Surface investigation on biomimetic materials to control cell adhesion: the case of RGD conjugation on PCL

On the Development of Polylactic Acid/Polycaprolactone Blended Films with High Retention Capacity

The retention capacity of polymers is related to the development of systems that combine high surface-to-volume ratio with good handling and specific functionality. Biodegradability and biocompatibility are also key features for extending the field of applications to areas such as biomedicine. With this in mind, the aim of this work is to develop biodegradable, biocompatible, and highly functionalized porous films, that ensure suitable handling and a good surface-to-volume ratio. Polylactic acid (PLA) is applied as a polymer matrix to which a polycaprolactone with a star-shaped architecture (PCL-COOH) to ensure a high concentration of carboxylic end functionalities is added. The porous films are prepared using the phase inversion technique, which, as shown by Scanning Electron Microscopy (SEM) analysis, promotes good dispersion of the PCL-COOH domains. Absorption and release measurements performed with a positively charged model molecule show that the retention capacity and release rate can be tuned by changing the PCL-COOH concentration in the systems. Moreover, the adsorption properties for the formulation with the highest PCL-COOH content are also demonstrated with a real and widely used drug, namely doxorubicin. Finally, the bio- and hemocompatibility of the films, which are enzymatically degradable, are evaluated by using human keratinocytes and red blood cells, respectively.

Surface-Conjugated Galactose on Electrospun Polycaprolactone Nanofibers: An Innovative Scaffold for Uterine Tissue Engineering

The uterus, a vital organ in the female reproductive system, nurtures and supports developing embryos until maturity. This study focuses on addressing uterine related problems by creating a nanofibrous scaffold to regenerate uterine myometrial tissue, closely resembling the native extracellular matrix (ECM) for enhanced efficacy. To achieve this, we utilized polycaprolactone (PCL) as a biomaterial and employed an electrospinning technique to generate PCL nanofibers in both random and aligned orientations. Due to the inherent hydrophobic nature of PCL nanofibers, a two-step wet chemistry surface modification technique is used, involving the conjugation of galactose onto them. Galactose, a lectin-binding sugar, was chosen to enhance the scaffold's hydrophilicity, thereby improving cell adhesion and fostering l-selectin-based interactions between the scaffold and uterine cells. These interactions, in turn, activated uterine fibroblasts, leading to ECM remodeling. The optimized electrospinning process successfully generated random and aligned nanofibers. Subsequent surface modification was carried out, and the modified scaffold was subjected to various physicochemical characterization, such as the ninhydrin assay, enzyme-linked lectin assay techniques that revealed successful galactose conjugation, and mechanical characterization to assess any changes in material bulk properties resulting from the modification. The tensile strength of random galactose-modified PCL fibers reached 0.041 ± 0.01 MPa, outperforming random unmodified PCL fibers (0.026 ± 0.01 MPa), aligned unmodified PCL fibers (0.011 ± 0.001 MPa), and aligned modified PCL fibers (0.016 ± 0.002 MPa). Cytocompatibility studies with human uterine fibroblast cells showed enhanced viability and proliferation on the modified scaffolds. Initial pilot studies were attempted in the current study involving subcutaneous implantation in the dorsal area of Wistar rats to assess biocompatibility and tissue response before proceeding to intrauterine implantation indicated that the modification did not induce adverse inflammation in vivo. In conclusion, our study introduces a surface-modified PCL nanofibrous material for myometrial tissue engineering, offering promise in addressing myometrial damage and advancing uterine health and reproductive well-being.

Magnetic Janus micromotors for fluorescence biosensing of tacrolimus in oral fluids

Tacrolimus (FK506) is a macrolide lactone immunosuppressive drug that is commonly used in transplanted patients to avoid organ rejection. FK506 exhibits high inter- and intra-patient pharmacokinetic variability, making monitoring necessary for organ graft survival. This work describes the development of a novel bioassay for monitoring FK506. The bioassay is based on using polycaprolactone-based (PCL) magnetic Janus micromotors and a recombinant chimera receptor that incorporates the immunophilin tacrolimus binding protein 1A (FKBP1A) tagged with Emerald Green Fluorescent Protein (EmGFP). The approach relies on a fluorescence competitive bioassay between the drug and the micromotors decorated with a carboxylated FK506 toward the specific site of the fluorescent immunophilin. The proposed homogeneous assay could be performed in a single step without washing steps to separate the unbound receptor. The proposed approach fits the therapeutic requirements, showing a limit of detection of 0.8 ng/mL and a wide dynamic range of up to 90 ng/mL. Assay selectivity was evaluated by measuring the competitive inhibition curves with other immunosuppressive drugs usually co-administered with FK506. The magnetic propulsion mechanism allows for efficient operation in raw samples without damaging the biological binding receptor (FKBP1A-EmGFP). The enhanced target recognition and micromixing strategies hold considerable potential for FK506 monitoring in practical clinical use.

