The promotion of endothelial cell attachment and spreading using FNIII10 fused to VEGF-A165

Bioactive triterpenoid compounds of Poria cocos (Schw.) Wolf in the treatment of diabetic ulcers via regulating the PI3K-AKT signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

Diabetic ulcers represent a chronic condition characterized by prolonged hyperglycemia and delayed wound healing, accompanied by endocrine disorders, inflammatory responses, and microvascular damage in the epidermal tissue, demanding effective clinical treatment approaches. For thousands of years, ancient Chinese ethnopharmacological studies have documented the use of Poria cocos (Schw.) Wolf in treating diabetic ulcers. Recent research has substantiated the diverse pharmacological effects of Poria cocos (Schw.) Wolf, including its potential to alleviate hyperglycemia and exhibit anti-inflammatory, antioxidant, and immune regulatory properties, which could effectively mitigate diabetic ulcer symptoms. Furthermore, being a natural medicine, Poria cocos (Schw.) Wolf has demonstrated promising therapeutic effects and safety in the management of diabetic ulcers, holding significant clinical value. Despite its potential clinical efficacy and applications in diabetic ulcer treatment, the primary active components and underlying pharmacological mechanisms of Poria cocos (Schw.) Wolf remains unclear. Further investigations are imperative to establish a solid foundation for drug development in this domain.

AIM OF THE STUDY AND MATERIALS AND METHODS

In this study, we aimed to identify the active compounds and potential targets of Poria cocos (Schw.) Wolf using UHPLC-Q-TOF-MS and TCMSP databases. Additionally, we attempt to identify targets related to diabetic ulcers. Following enrichment analysis, a network of protein-protein interactions was constructed to identify hub genes based on the common elements between the two datasets. To gain insights into the binding activities of the hub genes and active ingredients, molecular docking analysis was employed. Furthermore, to further validate the therapeutic effect of Poria cocos (Schw.) Wolf, we exerted in vitro experiments using human umbilical vein vascular endothelial cells and human myeloid leukemia monocytes (THP-1). The active ingredient of Poria cocos (Schw.) Wolf was applied in these experiments. Our investigations included various assays, such as CCK-8, scratch test, immunofluorescence, western blotting, RT-PCR, and flow cytometry, to explore the potential of Poria cocos (Schw.) Wolf triterpenoid extract (PTE) in treating diabetic ulcers.

RESULTS

The findings here highlighted PTE as the primary active ingredient in Poria cocos (Schw.) Wolf. Utilizing network pharmacology, we identified 74 potential targets associated with diabetic ulcer treatment for Poria cocos (Schw.) Wolf, with five hub genes (JUN, MAPK1, STAT3, AKT1, and CTNNB1). Enrichment analysis revealed the involvement of multiple pathways in the therapeutic process, with the PI3K-AKT signaling pathway showing significant enrichment. Through molecular docking, we discovered that relevant targets within this pathway exhibited strong binding with the active components of Poria cocos (Schw.) Wolf. In vitro experiments unveiled that PTE (10 mg/L) facilitated the migration of human umbilical vein vascular endothelial cells (P < 0.05). PTE also increased the expression of CD31 and VEGF mRNA (P < 0.05) while activating the expressions of p-PI3K and p-AKT (P < 0.05). Moreover, PTE demonstrated its potential by reducing the expression of IL-1β, IL-6, TNF-α, and NF-κB mRNA in THP-1 (P < 0.05) and fostering M2 macrophage polarization. These results signify the potential therapeutic effects of PTE in treating diabetic ulcers, with its beneficial actions mediated through the PI3K-AKT signaling pathway.

CONCLUSIONS

PTE is the main active ingredient in Poria cocos (Schw.) Wolf that exerts therapeutic effects. Through PI3K-AKT signaling pathway activation and inflammatory response reduction, PTE promotes angiogenesis, thereby healing diabetic ulcers.

Pristine gelatin incorporation as a strategy to enhance the biofunctionality of poly(vinyl alcohol)-based hydrogels for tissue engineering applications

