Simple Radical Polymerization of Poly(Alginate‐Graft‐N‐Isopropylacrylamide) Injectable Thermoresponsive Hydrogel with the Potential for Localized and Sustained Delivery of Stem Cells and Bioactive Molecules

In this study, thermoresponsive copolymers that are fully injectable, biocompatible, and biodegradable and are synthesized via graft copolymerization of poly(N‐isopropylacrylamide) onto alginate using a free‐radical reaction are presented. This new synthesis method does not involve multisteps or associated toxicity issues, and has the potential to reduce scale‐up difficulties. Chemical and physical analyses verify the resultant graft copolymer structure. The lower critical solution temperature, which is a characteristic of sol–gel transition, is observed at 32 °C. The degradation properties indicate suitable degradation kinetics for drug delivery and bone tissue engineering applications. The synthesized P(Alg‐g‐NIPAAm) hydrogel is noncytotoxic with both human osteosarcoma (MG63) cells and porcine bone marrow derived mesenchymal stem cells (pBMSCs). pBMSCs encapsulated in the P(Alg‐g‐NIPAAm) hydrogel remain viable, show uniform distribution within the injected hydrogel, and undergo osteogenic and chondrogenic differentiation under appropriate culture conditions. Furthermore, for the first time, this work will explore the influence of alginate viscosity on the viscoelastic properties of the resulting copolymer hydrogels, which influences the rate of medical device formation and subsequent drug release. Together the results of this study indicate that the newly synthesized P(Alg‐g‐NIPAAm) hydrogel has potential to serve as a versatile and improved injectable platform for drug delivery and bone tissue engineering applications.     

An Injectable,Bifunctional Hydrogel with Photothermal Effects for Tumor Therapy and Bone Regeneration

Significant attention has been focused on bone tumor therapy recently. At present, the treatment in clinic typically requires surgical intervention. However, a few tumor cells remain around bone defects after surgery and subsequently proliferate within several days. Thus, fabrication of biomaterials with dual functions of tumor therapy and bone regeneration is significant. Herein, the injectable hydrogel containing cisplatin (DDP) and polydopamine‐decorated nano‐hydroxyapatite is prepared via Schiff base reaction between the aldehyde groups on oxidized sodium alginate and amino groups on chitosan. The hydrogel exhibits sustained release properties for DDP due to the immobilization of DDP via abundant functional groups on polydopamine (PDA). Additionally, given the intense absorption of PDA in the near‐infrared region, the hydrogel exhibits excellent photothermal effects when exposed to the NIR laser (808 nm). Based on the properties, the hydrogel effectively ablates tumor cells (4T1 cells) in vitro and suppresses tumor growth in vivo. Furthermore, the hydrogel promotes the adhesion and proliferation of bone mesenchymal stem cells in vitro due to the abundant functional groups on PDA and further induces bone regeneration in vivo. Therefore, the study extends research on novel biomaterials with dual functions of tumor therapy and bone regeneration.     

Precisely Controlled Delivery of Abaloparatide through Injectable Hydrogel to Promote Bone Regeneration

Side‐effects from allograft, limited bone stock, and site morbidity from autograft are the major challenges to traditional bone defect treatments. With the advance of tissue engineering, hydrogel injection therapy is introduced as an alternative treatment. Therapeutic drugs and growth factors can be carried by hydrogels and delivered to patients. Abaloparatide, as an analog of human recombinant parathyroid hormone protein (PTHrp) and an alternative to teriparatide, has been considered as a drug for treating postmenopausal osteoporosis since 2017. Since only limited cases of receiving abaloparatide with polymeric scaffolds have been reported, the effects of abaloparatide on pre‐osteoblast MC3T3‐E1 are investigated in this study. It is found that in vitro abaloparatide treatment can promote pre‐osteoblast MC3T3‐E1 cells’ viability, differentiation, and mineralization significantly. For the drug delivery system, 3D porous structure of the methacrylated gelatin (GelMA) hydrogel is found effective for prolonging the release of abaloparatide (more than 10 days). Therefore, injectable photo‐crosslinked GelMA hydrogel is used in this study to prolong the release of abaloparatide and to promote healing of defected bones in rats. Overall, data collected in this study show no contradiction and imply that Abaloparatide‐loaded GelMA hydrogel is effective in stimulating bone regeneration.     

