Heparin-decorated, hyaluronic acid-based hydrogel particles for the controlled release of bone morphogenetic protein 2

Hyaluronan-based Hydrogels for 3D Modelling of Tumour Tissues

Although routine 2D cell culture techniques have advanced basic cancer research owing to their simplicity, cost-effectiveness, and reproducibility, they have limitations that necessitate the development of advanced 3D tumour models that better recapitulate the tumour microenvironment. Various biomaterials have been used to establish these 3D models, enabling the study of cancer cell behaviour within different matrices. Hyaluronic acid (HA), a key component of the extracellular matrix in tumour tissues, has been widely studied and employed in the development of multiple cancer models. This review first examines the role of HA in tumours, including its function as an extracellular matrix (ECM) component and regulator of signalling pathways that affect tumour progression. It then explores HA-based models for various cancers, focusing on HA as a central component of the 3D matrix and its mobilization within the matrix for targeted studies of cell behaviour and drug testing. The tumour models discussed included those for breast cancer, glioblastoma, fibrosarcoma, gastric cancer, hepatocellular carcinoma, and melanoma. The review concludes with a discussion of future prospects for developing more robust and high-throughput HA-based models to more accurately mimic the tumour microenvironment and improve drug testing.

Exploring the Role of Hyaluronic Acid in Reproductive Biology and Beyond: Applications in Assisted Reproduction and Tissue Engineering

Hyaluronic acid (HA) plays a prominent role in various aspects of reproductive biology and assisted reproductive technologies (ART). This review describes the multifaceted influence of HA, ranging from primordial germ cell migration, ovarian follicle development, and ovulation in females to sperm structure, physiology, motility, and capacitation in males. In addition, HA also plays an important role in fertilization and promotes embryo implantation by mediating cellular adhesion and communication within the uterus. Against this physiological background, the review examines the current applications of HA in the context of ART. In addition, the article addresses the emerging field of reproductive tissue engineering, where HA-based hydrogels offer promising perspectives as they can support the development of mature oocytes and spermatogenesis in vitro. Overall, this review highlights the integral role of HA in the intricate mechanisms of reproductive biology and its growing importance for improving ART outcomes and the field of tissue engineering of the reproductive system.

Sweet but Challenging: Tackling the Complexity of GAGs with Engineered Tailor-Made Biomaterials

Glycosaminoglycans (GAGs) play a crucial role in tissue homeostasis by regulating the activity and diffusion of bioactive molecules. Incorporating GAGs into biomaterials has emerged as a widely adopted strategy in medical applications, owing to their biocompatibility and ability to control the release of bioactive molecules. Nevertheless, immobilized GAGs on biomaterials can elicit distinct cellular responses compared to their soluble forms, underscoring the need to understand the interactions between GAG and bioactive molecules within engineered functional biomaterials. By controlling critical parameters such as GAG type, density, and sulfation, it becomes possible to precisely delineate GAG functions within a biomaterial context and to better mimic specific tissue properties, enabling tailored design of GAG-based biomaterials for specific medical applications. However, this requires access to pure and well-characterized GAG compounds, which remains challenging. This review focuses on different strategies for producing well-defined GAGs and explores high-throughput approaches employed to investigate GAG-growth factor interactions and to quantify cellular responses on GAG-based biomaterials. These automated methods hold considerable promise for improving the understanding of the diverse functions of GAGs. In perspective, the scientific community is encouraged to adopt a rational approach in designing GAG-based biomaterials, taking into account the in vivo properties of the targeted tissue for medical applications.

A Tunable Glycosaminoglycan-Peptide Nanoparticle Platform for the Protection of Therapeutic Peptides

The popularity of Glycosaminoglycans (GAGs) in drug delivery systems has grown as their innate ability to sequester and release charged molecules makes them adept in the controlled release of therapeutics. However, peptide therapeutics have been relegated to synthetic, polymeric systems, despite their high specificity and efficacy as therapeutics because they are rapidly degraded in vivo when not encapsulated. We present a GAG-based nanoparticle system for the easy encapsulation of cationic peptides, which offers control over particle diameter, peptide release behavior, and swelling behavior, as well as protection from proteolytic degradation, using a singular, organic polymer and no covalent linkages. These nanoparticles can encapsulate cargo with a particle diameter range spanning 130-220 nm and can be tuned to release cargo over a pH range of 4.5 to neutral through the modulation of the degree of sulfation and the molecular weight of the GAG. This particle system also confers better in vitro performance than the unencapsulated peptide via protection from enzymatic degradation. This method provides a facile way to protect therapeutic peptides via the inclusion of the presented binding sequence and can likely be expanded to larger, more diverse cargo as well, abrogating the complexity of previously demonstrated systems while offering broader tunability.

Immune homeostasis modulation by hydrogel-guided delivery systems: a tool for accelerated bone regeneration

Immune homeostasis is delicately mediated by the dynamic balance between effector immune cells and regulatory immune cells. Local deviations from immune homeostasis in the microenvironment of bone fractures, caused by an increased ratio of effector to regulatory cues, can lead to excessive inflammatory conditions and hinder bone regeneration. Therefore, achieving effective and localized immunomodulation of bone fractures is crucial for successful bone regeneration. Recent research has focused on developing localized and specific immunomodulatory strategies using local hydrogel-based delivery systems. In this review, we aim to emphasize the significant role of immune homeostasis in bone regeneration, explore local hydrogel-based delivery systems, discuss emerging trends in immunomodulation for enhancing bone regeneration, and address the limitations of current delivery strategies along with the challenges of clinical translation.

3D printed and stimulus responsive drug delivery systems based on synthetic polyelectrolyte hydrogels manufactured via digital light processing

Hydrogels are three-dimensional hydrophilic polymeric networks absorbing up to and even more than 90 wt% of water. These superabsorbent polymers retain their shape during the swelling process while enlarging their volume and mass. In addition to their swelling behavior, hydrogels can possess other interesting properties, such as biocompatibility, good rheological behavior, or even antimicrobial activity. This versatility qualifies hydrogels for many medical applications, especially drug delivery systems. As recently shown, polyelectrolyte-based hydrogels offer beneficial properties for long-term and stimulus-responsive applications. However, the fabrication of complex structures and shapes can be difficult to achieve with common polymerization methods. This obstacle can be overcome by the use of additive manufacturing. 3D printing technology is gaining more and more attention as a method of producing materials for biomedical applications and medical devices. Photopolymerizing 3D printing methods offer superior resolution and high control of the photopolymerization process, allowing the fabrication of complex and customizable designs while being less wasteful. In this work, novel synthetic hydrogels, consisting of [2-(acryloyloxy) ethyl]trimethylammonium chloride (AETMA) as an electrolyte monomer and poly(ethylene glycol)-diacrylate (PEGDA) as a crosslinker, 3D printed via Digital Light Processing (DLP) using a layer height of 100 μm, are reported. The hydrogels obtained showed a high swelling degree q∞m,t ∼ 12 (24 h in PBS; pH 7; 37 °C) and adjustable mechanical properties with high stretchability (ε_max ∼ 300%). Additionally, we embedded the model drug acetylsalicylic acid (ASA) and investigated its stimulus-responsive drug release behaviour in different release media. The stimulus responsiveness of the hydrogels is mirrored in their release behavior and could be exploited in triggered as well as sequential release studies, demonstrating a clear ion exchange behavior. The received 3D-printed drug depots could also be printed in complex hollow geometry, exemplarily demonstrated via an individualized frontal neo-ostium implant prototype. Consequently, a drug-releasing, flexible, and swellable material was obtained, combining the best of both worlds: the properties of hydrogels and the ability to print complex shapes.

