Sustained delivery of recombinant human bone morphogenetic protein-2 from perlecan domain I - functionalized electrospun poly (ε-caprolactone) scaffolds for bone regeneration

Surgical Site-Released Tissue Is Potent to Generate Bone onto TCP and PCL-TCP Scaffolds In Vitro

There is evidence that surgical site tissue (SSRT) released during orthopedic surgery has a strong mesenchymal regenerative potential. Some data also suggest that this tissue may activate synthetic or natural bone substitute materials and can thus upgrade its osteopromoting properties. In this comparative in vitro study, we investigate the composition of SSRT during total hip replacement (n = 20) harvested using a surgical suction handle. In addition, the osteopromoting effect of the cells isolated from SSRT is elucidated when incubated with porous beta-tricalcium phosphate (β-TCP) or 80% medical-grade poly-ε-caprolactone (PCL)/20% TCP composite material. We identified multiple growth factors and cytokines with significantly higher levels of PDGF and VEGF in SSRT compared to peripheral blood. The overall number of MSC was 0.09 ± 0.12‱ per gram of SSRT. A three-lineage specific differentiation was possible in all cases. PCL-TCP cultures showed a higher cell density and cell viability compared to TCP after 6 weeks in vitro. Moreover, PCL-TCP cultures showed a higher osteocalcin expression but no significant differences in osteopontin and collagen I synthesis. We could demonstrate the high regenerative potential from SSRT harvested under vacuum in a PMMA filter device. The in vitro data suggest advantages in cytocompatibility for the PCL-TCP composite compared to TCP alone.

Perlecan, A Multi-Functional, Cell-Instructive, Matrix-Stabilizing Proteoglycan With Roles in Tissue Development Has Relevance to Connective Tissue Repair and Regeneration

This review highlights the multifunctional properties of perlecan (HSPG2) and its potential roles in repair biology. Perlecan is ubiquitous, occurring in vascular, cartilaginous, adipose, lymphoreticular, bone and bone marrow stroma and in neural tissues. Perlecan has roles in angiogenesis, tissue development and extracellular matrix stabilization in mature weight bearing and tensional tissues. Perlecan contributes to mechanosensory properties in cartilage through pericellular interactions with fibrillin-1, type IV, V, VI and XI collagen and elastin. Perlecan domain I - FGF, PDGF, VEGF and BMP interactions promote embryonic cellular proliferation, differentiation, and tissue development. Perlecan domain II, an LDLR-like domain interacts with lipids, Wnt and Hedgehog morphogens. Perlecan domain III binds FGF-7 and 18 and has roles in the secretion of perlecan. Perlecan domain IV, an immunoglobulin repeat domain, has cell attachment and matrix stabilizing properties. Perlecan domain V promotes tissue repair through interactions with VEGF, VEGF-R2 and α2β1 integrin. Perlecan domain-V LG1-LG2 and LG3 fragments antagonize these interactions. Perlecan domain V promotes reconstitution of the blood brain barrier damaged by ischemic stroke and is neurogenic and neuroprotective. Perlecan-VEGF-VEGFR2, perlecan-FGF-2 and perlecan-PDGF interactions promote angiogenesis and wound healing. Perlecan domain I, III and V interactions with platelet factor-4 and megakaryocyte and platelet inhibitory receptor promote adhesion of cells to implants and scaffolds in vascular repair. Perlecan localizes acetylcholinesterase in the neuromuscular junction and is of functional significance in neuromuscular control. Perlecan mutation leads to Schwartz-Jampel Syndrome, functional impairment of the biomechanical properties of the intervertebral disc, variable levels of chondroplasia and myotonia. A greater understanding of the functional working of the neuromuscular junction may be insightful in therapeutic approaches in the treatment of neuromuscular disorders. Tissue engineering of salivary glands has been undertaken using bioactive peptides (TWSKV) derived from perlecan domain IV. Perlecan TWSKV peptide induces differentiation of salivary gland cells into self-assembling acini-like structures that express salivary gland biomarkers and secrete α-amylase. Perlecan also promotes chondroprogenitor stem cell maturation and development of pluripotent migratory stem cell lineages, which participate in diarthrodial joint formation, and early cartilage development. Recent studies have also shown that perlecan is prominently expressed during repair of adult human articular cartilage. Perlecan also has roles in endochondral ossification and bone development. Perlecan domain I hydrogels been used in tissue engineering to establish heparin binding growth factor gradients that promote cell migration and cartilage repair. Perlecan domain I collagen I fibril scaffolds have also been used as an FGF-2 delivery system for tissue repair. With the availability of recombinant perlecan domains, the development of other tissue repair strategies should emerge in the near future. Perlecan co-localization with vascular elastin in the intima, acts as a blood shear-flow endothelial sensor that regulates blood volume and pressure and has a similar role to perlecan in canalicular fluid, regulating bone development and remodeling. This complements perlecan’s roles in growth plate cartilage and in endochondral ossification to form the appendicular and axial skeleton. Perlecan is thus a ubiquitous, multifunctional, and pleomorphic molecule of considerable biological importance. A greater understanding of its diverse biological roles and functional repertoires during tissue development, growth and disease will yield valuable insights into how this impressive proteoglycan could be utilized successfully in repair biology.

