Oxidized alginate hydrogels for bone morphogenetic protein-2 delivery in long bone defects

Hydrogels in Gene Delivery Techniques for Regenerative Medicine and Tissue Engineering

Hydrogels are 3D networks swollen with water. They are biocompatible, strong, and moldable and are emerging as a promising biomedical material for regenerative medicine and tissue engineering to deliver therapeutic genes. The excellent natural extracellular matrix simulation properties of hydrogels enable them to be co-cultured with cells or enhance the expression of viral or non-viral vectors. Its biocompatibility, high strength, and degradation performance also make the action process of carriers in tissues more ideal, making it an ideal biomedical material. It has been shown that hydrogel-based gene delivery technologies have the potential to play therapy-relevant roles in organs such as bone, cartilage, nerve, skin, reproductive organs, and liver in animal experiments and preclinical trials. This paper reviews recent articles on hydrogels in gene delivery and explains the manufacture, applications, developmental timeline, limitations, and future directions of hydrogel-based gene delivery techniques.

Bovine serum albumin-modified 3D printed alginate dialdehyde-gelatin scaffolds incorporating polydopamine/SiO2-CaO nanoparticles for bone regeneration

Three-dimensional (3D) printing allows precise manufacturing of bone scaffolds for patient-specific applications and is one of the most recently developed and implemented technologies. In this study, bilayer and multimaterial alginate dialdehyde-gelatin (ADA-GEL) scaffolds incorporating polydopamine (PDA)/SiO2-CaO nanoparticle complexes were 3D printed using a pneumatic extrusion-based 3D printing technology and further modified on the surface with bovine serum albumin (BSA) for application in bone regeneration. The morphology, chemistry, and in vitro bioactivity of PDA/SiO2-CaO nanoparticle complexes were characterized (n = 3) and compared with those of mesoporous SiO2-CaO nanoparticles. Successful deposition of the PDA layer on the surface of the SiO2-CaO nanoparticles allowed better dispersion in a liquid medium and showed enhanced bioactivity. Rheological studies (n = 3) of ADA-GEL inks consisting of PDA/SiO2-CaO nanoparticle complexes showed results that may indicate better injectability and printability behavior compared to ADA-GEL inks incorporating unmodified nanoparticles. Microscopic observations of 3D printed scaffolds revealed that PDA/SiO2-CaO nanoparticle complexes introduced additional topography onto the surface of 3D printed scaffolds. Additionally, the modified scaffolds were mechanically stable and elastic, closely mimicking the properties of natural bone. Furthermore, protein-coated bilayer scaffolds displayed controllable absorption and biodegradation, enhanced bioactivity, MC3T3-E1 cell adhesion, proliferation, and higher alkaline phosphatase (ALP) activity (n = 3) compared to unmodified scaffolds. Consequently, the present results confirm that ADA-GEL scaffolds incorporating PDA/SiO2-CaO nanoparticle complexes modified with BSA offer a promising approach for bone regeneration applications.

Novel Strategies for Spatiotemporal and Controlled BMP-2 Delivery in Bone Tissue Engineering

Bone morphogenetic protein-2 (BMP-2) has been commercially approved by the Food and Drug Administration for use in bone defects and diseases. BMP-2 promotes osteogenic differentiation of mesenchymal stem cells. In bone tissue engineering, BMP-2 incorporated into scaffolds can be used for stimulating bone regeneration in organoid construction, drug testing platforms, and bone transplants. However, the high dosage and uncontrollable release rate of BMP-2 challenge its clinical application, mainly due to the short circulation half-life of BMP-2, microbial contamination in bone extracellular matrix hydrogel, and the delivery method. Moreover, in clinical translation, the requirement of high doses of BMP-2 for efficacy poses challenges in cost and safety. Based on these, novel strategies should ensure that BMP-2 is delivered precisely to the desired location within the body, regulating the timing of BMP-2 release to coincide with the bone healing process, as well as release BMP-2 in a controlled manner to optimize its therapeutic effect and minimize side effects. This review highlights improvements in bone tissue engineering applying spatiotemporal and controlled BMP-2 delivery, including molecular engineering, biomaterial modification, and synergistic therapy, aiming to provide references for future research and clinical trials.