Structure and drug delivery relationship of acidic polysaccharides: A review

Scientists from across the world are being inspired by recent development in polysaccharides and their use in medical administration. Due to their extraordinary physical, chemical, and biological characteristics, polysaccharides are excellent materials for use in medicine. Acidic polysaccharides, which include Pectin, Xanthan gum, Carrageenan, Alginate, and Glycosaminoglycan, are natural polymers with carboxyl groups that are being researched for their potential as drug delivery systems. Most publications do not discuss how the different polysaccharides interact structurally in terms of drug delivery, which limits the scope of their use. The purpose of this review is to inform readers about the structural activity correlations between acidic polysaccharides, their different modification process and effects of combination of various acidic polysaccharides which have been used in drug delivery systems and expanding their potential applications, and bringing new perspectives to the fore.

Partial sulfation of gellan gum produces cytocompatible, body temperature-responsive hydrogels

Gellan gum (GG) is a biodegradable polysaccharide and forms thermosensitive hydrogels by a helix-mediated mechanism. Unfortunately, the wide use of GG in tissue engineering has been restricted due to its dramatically higher gelation temperature than normal body temperature. Here, we show that partial sulfation of GG affords a cytocompatible body temperature-responsive hydrogel with an interesting thermoreversibility at 42 °C. The partial sulfation of GG was confirmed by FTIR, EDX and elemental analyses. The sulfated GGs (SGGs) had a higher swelling ratio and degradation in PBS compared to the neat GG. Based on the results of rheometry analysis, the SGG with a degree of sulfation of 0.27 (H3 sample) showed a gelation temperature close to the physiological temperature. In addition, the drop in mechanical properties of SGGs was compensated by a further calcium-mediated ionic crosslinking, where Young's modulus of H3 increased from 10.6 ± 1.9 kPa up to 38.4 ± 5.5 kPa. Finally, we showed that the partial sulfation reaction of GG is a simple and mild strategy to modify chemical structure of GG, and to produce a cytocompatible, body temperature-responsive hydrogel compared to other modifying reactions such as oxidation reaction.

Bone Formation on Murine Cranial Bone by Injectable Cross-Linked Hyaluronic Acid Containing Nano-Hydroxyapatite and Bone Morphogenetic Protein

New injection-type bone-forming materials are desired in dental implantology. In this study, we added nano-hydroxyapatite (nHAp) and bone morphogenetic protein (BMP) to cross-linkable thiol-modified hyaluronic acid (tHyA) and evaluated its usefulness as an osteoinductive injectable material using an animal model. The sol (ux-tHyA) was changed to a gel (x-tHyA) by mixing with a cross-linker. We prepared two sol−gel (SG) material series, that is, x-tHyA + BMP with and without nHAp (SG I) and x-tHyA + nHAp with and without BMP (SG II). SG I materials in the sol stage were injected into the cranial subcutaneous connective tissues of mice, followed by in vivo gelation, while SG II materials gelled in Teflon rings were surgically placed directly on the cranial bones of rats. The animals were sacrificed 8 weeks after implantation, followed by X-ray analysis and histological examination. The results revealed that bone formation occurred at a high rate (>70%), mainly as ectopic bone in the SG I tests in mouse cranial connective tissues, and largely as bone augmentation in rat cranial bones in the SG II experiments when x-tHyA contained both nHAp and BMP. The prepared x-tHyA + nHAp + BMP SG material can be used as an injection-type osteoinductive bone-forming material. Sub-periosteum injection was expected.

Tailored Polyelectrolyte Multilayer Systems by Variation of Polyelectrolyte Composition and EDC/NHS Cross-Linking: Controlled Drug Release vs. Drug Reservoir Capabilities and Cellular Response for Improved Osseointegration

Polyelectrolyte multilayers (PEM) are versatile tools used to investigate fundamental interactions between material-related parameters and the resulting performance in stem cell differentiation, respectively, in bone tissue engineering. In the present study, we investigate the suitability of PEMs with a varying collagen content for use as drug carriers for the human bone morphogenetic protein 2 (rhBMP-2). We use three different PEM systems consisting either of the positively charged poly-L-lysine or the glycoprotein collagen type I and the negatively charged glycosaminoglycan heparin. For a specific modification of the loading capacity and the release kinetics, the PEMs were stepwise cross-linked before loading with cytokine. We demonstrate the possibility of immobilizing significant amounts of rhBMP-2 in all multilayer systems and to specifically tune its release via cross-linking. Furthermore, we prove that the drug release of rhBMP-2 plays only a minor role in the differentiation of osteoprogenitor cells. We find a significantly higher influence of the immobilized rhBMP-2 within the collagen-rich coatings that obviously represent an excellent mimicry of the native extracellular matrix. The cytokine immobilized in its bioactive form was able to achieve an increase in orders of magnitude both in the early stages of differentiation and in late calcification compared to the unloaded layers.

Dopamine/DOPAC-assisted immobilization of bone morphogenetic protein-2 loaded Heparin/PEI nanogels onto three-dimentional printed calcium phosphate ceramics for enhanced osteoinductivity and osteogenicity

Nowadays, the three-dimensional (3D) printed calcium phosphate (CaP) ceramics have well-designed geometric structure, but suffer from relative weak osteoinductivity. Surface modification by incorporating bone morphogenetic protein-2 (BMP2) onto scaffolds is considered as an efficient approach to improve their bioactivity. However, high dose and uncontrolled burst release of BMP2 may cause undesired side effect. In the present study, porous BCP ceramics with inverse face-centred cube structure prepared by digital light processing (DLP)-based 3D printing technique were used as the substrates. BMP2 proteins were loaded in the self-assembled Heparin/PEI nanogels (NP/BMP2), and then immobilized onto BCP substrates through the intermediate mussel-derived bioactive dopamine and dihydroxyphenylacetic acid (DA/DOPAC) coating layers to construct functional BCP/layer/NP/BMP2 scaffolds. Our results showed that Heparin/PEI nanogel was a potent delivery system for BMP2, and BCP/layer/NP/BMP2 scaffolds exhibited the high loading capacity, controlled release rate, and sustained local delivery of BMP2. In vitro cell experiments with bone marrow stromal cells (BMSCs) found that BCP/layer/NP/BMP2 could promote cell proliferation, facilitate cell spreading, accelerate cell migration, up-regulate expression of osteogenic genes, and improve synthesis of osteoblast-related proteins. Moreover, the murine intramuscular implantation model suggested that BCP/layer/NP/BMP2 had a superior osteoinductive capacity, and the rat femoral condyle defect repair model showed that BCP/layer/NP/BMP2 could enhance in situ bone repair and regeneration. These findings demonstrate that the incorporation of BMP2 loaded Heparin/PEI nanogels to 3D printed scaffolds holds great promise in fabricating bone graft with a superior biological performance for orthopedic application.

Bioengineering Approaches for Delivering Growth Factors: A Focus on Bone and Cartilage Regeneration

Growth factors are bio-factors that target reparatory cells during bone regeneration. These growth factors are needed in complicated conditions of bone and joint damage to enhance tissue repair. The delivery of these growth factors is key to ensuring the effectiveness of regenerative therapy. This review discusses the roles of various growth factors in bone and cartilage regeneration. The methods of delivery of natural or recombinant growth factors are reviewed. Different types of scaffolds, encapsulation, Layer-by-layer assembly, and hydrogels are tools for growth factor delivery. Considering the advantages and limitations of these methods is essential to developing regenerative therapies. Further research can accordingly be planned to have new or combined technologies serving this purpose.