Proteoglycans and proteoglycan mimetics for tissue engineering

Proteoglycans play a crucial role in proper tissue morphology and function throughout the body that is defined by a combination of their core protein and the attached glycosaminoglycan chains. Although they serve a myriad of roles, the functions of extracellular proteoglycans can be generally sorted into four categories: modulation of tissue mechanical properties, regulation and protection of the extracellular matrix, sequestering of proteins, and regulation of cell signaling. The loss of proteoglycans can result in significant tissue disfunction, ranging from poor mechanical properties to uncontrolled inflammation. Because of the key roles they play in proper tissue function and due to their complex synthesis, the past two decades have seen significant research into the development of proteoglycan mimetic molecules to recapitulate the function of proteoglycans for therapeutic and tissue engineering applications. These strategies have ranged from semisynthetic graft copolymers to recombinant proteoglycan domains synthesized by genetically engineered cells. In this review, we highlight some of the important functions of extracellular proteoglycans, as well as the strategies developed to recapitulate these functions.

Potent Particle-Based Vehicles for Growth Factor Delivery from Electrospun Meshes: Fabrication and Functionalization Strategies for Effective Tissue Regeneration

Functionalization of electrospun meshes with growth factors (GFs) is a common strategy for guiding specific cell responses in tissue engineering. GFs can exert their intended biological effects only when they retain their bioactivity and can be subsequently delivered in a temporally controlled manner. However, adverse processing conditions encountered in electrospinning can potentially disrupt GFs and diminish their biological efficacy. Further, meshes prepared using conventional approaches often promote an initial burst and rely solely on intrinsic fiber properties to provide extended release. Sequential delivery of multiple GFs─a strategy that mimics the natural tissue repair cascade─is also not easily achievable with traditional fabrication techniques. These limitations have hindered the effective use and translation of mesh-based strategies for tissue repair. An attractive alternative is the use of carrier vehicles (e.g., nanoparticles, microspheres) for GF incorporation into meshes. This review presents advances in the development of particle-integrated electrospun composites for safe and effective delivery of GFs. Compared to traditional approaches, we reveal how particles can protect GF activity, permit the incorporation of multiple GFs, decouple release from fiber properties, help achieve spatiotemporal control over delivery, enhance surface bioactivity, exert independent biological effects, and augment matrix mechanics. In presenting innovations in GF functionalization and composite engineering strategies, we also discuss specific in vitro and in vivo biological effects and their implications for diverse tissue engineering applications.

Impact of perlecan, a core component of basement membrane, on regeneration of cartilaginous tissues

As an indispensable component of the extracellular matrix, perlecan (Pln) plays an essential role in cartilaginous tissue function. Although there exist studies suggesting that Pln expressed by cartilaginous tissues is critical for chondrogenesis, few papers have discussed the potential impact Pln may have on cartilage regeneration. In this review, we delineate Pln structure, biomechanical properties, and interactive ligands-which together contribute to the effect Pln has on cartilaginous tissue development. We also review how the signaling pathways of Pln affect cartilage development and scrutinize the potential application of Pln to divisions of cartilage regeneration, spanning vascularization, stem cell differentiation, and biomaterial improvement. The aim of this review is to deepen our understanding of the spatial and temporal interactions that occur between Pln and cartilaginous tissue and ultimately apply Pln in scaffold design to improve cell-based cartilage engineering and regeneration. STATEMENT OF SIGNIFICANCE: As a key component of the basement membrane, Pln plays a critical role in tissue development and repair. Recent findings suggest that Pln existing in the pericellular matrix surrounding mature chondrocytes is actively involved in cartilage regeneration and functionality. We propose that Pln is essential to developing an in vitro matrix niche within biological scaffolds for cartilage tissue engineering.