Biodegradable Cardiac Occluder with Surface Modification by Gelatin-Peptide Conjugate to Promote Endogenous Tissue Regeneration

Transcatheter intervention has been the preferred treatment for congenital structural heart diseases by implanting occluders into the heart defect site through minimally invasive access. Biodegradable polymers provide a promising alternative for cardiovascular implants by conferring therapeutic function and eliminating long-term complications, but inducing in situ cardiac tissue regeneration remains a substantial clinical challenge. PGAG (polydioxanone/poly (l-lactic acid)-gelatin-A5G81) occluders are prepared by covalently conjugating biomolecules composed of gelatin and layer adhesive protein-derived peptides (A5G81) to the surface of polydioxanone and poly (l-lactic acid) fibers. The polymer microfiber-biomacromolecule-peptide frame with biophysical and biochemical cues could orchestrate the biomaterial-host cell interactions, by recruiting endogenous endothelial cells, promoting their adhesion and proliferation, and polarizing immune cells into anti-inflammatory phenotypes and augmenting the release of reparative cytokines. In a porcine atrial septal defect (ASD) model, PGAG occluders promote in situ tissue regeneration by accelerating surface endothelialization and regulating immune response, which mitigate inflammation and fibrosis formation, and facilitate the fusion of occluder with surrounding heart tissue. Collectively, this work highlights the modulation of cell-biomaterial interactions for tissue regeneration in cardiac defect models, ensuring endothelialization and extracellular matrix remodeling on polymeric scaffolds. Bioinspired cell-material interface offers a highly efficient and generalized approach for constructing bioactive coatings on medical devices.

Exploiting the Features of Short Peptides to Recognize Specific Cell Surface Markers

Antibodies are the macromolecules of choice to ensure specific recognition of biomarkers in biological assays. However, they present a range of shortfalls including a relatively high production cost and limited tissue penetration. Peptides are relatively small molecules able to reproduce sequences of highly specific paratopes and, although they have less biospecificity than antibodies, they offer advantages like ease of synthesis, modifications of their amino acid sequences and tagging with fluorophores and other molecules required for detection. This work presents a strategy to design peptide sequences able to recognize the CD44 hyaluronic acid receptor present in the plasmalemma of a range of cells including human bone marrow stromal mesenchymal cells. The protocol of identification of the optimal amino acid sequence was based on the combination of rational design and in silico methodologies. This protocol led to the identification of two peptide sequences which were synthesized and tested on human bone marrow mesenchymal stromal cells (hBM-MSCs) for their ability to ensure specific binding to the CD44 receptor. Of the two peptides, one binds CD44 with sensitivity and selectivity, thus proving its potential to be used as a suitable alternative to this antibody in conventional immunostaining. In the context of regenerative medicine, the availability of this peptide could be harnessed to functionalize tissue engineering scaffolds to anchor stem cells as well as to be integrated into systems such as cell sorters to efficiently isolate MSCs from biological samples including various cell subpopulations. The data here reported can represent a model for developing peptide sequences able to recognize hBM-MSCs and other types of cells and for their integration in a range of biomedical applications.

Mixed polymer and bioconjugate core/shell electrospun fibres for biphasic protein release

Effective regenerative medicine requires delivery systems which can release multiple components at appropriate levels and at different phases of tissue growth and repair. However, there are few biomaterials and encapsulation techniques that are fully suitable for the loading and controlled release of multiple proteins. In this study we describe how proteins were physically and chemically loaded into a single coaxial electrospun fibre scaffold to obtain bi-phasic release profiles. Cyto-compatible polymers were used to construct the scaffold, using polyethylene oxide (PEO) for the core and polycaprolactone (PCL) reacted or mixed with (bis-aminopropyl)polyether (Jeffamine ED2003; JFA) for the shell. Horseradish peroxidase (HRP), a model protein, was loaded in the core and functionalised onto the scaffold surface by coupling of protein carboxyl groups to the available polymer amine groups. Fibre morphologies were evaluated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and functional group content was determined using X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (TOF SIMS). Hydrophobicity profiles of the fibres before and after protein loading were evaluated by water contact angle (WCA) and the mechanical properties of the electrospun scaffolds were determined by performing tensile tests. The electrospun fibre scaffolds generated by reacting PEO/PCL with 1,6-diaminohexane and those from mixing PEO/PCL with JFA were further characterised for protein conjugation and release. Fibres prepared by the mixed PEO/PCL/JFA system were found to be the most appropriate for the simultaneous release of protein from the core and the immobilisation of another protein on the shell of the same scaffold. Moreover, JFA enhanced scaffold properties in terms of porosity and elasticity. Finally, we successfully demonstrated the cytocompatibility and cell response to protein-loaded and -conjugated scaffolds using HepG2 cells. Enhanced cell attachment (2.5 fold) was demonstrated using bovine serum albumin (BSA)-conjugated scaffolds, and increased metabolic activity observed with retinoic acid (RA)-loaded scaffolds (2.7 fold).

3D PCL/Gelatin/Genipin Nanofiber Sponge as Scaffold for Regenerative Medicine

Recent advancements in tissue engineering and material science have radically improved in vitro culturing platforms to more accurately replicate human tissue. However, the transition to clinical relevance has been slow in part due to the lack of biologically compatible/relevant materials. In the present study, we marry the commonly used two-dimensional (2D) technique of electrospinning and a self-assembly process to construct easily reproducible, highly porous, three-dimensional (3D) nanofiber scaffolds for various tissue engineering applications. Specimens from biologically relevant polymers polycaprolactone (PCL) and gelatin were chemically cross-linked using the naturally occurring cross-linker genipin. Potential cytotoxic effects of the scaffolds were analyzed by culturing human dermal fibroblasts (HDF) up to 23 days. The 3D PCL/gelatin/genipin scaffolds produced here resemble the complex nanofibrous architecture found in naturally occurring extracellular matrix (ECM) and exhibit physiologically relevant mechanical properties as well as excellent cell cytocompatibility. Samples cross-linked with 0.5% genipin demonstrated the highest metabolic activity and proliferation rates for HDF. Scanning electron microscopy (SEM) images indicated excellent cell adhesion and the characteristic morphological features of fibroblasts in all tested samples. The three-dimensional (3D) PCL/gelatin/genipin scaffolds produced here show great potential for various 3D tissue-engineering applications such as ex vivo cell culturing platforms, wound healing, or tissue replacement.