Bioactive Materials for Bone Regeneration: Biomolecules and Delivery Systems

Novel tissue regeneration strategies are constantly being developed worldwide. Research on bone regeneration is noteworthy, as many promising new approaches have been documented with novel strategies currently under investigation. Innovative biomaterials that allow the coordinated and well-controlled repair of bone fractures and bone loss are being designed to reduce the need for autologous or allogeneic bone grafts eventually. The current engineering technologies permit the construction of synthetic, complex, biomimetic biomaterials with properties nearly as good as those of natural bone with good biocompatibility. To ensure that all these requirements meet, bioactive molecules are coupled to structural scaffolding constituents to form a final product with the desired physical, chemical, and biological properties. Bioactive molecules that have been used to promote bone regeneration include protein growth factors, peptides, amino acids, hormones, lipids, and flavonoids. Various strategies have been adapted to investigate the coupling of bioactive molecules with scaffolding materials to sustain activity and allow controlled release. The current manuscript is a thorough survey of the strategies that have been exploited for the delivery of biomolecules for bone regeneration purposes, from choosing the bioactive molecule to selecting the optimal strategy to synthesize the scaffold and assessing the advantages and disadvantages of various delivery strategies.

Diffusion-Limited Processes in Hydrogels with Chosen Applications from Drug Delivery to Electronic Components

Diffusion is one of the key nature processes which plays an important role in respiration, digestion, and nutrient transport in cells. In this regard, the present article aims to review various diffusion approaches used to fabricate different functional materials based on hydrogels, unique examples of materials that control diffusion. They have found applications in fields such as drug encapsulation and delivery, nutrient delivery in agriculture, developing materials for regenerative medicine, and creating stimuli-responsive materials in soft robotics and microrobotics. In addition, mechanisms of release and drug diffusion kinetics as key tools for material design are discussed.

Cissus quadrangularis L extract-loaded tricalcium phosphate reinforced natural polymer composite for guided bone regeneration

Natural medicines plants are significant considerable attention as potential therapeutic agents for bone tissue engineering. Cissus quadrangularis L (CQ). is a potent therapeutic plant known for its own osteogenic properties. In this research work, a phytoconstituents-filled composite was produced by incorporating CQ extract with gelatin (Gel) and pectin (Pec) polymers collective through β- tricalcium phosphate (β-TCP) bioceramic via a green template method. The effect of CQ-filled composite morphology and chemical structural properties, in vitro cytotoxicity, cell proliferation, and differentiation was investigated. FTIR spectroscopic results indicated the prepared materials' structural confirmation. The CQ extract was the alcoholic -OH merge with the hydroxyl and -NH groups in the range of 3000 cm^-1 to 3500 cm^-1. Scanning electron microscopy images showed that the β-TCP ceramic was perfectly embedded in Gel-Pec polymeric matrix, which is important for bone regeneration. In vitro cell culture results indicated that β-TCP/Gel-Pec/CQ composite provided 92.0% of a favorable substrate for mesenchymal stem cell viability. The gene expression and RT-PCR studies represent the materials with good osteogenic expression, especially the β-TCP/Gel-Pec/CQ composite is observed at 168.0% and 188.0% for RUNx2 and OCN, respectively. The result of the physicochemical characterizations and cell viability studies suggest that CQ-loaded β-TCP/Gel-Pec composite can serve as a potential biomaterial for bone tissue repair and regeneration.

Laser microgrooving and resorbable blast texturing for enhanced surface function of titanium alloy for dental implant applications

Long-term dental implant success is dependent on biocompatibility and osseointegration between the bone and the implant. Surface modifications such as laser-induced microgrooving which increase contact area can enhance osseointegration by establishing and directing a stable attachment between the implant surface and peri-implant bone. The objective of this study was to evaluate pre-osteoblast proliferation, morphology, and differentiation on titanium alloy (Ti64) surfaces-Laser-Lok^© (LL), resorbable blast textured (RBT), and machined (M)-compared to tissue culture plastic (TCP) control. We hypothesized the LL surfaces would facilitate increased cellular alignment compared to all other groups, and LL and RBT surfaces would demonstrate enhanced proliferation and differentiation compared to M and TCP surfaces. Surface roughness was quantified using a surface profilometer, and water contact angle was measured to evaluate the hydrophilicity of the surfaces. Cellular function was assessed using quantitative viability and differentiation assays and image analyses, along with qualitative fluorescent (viability and cytoskeletal) imaging and scanning electron microscopy. No differences in surface roughness were observed between groups. Water contact angle indicated LL was the least hydrophilic surface, with RBT and M surfaces exhibiting greater hydrophilicity. Cell proliferation on day 2 was enhanced on both LL and RBT surfaces compared to M, and all three groups had higher cell numbers on day 2 compared to day 1. Cell orientation was driven by the geometry of the surface modification, as cells were more highly aligned on LL surfaces compared to TCP (on day 2) and RBT (on day 3). At day 21, cell proliferation was greater on LL, RBT, and TCP surfaces compared to M, though no differences in osteogenic differentiation were observed. Collectively, our results highlight the efficacy of laser microgrooved and resorbable blast textured surface modifications of Ti64 for enhancing cellular functions, which may facilitate improved osseointegration of dental implants.