Increased connectivity of hiPSC-derived neural networks in multiphase granular hydrogel scaffolds

To reflect human development, it is critical to create a substrate that can support long-term cell survival, differentiation, and maturation. Hydrogels are promising materials for 3D cultures. However, a bulk structure consisting of dense polymer networks often leads to suboptimal microenvironments that impedes nutrient exchange and cell-to-cell interaction. Herein, granular hydrogel-based scaffolds were used to support 3D human induced pluripotent stem cell (hiPSC)-derived neural networks. A custom designed 3D printed toolset was developed to extrude hyaluronic acid hydrogel through a porous nylon fabric to generate hydrogel granules. Cells and hydrogel granules were combined using a weaker secondary gelation step, forming self-supporting cell laden scaffolds. At three and seven days, granular scaffolds supported higher cell viability compared to bulk hydrogels, whereas granular scaffolds supported more neurite bearing cells and longer neurite extensions (65.52 ± 11.59 μm) after seven days compared to bulk hydrogels (22.90 ± 4.70 μm). Long-term (three-month) cultures of clinically relevant hiPSC-derived neural cells in granular hydrogels supported well established neuronal and astrocytic colonies and a high level of neurite extension both inside and beyond the scaffold. This approach is significant as it provides a simple, rapid and efficient way to achieve a tissue-relevant granular structure within hydrogel cultures.

Recent Developments in Hyaluronic Acid-Based Hydrogels for Cartilage Tissue Engineering Applications

Articular cartilage lesions resulting from injurious impact, recurring loading, joint malalignment, etc., are very common and encompass the risk of evolving to serious cartilage diseases such as osteoarthritis. To date, cartilage injuries are typically treated via operative procedures such as autologous chondrocyte implantation (ACI), matrix-associated autologous chondrocyte implantation (MACI) and microfracture, which are characterized by low patient compliance. Accordingly, cartilage tissue engineering (CTE) has received a lot of interest. Cell-laden hydrogels are favorable candidates for cartilage repair since they resemble the native tissue environment and promote the formation of extracellular matrix. Various types of hydrogels have been developed so far for CTE applications based on both natural and synthetic biomaterials. Among these materials, hyaluronic acid (HA), a principal component of the cartilage tissue which can be easily modified and biofunctionalized, has been favored for the development of hydrogels since it interacts with cell surface receptors, supports the growth of chondrocytes and promotes the differentiation of mesenchymal stem cells to chondrocytes. The present work reviews the various types of HA-based hydrogels (e.g., in situ forming hydrogels, cryogels, microgels and three-dimensional (3D)-bioprinted hydrogel constructs) that have been used for cartilage repair, specially focusing on the results of their preclinical and clinical assessment.

A combined cell and growth factor delivery for the repair of a critical size tibia defect using biodegradable hydrogel implants

The ability to repair critical‐sized long‐bone injuries using growth factor and cell delivery was investigated using hydrogel biomaterials. Physiological doses of the recombinant human bone morphogenic protein‐2 (rhBMP2) were delivered in a sustained manner from a biodegradable hydrogel containing peripheral human blood‐derived endothelial progenitor cells (hEPCs). The biodegradable implants made from polyethylene glycol (PEG) and denatured fibrinogen (PEG‐fibrinogen, PF) were loaded with 7.7 μg/ml of rhBMP2 and 2.5 × 10⁶ cells/ml hEPCs. The safety and efficacy of the implant were tested in a rodent model of a critical‐size long‐bone defect. The hydrogel implants were formed ex‐situ and placed into defects in the tibia of athymic nude rats and analyzed for bone repair after 13 weeks following surgery. The hydrogels containing a combination of 7.7 μg/ml of rhBMP2 and 2.5 × 10⁶ cells/ml hEPCs were compared to control hydrogels containing 7.7 μg/ml of rhBMP2 only, 2.5 × 10⁶ cells/ml hEPCs only, or bare hydrogels. Assessments of bone repair include histological analysis, bone formation at the site of implantation using quantitative microCT, and assessment of implant degradation. New bone formation was detected in all treated animals, with the highest amounts found in the treatments that included animals that combined the PF implant with rhBMP2. Moreover, statistically significant increases in the tissue mineral density (TMD), trabecular number and trabecular thickness were observed in defects treated with rhBMP2 compared to non‐rhBMP2 defects. New bone formation was significantly higher in the hEPC‐treated defects compared to bare hydrogel defects, but there were no significant differences in new bone formation, trabecular number, trabecular thickness or TMD at 13 weeks when comparing the rhBMP2 + hEPCs‐treated defects to rhBMP2‐treated defects. The study concludes that the bone regeneration using hydrogel implants containing hEPCs are overshadowed by enhanced osteogenesis associated with sustained delivery of rhBMP2.

Local delivery of hydrogel encapsulated vascular endothelial growth factor for the prevention of medication-related osteonecrosis of the jaw

The anti-angiogenic effects of bisphosphonates have been hypothesized as one of the major etiologic factors in the development of medication-related osteonecrosis of the jaw (MRONJ), a severe debilitating condition with limited treatment options. This study evaluated the potential of a gelatine-hyaluronic acid hydrogel loaded with the angiogenic growth factor, vascular endothelial growth factor (VEGF), as a local delivery system to aid in maintaining vascularization in a bisphosphonate-treated (Zoledronic Acid) rodent maxillary extraction defect. Healing was assessed four weeks after implantation of the VEGF-hydrogel into extraction sockets. Gross examination and histological assessment showed that total osteonecrosis and inflammatory infiltrate was significantly reduced in the presence of VEGF. Also, total vascularity and specifically neovascularization, was significantly improved in animals that received VEGF hydrogel. Gene expression of vascular, inflammatory and bone specific markers within the defect area were also significantly altered in the presence of VEGF. Furthermore, plasma cytokine levels were assessed to determine the systemic effect of locally delivered VEGF and showed similar outcomes. In conclusion, the use of locally delivered VEGF within healing extraction sockets assists bone healing and prevents MRONJ via a pro-angiogenic and immunomodulatory mechanism.

The Influence of Hyaluronic Acid Biofunctionalization of a Bovine Bone Substitute on Osteoblast Activity In Vitro

Bovine bone substitute materials (BSMs) are used for oral bone regeneration. The objective was to analyze the influence of BSM biofunctionalization via hyaluronic acid (HA) on human osteoblasts (HOBs). BSMs with ± HA were incubated with HOBs including HOBs alone as a negative control. On days 3, 7 and 10, cell viability, migration and proliferation were analyzed by fluorescence staining, scratch wound assay and MTT assay. On days 3, 7 and 10, an increased cell viability was demonstrated for BSM+ compared with BSM- and the control (each p ≤ 0.05). The cell migration was enhanced for BSM+ compared with BSM- and the control after day 3 and day 7 (each p ≤ 0.05). At day 10, an accelerated wound closure was found for the control compared with BSM+/- (each p < 0.05). The highest proliferation rate was observed for BSM+ on day 3 (p ≤ 0.05) followed by BSM- and the control (each p ≤ 0.05). At day 7, a non-significantly increased proliferation was shown for BSM+ while the control was higher than BSM- (each p < 0.05). The least proliferation activity was observed for BSM- (p < 0.05) at day 10. HA biofunctionalization of the BSMs caused an increased HOB activity and might represent a promising alternative to BSM- in oral bone regeneration.