A study of hydrophobins-modified menaquinone-7 on osteoblastic cells differentiation

Menaquinone-7 is involved in bone metabolism and can be used to prevent and treat osteoporosis. However, as a fat-soluble vitamin, menaquinone-7 has poor water solubility. As a surfactant, hydrophobins can change the affinity/hydrophobicity of the covered interface. In this study, menaquinone-7 was modified by hydrophobins, and the different addition ratios were explored. Moreover, Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and water contact angle (WCA) measurements indicated that hydrophobins effectively bind to menaquinone-7 and greatly increase the hydrophilicity of the surface of menaquinone-7. Studies on the metabolism of MC3T3-E1 cells showed that compared with native menaquinone-7, HGFI-modified menaquinone-7 can significantly promote osteoblast differentiation but inhibit osteoclast differentiation. Besides, the Mito-Tracker Green experiments show that HGFI-modified menaquinone-7 can significantly promote the activity of mitochondria in cells. These findings indicate that hydrophobins can be used as an effective biomaterial to modify menaquinone-7, promote the formation of osteoblasts, and better to bone balance.

Functionalization of Electrospun Nanofibers and Fiber Alignment Enhance Neural Stem Cell Proliferation and Neuronal Differentiation

Neural stem cells (NSCs) have the potential to generate the cells of the nervous system and, when cultured on nanofiber scaffolds, constitute a promising approach for neural tissue engineering. In this work, the impact of combining nanofiber alignment with functionalization of the electrospun poly-ε-caprolactone (PCL) nanofibers with biological adhesion motifs on the culture of an NSC line (CGR8-NS) is evaluated. A five-rank scale for fiber density was introduced, and a 4.5 level, corresponding to 70–80% fiber density, was selected for NSC in vitro culture. Aligned nanofibers directed NSC distribution and, especially in the presence of laminin (PCL-LN) and the RGD-containing peptide GRGDSP (PCL-RGD), promoted higher cell elongation, quantified by the eccentricity and axis ratio. In situ differentiation resulted in relatively higher percentage of cells expressing Tuj1 in PCL-LN, as well as significantly longer neurite development (41.1 ± 1.0 μm) than PCL-RGD (32.0 ± 1.0 μm), pristine PCL (25.1 ± 1.2 μm), or PCL-RGD randomly oriented fibers (26.5 ± 1.4 μm), suggesting that the presence of LN enhances neuronal differentiation. This study demonstrates that aligned nanofibers, functionalized with RGD, perform as well as PCL-LN fibers in terms of cell adhesion and proliferation. The presence of the full LN protein improves neuronal differentiation outcomes, which may be important for the use of this system in tissue engineering applications.

Polycaprolactone Films Modified by L-Arginine for Mesenchymal Stem Cell Cultivation

This article describes the modification conditions and properties of polymer films obtained using a solution of poly(ε-caprolactone) modified with arginine. We investigated the effects on the surface and biological properties of films created using various arginine concentrations and temperature conditions during the modification process. We found that both increasing the arginine concentration of the treatment solution or the temperature of the treatment reaction increased the arginine content of the film. Following a cellular cultivation period of 3 days, greater levels of cell proliferation were observed on all modified poly(ε-caprolactone) films compared to unmodified polymer films. Experiments using fluorescence microscopy showed that the modification conditions also had a significant effect on cellular spreading and the organization of the actin cytoskeleton following 2 h of cultivation. The degree of spreading and actin cytoskeleton organization observed in cells on these modified polymer films was superior to that of the control films.

Endothelialization of cardiovascular devices

Blood-contacting surfaces of cardiovascular devices are not biocompatible for creating an endothelial layer on them. Numerous research studies have mainly sought to modify these surfaces through physical, chemical and biological means to ease early endothelial cell (EC) adhesion, migration and proliferation, and eventually to build an endothelial layer on the surfaces. The first priority for surface modification is inhibition of protein adsorption that leads to inhibition of platelet adhesion to the device surfaces, which may favor EC adhesion. Surface modification through surface texturing, if applicable, can bring some hopeful outcomes in this regard. Surface modifications through chemical and/or biological means may play a significant role in easy endothelialization of cardiovascular devices and inhibit smooth muscle cell proliferation. Cellular engineering of cells relevant to endothelialization can boost the positive outcomes obtained through surface engineering. This review briefly summarizes recent developments and research in early endothelialization of cardiovascular devices. STATEMENT OF SIGNIFICANCE: Endothelialization of cardiovascular implants, including heart valves, vascular stents and vascular grafts is crucial to solve many problems in our health care system. Numerous research efforts have been made to improve endothelialization on the surfaces of cardiovascular implants, mainly through surface modifications in three ways - physically, chemically and biologically. This review is intended to highlight comprehensive research studies to date on surface modifications aiming for early endothelialization on the blood-contacting surfaces of cardiovascular implants. It also discusses future perspectives to help guide endothelialization strategies and inspire further innovations.