Drug‐Loaded Elastin‐Like Polypeptide–Collagen Hydrogels with High Modulus for Bone Tissue Engineering

Emphasizing the role of hydrogel stiffness and cellular differentiation, this study develops collagen and elastin‐like polypeptide (ELP)–based bone regenerative hydrogels loaded with recombinant human bone morphogenetic protein‐2 (rhBMP‐2) and doxycycline with mechanical properties suitable for osteogenesis. The drug‐incorporated collagen–ELP hydrogels has significantly higher modulus of 35 ± 5 kPa compared to collagen‐only hydrogels. Doxycycline shows a bi‐phasic release with an initial burst release followed by a gradual release, while rhBMP‐2 exhibits a nearly linear release profile for all hydrogels. The released doxycycline shows anti‐microbial activity against Pseudomonas aeruginosa, Streptococcus sanguinis, and Escherichia coli. Microscopic observation of the hydrogels reveals their interconnected, macroporous, 3D open architecture with pore diameters between 160 and 400 µm. This architecture supports human adipose–derived stem cell attachment and proliferation from initial days of cell seeding, forming a thick cellular sheath by day 21. Interestingly, in collagen and collagen–ELP hydrogels, cell morphology is elongated with stretched slender lamellipodial formation, while cells assemble as spheroidal aggregates in crosslinked as well as drug‐loaded hydrogels. Osteogenic markers, alkaline phosphatase and osteocalcin, are expressed maximally for drug‐loaded hydrogels compared to those without drugs. The drug‐loaded collagen–ELP hydrogels are thus promising for combating bacterial infection and promoting guided bone regeneration.     

Decellularized Periosteum‐Covered Chitosan Globule Composite for Bone Regeneration in Rabbit Femur Condyle Bone Defects

Critical‐sized bone defects are incapable of self‐healing and are commonly seen in clinical practice. The authors explore a new treatment for this, decellularized periosteum is applied to chitosan globules (chitosan‐DP globules) as a hybrid material. The efficacy of chitosan‐DP globules on rabbit femoral condyle bone defects is assessed with biocompatibility, biomechanics, and osteogenic efficiency measurements, and compared with the results of chitosan globules and empty control. No difference in cytotoxicity is observed among chitosan‐DP globules, chitosan globules, and the empty control. Chitosan‐DP globules possesse a better surface for cell adhesion than did chitosan globules. Chitosan‐DP globules demonstrate superior efficiency for osteogenesis in the defect area compared to chitosan globules as per microcomputed tomography examination and push‐out testing, with relatively minor histological differences. Both chitosan globule groups show more satisfactory results than those for the empty control. The results implicate chitosan‐DP globules as a promising solution for bone defects.     

A General Strategy for Targeting Drugs to Bone

Targeting drugs to their desired site of action can increase their safety and efficacy. Bisphosphonates are prototypical examples of drugs targeted to bone. However, bisphosphonate bone affinity is often considered too strong and cannot be significantly modulated without losing activity on the enzymatic target, farnesyl pyrophosphate synthase (FPPS). Furthermore, bisphosphonate bone affinity comes at the expense of very low and variable oral bioavailability. FPPS inhibitors were developed with a monophosphonate as a bone‐affinity tag that confers moderate affinity to bone, which can furthermore be tuned to the desired level, and the relationship between structure and bone affinity was evaluated by using an NMR‐based bone‐binding assay. The concept of targeting drugs to bone with moderate affinity, while retaining oral bioavailability, has broad application to a variety of other bone‐targeted drugs.     