Staphylococcus aureus Specific Electrospun Wound Dressings: Influence of Immobilization Technique on Antibacterial Efficiency of Novel Enzybiotic

The spread of antimicrobial resistance requires the development of novel strategies to combat superbugs. Bacteriolytic enzymes (enzybiotics) that selectively eliminate pathogenic bacteria, including resistant strains and biofilms, are attractive alternatives to antibiotics, also as a component of a new generation of antimicrobial wound dressings. AuresinePlus is a novel, engineered enzybiotic effective against Staphylococcus aureus-one of the most common pathogenic bacteria, found in infected wounds with a very high prevalence of antibiotic resistance. We took advantage of its potent lytic activity, selectivity, and safety to prepare a set of biodegradable PLGA/chitosan fibers generated by electrospinning. Our aim was to produce antimicrobial nonwovens to deliver enzybiotics directly to the infected wound and better control its release and activity. Three different methods of enzyme immobilization were tested: physical adsorption on the previously hydrolyzed surface, and covalent bonding formation using N-hydroxysuccinimide/N-(3-Dimethylaminopropyl)-N'-ethylcarbodiimide (NHS/EDC) or glutaraldehyde (GA). The supramolecular structure and functional properties analysis revealed that the selected methods resulted in significant development of nanofibers surface topography resulting in an efficient enzybiotic attachment. Both physically adsorbed and covalently bound enzymes (by NHS/EDC method) exhibited prominent antibacterial activity. Here, we present the extensive comparison between methods for the effective attachment of the enzybiotic to the electrospun nonwovens to generate biomaterials effective against antibiotic-resistant strains. Our intention was to present a comprehensive proof-of-concept study for future antimicrobial wound dressing development.

Perlecan domain I gradients establish stable biomimetic heparin binding growth factor gradients for cell migration in hydrogels

Growth factor gradients orchestrate many biological processes including organogenesis, wound healing, cancer invasion, and metastasis. Heparin-binding growth factor (HBGF) gradients are established in living systems by proteoglycans including the extracellular matrix heparan sulfate proteoglycan, perlecan/HSPG2. Three potential HBGF-binding glycosaminoglycan attachment sites occur in N-terminal domain I of perlecan's five domains. Our overarching goal was to form stable, biomimetic non-covalently bound HBGF gradients surrounding cells encapsulated in hyaluronate-based hydrogels by first establishing perlecan domain I (PlnD1) gradients. A versatile multichannel gradient maker device (MGMD) was designed and 3D printed, then used to create desired gradients of microparticles in hydrogels. Next, we used the device to covalently incorporate gradients of PEGylated PlnD1 in hydrogels with high-low-high or high-medium-low concentrations across the hydrogel width. Fluorescently-labeled fibroblast growth factor-2 was delivered to hydrogels in phosphate-buffered saline and allowed to electrostatically bind to the covalently pre-incorporated PlnD1, producing stable non-covalent HBGF gradients. To test cell viability after flow through the MGMD, delicate primary human salivary stem/progenitor cells were encapsulated in gradient hydrogels where they showed high viability and continued to grow. Next, to test migratory behavior in response to HBGF gradients, two cell types, preosteoblastic MC3T3-E1 cell line and breast cancer cell line MDA-MB-231 were encapsulated in or adjacent to PlnD1-modified hydrogels. Both cell lines migrated toward HBGFs bound to PlnD1. We conclude that establishing covalently-bound PlnD1 gradients in hydrogels provides a new means to establish physiologically-relevant gradients of HBGFs that are useful for a variety of applications in tissue engineering and cancer biology. STATEMENT OF SIGNIFICANCE: Gradients of heparin binding growth factors (HBGFs) direct cell behavior in living systems. HBGFs bind electrostatically to gradients of HS proteoglycans in the extracellular matrix creating HBGF gradients. We recreated HBGF gradients in physiological hyaluronate-based hydrogels using a 3D-printed multichannel gradient maker device (MGMD) that created gradients of HS proteoglycan-derived perlecan/HSPG2 domain I. We demonstrated the ability of a variety of cells, including primary salivary stem/progenitor cells, pre-osteoblastic cells and an invasive breast cancer cell line, to be co-encapsulated in gradient hydrogels by flowing them together through the MGMD. The versatile device and the ability to create HBGF gradients in hydrogels for a variety of applications is innovative and of broad utility in both cancer biology and tissue engineering applications.