Aminolysis of Various Aliphatic Polyesters in a Form of Nanofibers and Films

Surface functionalization of polymer scaffolds is a method used to improve interactions of materials with cells. A frequently used method for polyesters is aminolysis reaction, which introduces free amine groups on the surface. In this study, nanofibrous scaffolds and films of three different polyesters-polycaprolactone (PCL), poly(lactide-co-caprolactone) (PLCL), and poly(l-lactide) (PLLA) were subjected to this type of surface modification under the same conditions. Efficiency of aminolysis was evaluated on the basis of ninhydrin tests and ATR-FTIR spectroscopy. Also, impact of this treatment on the mechanical properties, crystallinity, and wettability of polyesters was compared and discussed from the perspective of aminolysis efficiency. It was shown that aminolysis is less efficient in the case of nanofibers, particularly for PCL nanofibers. Our hypothesis based on the fundamentals of classical high speed spinning process is that the lower efficiency of aminolysis in the case of nanofibers is associated with the radial distribution of crystallinity of electrospun fiber with more crystalline skin, strongly inhibiting the reaction. Moreover, the water contact angle results demonstrate that the effect of free amino groups on wettability is very different depending on the type and the form of polymer. The results of this study can help to understand fundamentals of aminolysis-based surface modification.

Functional peptide presentation on different hydrogen bonding biomaterials using supramolecular additives

Supramolecular biomaterials based on hydrogen bonding units can be conveniently functionalized in a mix-and-match approach using supramolecular additives. The presentation of bioactive additives has been sparsely investigated in supramolecular-based elastomeric biomaterials. Here it was investigated how cell adhesive peptides are presented and affect the surface in supramolecular biomaterials based either on ureido-pyrimidinone (UPy) or bisurea (BU) moieties. Polycaprolactone modified with UPy or BU moieties served as the base material. RGD or cyclic (c)RGD were conjugated to complementary supramolecular motifs, and were mixed with the corresponding base materials as supramolecular additives. Biomaterial surface morphology changed upon bioactivation, resulting in the formation of random aggregates on UPy-based materials, and fibrous aggregates on BU-materials. Moreover, peptide type affected aggregation morphology, in which RGD led to larger cluster formation than cRGD. Increased cRGD concentrations led to reduced focal adhesion size and cell migration velocity, and increased focal adhesion numbers in both systems, yet most prominent on functionalized BU-biomaterials. In conclusion, both systems exhibited distinct peptide presenting properties, of which the BU-system most strongly affected cellular adhesive behavior on the biomaterial. This research provided deeper insights in the differences between supramolecular elastomeric platforms, and the level of peptide introduction for biomaterial applications.

Biocompatibility of Cyclopropylamine-Based Plasma Polymers Deposited at Sub-Atmospheric Pressure on Poly (ε-caprolactone) Nanofiber Meshes

In this work, cyclopropylamine (CPA) monomer was plasma-polymerized on poly (ε-caprolactone) nanofiber meshes using various deposition durations to obtain amine-rich surfaces in an effort to improve the cellular response of the meshes. Scanning electron microscopy and X-ray photoelectron spectroscopy (XPS) were used to investigate the surface morphology and surface chemical composition of the PCL samples, respectively. The measured coating thickness was found to linearly increase with deposition duration at a deposition rate of 0.465 nm/s. XPS analysis revealed that plasma exposure time had a considerable effect on the surface N/C and O/C ratio as well as on amino grafting efficiency and amino selectivity. In addition, cell studies showed that cell adhesion and proliferation significantly improved for all coated samples.

3D printing with peptide-polymer conjugates for single-step fabrication of spatially functionalized scaffolds

Biodegradable polymer-based scaffolds are widely used to provide support during early stages of regeneration and can be functionalized with various chemical groups or bioactive cues to promote desired cellular behavior. However, these scaffolds are often modified post-fabrication, which can lead to undesired changes and homogeneously distributed chemistries that fail to mimic the spatial biochemical organization found in native tissues. To address these challenges, surface functionalization can be achieved by 3D printing with pre-functionalized biodegradable polymers, such as peptide-modified polymer conjugates, to control the deposition of preferred chemistries. Peptide-PCL conjugates were synthesized with the canonical cell adhesion peptide motif RGDS or its negative control RGES and 3D printed into scaffolds displaying one or both peptides. The peptides were also modified with bioorthogonal groups, biotin and azide, to visualize peptide concentration and location by labeling with complementary fluorophores. Peptide concentration on the scaffold surface increased with increasing peptide-PCL conjugate concentration added to the ink prior to 3D printing, and scaffolds printed with the highest RGDS(biotin)-PCL concentrations showed a significant increase in NIH3T3 fibroblast adhesion. To demonstrate spatial control of peptide functionalization, multiple printer heads were used to print both peptide-PCL conjugates into the same construct in alternating patterns. Cells preferentially attached and spread on RGDS(biotin)-PCL fibers compared to RGES(azide)-PCL fibers, illustrating how spatial functionalization can be used to influence local cell behavior within a single biomaterial. This presents a versatile platform to generate multifunctional biomaterials that can mimic the biochemical organization found in native tissues to support functional regeneration.