Synthetic polymers, such as poly(vinyl alcohol) (PVA), are popular biomaterials for the fabrication of hydrogels for tissue engineering and regenerative medicine (TERM) applications, as they provide excellent control over the physico-chemical properties of the hydrogel. However, their bioinert nature is known to limit cell-biomaterial interactions by hindering cell infiltration, blood vessel recruitment and potentially limiting their integration with the host tissue. Efforts in the field have therefore focused on increasing the biofunctionality of synthetic hydrogels, without limiting the advantages associated with their tailorability and controlled release capacity. The aim of this study was to investigate the suitability of pristine gelatin to enhance the biofunctionality of tyraminated PVA (PVA-Tyr) hydrogels, by promoting cell infiltration and host blood vessel recruitment for TERM applications. Pure PVA-Tyr hydrogels and PVA-Tyr hydrogels incorporated with vascular endothelial growth factor (VEGF), a well-known pro-angiogenic stimulus, were used for comparison. Incorporating increasing concentrations of VEGF (0.01-10 μg mL-1) or gelatin (0.01-5 wt%) did not influence the physical properties of PVA-Tyr hydrogels. However, their presence within the polymer network (>0.1 μg mL-1 VEGF and >0.1 wt% gelatin) promoted endothelial cell interactions with the hydrogels. The covalent binding of unmodified gelatin or VEGF to the PVA-Tyr network did not hamper their inherent bioactivity, as they both promoted angiogenesis in a chick chorioallantoic membrane (CAM) assay, performing comparably with the unbound VEGF control. When the PVA-Tyr hydrogels were implanted subcutaneously in mice, it was observed that cell infiltration into the hydrogels was possible in the absence of gelatin or VEGF at 1- or 3-weeks post-implantation, highlighting a clear difference between in vitro an in vivo cell-biomaterial interaction. Nevertheless, the presence of gelatin or VEGF was necessary to enhance blood vessel recruitment and infiltration, although no significant difference was observed between these two biological molecules. Overall, this study highlights the potential of gelatin as a standalone pro-angiogenic cue to enhance biofunctionality of synthetic hydrogels and provides promise for their use in a variety of TERM applications.

Pushing the Natural Frontier: Progress on the Integration of Biomaterial Cues toward Combinatorial Biofabrication and Tissue Engineering

The engineering of fully functional, biological-like tissues requires biomaterials to direct cellular events to a near-native, 3D niche extent. Natural biomaterials are generally seen as a safe option for cell support, but their biocompatibility and biodegradability can be just as limited as their bioactive/biomimetic performance. Furthermore, integrating different biomaterial cues and their final impact on cellular behavior is a complex equation where the outcome might be very different from the sum of individual parts. This review critically analyses recent progress on biomaterial-induced cellular responses, from simple adhesion to more complex stem cell differentiation, looking at the ever-growing possibilities of natural materials modification. Starting with a discussion on native material formulation and the inclusion of cell-instructive cues, the roles of shape and mechanical stimuli, the susceptibility to cellular remodeling, and the often-overlooked impact of cellular density and cell-cell interactions within constructs, are delved into. Along the way, synergistic and antagonistic combinations reported in vitro and in vivo are singled out, identifying needs and current lessons on the development of natural biomaterial libraries to solve the cell-material puzzle efficiently. This review brings together knowledge from different fields envisioning next-generation, combinatorial biomaterial development toward complex tissue engineering.

Vascularization in skin wound healing: where do we stand and where do we go?

Cutaneous healing is a highly complex process that, if altered due to, for example, impaired vascularization, results in chronic wounds or repaired neotissue of poor quality. Significant progress has been achieved in promoting neotissue vascularization during tissue repair/regeneration. In this review, we discuss the strategies that have been explored and how each one of them contributes to regulate vascularization in the context of cutaneous wound healing from two different perspectives - biomaterial-based and a cell-based approaches. Finally, we discuss the implications of these findings on the development of the 'next generation' approaches to target vascularization in wound healing highlighting the importance of going beyond its contribution to regulate vascularization and take into consideration the temporal features of the healing process and of different types of wounds.

Structurally Dynamic Hydrogels for Biomedical Applications: Pursuing a Fine Balance between Macroscopic Stability and Microscopic Dynamics

Owing to their unique chemical and physical properties, hydrogels are attracting increasing attention in both basic and translational biomedical studies. Although the classical hydrogels with static networks have been widely reported for decades, a growing number of recent studies have shown that structurally dynamic hydrogels can better mimic the dynamics and functions of natural extracellular matrix (ECM) in soft tissues. These synthetic materials with defined compositions can recapitulate key chemical and biophysical properties of living tissues, providing an important means to understanding the mechanisms by which cells sense and remodel their surrounding microenvironments. This review begins with the overall expectation and design principles of dynamic hydrogels. We then highlight recent progress in the fabrication strategies of dynamic hydrogels including both degradation-dependent and degradation-independent approaches, followed by their unique properties and use in biomedical applications such as regenerative medicine, drug delivery, and 3D culture. Finally, challenges and emerging trends in the development and application of dynamic hydrogels are discussed.