Magnetic microspheres mimicking certain functions of macrophages: Towards precise antibacterial potency for bone defect healing

A variety of novel biomaterials have recently been developed to promote bone regeneration. However, the current biomaterials cannot accurately and effectively resist bacterial invasion. In this study, we constructed microspheres that mimic certain functions of macrophages as additives to bone repair materials, which can be manipulated as demanded to resist bacteria effectively and protect bone defect healing. Firstly, we prepared gelatin microspheres (GMSs) by an emulsion-crosslinking method, which were subsequently coated with polydopamine (PDA). Then, amino antibacterial nanoparticles obtained by a nanoprecipitation-self-assembly method and commercial amino magnetic nanoparticles were modified onto these PDA-coated GMSs to construct the functionalized microspheres (FMSs). The results showed that the FMSs possessed a rough topography and could be manipulated by a 100-400 ​mT static magnetic field to migrate directionally in unsolidified hydrogels. Moreover, in vitro experiments with near-infrared (NIR) showed that the FMSs had a sensitive and recyclable photothermal performance and could capture and kill Porphyromonas gingivalis by releasing reactive oxygen species. Finally, the FMSs were mixed with osteogenic hydrogel precursor, injected into the Sprague-Dawley rat periodontal bone defect of maxillary first molar (M1), and subsequently driven by magnetism to the cervical surface of M1 and the outer surface of the gel system for targeted sterilization under NIR, thus protecting the bone defect healing. In conclusion, the FMSs had excellent manipulation and antimicrobial performances. This provided us with a promising strategy to construct light-magnetism-responsive antibacterial materials to build a beneficial environment for bone defect healing.

Tunable Surface Charge Enables the Electrostatic Adsorption-Controlled Release of Neuroprotective Peptides from a Hydrogel-Nanoparticle Drug Delivery System

We exploit the electrostatic interactions between the positively charged neuroprotective peptide, pituitary adenylate cyclase-activating polypeptide (PACAP), and negatively charged poly(lactic-co-glycolic acid) (PLGA) nanoparticles to control PACAP release from the surface of nanoparticles dispersed in a hyaluronan-methylcellulose (HAMC) hydrogel composite. PACAP is a promising therapeutic for the treatment of neurological disorders, yet it has been difficult to deliver in vivo. Herein, the PACAP release rate was tuned by manipulating peptide adsorption onto the surface of blank nanoparticles by modifying either nanoparticle loading in the hydrogel or nanoparticle surface charge. This peptide-nanoparticle interaction was controlled by the pH-responsive carboxylic acid end terminal groups of PLGA. We further validated this system with the controlled release of a novel stabilized PACAP analog: Ac-[Ala¹⁵, Ala²⁰]PACAP-propylamide, which masks its recognition to peptidases in circulation. Both wild-type and stabilized PACAP released from the vehicle increased the production of neuroprotective Interleukin-6 from cultured primary astrocytes. Using computational fluid dynamics methods, PACAP release from the composite was predicted based on experimentally derived adsorption isotherms, which exhibited similar release profiles to experimental data. This versatile adsorption-based system was used to deliver PACAP locally to the brains of stroke-injured mice over a 10 day period in vivo, highlighting its effectiveness for the controlled release of PACAP to the central nervous system.

Amniotic membrane attenuates heterotopic ossification following high-dose bone morphogenetic protein-2 treatment of segmental bone defects

Treatment of large bone defects with supraphysiological doses of bone morphogenetic protein-2 (BMP-2) has been associated with complications including heterotopic ossification (HO), inflammation, and pain, presumably due to poor spatiotemporal control of BMP-2. We have previously recapitulated extensive HO in our rat femoral segmental defect model by treatment with high-dose BMP-2 (30 μg). Using this model and BMP-2 dose, our objective was to evaluate the utility of a clinically available human amniotic membrane (AM) around the defect space for guided bone regeneration and reduction of HO. We hypothesized that AM surrounding collagen sponge would attenuate heterotopic ossification compared with collagen sponge alone. In vitro, AM retained more BMP-2 than a synthetic poly(ε-caprolactone) membrane through 21 days. In vivo, as hypothesized, the collagen + AM resulted in significantly less heterotopic ossification and correspondingly, lower total bone volume (BV), compared with collagen sponge alone. Although bone formation within the defect was delayed with AM around the defect, by 12 weeks, defect BVs were equivalent. Torsional stiffness was significantly reduced with AM but was equivalent to that of intact bone. Collagen + AM resulted in the formation of dense fibrous tissue and mineralized tissue, while the collagen group contained primarily mineralized tissue surrounded by marrow-like structures. Especially in conjunction with high doses of growth factor delivered via collagen sponge, these findings suggest AM may be effective as an overlay adjacent to bone healing sites to spatially direct bone regeneration and minimize heterotopic ossification.