3D and Porous RGDC-Functionalized Polyester-Based Scaffolds as a Niche to Induce Osteogenic Differentiation of Human Bone Marrow Stem Cells

Polyester-based scaffolds covalently functionalized with arginine-glycine-aspartic acid-cysteine (RGDC) peptide sequences support the proliferation and osteogenic differentiation of stem cells. The aim is to create an optimized 3D niche to sustain human bone marrow stem cell (hBMSC) viability and osteogenic commitment, without reliance on differentiation media. Scaffolds consisting of poly(lactide-co-trimethylene carbonate), poly(LA-co-TMC), and functionalized poly(lactide) copolymers with pendant thiol groups are prepared by salt-leaching technique. The availability of functional groups on scaffold surfaces allows for an easy and straightforward method to covalently attach RGDC peptide motifs without affecting the polymerization degree. The strategy enables the chemical binding of bioactive motifs on the surfaces of 3D scaffolds and avoids conventional methods that require harsh conditions. Gene and protein levels and mineral deposition indicate the osteogenic commitment of hBMSC cultured on the RGDC functionalized surfaces. The osteogenic commitment of hBMSC is enhanced on functionalized surfaces compared with nonfunctionalized surfaces and without supplementing media with osteogenic factors. Poly(LA-co-TMC) scaffolds have potential as scaffolds for osteoblast culture and bone grafts. Furthermore, these results contribute to the development of biomimetic materials and allow a deeper comprehension of the importance of RGD peptides on stem cell transition toward osteoblastic lineage.

Multifunctional PLGA-based nanoparticles as a controlled release drug delivery system for antioxidant and anticoagulant therapy

Background

Ischemia/reperfusion (I/R) injury causes the generation of many ROS such as H₂O₂ and leads to vascular thrombosis, which causes tissue damage.

Purpose

In this investigation, poly (lactideco-glycolide) (PLGA)-based nanoparticles are used for their anticoagulant and antioxidant properties in vascular therapy.

Methods

Both heparin and glutathione are entrapped on PLGA-stearylamine nanoparticles by layer-by-layer interactions.

Results

The drug release rate is successfully controlled with only 10.3% of the heparin released after 96 hours. An H₂O₂-responsive platform is also developed by combining silk fibroin and horse peroxidase to detect H₂O₂ in this drug delivery system. Besides, hyaluronic acid was decorated on the surface of nanoparticles to target the human bone marrow mesenchymal stem cells (hBMSCs) for cell therapy. The results of an in vitro study indicate that the nanoparticles could be taken up by hBMSCs within 2 hours and exocytosis occurred 6 hours after cellular uptake.

Conclusion

We propose that the multifunctional nanoparticles that are formed herein can be effectively delivered to the site of an I/R injury via the hBMSC homing effect. The proposed approach can potentially be used to treat vascular diseases, providing a platform for hBMSCs for the controlled delivery of a wide range of drugs.

Determination of polyurethane-grafted peptide (GSGREDVGSG) using bicinchoninic acid assay

The goal in the presented study was to develop a simple, fast and accurate method for measuring the surface density of a short peptide sequence bound to a polymeric substrate. We analyzed polyurethane samples chemically modified with acrylic acid and polyurethane-grafted peptide (GSGREDVGSG) and investigated the possibility of using the bicinchoninic acid (BCA) assay to determine surface density of the solid-supported peptide. We set the conditions (temperature, time) under which the test should be conducted. We also studied the interaction of the BCA reagent with polyurethane substrate and the effect of drying conditions as well as material type and form on the test response. We have proposed potential factors that might interfere with the BCA assay and chosen the proper control materials.

Theoretical Design of Multilayer Dental Posts Using CAD-Based Approach and Sol-Gel Chemistry

A computer-aided design (CAD)-based approach and sol-gel chemistry were used to design a multilayer dental post with a compositional gradient and a Young’s modulus varying from 12.4 to 2.3 GPa in the coronal-apical direction. Specifically, we propose a theoretical multilayer post design, consisting of titanium dioxide (TiO₂) and TiO₂/poly(ε-caprolactone) (PCL) hybrid materials containing PCL up to 24% by weight obtained using the sol-gel method. The current study aimed to analyze the effect of the designed multilayer dental post in endodontically treated anterior teeth. Stress distribution was investigated along and between the post and the surrounding structures. In comparison to a metal post, the most uniform distributions with lower stress values and no significant stress concentration were found when using the multilayer post.

Further Theoretical Insight into the Mechanical Properties of Polycaprolactone Loaded with Organic-Inorganic Hybrid Fillers

Experimental/theoretical analyses have already been performed on poly(ε-caprolactone) (PCL) loaded with organic-inorganic fillers (PCL/TiO₂ and PCL/ZrO₂) to find a correlation between the results from the small punch test and Young's modulus of the materials. PCL loaded with Ti2 (PCL = 12, TiO₂ = 88 wt %) and Zr2 (PCL = 12, ZrO₂ = 88 wt %) hybrid fillers showed better performances than those obtained for the other particle composition. In this context, the aim of current research is to provide further insight into the mechanical properties of PCL loaded with sol-gel-synthesized organic-inorganic hybrid fillers for bone tissue engineering. For this reason, theoretical analyses were performed by the finite element method. The results from the small punch test and Young's modulus of the materials were newly correlated. The obtained values of Young's modulus (193 MPa for PCL, 378 MPa for PCL/Ti2 and 415 MPa for PCL/Zr2) were higher than those obtained from a previous theoretical modelling (144 MPa for PCL, 282 MPa for PCL/Ti2 and 310 MPa for PCL/Zr2). This correlation will be an important step for the evaluation of Young's modulus, starting from the small punch test data.