Growth Factors VEGF-A165 and FGF-2 as Multifunctional Biomolecules Governing Cell Adhesion and Proliferation

Vascular endothelial growth factor-A165 (VEGF-A165) and fibroblast growth factor-2 (FGF-2) are currently used for the functionalization of biomaterials designed for tissue engineering. We have developed a new simple method for heterologous expression and purification of VEGF-A165 and FGF-2 in the yeast expression system of Pichia pastoris. The biological activity of the growth factors was assessed in cultures of human and porcine adipose tissue-derived stem cells (ADSCs) and human umbilical vein endothelial cells (HUVECs). When added into the culture medium, VEGF-A165 stimulated proliferation only in HUVECs, while FGF-2 stimulated the proliferation of both cell types. A similar effect was achieved when the growth factors were pre-adsorbed to polystyrene wells. The effect of our recombinant growth factors was slightly lower than that of commercially available factors, which was attributed to the presence of some impurities. The stimulatory effect of the VEGF-A165 on cell adhesion was rather weak, especially in ADSCs. FGF-2 was a potent stimulator of the adhesion of ADSCs but had no to negative effect on the adhesion of HUVECs. In sum, FGF-2 and VEGF-A165 have diverse effects on the behavior of different cell types, which maybe utilized in tissue engineering.

Growth Factor Engineering Strategies for Regenerative Medicine Applications

Growth factors are critical molecules for tissue repair and regeneration. Therefore, recombinant growth factors have raised a lot of hope for regenerative medicine applications. While using growth factors to promote tissue healing has widely shown promising results in pre-clinical settings, their success in the clinic is not a forgone conclusion. Indeed, translation of growth factors is often limited by their short half-life, rapid diffusion from the delivery site, and low cost-effectiveness. Trying to circumvent those limitations by the use of supraphysiological doses has led to serious side-effects in many cases and therefore innovative technologies are required to improve growth factor-based regenerative strategies. In this review, we present protein engineering approaches seeking to improve growth factor delivery and efficacy while reducing doses and side effects. We focus on engineering strategies seeking to improve affinity of growth factors for biomaterials or the endogenous extracellular matrix. Then, we discuss some examples of increasing growth factor stability and bioactivity, and propose new lines of research that the field of growth factor engineering for regenerative medicine may adopt in the future.

Heparin potentiates Avastin-mediated inhibition of VEGF binding to fibronectin and rescues Avastin activity at acidic pH

Vascular endothelial growth factor-A (VEGF) plays a critical role in stimulating angiogenesis in normal and disease states. Anti-VEGF antibodies have been developed to manage pathological angiogenesis. Bevacizumab, sold under the brand name Avastin, is a humanized mAb that binds VEGF and blocks its binding to its signaling receptor, VEGF receptor 2, and is used to treat patients with a variety of cancers or retinal disorders. The ability of Avastin to modulate other nonreceptor interactions of VEGF has not been fully defined. In this study, we investigated Avastin's capacity to modulate VEGF165 binding to porcine aortic endothelial cells and to heparin and fibronectin (FN) across a range of pH values (pH 5-8). We observed that Avastin slightly enhanced VEGF binding to heparin and that heparin increased VEGF binding to Avastin. In contrast, Avastin inhibited VEGF binding to cells and FN, yet Avastin could still bind to VEGF that was bound to FN, indicating that these binding events are not mutually exclusive. Avastin binding to VEGF was dramatically reduced at acidic pH values (pH 5.0-6.5), whereas VEGF binding to FN and nonreceptor sites on cells was enhanced. Interestingly, the reduced Avastin-VEGF binding at acidic pH was rescued by heparin, as was Avastin's ability to inhibit VEGF binding to cells. These results suggest that heparin might be used to expand the clinical utility of Avastin. Our findings highlight the importance of defining the range of VEGF interactions to fully predict antibody activity within a complex biological setting.

Growth factors with enhanced syndecan binding generate tonic signalling and promote tissue healing

Growth factors can stimulate tissue regeneration, but the side effects and low effectiveness associated with suboptimal delivery systems have impeded their use in translational regenerative medicine. Physiologically, growth factor interactions with the extracellular matrix control their bioavailability and spatiotemporal cellular signalling. Growth factor signalling is also controlled at the cell surface level via binding to heparan sulfate proteoglycans, such as syndecans. Here we show that vascular endothelial growth factor-A (VEGF-A) and platelet-derived growth factor-BB (PDGF-BB) that were engineered to have a syndecan-binding sequence trigger sustained low-intensity signalling (tonic signalling) and reduce the desensitization of growth factor receptors. We also show in mouse models that tonic signalling leads to superior morphogenetic activity, with syndecan-binding growth factors inducing greater bone regeneration and wound repair than wild-type growth factors, as well as reduced tumour growth (associated with PDGF-BB delivery) and vascular permeability (triggered by VEGF-A). Tonic signalling via syndecan binding may also enhance the regenerative capacity of other growth factors.