Controllable multi-phase protein release from in-situ hydrolyzable hydrogel

Using hydrogels to control the long-term release of protein remains challenging, especially for in-situ forming formulations. The uncontrollable burst release in the initial phase, the halted release in the subsequent phase, and the undesired drug dumping at the late stage are some obstacles hydrogel-based depots commonly encounter. In this study, we report hydrolyzable dextran-based hydrogels crosslinked by Michael addition to demonstrate a systematic solution to solve these problems. First, the polymer concentration was used as the critical parameter to control the proportion of releasable versus physically trapped protein molecules in the initial hydrogel meshwork. Subsequently, the dynamic change of the hydrogel meshwork was modulated by the crosslinking density and the cleavage rate of ester linkers. To this end, we designed and synthesized a series of ester linkers with hydrolytic half-life ranging from 4 h to 4 months and incorporate them into the hydrogel. Controlled release was demonstrated for model proteins varied in size, including lysozyme (14 kDa), bovine serum albumin (66 kDa), immunoglobulin G (150 kDa), and bevacizumab (149 kDa). In particular, sustained release of IgG ranging from 10 days to 8 months was achieved. Lastly, a tunable multi-phase release profile was made feasible by incorporating multiple ester linkers into one hydrogel formulation. The linker's half-life determined each phase's release duration, and the linkers' mixing ratio determined the corresponding release fraction. The reported hydrogel design engenders a versatile platform to address the needs for long-term and readily adjustable protein release for biomedical applications.

Synergistic effect between 2-N,6-O-sulfonated chitosan and bone morphogenetic protein-2

The molecular structure of sulfonated chitosan is similar to heparin, and it has been proved to have some heparin functions. Studies have shown that heparin and bone morphogenetic protein-2 (BMP-2) have synergistic effects, but heparin has limitations in clinical application. In this paper, the synergistic effect of 2-N,6-O-sulfonated chitosan (26SCS) and BMP-2 was studied. The preparation of 26SCS was explored and 26SCS was co-cultured with bone marrow mesenchymal stem cells (BMSCs) to study the effects of 26SCS on the proliferation, adhesion behavior and osteogenic differentiation of BMSCs. The synergistic mechanism of 26SCS and BMP-2 was explored by circular dichroism and isothermal calorimetric titration. The results showed that 26SCS affected the secondary structure of BMP-2 protein, mainly caused the significant change of antiparallel conformation in β-fold, and then improved the biological activity of BMP-2 and showed a dose-dependent manner. 26SCS was expected to be a synergistic factor of BMP-2.

Hyaluronic acid as a bioactive component for bone tissue regeneration: Fabrication, modification, properties, and biological functions

Hyaluronic acid (HA) is widely distributed in the human body, and it is heavily involved in many physiological functions such as tissue hydration, wound repair, and cell migration. In recent years, HA and its derivatives have been widely used as advanced bioactive polymers for bone regeneration. Many medical products containing HA have been developed because this natural polymer has been proven to be nontoxic, noninflammatory, biodegradable, and biocompatible. Moreover, HA-based composite scaffolds have shown good potential for promoting osteogenesis and mineralization. Recently, many HA-based biomaterials have been fabricated for bone regeneration by combining with electrospinning and 3D printing technology. In this review, the polymer structures, processing, properties, and applications in bone tissue engineering are summarized. The challenges and prospects of HA polymers are also discussed.

Hyaluronic Acid and Controlled Release: A Review

Hyaluronic acid (HA) also known as hyaluronan, is a natural polysaccharide—an anionic, non-sulfated glycosaminoglycan—commonly found in our bodies. It occurs in the highest concentrations in the eyes and joints. Today HA is used during certain eye surgeries and in the treatment of dry eye disease. It is a remarkable natural lubricant that can be injected into the knee for patients with knee osteoarthritis. HA has also excellent gelling properties due to its capability to bind water very quickly. As such, it is one the most attractive controlled drug release matrices and as such, it is frequently used in various biomedical applications. Due to its reactivity, HA can be cross-linked or conjugated with assorted bio-macromolecules and it can effectively encapsulate several different types of drugs, even at nanoscale. Moreover, the physiological significance of the interactions between HA and its main membrane receptor, CD44 (a cell-surface glycoprotein that modulates cell–cell interactions, cell adhesion and migration), in pathological processes, e.g., cancer, is well recognized and this has resulted in an extensive amount of studies on cancer drug delivery and tumor targeting. HA acts as a therapeutic but also as a tunable matrix for drug release. Thus, this review focuses on controlled or sustained drug release systems assembled from HA and its derivatives. More specifically, recent advances in controlled release of proteins, antiseptics, antibiotics and cancer targeting drugs from HA and its derivatives were reviewed. It was shown that controlled release from HA has many benefits such as optimum drug concentration maintenance, enhanced therapeutic effects, improved efficiency of treatment with less drug, very low or insignificant toxicity and prolonged in vivo release rates.

Heparin-based hydrogel scaffolding alters the transcriptomic profile and increases the chemoresistance of MDA-MB-231 triple-negative breast cancer cells

The tumor microenvironment plays a critical role in the proliferation and chemoresistance of cancer cells. Growth factors (GFs) are known to interact with the extracellular matrix (ECM) via heparin binding sites, and these associations influence cell behavior. In the present study, we demonstrate the ability to define signals presented by the scaffold by pre-mixing growth factors, such as epidermal growth factor, into the heparin-based (HP-B) hydrogel prior to gelation. In the 3D biomimetic microenvironment, breast cancer cells formed spheroids within 24 hours of initial seeding. Despite higher number of proliferating cells in 2D cultures, 3D spheroids exhibited a higher degree of chemoresistance after 72 hours. Further, our RNA sequencing results highlighted the phenotypic changes influenced by solid-phase GF presentation. Wnt/β-catenin and TGF-β signaling were upregulated in the cells grown in the hydrogel, while apoptosis, IL2-STAT5 and PI3K-AKT-mTOR signaling were downregulated. With emerging technologies for precision medicine in cancer, this nature of fine-tuning the microenvironment is paramount for cultivation and downstream characterization of primary cancer cells and rare circulating tumor cells (CTCs), and effective screening of chemotherapeutic agents.

Heparin-hyaluronic acid nanofibers for growth factor sequestration in spinal cord repair

Growth factor (GF) delivery is a common strategy for spinal cord injury repair, however, GF degradation can impede long-term therapies. GF sequestration via heparin is known to protect bioactivity after delivery. We tested two heparin modifications, methacrylated heparin and thiolated heparin, and electrospun these with methacrylated hyaluronic acid (MeHA) to form HepMAHA and HepSHHA nanofibers. For loaded conditions, MeHA, HepMAHA, and HepSHHA fibers were incubated with soluble basic fibroblast growth factor (bFGF) or nerve growth factor (NGF) and rinsed with PBS. Control groups were hydrated in PBS. L929 fibroblast proliferation was analyzed after 24 hr of culture in either growth media or bFGF-supplemented media. Dissociated chick dorsal root ganglia neurites were measured after 3 days of cell culture in serum free media (SFM) or NGF-supplemented SFM (SFM + NGF). In growth media, fibroblast proliferation was significantly increased in loaded HepMAHA (α < .05) compared to other groups. In SFM, loaded HepMAHA had the longest average neurite length compared to all other groups. In SFM + NGF, HepMAHA and HepSHHA had increased neurite lengths compared to MeHA, regardless of loading (α < .01), suggesting active sequestration of soluble NGF. HepMAHA is a promising biomaterial for sequestering released GFs in a spinal cord injury environment and will be combined with GF filled microspheres for future studies.