The Influence of the Polymer Amount on the Biological Properties of PCL/ZrO₂ Hybrid Materials Synthesized via Sol-Gel Technique

Organic/inorganic hybrid materials are attracting considerable attention in the biomedical area. The sol-gel process provides a convenient way to produce many bioactive organic-inorganic hybrids. Among those, poly(e-caprolactone)/zirconia (PCL/ZrO₂) hybrids have proved to be bioactive with no toxic materials. The aim of this study was to investigate the effects of these materials on the cellular response as a function of the PCL content, in order to evaluate their potential use in the biomedical field. For this purpose, PCL/ZrO₂ hybrids containing 6, 12, 24, and 50 wt % of PCL were synthesized by the sol-gel method. The effects of their presence on the NIH-3T3 fibroblast cell line carrying out direct cell number counting, MTT, cell damage assays, flow cytometry-based analysis of cell-cycle progression, and immunoblotting experiments. The results confirm and extend the findings that PCL/ZrO₂ hybrids are free from toxicity. The hybrids containing 12 and 24 wt % PCL, (more than 6 and 50 wt % ones) enhance cell proliferation when compared to pure ZrO₂ by affecting cell cycle progression. The finding that the content of PCL in PCL/ZrO₂ hybrids differently supports cell proliferation suggests that PCL/ZrO₂ hybrids could be useful tools with different potential clinical applications.

Collagen density gradient on three-dimensional printed poly(ε-caprolactone) scaffolds for interface tissue engineering

The ability to engineer scaffolds that resemble the transition between tissues would be beneficial to improve repair of complex organs, but has yet to be achieved. In order to mimic tissue organization, such constructs should present continuous gradients of geometry, stiffness and biochemical composition. Although the introduction of rapid prototyping or additive manufacturing techniques allows deposition of heterogeneous layers and shape control, the creation of surface chemical gradients has not been explored on three-dimensional (3D) scaffolds obtained through fused deposition modelling technique. Thus, the goal of this study was to introduce a gradient functionalization method in which a poly(ε-caprolactone) surface was first aminolysed and subsequently covered with collagen via carbodiimide reaction. The 2D constructs were characterized for their amine and collagen contents, wettability, surface topography and biofunctionality. Finally, chemical gradients were created in 3D printed scaffolds with controlled geometry and porosity. The combination of additive manufacturing and surface modification is a viable tool for the fabrication of 3D constructs with controlled structural and chemical gradients. These constructs can be employed for mimicking continuous tissue gradients for interface tissue engineering.

Physicochemical properties of polycaprolactone/collagen/elastin nanofibers fabricated by electrospinning

Collagen and elastin are the two most abundant proteins in the human body, and as biomaterials offer fascinating properties to composite materials. More detailed investigations including these biomaterials within reinforced composites are still needed. This report describes physicochemical properties of fibers composed of collagen type I, collagen III, elastin and polycaprolactone (PCL). Prior to the electrospinning process, PCL was functionalized through covalent attachment of -NH₂ groups by aminolysis reaction with hexamentilendiamine. The fibers were fabricated by electrospinning technique set up with a non-conventional collector. A morphological comparative study was developed at different rations of collagen type I, observing in some cases two populations of fibers. The diameters and morphology were analyzed by SEM, observing a wide array of nanostructures with diameters of ~310 to 693nm. Chemical characterization was assessed by FT-IR spectroscopy and the functionalized PCL was characterized through ninhydrin assay resulting in 0.36mM NH₂/mg fiber. Swelling tests were performed for 24h, obtaining 320% for the majority of the fibers indicating morphological stability and good water uptake. In addition, contact angle analysis demonstrated adequate permeability and differences for each system depending mainly upon the type of biopolymer incorporated and the functionalization of PCL, ranging the values from 108° to 17°. Moreover, differential scanning calorimetry results showed a melting temperature (T_m) of ~60°C. The onset degradation temperatures (T_d,onset) ranged between 115 and 148°C, and were obtained by thermogravimetric analysis. The local mechanical properties of individual fibers were quantified by atomic force acoustic microscopy. These results propose that the physicochemical and mechanical properties of these scaffolds offer the possibility for enhanced biological activity Thus, they have a great potential as candidate scaffolds in tissue engineering applications.

Easy access to triazolinedione-endcapped peptides for chemical ligation

A triazolinedione-precursor is directly built up from N-terminal peptide amines on resin, enabling a versatile route towards peptide–polymer conjugates.

Conjugation with RGD Peptides and Incorporation of Vascular Endothelial Growth Factor Are Equally Efficient for Biofunctionalization of Tissue-Engineered Vascular Grafts

The blend of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(ε-caprolactone) (PCL) has recently been considered promising for vascular tissue engineering. However, it was shown that PHBV/PCL grafts require biofunctionalization to achieve high primary patency rate. Here we compared immobilization of arginine-glycine-aspartic acid (RGD)-containing peptides and the incorporation of vascular endothelial growth factor (VEGF) as two widely established biofunctionalization approaches. Electrospun PHBV/PCL small-diameter grafts with either RGD peptides or VEGF, as well as unmodified grafts were implanted into rat abdominal aortas for 1, 3, 6, and 12 months following histological and immunofluorescence assessment. We detected CD31⁺/CD34⁺/vWF⁺ cells 1 and 3 months postimplantation at the luminal surface of PHBV/PCL/RGD and PHBV/PCL/VEGF, but not in unmodified grafts, with the further observation of CD31⁺CD34-vWF⁺ phenotype. These cells were considered as endothelial and produced a collagen-positive layer resembling a basement membrane. Detection of CD31⁺/CD34⁺ cells at the early stages with subsequent loss of CD34 indicated cell adhesion from the bloodstream. Therefore, either conjugation with RGD peptides or the incorporation of VEGF promoted the formation of a functional endothelial cell layer. Furthermore, both modifications increased primary patency rate three-fold. In conclusion, both of these biofunctionalization approaches can be considered as equally efficient for the modification of tissue-engineered vascular grafts.