Engineered delivery strategies for enhanced control of growth factor activities in wound healing

Growth factors (GFs) are versatile signalling molecules that orchestrate the dynamic, multi-stage process of wound healing. Delivery of exogenous GFs to the wound milieu to mediate healing in an active, physiologically-relevant manner has shown great promise in laboratories; however, the inherent instability of GFs, accompanied with numerous safety, efficacy and cost concerns, has hindered the clinical success of GF delivery. In this article, we highlight that the key to overcoming these challenges is to enhance the control of the activities of GFs throughout the delivering process. We summarise the recent strategies based on biomaterials matrices and molecular engineering, which aim to improve the conditions of GFs for delivery (at the 'supply' end of the delivery), increase the stability and functions of GFs in extracellular matrix (in transportation to target cells), as well as enhance the GFs/receptor interaction on the cell membrane (at the 'destination' end of the delivery). Many of these investigations have led to encouraging outcomes in various in vitro and in vivo regenerative models with considerable translational potential.

Puerarin 6″-O-xyloside possesses significant antitumor activities on colon cancer through inducing apoptosis

Puerarin 6″-O-xyloside (PRX) is a major compound found in the root of the Pueraria lobata (Willd.) Ohwi. The present study aimed to investigate the antitumor activity of PRX against colon cancer and examine its possible mechanism. In the present study, the anti-proliferative effects of PRX against colon cell lines (SW480, LoVo and HCT-116) were evaluated using a Cell Counting Kit-8 assay, and the half maximal inhibitory concentration values of the SW480, LoVo and HCT-11 cells were 37.114, 49.213 and 43.022 µg/ml, respectively. Furthermore, the apoptosis of SW480 cells was detected using flow cytometry with Annexin V-fluorescein isothiocyanate/propidium iodide staining. Subsequently, western blot analysis was performed to examine the expression of proteins associated with apoptosis, invasion and metastasis of tumors. The results showed that PRX possessed antitumor activity against colon cancer cell lines in a dose-dependent and time-dependent manner. In addition, PRX significantly upregulated the expression levels of cleaved (c)-caspase-3, c-caspase-9, B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X protein and phosphorylated c-Jun terminal kinase, and downregulated the expression levels of Bcl-2, matrix metalloproteinase (MMP)-3, MMP-9 and vascular endothelial growth factor (P<0.01). Therefore, the present study demonstrated the PRX exerted antitumor activity against colon cancer cell lines and that the anticancer mechanisms of PRX may be associated with the induction of mitochondria-mediated intrinsic apoptosis, and inhibition of tumor invasion and metastasis. The present study provides a scientific basis for the clinical use of PRX for the treatment of colon cancer.

Enhanced vascularization of PCL porous scaffolds through VEGF-Fc modification

To accelerate the vascularization of engineered tissue, an endothelial-specific fusion protein (VEGF-Fc), which consists of a human vascular endothelial growth factor (VEGF) and an immunoglobulin G Fc region, was fabricated and used to construct a bioactive interface in a porous scaffold. In this study, VEGF-Fc was immobilized on polycarprolactone (PCL) porous scaffolds by steeping, which is mediated by the hydrophobic binding of the Fc domain. The VEGF-Fc proteins were distributed stably and uniformly throughout the PCL porous scaffolds without affecting their surface morphology and mechanical properties. The immobilized VEGF-Fc activated the phosphorylation of VEGF2 receptor continuously, and further promoted the expressions of PI3K and MAPK, which effectively enhanced the adhesion and proliferation of human vascular endothelial cells (HUVECs). Furthermore, the immobilized VEGF-Fc promoted the migration of HUVECs into the scaffolds, and also enhanced the cellularization and ECM deposition in the subcutaneous implanted scaffolds in rats, which synergistically supported the vascularization of the scaffold in vivo. In view of the advantages of easy use, stability and efficiency, the VEGF-Fc fusion protein appeared to be a promising candidate for surface modification of porous scaffolds for tissue engineering.

Phosphonium hydrogels for controlled release of ionic cargo

Hydrogels containing phosphonium cations were synthesized and demonstrated to electrostatically bind and release anionic drug molecules depending on their structures.