Chemokine releasing particle implants for trapping circulating prostate cancer cells

Prostate cancer (PCa) is the most prevalent cancer in U.S. men and many other countries. Although primary PCa can be controlled with surgery or radiation, treatment options of preventing metastatic PCa are still limited. To develop a new treatment of eradicating metastatic PCa, we have created an injectable cancer trap that can actively recruit cancer cells in bloodstream. The cancer trap is composed of hyaluronic acid microparticles that have good cell and tissue compatibility and can extend the release of chemokines to 4 days in vitro. We find that erythropoietin (EPO) and stromal derived factor-1α can attract PCa in vitro. Animal results show that EPO-releasing cancer trap attracted large number of circulating PCa and significantly reduced cancer spreading to other organs compared with controls. These results support that cancer trap may serve as a unique device to sequester circulating PCa cells and subsequently reduce distant metastasis.

Recruitment of endogenous progenitor cells by erythropoietin loaded particles for in situ cartilage regeneration

Cartilage injury affects millions of people throughout the world, and at this time there is no cure. While transplantation of stem cells has shown some success in the treatment of injured cartilage, such treatment is limited by limited cell sources and safety concerns. To overcome these drawbacks, a microscaffolds system was developed capable of targeting, reducing the inflammatory response and recruiting endogenous progenitor cells to cartilage-defect. Erythropoietin (EPO)-loaded-hyaluronic acid (HA) microscaffolds (HA + EPO) were fabricated and characterized. HA-microscaffolds showed good cell-compatibility and could target chondrocytes via CD44 receptors. HA + EPO was designed to slowly release EPO while recruiting progenitor cells. Finally, the ability of HA + EPO to repair cartilage-defects was assessed using a rabbit model of full-thickness cartilage-defect. Our results showed that the intra-articular administration of EPO, HA, and EPO + HA reduced the number of inflammatory cells inside the synovial-fluid, while EPO + HA had the greatest anti-inflammatory effects. Furthermore, among all groups, EPO + HA achieved the greatest progenitor cell recruitment and subsequent chondrogenesis. The results of this work support that, by targeting and localizing the release of growth-factors, HA + EPO can reduce inflammatory responses and promote progenitor cells responses. This new platform represents an alternative treatment to stem-cell transplantation for the treatment of cartilage injury.

Vital Pulp Therapy an Insight Over the Available Literature and Future Expectations

Vital pulp therapy (VPT) defined as “treatment which aims at preserving and maintaining the pulp tissue that has been compromised but not destroyed by extensive dental caries, dental trauma, and restorative procedures or for iatrogenic reasons”, offers some beneficial advantages over the conventional root canal treatment such as protective resistance for mastication forces or to prevent the loss of environmental changes sensation ability, which can lead to unnoticeable progression of caries and later fracture. A wide range of materials are suggested in the literature to be used as pulp capping protective dressing materials that varies from ready-made synthetic materials to biological based scaffolds and composites. The aim of the present review is to provide a full understanding of currently used materials to clinicians in order to help in their decision-making process delivering the best available evidence-based treatments to their patients. An extensive search for recent available data regarding direct pulp capping materials and potential suggestions for future use have been made. Newly developed biological based scaffolds showed promising results in dentine regeneration therefore strengthening the tooth structure and overcoming potential drawbacks of use of currently available recommended materials.

Proteins, peptides and peptidomimetics as active agents in implant surface functionalization

The recent impact of implants on improving the human life quality has been enormous. During the past two decades we witnessed major advancements in both material and structural development of implants. They were driven mainly by the increasing patients' demand and the need to address the major issues that come along with the initially underestimated complexity of the bone-implant interface. While both, the materials and design of implants reached a certain, balanced state, recent years brought a shift in focus towards the bone-implant interface as the weakest link in the increasing implant long-term usability. As a result, several approaches were developed. They aimed at influencing and enhancing the implant osseointegration and its proper behavior when under load and stress. With this review, we would like to discuss the recent advancements in the field of implant surface modifications, emphasizing the importance of chemical methods, focusing on proteins, peptides and peptidomimetics as promising agents for titanium surface coatings.

Osteogenic and Chondrogenic Potential of the Supramolecular Aggregate T-LysYal®

Hard tissue regeneration represents a challenge for the Regenerative Medicine and Mesenchymal stem cells (MSCs) could be a successful therapeutic strategy. T-LysYal® (T-Lys), a new derivative of Hyaluronic Acid (HA) possessing a superior stability, has already been proved efficient in repairing corneal epithelial cells damaged by dry conditions in vitro. We investigated the regenerative potential of T-Lys in the hard tissues bone and cartilage. We have previously demonstrated that cells isolated from the tooth germ, Dental Bud Stem Cells (DBSCs), differentiate into osteoblast-like cells, representing a promising source of MSCs for bone regeneration. Herewith, we show that T-Lys treatment stimulates the expression of typical osteoblastic markers, such as Runx-2, Collagen I (Col1) and Alkaline Phosphatase (ALP), determining a higher production of mineralized matrix nodules. In addition, we found that T-Lys treatment positively affects α_Vβ₃ integrin expression, key integrin in the osteoblastic commitment, leading to the formation of focal adhesions (FAs). The efficacy of T-Lys was also tested on chondrogenic differentiation starting from human articular chondrocytes (HACs) resulting in an increase of differentiation markers and cell number.

The application of hyaluronic acid in bone regeneration

Hyaluronic acid (HA) exists naturally as an important component of the extracellular matrix (ECM) in the human body. In recent decades, HA has been widely used in bone regeneration, and is currently a popular topic, particularly in the craniofacial and dental fields. From maxilla augmentation to craniofacial bone trauma, there is now a large demand for bone regenerative therapy. Serving as a cell-seeding scaffold or a carrier for bioactive components, hyaluronic acid-incorporated scaffolds and carriers in bone regeneration can be fabricated into either rigid or colloidal forms. Since the type of material used is a critical factor in the biological properties of a scaffold, HA derivatives or HA-incorporated composite scaffolds have shown excellent potential for improving osteogenesis and mineralization. Furthermore, in order to better enhance osteogenesis, local delivery carriers based on hyaluronic acid derivatives, rather than specifically serving as scaffolds, can be established by loading different osteoinductive or osteogenetic components and acquiring different release patterns. Such osteoinductive carriers immobilized on implant surfaces are also effective in improving osseointegration. Thus, as such a competent biomaterial, hyaluronic acid should be considered a promising tool in bone regeneration.

Developing hyaluronic acid microgels for sustained delivery of platelet lysate for tissue engineering applications

Platelet lysate (PL), a blood product that contains high concentrations of growth factors (GFs), can be considered as a cost-effective source of multiple GFs. In this study, hyaluronic acid (HA) based microgels were developed for delivery of PL proteins. Spherical microgel were prepared using a water in oil emulsion method. First, hyaluronic acid was grafted with tyramine groups, after which prepared microdroplets were crosslinked via an enzymatic reaction in the presence of hydrogen peroxide and horseradish peroxidase. Because of electrostatic interactions, these microgels are promising carriers for positively charged proteins entrapment like most of the GFs. When microgels are incubated in PL solution, protein loading takes place which is mainly governed by nonspecific adsorption of plasma proteins. Although this hampered loading efficiency, loading could be increased by repeated washing and incubation steps. The loaded microgels presented a sustained release of PL growth factors for a period of two weeks. When PL enriched microgels were embedded in a HA bulk hydrogel, cell proliferation was higher compared to constructs without microgels. These findings suggest that the developed microgels are a potential candidate for sustained delivery of PL growth factors and present a solution to the issue of their short half-lives in vivo.