Controlling integrin-based adhesion to a degradable electrospun fibre scaffold via SI-ATRP

While polycaprolactone (PCL) and similar polyesters are commonly used as degradable scaffold materials in tissue engineering and related applications, non-specific adsorption of environmental proteins typically precludes any control over the signalling pathways that are activated during cell adhesion to these materials. Here we describe the preparation of PCL-based fibres that facilitate cell adhesion through well-defined pathways while preventing adhesion via adsorbed proteins. Surface-initiated atom transfer radical polymerisation (SI-ATRP) was used to graft a protein-resistant polymer brush coating from the surface of fibres, which had been electrospun from a brominated PCL macroinitiator. This coating also provided alkyne functional groups for the attachment of specific signalling molecules via the copper-mediated azide-alkyne click reaction; in this case, a cyclic RGD peptide with high affinity for α_vβ₃ integrins. Mesenchymal stem cells were shown to attach to the fibres via the peptide, but did not attach in its absence, nor when blocked with soluble peptide, demonstrating the effective control of cell adhesion pathways.

Receptor-ligand interactions: Advanced biomedical applications

Receptor-ligand interactions (RLIs) are at the base of all biological events occurring in living cells. The understanding of interactions between complementary macromolecules in biological systems represents a high-priority research area in bionanotechnology to design the artificial systems mimicking natural processes. This review summarizes and analyzes RLIs in some cutting-edge biomedical fields, in particular, for the preparation of novel stationary phases to separate complex biological mixtures in medical diagnostics, for the design of ultrasensitive biosensors for identification of biomarkers of various diseases at early stages, as well as in the development of innovative biomaterials and approaches for regenerative medicine. All these biotechnological fields are closely related, because their success depends on a proper choice, combination and spatial disposition of the single components of ligand-receptor pairs on the surface of appropriately designed support.

Regulation of Epithelial-to-Mesenchymal Transition Using Biomimetic Fibrous Scaffolds

Epithelial-to-mesenchymal transition (EMT) is a well-studied biological process that takes place during embryogenesis, carcinogenesis, and tissue fibrosis. During EMT, the polarized epithelial cells with a cuboidal architecture adopt an elongated fibroblast-like morphology. This process is accompanied by the expression of many EMT-specific molecular markers. Although the molecular mechanism leading to EMT has been well-established, the effects of matrix topography and microstructure have not been clearly elucidated. Synthetic scaffolds mimicking the meshlike structure of the basement membrane with an average fiber diameter of 0.5 and 5 μm were produced via the electrospinning of poly(ε-caprolactone) (PCL) and were used to test the significance of fiber diameter on EMT. Cell-adhesive peptide motifs were conjugated to the fiber surface to facilitate cell attachment. Madin-Darby Canine Kidney (MDCK) cells grown on these substrates showed distinct phenotypes. On 0.5 μm substrates, cells grew as compact colonies with an epithelial phenotype. On 5 μm scaffolds, cells were more individually dispersed and appeared more fibroblastic. Upon the addition of hepatocyte growth factor (HGF), an EMT inducer, cells grown on the 0.5 μm scaffold underwent pronounced scattering, as evidenced by the alteration of cell morphology, localization of focal adhesion complex, weakening of cell-cell adhesion, and up-regulation of mesenchymal markers. In contrast, HGF did not induce a pronounced scattering of MDCK cells cultured on the 5.0 μm scaffold. Collectively, our results show that the alteration of the fiber diameter of proteins found in the basement membrane may create enough disturbances in epithelial organization and scattering that might have important implications in disease progression.

Engineering Cell Instructive Materials To Control Cell Fate and Functions through Material Cues and Surface Patterning

Mastering the interaction between cells and extracellular environment is a fundamental prerequisite in order to engineer functional biomaterial interfaces able to instruct cells with specific commands. Such advanced biomaterials might find relevant application in prosthesis design, tissue engineering, diagnostics and stem cell biology. Because of the highly complex, dynamic, and multifaceted context, a thorough understanding of the cell-material crosstalk has not been achieved yet; however, a variety of material features including biological cues, topography, and mechanical properties have been proved to impact the strength and the nature of the cell-material interaction, eventually affecting cell fate and functions. Although the nature of these three signals may appear very different, they are equated by their participation in the same material-cytoskeleton crosstalk pathway as they regulate cell adhesion events. In this work we present recent and relevant findings on the material-induced cell responses, with a particular emphasis on how the presentation of biochemical/biophysical signals modulates cell behavior. Finally, we summarize and discuss the literature data to draw out unifying elements concerning cell recognition of and reaction to signals displayed by material surfaces.