Partially Oxidized Alginate as a Biodegradable Carrier for Glucose-Responsive Insulin Delivery and Islet Cell Replacement Therapy

Self-regulated insulin delivery that mimics native pancreas function has been a long-term goal for diabetes therapies. Two approaches towards this goal are glucose-responsive insulin delivery and islet cell transplantation therapy. Here, biodegradable, partially oxidized alginate carriers for glucose-responsive nanoparticles or islet cells are developed. Material composition and formulation are tuned in each of these contexts to enable glycemic control in diabetic mice. For injectable, glucose-responsive insulin delivery, 0.5 mm 2.5% oxidized alginate microgels facilitate repeat dosing and consistently provide 10 days of glycemic control. For islet cell transplantation, 1.5 mm capsules comprised of a blend of unoxidized and 2.5% oxidized alginate maintain cell viability and glycemic control over a period of more than 2 months while reducing the volume of nondegradable material implanted. These data show the potential of these biodegradable carriers for controlled drug and cell delivery for the treatment of diabetes with limited material accumulation in the event of multiple doses.

Oxidized sodium alginate crosslinked silk fibroin composite scaffold for skin tissue engineering

Engineering skin substitutes represent a prospective source of advanced therapy in repairing severe traumatic wounds. Sodium alginate (SA) and silk fibroin (SF) are natural biomaterials, which are widely used in tissue engineering and other fields because of their low price, high safety, and good biocompatibility. However, SA itself degrades slowly, its degradation mode is difficult to control, and the degradation products are difficult to remove from the body because of its high molecular weight. Therefore, the composite scaffolds were prepared by freeze-drying composite technology by using the Schiff base reaction between biocompatible SF and permeable oxidized sodium alginate (OSA). Sodium periodate was used as oxidant to modify SA. The results showed that higher oxidation degree of OSA could be obtained by increasing the proportion of oxidant, and the relative molecular weight of the oxidized products could also be reduced. The composite scaffolds were prepared by using sodium tetraborate as a crosslinking accelerator of the Schiff base reaction between OSA and SF. FT-IR confirmed that the Schiff base group appeared in the material. In vitro biodegradation experiments showed that the biodegradation of the composite scaffolds was controllable, and the cytocompatibility experiment showed that the composite scaffolds had good biocompatibility.

Carrier systems for bone morphogenetic proteins: An overview of biomaterials used for dentoalveolar and maxillofacial bone regeneration

Different types of biomaterials have been used to fabricate carriers to deliver bone morphogenetic proteins (BMPs) in both dentoalveolar and maxillofacial bone regeneration procedures. Despite that absorbable collagen sponge (ACS) is considered the gold standard for BMP delivery, there is still some concerns regarding its use mainly due to its poor mechanical properties. To overcome this, novel systems are being developed, however, due to the wide variety of biomaterial combination, the heterogeneous assessment of newly formed tissue, and the intended clinical applications, there is still no consensus regarding which is more efficient in a particular clinical scenario. The combination of two or more biomaterials in different topological configurations has allowed specific controlled-release patterns for BMPs, improving their biological and mechanical properties compared with classical single-material carriers. However, more basic research is needed. Since the BMPs can be used in multiple clinical scenarios having different biological and mechanical needs, novel carriers should be developed in a context-specific manner. Thus, the purpose of this review is to gather current knowledge about biomaterials used to fabricate delivery systems for BMPs in both dentoalveolar and maxillofacial contexts. Aspects related with the biological, physical and mechanical characteristics of each biomaterial are also presented and discussed.

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Strategies for bone formation and regeneration are a major concern in dentistry.

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Topical delivery of bone morphogenetic proteins (BMPs) allows rapid bone formation.

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BMPs requires proper carrier system to allow controlled and sustained release.

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Carrier should also fulfill mechanical requirements of bone defect sites.

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By using complex composites, it would be possible to develop new carriers for BMPs.