Growth Factor Delivery for the Repair of a Critical Size Tibia Defect Using an Acellular, Biodegradable Polyethylene Glycol-Albumin Hydrogel Implant

Growth factor delivery using acellular matrices presents a promising alternative to current treatment options for bone repair in critical-size injuries. However, supra-physiological doses of the factors can introduce safety concerns that must be alleviated, mainly by sustaining delivery of smaller doses using the matrix as a depot. We developed an acellular, biodegradable hydrogel implant composed of poly(ethylene glycol) (PEG) and denatured albumin to be used for sustained delivery of bone morphogenic protein-2 (BMP2). In this study, poly(ethylene glycol)-albumin (PEG-Alb) hydrogels were produced and loaded with 7.7 μg/mL of recombinant human BMP2 (rhBMP2) to be tested for safety and performance in a critical-size long-bone defect, using a rodent model. The hydrogels were formed ex situ in a 5 mm long cylindrical mold of 3 mm diameter, implanted into defects made in the tibia of Sprague-Dawley rats and compared to non-rhBMP2 control hydrogels at 13 weeks following surgery. The hydrogels were also compared to the more established PEG-fibrinogen (PEG-Fib) hydrogels we have tested previously. Comprehensive in vitro characterization as well as in vivo assessments that include: histological analyses, including safety parameters (i.e., local tolerance and toxicity), assessment of implant degradation, bone formation, as well as repair tissue density using quantitative microCT analysis were performed. The in vitro assessments demonstrated similarities between the mechanical and release properties of the PEG-Alb hydrogels to those of the PEG-Fib hydrogels. Safety analysis presented good local tolerance in the bone defects and no signs of toxicity. A significantly larger amount of bone was detected at 13 weeks in the rhBMP2-treated defects as compared to non-rhBMP2 defects. However, no significant differences were noted in bone formation at 13 weeks when comparing the PEG-Alb-treated defects to PEG-Fib-treated defects (with or without BMP2). The study concludes that hydrogel scaffolds made from PEG-Alb containing 7.7 μg/mL of rhBMP2 are effective in accelerating the bridging of boney defects in the tibia.

The effect of hyaluronic acid hydrogels on dental pulp stem cells behavior

Dental caries and trauma, particularly in childhood, are among the most prevalent teeth problems, which result in the creation of cavities and probably tooth loss. Thus, novel regenerative approaches with high efficiency and less toxicity are required. Stem cell therapy along with the implementation of scaffolds has provided excellent opportunities in the regeneration of teeth structure. Hyaluronic acid (HA) hydrogels have enticed great attention in the field of regenerative medicine. The unique chemical and structural properties of HA and its derivatives have enabled their application in tissue engineering. Several factors such as the location and type of the lesion, teeth age, the type of capping materials determine the success rate of pulp therapy. HA hydrogels have been considered as biocompatible and safe scaffold supports in human dental cell therapies.

Biomaterial-assisted local and systemic delivery of bioactive agents for bone repair

Although bone tissues possess an intrinsic capacity for repair, there are cases where bone healing is either impaired or insufficient, such as fracture non-union, osteoporosis, osteomyelitis, and cancers. In these cases, treatments like surgical interventions are used, either alone or in combination with bioactive agents, to promote tissue repair and manage associated clinical complications. Improving the efficacy of bioactive agents often requires carriers, with biomaterials being a pivotal player. In this review, we discuss the role of biomaterials in realizing the local and systemic delivery of biomolecules to the bone tissue. The versatility of biomaterials enables design of carriers with the desired loading efficiency, release profile, and on-demand delivery. Besides local administration, systemic administration of drugs is necessary to combat diseases like osteoporosis, warranting bone-targeting drug delivery systems. Thus, chemical moieties with the affinity towards bone extracellular matrix components like apatite minerals have been widely utilized to create bone-targeting carriers with better biodistribution, which cannot be achieved by the drugs alone. Bone-targeting carriers combined with the desired drugs or bioactive agents have been extensively investigated to enhance bone healing while minimizing off-target effects. Herein, these advancements in the field have been systematically reviewed. STATEMENT OF SIGNIFICANCE: Drug delivery is imperative when surgical interventions are not sufficient to address various bone diseases/defects. Biomaterial-assisted delivery systems have been designed to provide drugs with the desired loading efficiency, sustained release, and on-demand delivery to enhance bone healing. By surveying recent advances in the field, this review outlines the design of biomaterials as carriers for the local and systemic delivery of bioactive agents to the bone tissue. Particularly, biomaterials that bear chemical moieties with affinity to bone are attractive, as they can present the desired bioactive agents to the bone tissue efficiently and thus enhance the drug efficacy for bone repair.

Sulfated polysaccharide-based scaffolds for orthopaedic tissue engineering

Given their native-like biological properties, high growth factor retention capacity and porous nature, sulfated-polysaccharide-based scaffolds hold great promise for a number of tissue engineering applications. Specifically, as they mimic important properties of tissues such as bone and cartilage they are ideal for orthopaedic tissue engineering. Their biomimicry properties encompass important cell-binding motifs, native-like mechanical properties, designated sites for bone mineralisation and strong growth factor binding and signaling capacity. Even so, scientists in the field have just recently begun to utilise them as building blocks for tissue engineering scaffolds. Most of these efforts have so far been directed towards in vitro studies, and for these reasons the clinical gap is still substantial. With this review paper, we have tried to highlight some of the important chemical, physical and biological features of sulfated-polysaccharides in relation to their chondrogenic and osteogenic inducing capacity. Additionally, their usage in various in vivo model systems is discussed. The clinical studies reviewed herein paint a promising picture heralding a brave new world for orthopaedic tissue engineering.

Controlled Release Strategies for the Combination of Fresh and Lyophilized Platelet-Rich Fibrin on Bone Tissue Regeneration

The aim of the present study was to investigate growth factors release kinetics for the combination of fresh platelet-rich fibrin (F-PRF) and lyophilized PRF (L-PRF) with different ratios to promote bone tissue regeneration. First, we quantified the level of transforming growth factor-β1 (TGF-β1), vascular endothelial growth factor (VEGF), and platelet-derived growth factor-AB (PDGF-AB) in vitro and analyzed their release kinetics from F-PRF, L-PRF, and the fresh/lyophilized PRF in different weight ratios (F:L=1:1, 1:3, 1:5). The second experimental phase was to investigate the proliferation and differentiation of bone mesenchymal stem cells (BMSCs) as a functional response to the factors released. To further test the osteogenic potential in vivo, different scaffolds (F-PRF, or L-PRF, or F:L=1:1) were implanted in rabbit cranial bone defects. There was a statistically significant increase in proliferation and differentiation of BMSCs when the culture medium contained different PRF exudates collected at day 14 compared with the negative control group. The results showed that the new bone formation in the fresh/lyophilized PRF (1:1) was much more than that of other groups in defects at both 6 and 12 weeks. Our data suggested growth factor concentration and release kinetics as a consequence of fresh and lyophilized PRF combination, which is an effective way for promoting bone regeneration.

Efficient Synthesis of Heparinoid Bioconjugates for Tailoring FGF2 Activity at the Stem Cell-Matrix Interface

Heparan sulfate glycosaminoglycans (HS GAGs) attached to proteoglycans harbor high affinity binding sites for various growth factors (GFs) and direct their organization and activity across the cell-matrix interface. Here, we describe a mild and efficient method for generating HS-protein conjugates. The two-step process utilizes a "copper-free click" coupling between differentially sulfated heparinoids primed at their reducing end with an azide handle and a bovine serum albumin protein modified with complementary cyclooctyne functionality. When adsorbed on tissue culture substrates, the glycoconjugates served as extracellular matrix proteoglycan models with the ability to sequester FGF2 and influence mesenchymal stem cell proliferation based on the structure of their HS GAG component.