Engineered microenvironments for synergistic VEGF - Integrin signalling during vascularization

We have engineered polymer-based microenvironments that promote vasculogenesis both in vitro and in vivo through synergistic integrin-growth factor receptor signalling. Poly(ethyl acrylate) (PEA) triggers spontaneous organization of fibronectin (FN) into nanonetworks which provide availability of critical binding domains. Importantly, the growth factor binding (FNIII_12-14) and integrin binding (FNIII_9-10) regions are simultaneously available on FN fibrils assembled on PEA. This material platform promotes synergistic integrin/VEGF signalling which is highly effective for vascularization events in vitro with low concentrations of VEGF. VEGF specifically binds to FN fibrils on PEA compared to control polymers (poly(methyl acrylate), PMA) where FN remains in a globular conformation and integrin/GF binding domains are not simultaneously available. The vasculogenic response of human endothelial cells seeded on these synergistic interfaces (VEGF bound to FN assembled on PEA) was significantly improved compared to soluble administration of VEGF at higher doses. Early onset of VEGF signalling (PLCγ1 phosphorylation) and both integrin and VEGF signalling (ERK1/2 phosphorylation) were increased only when VEGF was bound to FN nanonetworks on PEA, while soluble VEGF did not influence early signalling. Experiments with mutant FN molecules with impaired integrin binding site (FN-RGE) confirmed the role of the integrin binding site of FN on the vasculogenic response via combined integrin/VEGF signalling. In vivo experiments using 3D scaffolds coated with FN and VEGF implanted in the murine fat pad demonstrated pro-vascularization signalling by enhanced formation of new tissue inside scaffold pores. PEA-driven organization of FN promotes efficient presentation of VEGF to promote vascularization in regenerative medicine applications.

Designing hydrogels for controlled drug delivery

Hydrogel delivery systems can leverage therapeutically beneficial outcomes of drug delivery and have found clinical use. Hydrogels can provide spatial and temporal control over the release of various therapeutic agents, including small-molecule drugs, macromolecular drugs and cells. Owing to their tunable physical properties, controllable degradability and capability to protect labile drugs from degradation, hydrogels serve as a platform in which various physiochemical interactions with the encapsulated drugs control their release. In this Review, we cover multiscale mechanisms underlying the design of hydrogel drug delivery systems, focusing on physical and chemical properties of the hydrogel network and the hydrogel-drug interactions across the network, mesh, and molecular (or atomistic) scales. We discuss how different mechanisms interact and can be integrated to exert fine control in time and space over the drug presentation. We also collect experimental release data from the literature, review clinical translation to date of these systems, and present quantitative comparisons between different systems to provide guidelines for the rational design of hydrogel delivery systems.

Co-immobilization of adhesive peptides and VEGF within a dextran-based coating for vascular applications

Multifunctional constructs providing a proper environment for adhesion and growth of selected cell types are needed for most tissue engineering and regenerative medicine applications. In this context, vinylsulfone (VS)-modified dextran was proposed as a matrix featuring low-fouling properties as well as multiple versatile moieties. The displayed VS groups could indeed react with thiol, amine or hydroxyl groups, be it for surface grafting, crosslinking or subsequent tethering of biomolecules. In the present study, a library of dextran-VS was produced, grafted to aminated substrates and characterized in terms of degree of VS modification (%VS), cell-repelling properties and potential for the oriented grafting of cysteine-tagged peptides. As a bioactive coating of vascular implants, ECM peptides (e.g. RGD) as well as vascular endothelial growth factor (VEGF) were co-immobilized on one of the most suitable dextran-VS coating (%VS=ca. 50% of saccharides units). Both RGD and VEGF were efficiently tethered at high densities (ca. 1nmol/cm(2) and 50fmol/cm(2), respectively), and were able to promote endothelial cell adhesion as well as proliferation. The latter was enhanced to the same extent as with soluble VEGF and proved selective to endothelial cells over smooth muscle cells. Altogether, multiple biomolecules could be efficiently incorporated into a dextran-VS construct, while maintaining their respective biological activity.

STATEMENT OF SIGNIFICANCE

This work addresses the need for multifunctional coatings and selective cell response inherent to many tissue engineering and regenerative medicine applications, for instance, vascular graft. More specifically, a library of dextrans was first generated through vinylsulfone (VS) modification. Thoroughly selected dextran-VS provided an ideal platform for unbiased study of cell response to covalently grafted biomolecules. Considering that processes such as healing and angiogenesis require multiple factors acting synergistically, vascular endothelial growth factor (VEGF) was then co-immobilized with the cell adhesive RGD peptide within our dextran coating through a relevant strategy featuring orientation and specificity. Altogether, both adhesive and proliferative cues could be incorporated into our construct with additive, if not synergetic, effects.