Glucose‐Responsive Trehalose Hydrogel for Insulin Stabilization and Delivery

Effective delivery of therapeutic proteins is important for many biomedical applications. Yet, the stabilization of proteins during delivery and long‐term storage remains a significant challenge. Herein, a trehalose‐based hydrogel is reported that stabilizes insulin to elevated temperatures prior to glucose‐triggered release. The hydrogel is synthesized using a polymer with trehalose side chains and a phenylboronic acid end‐functionalized 8‐arm poly(ethylene glycol) (PEG). The hydroxyls of the trehalose side chains form boronate ester linkages with the PEG boronic acid cross‐linker to yield hydrogels without any further modification of the original trehalose polymer. Dissolution of the hydrogel is triggered upon addition of glucose as a stronger binder to boronic acid (K_b = 2.57 vs 0.48 m ⁻¹ for trehalose), allowing the insulin that is entrapped during gelation to be released in a glucose‐responsive manner. Moreover, the trehalose hydrogel stabilizes the insulin as determined by immunobinding after heating up to 90 °C. After 30 min heating, 74% of insulin is detected by enzyme‐linked immunosorbent assay in the presence of the trehalose hydrogel, whereas only 2% is detected without any additives.     

Synthesis of dendritic bisphosphonates as bone targeting ligands

A dendritic bisphosphonate carrying three bisphosphonate (BP) units in close proximity was designed as a ligand to conjugate large therapeutic molecules for their bone selective delivery. The Bu₃P-catalyzed conjugate addition of nitromethane to vinylidene bisphosphonate was effective to construct a quaternary carbon center carrying BP units. Owing to multivalent interactions, the dendritic bisphosphonate showed considerable affinity for the bone mineral hydroxyapatite even in the presence of a competitor, demonstrating potential as a bone targeting ligand.     

Synthesis of millimeter‐sized hydrogel beads by inverse Pickering polymerization using starch‐based nanoparticles as emulsifier

The preparation of millimeter‐sized poly(acrylamide‐co‐acrylic acid) hydrogel beads via inverse Pickering emulsion polymerization using starch‐based nanoparticles (SNPs) as stabilizers is reported. Amphiphilic starch is fabricated by the introduction of butyl glycidyl ether groups and palmitate groups, and the hydrophobically modified SNPs are fabricated by a nanoprecipitation process. The obtained SNPs could adsorb at oil‐water interfaces to stabilize an inverse Pickering emulsion, and the effects of oil/water volume fraction ratio and SNP concentration on emulsions are comprehensively studied. Poly(acrylamide‐co‐acrylic acid) hydrogel beads with a size of approximately 1 mm are obtained by inverse Pickering emulsion polymerization stabilized by SNPs. The morphology and structure of hydrogel beads are extensively investigated, which confirms that SNPs locate on the surface of hydrogel beads and act as emulsifiers and network structures present inside the beads. Polymerization is also detected to investigate the potential formation mechanism of hydrogel beads. The pH‐responsive property of hydrogel beads and its potential application for drug delivery are also explored.     

Adsorption-Desorption Properties of Bisphosphonates

Abstract

Aminobisphosphonates have generated substantial interest recently for the treatment of bone diseases and as plant growth regulators, both alone and as a carrier for other drugs, because of the high affinity to the hydroxyapatite (HAP). We are investigating the drug delivery action of bisphosphonates for the treatment of osteoporosis and other bone diseases. Current studies include analysis of the adsorption-desorption processes of bisphosphonate drug carriers to bone mineral, as well as the design and synthesis of new bisphosphonate derivatives. The HAP adsorption data of aminomethylenebis-phosphonate (M P) (1). alendronate (2), and the prostaglandin derivative of bisphosphonate (PGE,-BP) (3) is shown on the graph.     