Carbon nanotubes as electrophysiological building blocks for a bioactive cell scaffold through biological assembly to induce osteogenesis

Bio-functional cell scaffolds have great potential in the field of tissue regenerative medicine. In this work, a carbon nanotube (CNT) gel scaffold via specific pairing of functionalized nucleobases was developed for specifically targeted drug delivery and in vitro osteogenesis. The CNT gel scaffold with nano-fibrous architectures was established by Watson–Crick base pairing between thymine and adenine of low molecular weight heparin, respectively. As scaffold precursors, adenine and thymine functionalized heparin derivatives could additionally bind cell growth factors by the affinity interaction. The resulting nano-fibrous gel scaffolds showed excellent mechanical integrity and advanced electro-physiological functions. Potential application of the electrophysiological CNT gel scaffold in bone tissue engineering was confirmed by encapsulation of human adipose-derived stem cells (ASCs). Our results indicate that the electrically conductive networks formed by CNTs within the nano-fibrous framework are the key characteristics of cell scaffolds leading to improved ASC organization and differentiation by an extra electrical stimulus (ES). Specifically, ASCs cultured in bio-electrical gel scaffolds showed ∼4 times higher spontaneous osteogenesis in combination with bone morphogenetic protein 2 (BMP-2), compared to those cultured on pristine hydrogels. This electrophysiological CNT gel scaffold containing BMP-2 exhibited beneficial effects on ASC activity and osteogenetic differentiation, which suggested a promising future for local treatment of bone regeneration.

Bio-functional cell scaffolds have great potential in the field of tissue regenerative medicine.

Enhancing chondrogenesis and mechanical strength retention in physiologically relevant hydrogels with incorporation of hyaluronic acid and direct loading of TGF-β

Cell-loaded hydrogels are frequently applied in cartilage tissue engineering for their biocompatibility, ease of application, and ability to conform to various defect sites. As a bioactive adjunct to the biomaterial, transforming growth factor beta (TGF-β) has been shown to be essential for cell differentiation into a chondrocyte phenotype and maintenance thereof, but the low amounts of endogenous TGF-β in the in vivo joint microenvironment necessitate a mechanism for controlled delivery and release of this growth factor. In this study, TGF-β3 was directly loaded with human bone marrow-derived mesenchymal stem cells (MSCs) into poly-d,l-lactic acid/polyethylene glycol/poly-d,l-lactic acid (PDLLA-PEG) hydrogel, or PDLLA-PEG with the addition of hyaluronic acid (PDLLA/HA), and cultured in vitro. We hypothesize that the inclusion of HA within PDLLA-PEG would result in a controlled release of the loaded TGF-β3 and lead to a robust cartilage formation without the use of TGF-β3 in the culture medium. ELISA analysis showed that TGF-β3 release was effectively slowed by HA incorporation, and retention of TGF-β3 in the PDLLA/HA scaffold was detected by immunohistochemistry for up to 3 weeks. By means of both in vitro culture and in vivo implantation, we found that sulfated glycosaminoglycan production was higher in PDLLA/HA groups with homogenous distribution throughout the scaffold than PDLLA groups. Finally, with an optimal loading of TGF-β3 at 10 μg/mL, as determined by RT-PCR and glycosaminoglycan production, an almost twofold increase in Young's modulus of the construct was seen over a 4-week period compared to TGF-β3 delivery in the culture medium. Taken together, our results indicate that the direct loading of TGF-β3 and stem cells in PDLLA/HA has the potential to be a one-step point-of-care treatment for cartilage injury. STATEMENT OF SIGNIFICANCE: Stem cell-seeded hydrogels are commonly used in cell-based cartilage tissue engineering, but they generally fail to possess physiologically relevant mechanical properties suitable for loading. Moreover, degradation of the hydrogel in vivo with time further decreases mechanical suitability of the hydrogel due in part to the lack of TGF-β3 signaling. In this study, we demonstrated that incorporation of hyaluronic acid (HA) into a physiologically stiff PDLLA-PEG hydrogel allowed for slow release of one-time preloaded TGF-β3, and when loaded with adult mesenchymal stem cells and cultured in vitro, it resulted in higher chondrogenic gene expression and constructs of significantly higher mechanical strength than constructs cultured in conventional TGF-β3-supplemented medium. Similar effects were also observed in constructs implanted in vivo. Our results indicate that direct loading of TGF-β3 combined with HA in the physiologically stiff PDLLA-PEG hydrogel has the potential to be used for one-step point-of-care treatment of cartilage injury.

Nanoparticle-modified chitosan-agarose-gelatin scaffold for sustained release of SDF-1 and BMP-2

Background

Stromal cell-derived factor 1 (SDF-1) is an important chemokine for stem cell mobilization, and plays a critical role in mobilization of mesenchymal stem cells (MSCs). Bone morphogenetic protein 2 (BMP-2) plays a critical role in osteogenesis of MSCs. However, the use of SDF-1 and BMP-2 in bone tissue engineering is limited by their short half-lives and rapid degradation in vitro and in vivo.

Methods

The chitosan oligosaccharide/heparin nanoparticles (CSO/H NPs) were first prepared via self-assembly. Chitosan-agarose-gelatin (CAG) Scaffolds were then synthesized via gelation technology using cross-linked chitosan, agarose, and gelatin, and were modified by CSO/H NPs. The encapsulation efficiency and release kinetics of SDF-1 and BMP-2 were quantified using an enzyme-linked immunosorbent assay. A CCK-8 assays were used to evaluate biocompatibility of NP-modified scaffolds. The biological activity of the loaded SDF-1 and BMP-2 was evaluated using the transwell migration assay and osteogenic induction assay. An animal MSC recruitment model was used to study the ability of SDF-1 released from NP-modified scaffolds to induce migration of MSCs.

Results

In this study, we developed a novel nanoparticle-modified CAG scaffold for the delivery of SDF-1 and BMP-2. CCK-8 assays demonstrated excellent biocompatibility of NP-modified scaffolds. In addition, we investigated the release of SDF-1 and BMP-2 from NP-modified scaffolds, and evaluated the effect of released SDF-1 on MSC migration. The effect of released BMP-2 on MSC osteogenesis was also examined. In vitro cell migration assays showed that SDF-1 released from NP-modified scaffolds retained its migration activity; osteogenesis studies demonstrated that released BMP-2 exhibited a strong ability to induce differentiation towards osteoblasts. Our in vivo recruitment assays showed continuous chemotactic response of MSCs to SDF-1 released from the NP-modified scaffold.

Conclusion

The simplicity of synthesizing CSO/H NP-modified CAG scaffolds, combined with its high cytokine loading capacity and sustained release effect, renders NP-modified CAG scaffold an attractive candidate for sustained release of SDF-1 and BMP-2 to promote bone repair and regeneration.

Sustained Protein Release from a Core-Shell Drug Carrier System Comprised of Mesoporous Nanoparticles and an Injectable Hydrogel

The manufacture of a biocompatible carrier for controlled delivery of bioactive compounds is described. This carrier is composed of a mesoporous silica nanoparticle as core that is homogenously distributed in an injectable hydrogel. For the synthesis of nanoparticles, a one step sol-gel method is developed to produce pores with the range of 100 nm. BMP2 and Fluorescein-conjugated bovine serum albumin is used as proteinaceous agents for measuring release, and is loaded into mesoporous silica nanoparticles at the optimum conditions of 48 h incubation period using 1:10 ratio of protein to nanoparticles. The release of proteins from either mesoporous nanoparticles or hydrogel individually involves a burst release stage, however the release from the core/shell carrier designed in this study follows a zero order kinetic. In summary, this biomaterial may be favorable for delivery of bioactive compounds such as BMP2 for a range of applications including bone tissue regeneration.