Surface bound VEGF mimicking peptide maintains endothelial cell proliferation in the absence of soluble VEGF in vitro

Continuous glucose monitoring is an efficient method for the management of diabetes and in limiting the complications induced by large fluctuations in glucose levels. For this, intravascular systems may assist in producing more reliable and accurate devices. However, neovascularization is a key factor to be addressed in improving their biocompatibility. In this scope, the perennial modification of the surface of an implant with the proangiogenic Vascular Endothelial Growth Factor mimic peptide (SVVYGLR peptide sequence) holds great promise. Herein, we report on the preparation of gold substrates presenting the covalently grafted SVVYGLR peptide sequence and their effect on HUVEC behavior. Effective coupling was demonstrated using XPS and PM-IRRAS. The produced surfaces were shown to be beneficial for HUVEC adhesion. Importantly, surface bound SVVYGLR is able to maintain HUVEC proliferation even in the absence of soluble VEGF. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1425-1436, 2016.

Tuning Mesenchymal Stem Cell Response onto Titanium-Niobium-Hafnium Alloy by Recombinant Fibronectin Fragments

Since metallic biomaterials used for bone replacement possess low bioactivity, the use of cell adhesive moieties is a common strategy to improve cellular response onto these surfaces. In recent years, the use of recombinant proteins has emerged as an alternative to native proteins and short peptides owing to the fact that they retain the biological potency of native proteins, while improving their stability. In the present study, we investigated the biological effect of two different recombinant fragments of fibronectin, spanning the 8-10th and 12-14th type III repeats, covalently attached to a new TiNbHf alloy using APTES silanization. The fragments were studied separately and mixed at different concentrations and compared to a linear RGD, a cyclic RGD and the full-length fibronectin protein. Cell culture studies using rat mesenchymal stem cells demonstrated that low to medium concentrations (30% and 50%) of type III 8-10th fragment mixed with type III 12-14th fragment stimulated cell spreading and proliferation compared to RGD peptides and the fragments separately. On the other hand, type III 12-14th fragment alone or mixed at low volume percentages ≤50% with type III 8-10th fragment increased alkaline phosphatase levels compared to the other molecules. These results are significant for the understanding of the role of fibronectin recombinant fragments in cell responses and thus to design bioactive coatings for biomedical applications.

Synergistic growth factor microenvironments

This paper focuses on developments in materials to stimulate growth factors effects by engineering presentation in synergy with integrins.

Cell sensing of physical properties at the nanoscale: Mechanisms and control of cell adhesion and phenotype

The chemistry, geometry, topography and mechanical properties of biomaterials modulate biochemical signals (in particular ligand-receptor binding events) that control cells-matrix interactions. In turn, the regulation of cell adhesion by the biochemical and physical properties of the matrix controls cell phenotypes such as proliferation, motility and differentiation. In particular, nanoscale geometrical, topographical and mechanical properties of biomaterials are essential to achieve control of the cell-biomaterials interface. The design of such nanoscale architectures and platforms requires understanding the molecular mechanisms underlying adhesion formation and the assembly of the actin cytoskeleton. This review presents some of the important molecular mechanisms underlying cell adhesion to biomaterials mediated by integrins and discusses the nanoscale engineered platforms used to control these processes. Such nanoscale understanding of the cell-biomaterials interface offers exciting opportunities for the design of biomaterials and their application to the field of tissue engineering.

STATEMENT OF SIGNIFICANCE

Biomaterials design is important in the fields of regenerative medicine and tissue engineering, in particular to allow the long term expansion of stem cells and the engineering of scaffolds for tissue regeneration. Cell adhesion to biomaterials often plays a central role in regulating cell phenotype. It is emerging that physical properties of biomaterials, and more generally the microenvironment, regulate such behaviour. In particular, cells respond to nanoscale physical properties of their matrix. Understanding how such nanoscale physical properties control cell adhesion is therefore essential for biomaterials design. To this aim, a deeper understanding of molecular processes controlling cell adhesion, but also a greater control of matrix engineering is required. Such multidisciplinary approaches shed light on some of the fundamental mechanisms via which cell adhesions sense their nanoscale physical environment.