Matrilysin/MMP-7 Cleavage of Perlecan/HSPG2 Complexed with Semaphorin 3A Supports FAK-Mediated Stromal Invasion by Prostate Cancer Cells

Interrupting the interplay between cancer cells and extracellular matrix (ECM) is a strategy to halt tumor progression and stromal invasion. Perlecan/heparan sulfate proteoglycan 2 (HSPG2) is an extracellular proteoglycan that orchestrates tumor angiogenesis, proliferation, differentiation and invasion. Metastatic prostate cancer (PCa) cells degrade perlecan-rich tissue borders to reach bone, including the basement membrane, vasculature, reactive stromal matrix and bone marrow. Domain IV-3, perlecan’s last 7 immunoglobulin repeats, mimics native proteoglycan by promoting tumoroid formation. This is reversed by matrilysin/matrix metalloproteinase-7 (MMP-7) cleavage to favor cell dispersion and tumoroid dyscohesion. Both perlecan and Domain IV-3 induced a strong focal adhesion kinase (FAK) dephosphorylation/deactivation. MMP-7 cleavage of perlecan reversed this, with FAK in dispersed tumoroids becoming phosphorylated/activated with metastatic phenotype. We demonstrated Domain IV-3 interacts with the axon guidance protein semaphorin 3A (Sema3A) on PCa cells to deactivate pro-metastatic FAK. Sema3A antibody mimicked the Domain IV-3 clustering activity. Direct binding experiments showed Domain IV-3 binds Sema3A. Knockdown of Sema3A prevented Domain IV-3-induced tumoroid formation and Sema3A was sensitive to MMP-7 proteolysis. The perlecan-Sema3A complex abrogates FAK activity and stabilizes PCa cell interactions. MMP-7 expressing cells destroy the complex to initiate metastasis, destroy perlecan-rich borders, and favor invasion and progression to lethal bone disease.

Nano-biphasic calcium phosphate/polyvinyl alcohol composites with enhanced bioactivity for bone repair via low-temperature three-dimensional printing and loading with platelet-rich fibrin

Background and aim

As a newly emerging three-dimensional (3D) printing technology, low-temperature robocasting can be used to fabricate geometrically complex ceramic scaffolds at low temperatures. Here, we aimed to fabricate 3D printed ceramic scaffolds composed of nano-biphasic calcium phosphate (BCP), polyvinyl alcohol (PVA), and platelet-rich fibrin (PRF) at a low temperature without the addition of toxic chemicals.

Methods

Corresponding nonprinted scaffolds were prepared using a freeze-drying method. Compared with the nonprinted scaffolds, the printed scaffolds had specific shapes and well-connected internal structures.

Results

The incorporation of PRF enabled both the sustained release of bioactive factors from the scaffolds and improved biocompatibility and biological activity toward bone marrow-derived mesenchymal stem cells (BMSCs) in vitro. Additionally, the printed BCP/PVA/PRF scaffolds promoted significantly better BMSC adhesion, proliferation, and osteogenic differentiation in vitro than the printed BCP/PVA scaffolds. In vivo, the printed BCP/PVA/PRF scaffolds induced a greater extent of appropriate bone formation than the printed BCP/PVA scaffolds and nonprinted scaffolds in a critical-size segmental bone defect model in rabbits.

Conclusion

These experiments indicate that low-temperature robocasting could potentially be used to fabricate 3D printed BCP/PVA/PRF scaffolds with desired shapes and internal structures and incorporated bioactive factors to enhance the repair of segmental bone defects.

Delivery of Therapeutic Proteins Using Electrospun Fibers-Recent Developments and Current Challenges

Proteins play a vital role within the human body by regulating various functions and even serving as structural constituent of many body parts. In this context, protein-based therapeutics have attracted a lot of attention in the last few decades as potential treatment of different diseases. Due to the steadily increasing interest in protein-based therapeutics, different dosage forms were investigated for delivering such complex macromolecules to the human body. Here, electrospun fibers hold a great potential for embedding proteins without structural damage and for controlled release of the protein for therapeutic applications. This review provides a comprehensive overview of the current state of protein-based carrier systems using electrospun fibers, with special emphasis on discussing their potential and key challenges in developing such therapeutic strategies, along with a prospective view of anticipated future directions.

Electrospun polymeric micro/nanofibrous scaffolds for long-term drug release and their biomedical applications

Electrospun polymeric micro/nanofibrous scaffolds have been investigated extensively as drug delivery platforms capable of controlled and sustained release of therapeutic agents in situ. Such scaffolds exhibit excellent physicochemical and biological properties and can encapsulate and release various drugs in a controlled fashion. This article reviews recent advances in the design and manufacture of electrospun scaffolds for long-term drug release, placing particular emphasis on polymer selection, types of incorporated drugs and the latest drug-loading techniques. Finally, applications of such devices in traumatic or disease states requiring effective and sustained drug action are discussed and critically appraised in their biomedical context.