Native-mimicking in vitro microenvironment: an elusive and seductive future for tumor modeling and tissue engineering

Human connective tissues are complex physiological microenvironments favorable for optimal survival, function, growth, proliferation, differentiation, migration, and death of tissue cells. Mimicking native tissue microenvironment using various three-dimensional (3D) tissue culture systems in vitro has been explored for decades, with great advances being achieved recently at material, design and application levels. These achievements are based on improved understandings about the functionalities of various tissue cells, the biocompatibility and biodegradability of scaffolding materials, the biologically functional factors within native tissues, and the pathophysiological conditions of native tissue microenvironments. Here we discuss these continuously evolving physical aspects of tissue microenvironment important for human disease modeling, with a focus on tumors, as well as for tissue repair and regeneration. The combined information about human tissue spaces reflects the necessities of considerations when configuring spatial microenvironments in vitro with native fidelity to culture cells and regenerate tissues that are beyond the formats of 2D and 3D cultures. It is important to associate tissue-specific cells with specific tissues and microenvironments therein for a better understanding of human biology and disease conditions and for the development of novel approaches to treat human diseases.

Hyaluronic Acid-Based Optical Probe for the Diagnosis of Human Osteoarthritic Cartilage

Osteoarthritis is typically caused by cartilage injury, followed by localized inflammatory responses and tissue deterioration. Early treatment of osteoarthritis is often impossible due to the lack of diagnostic options. Recent studies have supported that different imaging probes can be used for arthritis detection in mice. However, none of these diagnostic tools have been tested on human articular cartilage. To fill this gap, an optical imaging probe was developed to target activated macrophages and the accumulation of imaging probes on tissue was used to assess the severity of human osteoarthritis. Methods: The probe was fabricated using hyaluronic acid (HA) particles conjugated with near-infrared dye and folic acid (FA). The ability of the FA-HA probes to detect activated macrophages and quantify cartilage injury was evaluated using a cell culture model in vitro and human osteoarthritic cartilage explants ex vivo. Results: Our cell study results supported that the FA-HA probes are cell compatible (up to 0.5mg/mL) and can detect activated macrophages in 30 minutes. Using human articular cartilage, we verified the existence of activated macrophages on osteoarthritic cartilage with highly up-regulated expression of folate receptors (~13 folds by comparison with healthy control). In addition, we found that FA-HA probes had higher binding amounts (~3 folds) to osteoarthritic tissue than healthy ones. Histological analyses confirmed that there was a strong linear relationship (R=0.933) between the fluorescent intensity of tissue-associated probe and the extent of folate receptors on osteoarthritic cartilage. Finally, the co-localization of the imaging probe, folate receptors and cartilage degeneration on the tissue sections indicated the extraordinary accuracy and efficiency of this osteoarthritis diagnostic probe. Conclusions: Our results support the probe as an effective diagnostic tool to detect the area and severity of osteoarthritic human articular cartilage.

Incorporation of BMP-2 nanoparticles on the surface of a 3D-printed hydroxyapatite scaffold using an ε-polycaprolactone polymer emulsion coating method for bone tissue engineering

Hydroxyapatite (HAp)-based three-dimensional (3D) scaffolding is an excellent method for the fabrication of complex-shaped scaffolds to reconstruct bone defects. This study aimed at improving the osteoinductivity and compressive strength of the HAp-based 3D scaffold for bone regeneration. Bone morphogenetic protein-2-loaded nanoparticles (BMP-2/NPs) were prepared by a double emulsion-solvent evaporation method and incorporated onto the surface of 3D scaffolds using ε-polycaprolactone (PCL) and NPs emulsion solution. The surface morphology of the scaffold was characterized using scanning electron microscopy and its biocompatibility and osteogenic effects evaluated in vitro using human mesenchymal stem cells. The in vivo bone regeneration efficiency was determined using a rabbit calvarial bone defect model. We obtained 3D HAp scaffolds with NPs using PCL coating process. BMP-2/NPs were uniformly distributed on the scaffold surface and BMP-2 was gradually released. Furthermore, PCL coating improved the compressive strength of the scaffold. The cell proliferation, adhesion, and osteogenic differentiation properties were improved with PCL_BMP-2/NPs coated scaffold. In vivo experiments showed that the formation of new bone was significantly higher in the PCL_BMP-2/NPs group than in the uncoated scaffold-implanted group. The coating method using PCL and NPs emulsion solutions was useful not only to incorporate BMP-2/NPs onto the surface of the scaffold, but also to improve the compressive strength, which enhanced bone regeneration.

Localized SDF-1α Delivery Increases Pro-Healing Bone Marrow-Derived Cells in the Supraspinatus Muscle Following Severe Rotator Cuff Injury

To examine how the chemotactic agent stromal cell-derived factor-1alpha (SDF-1α) modulates the unique cellular milieu within rotator cuff muscle following tendon injury, we developed an injectable, heparin-based microparticle platform to locally present SDF-1α within the supraspinatus muscle following severe rotator cuff injury. SDF-1α loaded, degradable, N-desulfated heparin-based microparticles were fabricated, injected into a rat model of severe rotator cuff injury, and were retained for up to 7 days at the site. The resultant inflammatory cell and mesenchymal stem cell populations were analyzed compared to uninjured contralateral controls and, after 7 days, the fold-change in anti-inflammatory, M2-like macrophages (CD11b+CD68+CD163+, 4.3X fold-change) and mesenchymal stem cells (CD29+CD44+CD90+, 3.0X, respectively) was significantly greater in muscles treated with SDF-1α loaded microparticles than unloaded microparticles or injury alone. Our results indicate that SDF-1α loaded microparticles may be a novel approach to shift the cellular composition within the supraspinatus muscle and create a more pro-regenerative milieu, which may provide a platform to improve muscle repair following rotator cuff injury in the future.

Dynamical release nanospheres containing cell growth factor from biopolymer hydrogel via reversible covalent conjugation

For practical adipose regeneration, the challenge is to dynamically deliver the key adipogenic insulin-like growth factors in hydrogels to induce adipogenesis. In order to achieve dynamic release, smart hydrogels to sense the change in the blood glucose concentration is required when glucose concentration increases. In this study, a heparin-based hydrogel has been developed for use in dynamic delivery of heparin nanospheres containing insulin-like growth factor. The gel scaffold was facilely prepared in physiological conditions by the formation of boronate-maltose ester cross-links between boronate and maltose groups of heparin derivatives. Due to its intrinsic glucose-sensitivity, the exposure of gel scaffold to glucose induces maltose functionalized nanospheres dissociation off hydrogel network and thereby could dynamically move into the microenvironment. The potential of the hydrogel as a cell scaffold was demonstrated by encapsulation of human adipose-derived stem cells (ASCs) within the gel matrix in vitro. Cell culture showed that this dynamic hydrogel could support survival and proliferation of ASCs. This biocompatible coupling chemistry has the advantage that it introduces no potentially cytotoxic groups into injectable gel scaffolds formed and can create a more biomimetic microenvironment for drug and cell delivery, rendering them more suitable for potential in vivo biomedical applications. All these results indicate that this biocompatible gel scaffold can render the formulation of a therapeutically effective platform for diabetes treatment and adipose regeneration.