Astrocytes spatially restrict VEGF signaling by polarized secretion and incorporation of VEGF into the actively assembling extracellular matrix

The spatial organization of vascular endothelial growth factor (VEGF) signaling is a key determinant of vascular patterning during development and tissue repair. How VEGF signaling becomes spatially restricted and the role of VEGF secreting astrocytes in this process remains poorly understood. Using a VEGF-GFP fusion protein and confocal time-lapse microscopy, we observed the intracellular routing, secretion and immobilization of VEGF in scratch-activated living astrocytes. We found VEGF to be directly transported to cell-extracellular matrix attachments where it is incorporated into fibronectin fibrils. VEGF accumulated at β1 integrin containing fibrillar adhesions and was translocated along the cell surface prior to internalization and degradation. We also found that only the astrocyte-derived, matrix-bound, and not soluble VEGF decreases β1 integrin turnover in fibrillar adhesions. We suggest that polarized VEGF release and ECM remodeling by VEGF secreting cells is key to control the local concentration and signaling of VEGF. Our findings highlight the importance of astrocytes in directing VEGF functions and identify these mechanisms as promising target for angiogenic approaches.

Extracellular matrix-inspired growth factor delivery systems for bone regeneration

Growth factors are very promising molecules to enhance bone regeneration. However, their translation to clinical use has been seriously limited, facing issues related to safety and cost-effectiveness. These problems derive from the vastly supra-physiological doses of growth factor used without optimized delivery systems. Therefore, these issues have motivated the development of new delivery systems allowing better control of the spatiotemporal release and signaling of growth factors. Because the extracellular matrix (ECM) naturally plays a fundamental role in coordinating growth factor activity in vivo, a number of novel delivery systems have been inspired by the growth factor regulatory function of the ECM. After introducing the role of growth factors during the bone regeneration process, this review exposes different issues that growth factor-based therapies have encountered in the clinic and highlights recent delivery approaches based on the natural interaction between growth factor and the ECM.

Extracellular Matrix-Inspired Growth Factor Delivery Systems for Skin Wound Healing

Significance: Growth factors are very promising molecules for the treatment of skin wounds. However, their translation to clinical use has been seriously limited, facing issues related to safety and cost-effectiveness. These problems may derive from the fact that growth factors are used at vastly supra-physiological levels without optimized delivery systems. Recent Advances: The extracellular matrix (ECM) plays a fundamental role in coordinating growth factor signaling. Therefore, understanding the mechanisms by which the ECM modulates growth factor activity is key for designing efficient growth factor-based therapies. Recently, several growth factor-binding domains have been discovered within various ECM proteins, and growth factor delivery systems integrating these ECM growth factor-binding domains showed promising results in animal models of skin wound healing. Moreover, a novel strategy consisting of engineering growth factors to target endogenous ECM could substantially enhance their efficacy, even when used at low doses. Critical Issues: Optimal delivery of growth factors often requires complex engineered biomaterial matrices, which can face regulatory issues for clinical translation. To simplify delivery systems and render strategies more applicable, growth factors can be engineered to optimally function with clinically approved biomaterials or with endogenous ECM present at the delivery site. Future Directions: Further development and clinical trials will reveal whether growth factor-based therapies can be used as main therapeutic approaches for skin wound healing. The future impact of these therapies will depend on our capacity to deliver growth factors more precisely, to improve efficacy, safety, and cost-effectiveness.

Extracellular matrix and growth factor engineering for controlled angiogenesis in regenerative medicine

Blood vessel growth plays a key role in regenerative medicine, both to restore blood supply to ischemic tissues and to ensure rapid vascularization of clinical-size tissue-engineered grafts. For example, vascular endothelial growth factor (VEGF) is the master regulator of physiological blood vessel growth and is one of the main molecular targets of therapeutic angiogenesis approaches. However, angiogenesis is a complex process and there is a need to develop rational therapeutic strategies based on a firm understanding of basic vascular biology principles, as evidenced by the disappointing results of initial clinical trials of angiogenic factor delivery. In particular, the spatial localization of angiogenic signals in the extracellular matrix (ECM) is crucial to ensure the proper assembly and maturation of new vascular structures. Here, we discuss the therapeutic implications of matrix interactions of angiogenic factors, with a special emphasis on VEGF, as well as provide an overview of current approaches, based on protein and biomaterial engineering that mimic the regulatory functions of ECM to optimize the signaling microenvironment of vascular growth factors.

Wound repair and regeneration: mechanisms, signaling, and translation

The cellular and molecular mechanisms underpinning tissue repair and its failure to heal are still poorly understood, and current therapies are limited. Poor wound healing after trauma, surgery, acute illness, or chronic disease conditions affects millions of people worldwide each year and is the consequence of poorly regulated elements of the healthy tissue repair response, including inflammation, angiogenesis, matrix deposition, and cell recruitment. Failure of one or several of these cellular processes is generally linked to an underlying clinical condition, such as vascular disease, diabetes, or aging, which are all frequently associated with healing pathologies. The search for clinical strategies that might improve the body's natural repair mechanisms will need to be based on a thorough understanding of the basic biology of repair and regeneration. In this review, we highlight emerging concepts in tissue regeneration and repair, and provide some perspectives on how to translate current knowledge into viable clinical approaches for treating patients with wound-healing pathologies.

