminin. However, cells can only aggregate on uncoated or Fn-coated EVAL. Quantitatively, Fn coating increases the number of spheroids by 67%. Analysis of cell migration reveals that collagen I, collagen IV and laminin coatings reduce cell motility, while Fn coating keeps cells highly motile. Inhibition of cell migration hinders spheroid formation. In addition, disruption of Fn function does not significantly compromise intercellular adhesion. Hence, Fn enhances cell aggregation by enhancing cell attachment, cell growth and cell motility. Our study demonstrates that intercellular organization as spheroids or flat monolayers is switchable by specific ECM protein coating and preserving cell motility is vital to cell aggregation. In addition to generation of spheroidal DP microtissues for hair follicle regeneration and large-scale production of aggregates of other cells, this strategy can help to regulate the tissue-substrate adhesivity and tissue spreadability on the surface of implantable materials.

Coating electrospun poly(epsilon-caprolactone) fibers with gelatin and calcium phosphate and their use as biomimetic scaffolds for bone tissue engineering

Electrospinning was employed to fabricate fibrous scaffolds of poly(epsilon-caprolactone) in the form of nonwoven mats. The surfaces of the fibers were then coated with gelatin through layer-by-layer self-assembly, followed by functionalization with a uniform coating of bonelike calcium phosphate by mineralization in the 10 times concentrated simulated body fluid for 2 h. Transmission electron microscopy, water contact angle, and scanning electron microscopy measurements confirmed the presence of gelatin and calcium phosphate coating layers, and X-ray diffraction results suggested that the deposited mineral phase was a mixture of dicalcium phosphate dehydrate (a precursor to apatite) and apatite. It was also demonstrated that the incorporation of gelatin promoted nucleation and growth of calcium phosphate. The porous scaffolds could mimic the structure, composition, and biological function of bone extracellular matrix. It was found that the preosteoblastic MC3T3-E1 cells attached, spread, and proliferated well with a flat morphology on the mineralized scaffolds. The proliferation rate of the cells on the mineralized scaffolds was significantly higher (by 1.9-fold) than that on the pristine fibrous scaffolds after culture for 7 days. These results indicated that the hybrid system containing poly(epsilon-caprolactone), gelatin, and calcium phosphate could serve as a new class of biomimetic scaffolds for bone tissue engineering.