Xylan hemicellulose improves chitosan hydrogel for bone tissue regeneration

The hemicellulose xylan, which has immunomodulatory effects, has been combined with chitosan to form a composite hydrogel to improve the healing of bone fractures. This thermally responsive and injectable hydrogel, which is liquid at room temperature and gels at physiological temperature, improves the response of animal host tissue compared with similar pure chitosan hydrogels in tissue engineering models. The composite hydrogel was placed in a subcutaneous model where the composite hydrogel is replaced by host tissue within 1 week, much earlier than chitosan hydrogels. A tibia fracture model in mice showed that the composite encourages major remodeling of the fracture callus in less than 4 weeks. A non‐union fracture model in rat femurs was used to demonstrate that the composite hydrogel allows bone regeneration and healing of defects that with no treatment are unhealed after 6 weeks. These results suggest that the xylan/chitosan composite hydrogel is a suitable bone graft substitute able to aid in the repair of large bone defects. Copyright © 2016 John Wiley & Sons, Ltd.     

In Vivo Biological Behavior of Polymer Scaffolds of Natural Origin in the Bone Repair Process

Autologous bone grafts, used mainly in extensive bone loss, are considered the gold standard treatment in regenerative medicine, but still have limitations mainly in relation to the amount of bone available, donor area, morbidity and creation of additional surgical area. This fact encourages tissue engineering in relation to the need to develop new biomaterials, from sources other than the individual himself. Therefore, the present study aimed to investigate the effects of an elastin and collagen matrix on the bone repair process in critical size defects in rat calvaria. The animals (Wistar rats, n = 30) were submitted to a surgical procedure to create the bone defect and were divided into three groups: Control Group (CG, n = 10), defects filled with blood clot; E24/37 Group (E24/37, n = 10), defects filled with bovine elastin matrix hydrolyzed for 24 h at 37 °C and C24/25 Group (C24/25, n = 10), defects filled with porcine collagen matrix hydrolyzed for 24 h at 25 °C. Macroscopic and radiographic analyses demonstrated the absence of inflammatory signs and infection. Microtomographical 2D and 3D images showed centripetal bone growth and restricted margins of the bone defect. Histologically, the images confirmed the pattern of bone deposition at the margins of the remaining bone and without complete closure by bone tissue. In the morphometric analysis, the groups E24/37 and C24/25 (13.68 ± 1.44; 53.20 ± 4.47, respectively) showed statistically significant differences in relation to the CG (5.86 ± 2.87). It was concluded that the matrices used as scaffolds are biocompatible and increase the formation of new bone in a critical size defect, with greater formation in the polymer derived from the intestinal serous layer of porcine origin (C24/25).     

A Polysaccharide-based Hydrogel and PLGA Microspheres for Sustained P24 Peptide Delivery: An In vitro and In vivo Study Based on Osteogenic Capability

A bone morphogenetic protein-2(BMP-2) derived synthetic oligopeptide, S [PO4]KIPKASSVPTELSAISTLYLDDD(P24), has shown great potential for facilitating bone regeneration. However, P24 cannot be directly used onto bone defects, while a continuous sustained delivery of P24 may lead to a better formation of bone tissue. Based on this issue, we have developed a sustained delivery system incorporating P24-loaded poly(lactide-co-glycolide)(PLGA) microspheres and nano-hydroxyapatite(n-HA) into the composite hydrogel. The P24-contained compound material was characterized with NMR, FTIR and SEM to demonstrate the fomiation of compound structure containing P24, PLGA and n-HA. A continuous drug release of P24 was observed for over 60 d that evidently enhanced the efficiency in promoting the proliferation of MC3T3-E1 cells and the secrete of alkaline phosphatase(ALP) in vitro. Moreover, the osteoinduction eflect of the hydrogel system with P24 peptide niicrospheres was demonstrated in vivo and manifested by the result of immunohistochemistry. This novel injectable composite hydrogel is expected to be applied to improving the bone defect treatment in bone tissue engineering.     