Harnessing developmental processes for vascular engineering and regeneration

The formation of vasculature is essential for tissue maintenance and regeneration. During development, the vasculature forms via the dual processes of vasculogenesis and angiogenesis, and is regulated at multiple levels: from transcriptional hierarchies and protein interactions to inputs from the extracellular environment. Understanding how vascular formation is coordinated in vivo can offer valuable insights into engineering approaches for therapeutic vascularization and angiogenesis, whether by creating new vasculature in vitro or by stimulating neovascularization in vivo. In this Review, we will discuss how the process of vascular development can be used to guide approaches to engineering vasculature. Specifically, we will focus on some of the recently reported approaches to stimulate therapeutic angiogenesis by recreating the embryonic vascular microenvironment using biomaterials for vascular engineering and regeneration.

Cellular behavior as a dynamic field for exploring bone bioengineering: a closer look at cell-biomaterial interface

Bone is a highly dynamic and specialized tissue, capable of regenerating itself spontaneously when afflicted by minor injuries. Nevertheless, when major lesions occur, it becomes necessary to use biomaterials, which are not only able to endure the cellular proliferation and migration, but also to substitute the original tissue or integrate itself to it. With the life expectancy growth, regenerative medicine has been gaining constant attention in the reconstructive field of dentistry and orthopedy. Focusing on broadening the therapeutic possibilities for the regeneration of injured organs, the development of biomaterials allied with the applicability of gene therapy and bone bioengineering has been receiving vast attention over the recent years. The progress of cellular and molecular biology techniques gave way to new-guided therapy possibilities. Supported by multidisciplinary activities, tissue engineering combines the interaction of physicists, chemists, biologists, engineers, biotechnologist, dentists and physicians with common goals: the search for materials that could promote and lead cell activity. A well-oriented combining of scaffolds, promoting factors, cells, together with gene therapy advances may open new avenues to bone healing in the near future. In this review, our target was to write a report bringing overall concepts on tissue bioengineering, with a special attention to decisive biological parameters for the development of biomaterials, as well as to discuss known intracellular signal transduction as a new manner to be explored within this field, aiming to predict in vitro the quality of the host cell/material and thus contributing with the development of regenerative medicine.

Long-lasting fibrin matrices ensure stable and functional angiogenesis by highly tunable, sustained delivery of recombinant VEGF164

Clinical trials of therapeutic angiogenesis by vascular endothelial growth factor (VEGF) gene delivery failed to show efficacy. Major challenges include the need to precisely control in vivo distribution of growth factor dose and duration of expression. Recombinant VEGF protein delivery could overcome these issues, but rapid in vivo clearance prevents the stabilization of induced angiogenesis. Here, we developed an optimized fibrin platform for controlled delivery of recombinant VEGF, to robustly induce normal, stable, and functional angiogenesis. Murine VEGF164 was fused to a sequence derived from α2-plasmin inhibitor (α2-PI1-8) that is a substrate for the coagulation factor fXIIIa, to allow its covalent cross-linking into fibrin hydrogels and release only by enzymatic cleavage. An α2-PI1-8-fused variant of the fibrinolysis inhibitor aprotinin was used to control the hydrogel degradation rate, which determines both the duration and effective dose of factor release. An optimized aprotinin-α2-PI1-8 concentration ensured ideal degradation over 4 wk. Under these conditions, fibrin-α2-PI1-8-VEGF164 allowed exquisitely dose-dependent angiogenesis: concentrations ≥25 μg/mL caused widespread aberrant vascular structures, but a 500-fold concentration range (0.01-5.0 μg/mL) induced exclusively normal, mature, nonleaky, and perfused capillaries, which were stable after 3 mo. Optimized delivery of fibrin-α2-PI1-8-VEGF164 was therapeutically effective both in ischemic hind limb and wound-healing models, significantly improving angiogenesis, tissue perfusion, and healing rate. In conclusion, this optimized platform ensured (i) controlled and highly tunable delivery of VEGF protein in ischemic tissue and (ii) stable and functional angiogenesis without introducing genetic material and with a limited and controllable duration of treatment. These findings suggest a strategy to improve safety and efficacy of therapeutic angiogenesis.