Bioabsorbable Bypass Grafts Biofunctionalised with RGD Have Enhanced Biophysical Properties and Endothelialisation Tested In vivo

Small diameter arterial bypass grafts are considered as unmet clinical need since the current grafts have poor patency of 25% within 5 years. We have developed a 3D scaffold manufactured from natural and synthetic biodegradable polymers, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and poly(𝜀-caprolactone) (PCL), respectively. Further to improve the biophysical properties as well as endothelialisation, the grafts were covalently conjugated with arginine-glycine-aspartic acid (RGD) bioactive peptides. The biophysical properties as well as endothelialisation of PHBV/PCL and PCL 2 mm diameter bypass grafts were assessed with and without biofunctionalisation with RGD peptides in vitro and in vivo. Morphology of the grafts was assessed by scanning electron microscopy, whereas physico-mechanical properties were evaluated using a physiological circulating system equipped with a state of art ultrasound vascular wall tracking system. Endothelialisation of the grafts in vitro and in vivo were assessed using a cell viability assay and rat abdominal aorta replacement model, respectively. The biofunctionalisation with RGD bioactive peptides decreased mean fiber diameter and mean pore area in PHBV/PCL grafts; however, this was not the case for PCL grafts. Both PHBV/PCL and PCL grafts with RGD peptides had lower durability compared to those without; these durability values were similar to those of internal mammary artery. Modification of PHBV/PCL and PCL grafts with RGD peptides increased endothelial cell viability in vitro by a factor of eight and enhanced the formation of an endothelial cell monolayer in vivo 1 month postimplantation. In conclusion, PHBV/PCL small-caliber graft can be a suitable 3D scaffold for the development of a tissue engineering arterial bypass graft.

Surface grafting of chitosan shell, polycaprolactone core fiber meshes to confer bioactivity

Electrospinning of polyesters (e.g. polycaprolactone) is an attractive approach for fabricating meshes with mechanical properties suitable for orthopedic tissue engineering applications. However, the resultant fused-fiber meshes are biologically inert, necessitating surface grafting of bioactive factors to stimulate cell adhesion. In this study, hydrophilic meshes displaying primary amine groups were prepared by coaxially electrospinning fibers with a chitosan/poly(ethylene oxide) shell and a polycaprolactone core. These chitosan–polycaprolactone fiber meshes were mechanically robust (Young’s modulus of 10.1 ± 1.6 MPa under aqueous conditions) with tensile properties comparable to polycaprolactone fiber meshes. Next, the integrin adhesion peptide arginine–glycine–aspartic acid was grafted to chitosan–polycaprolactone fiber meshes. Cell culture studies using bone marrow stromal cells indicated significantly better initial attachment and spreading on arginine–glycine–aspartic acid–conjugated fiber meshes. Specifically, metabolic activity, projected cell area, and cell aspect ratio were all elevated relative to cells seeded on polycaprolactone and unmodified chitosan–polycaprolactone meshes. These results demonstrate a flexible two-step process for creating bioactive electrospun fiber meshes.

Ligand engagement on material surfaces is discriminated by cell mechanosensoring

Peptide or protein ligands can be used for molecular decoration to enhance the functionality of synthetic materials. However, some skepticism has arisen about the efficacy of such strategy in practical contexts since serum proteins largely adsorb. To address this issue, it is crucial to ascertain whether a chemically conjugated integrin-binding peptide is fully recognized by a cell even if partially covered by a physisorbed layer of serum protein; in more general terms, if competitive protein fragments physisorbed onto the surface are distinguishable from those chemically anchored to it. Here, we engraft an RGD peptide on poly-ε-caprolactone (PCL) surfaces and follow the dynamics of focal adhesion (FA) and cytoskeleton assembly at different times and culture conditions using a variety of analytical tools. Although the presence of serum protein covers the bioconjugated RGD significantly, after the first adhesion phase cells dig into the physisorbed layer and reach the submerged signal to establish a more stable adhesion structure (mature FAs). Although the spreading area index is not substantially affected by the presence of the RGD peptide, cells attached to chemically bound signals develop a stronger adhesive interaction with the materials and assemble a mechanically stable cytoskeleton. This demonstrates that cells are able to discriminate, via mechanosensoring, between adhesive motives belonging to physisorbed proteins and those firmly anchored on the material surface.

Surface modification and endothelialization of biomaterials as potential scaffolds for vascular tissue engineering applications

This review highlights the recent developments of surface modification and endothelialization of biomaterials in vascular tissue engineering applications.

PCL microspheres tailored with carboxylated poly(glycidyl methacrylate)–REDV conjugates as conducive microcarriers for endothelial cell expansion

PCL microspheres were functionalized with carboxylated PGMA-REDV conjugates by a combination of surface-initiated ATRP and click reaction.

Improved immobilization of gelatin on a modified polyurethane urea

In this study, polyurethane urea was surface-modified to elevate cell recognition through immobilization of bioactive gelatin. The poly(urethane urea) was synthesized using poly(ε-caprolactone) diol in the absence of a chain extender. The synthesized polyurethane urea was then functionalized with gelatin (gelatin-grafted poly(urethane urea)) via aminolysis. Chemical changes at the polyurethane urea surface were monitored using titration, water contact angle. Fourier transform infrared, and zeta potential measurements. Significantly larger amounts of gelatin were grafted on the polyurethane urea surface compared to those previously reported for poly(ε-caprolactone) diol (three times more) and polyurethanes (two times more), while the mechanical properties were not compromised. Proliferation of human adipose–derived mesenchymal stem cells on the polyurethane urea and the gelatin-grafted polyurethane urea was evaluated through MTT assay. Although both samples enhanced human adipose–derived mesenchymal stem cells’ proliferation, gelatin-grafted polyurethane urea supported human adipose–derived mesenchymal stem cells’ proliferation at a remarkably higher rate.