Hydrogels as Scaffolds in Bone-Related Tissue Engineering and Regeneration

Several years have passed since the medical and scientific communities leaned toward tissue engineering as the most promising field to aid bone diseases and defects resulting from degenerative conditions or trauma. Owing to their histocompatibility and non-immunogenicity, bone grafts, precisely autografts, have long been the gold standard in bone tissue therapies. However, due to issues associated with grafting, especially the surgical risks and soaring prices of the procedures, alternatives are being extensively sought and researched. Fibrous and non-fibrous materials, synthetic substitutes, or cell-based products are just a few examples of research directions explored as potential solutions. A very promising subgroup of these replacements involves hydrogels. Biomaterials resembling the bone extracellular matrix and therefore acting as 3D scaffolds, providing the appropriate mechanical support and basis for cell growth and tissue regeneration. Additional possibility of using various stimuli in the form of growth factors, cells, etc., within the hydrogel structure, extends their use as bioactive agent delivery platforms and acts in favor of their further directed development. The aim of this review is to bring the reader closer to the fascinating subject of hydrogel scaffolds and present the potential of these materials, applied in bone and cartilage tissue engineering and regeneration.     

Mineralized Synthetic Matrices as an Instructive Microenvironment for Osteogenic Differentiation of Human Mesenchymal Stem Cells

The effect of substrate‐mediated signals on osteogenic differentiation of hMSCs is studied using a synthetic bone‐like material comprising both organic and inorganic components that supports adhesion, spreading, and proliferation of hMSCs. hMSCs undergo osteogenic differentiation even in the absence of osteogenesis‐inducing supplements. They exhibit higher expressions of Runx2, BSP, and OCN compared to their matrix‐rigidity‐matched, non‐mineralized hydrogel counterparts. The mineralized‐hydrogel‐assisted osteogenic differentiation of hMSCs could be attributed to their exposure to high local concentrations of calcium and phosphate ions in conjunction with chemical and topological cues arising from the hydrogel‐bound calcium phosphate mineral layer.

     

Use of 5‐Fluorouracil Loaded Micelles and Cisplatin in Thermosensitive Chitosan Hydrogel as an Efficient Therapy against Colorectal Peritoneal Carcinomatosis

Colorectal peritoneal carcinomatosis (CRPC) is a common systemic metastasis of intra‐abdominal cancers. Intraperitoneal chemotherapy against CRPC is at present the preferred treatment. The aim of this study is to develop a novel hydrogel drug delivery system through the combination of 5‐fluorouracil (5‐FU) loaded polymeric micelles and cisplatin (DDP) in biodegradable thermosensitive chitosan (CS) hydrogel. The prepared CS hydrogel drug is a free‐flowing solution at room temperature and forms a stationary gel at body temperature. Therefore, a CRPC mouse model is established to investigate the antitumor activity of CS hydrogel drug system. The results suggest that intraperitoneal administration of CS hydrogel drug can inhibit tumor growth and metastasis, and prolong survival time compared with other groups, thus improving the chemotherapeutic effect. Ki‐67 immunohistochemical analysis reveals that tumors in the CS hydrogel drug group has lower cell proliferation in contrast to other groups (P < 0.001). Furthermore, hematoxylin‐eosin staining of liver and lung tissue indicates that the CS hydrogel drug has also a certain inhibitory effect on colorectal cancer metastasis to the liver and lung. Hence, the work highlights the potential clinical applications of the CS hydrogel drug.

     

A fast on-demand preparation of injectable self-healing nanocomposite hydrogels for efficient osteoinduction

Injectable hydrogels have been considered as promising materials for bone regeneration,but their osteoinduction and mechanical performance are yet to be improved.In this study,a novel biocompatible injectable and self-healing nano hybrid hydrogel was on-demand prepared via a fast(within 30 s) and easy gelation approach by reversible Schiff base formed between-CH=O of oxidized sodium alginate(OSA) and-NH_2 of glycol chitosan(GCS) mixed with calcium phosphate nanoparticles(CaP NPs).Its raw materials can be ready in large quantities by a simple synthesis process.The mechanical strength,degradation and swelling behavior of the hydrogel can be readily controlled by simply controlling the molar ratio of-CH=O and-NH_2.This hydrogel exhibits pH responsiveness,good degradability and biocompatibility.The hydrogel used as the matrix for mesenchymal stem cells can significantly induce the proliferation,differentiation and osteoinduction in vitro.These results showed this novel hydrogel is an ideal candidate for applications in bone tissue regeneration and drug delivery.     

Polymeric microspheres: a delivery system for osteogenic differentiation

Advanced drug delivery systems employing controlled release technology are being developed to address many of the difficulties associated with traditional methods of drug administration. Controlled release technology involves the use of devices such as polymer‐based disks, rods, pellets, or microspheres (MSs) that encapsulate drugs, genes, cytokines, and growth factors and release them in specific location within the body in a controlled fashion, for relatively long periods of time. Among these, microencapsulation is one of the core technologies used in polymer‐based drug delivery systems. In this regard, MS serves as microcarriers for sustain drug release facilitating their use for invasive or minimally invasive treatment. MS has significant potential for the application in bone repair, intra‐articular treatment of osteoarthritis, and biological bone growth. The present review compiles the recent advances in polymeric MS for application in bone and cartilage regeneration. Copyright © 2017 John Wiley & Sons, Ltd.     

Engineering of new crosslinked near‐infrared fluorescent polyethylene glycol bisphosphonate nanoparticles for bone targeting

Bisphosphonates (BPs) are nonhydrolysable pyrophosphate analogs with high affinity to hydroxyapatite (HAP, bone mineral) and are mainly used for treatment of various bone diseases. In this study, we designed and prepared crosslinked BP nanoparticles by dispersion copolymerization of three monomers: methacrylate PEG bisphosphonate, N‐(3‐aminopropyl) methacrylamide, and tetra(ethylene glycol) diacrylate. The size and size distribution of these PEG‐BP nanoparticles were controlled by changing various polymerization parameters. These BP particles possess dual functionality: covalent attachment of a dye (e.g., near IR fluorescent dye) or drug to the nanoparticles through the primary amine groups belonging to the aminopropyl methacrylamide monomeric units and chelation to the bone mineral HAP through the BP groups belonging to the methacrylate PEG bisphosphonate monomeric units, for enhanced long term bone‐targeted imaging and therapy applications. Body distribution of the optimal crosslinked BP nanoparticles was tested on a chicken embryo model via intravenous administration. This study indicated that the fluorescence intensity of the all organs (e.g., blood, spleen, liver, kidney, and heart) except the bones decreased significantly within 48 h (p < 0.05) while that of the bones hardly changed over that time (p > 0.05). © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 4282–4291     

Thermosensitive acetylated carboxymethyl chitosan gel depot systems sustained release caffeic acid phenethyl ester for periodontitis treatment

Periodontitis is a chronic inflammatory disease of tooth support tissues leading to progressive destruction of periodontal soft tissues as well as alveolar bone, and can be treated with anti-inflammatory and bone-protective agents to prevent disease progression. Caffeic acid phenethyl ester (CAPE) is a natural polyphenolic compound with anti-inflammation, anti-oxidation and bone tissue repair efficacy. In this work, we synthesized a thermosensitive hydrogel matrix of acetylated carboxymethyl chitosan (A-CC), and firstly applied for periodontal local drug delivery. The biocompatible CAPE-loaded A-CC hydrogel (CAPE-A-CC) has the advantages of forming a drug depot in situ, sustained release and precisely improving the drug concentration in the lesion sites compared with traditional systemic administration. In addition, CAPE-A-CC could significantly inhibit the expression of inflammatory cytokines of TNF-α, IL-1β, IL-6, and IL-17 in macrophages, and increased the expression of alkaline phosphatase (ALP) in human periodontal ligament stem cells (hPDLSC) related to osteogenesis. This study develops a novel in situ thermosensitive hydrogel delivery system to improve the therapeutic potential of natural active ingredient for periodontitis therapy.