Degradation-Kinetics-Controllable and Tissue-Regeneration-Matchable Photocross-linked Alginate Hydrogels for Bone Repair

Photocross-linked alginate hydrogels, due to their biodegradability, biocompatibility, strong control for gelling kinetics in space and time, and admirable adaptability for in situ polymerization with a minimally invasive approach in surgical procedures, have created great expectations in bone regeneration. However, hydrogels with suitable degradation kinetics that can match the tissue regeneration process have not been designed, which limits their further application in bone tissue engineering. Herein, we finely developed an oxidation strategy for alginate to obtain hydrogels with more suitable degradation rates and comprehensively explored their physical and biological performances in vitro and in vivo to further advance the clinical application for the hydrogels in bone repair. The physical properties of the gels can be tuned via tailoring the degree of alginate oxidation. In particular, in vivo degradation studies showed that the degradation rates of the gels were significantly increased by oxidizing alginate. The activity, proliferation, initial adhesion, and osteogenic differentiation of rat and rabbit bone marrow stromal cells (BMSCs) cultured with/in the hydrogels were explored, and the results demonstrated that the gels possessed excellent biocompatibility and that the encapsulated BMSCs were capable of osteogenic differentiation. Furthermore, in vivo implantation of rabbit BMSC-loaded gels into tibial plateau defects of rabbits demonstrated the feasibility of hydrogels with appropriate degradation rates for bone repair. This study indicated that hydrogels with increasingly controllable and matchable degradation kinetics and satisfactory bioproperties demonstrate great clinical potential in bone tissue engineering and regenerative medicine and could also provide references for drug/growth-factor delivery therapeutic strategies for diseases requiring specific drug/growth-factor durations of action.

A Study on the Correlation between the Oxidation Degree of Oxidized Sodium Alginate on Its Degradability and Gelation

Oxidized sodium alginate (OSA) is selected as an appropriate material to be extensively applied in regenerative medicine, 3D-printed/composite scaffolds, and tissue engineering for its excellent physicochemical properties and biodegradability. However, few literatures have systematically investigated the structure and properties of the resultant OSA and the effect of the oxidation degree (OD) of alginate on its biodegradability and gelation ability. Herein, we used NaIO₄ as the oxidant to oxidize adjacent hydroxyl groups at the C-2 and C-3 positions on alginate uronic acid monomer to obtain OSA with various ODs. The structure and physicochemical properties of OSA were evaluated by Fourier transform infrared spectroscopy (FT-IR), ¹H nuclear magnetic resonance (¹H NMR), X-ray Photoelectron Spectroscopy (XPS), X-ray Diffraction (XRD), and thermogravimetric analysis (TGA). At the same time, gel permeation chromatography (GPC) and a rheometer were used to determine the hydrogel-forming ability and biodegradation performance of OSA. The results showed that the two adjacent hydroxyl groups of alginate uronic acid units were successfully oxidized to form the aldehyde groups; as the amount of NaIO₄ increased, the OD of OSA gradually increased, the molecular weight decreased, the gelation ability continued to weaken, and degradation performance obviously rose. It is shown that OSA with various ODs could be prepared by regulating the molar ratio of NaIO₄ and sodium alginate (SA), which could greatly broaden the application of OSA-based hydrogel in tissue engineering, controlled drug release, 3D printing, and the biomedical field.

A bioactive synthetic membrane improves bone healing in a preclinical nonunion model

OBJECTIVES

High energy long bone fractures with critical bone loss are at risk for nonunion without strategic intervention. We hypothesize that a synthetic membrane implanted at a single stage improves bone healing in a preclinical nonunion model.

METHODS

Using standard laboratory techniques, microspheres encapsulating bone morphogenic protein-2 (BMP2) or platelet derived growth factor (PDGF) were designed and coupled to a type 1 collagen sheet. Critical femoral defects were created in rats and stabilized by locked retrograde intramedullary nailing. The negative control group had an empty defect. The induced membrane group (positive control) had a polymethylmethacrylate spacer inserted into the defect for four weeks and replaced with a bare polycaprolactone/beta-tricalcium phosphate (PCL/β-TCP) scaffold at a second stage. For the experimental groups, a bioactive synthetic membrane embedded with BMP2, PDGF or both enveloped a PCL/β-TCP scaffold was implanted in a single stage. Serial radiographs were taken at 1, 4, 8, and 12 weeks postoperatively from the definitive procedure and evaluated by two blinded observers using a previously described scoring system to judge union as primary outcome.

RESULTS

All experimental groups demonstrated better union than the negative control (p = 0.01). The groups with BMP2 incorporated into the membrane demonstrated higher average union scores than the other groups (p = 0.01). The induced membrane group performed similarly to the PDGF group. Complete union was only demonstrated in groups with BMP2-eluting membranes.

CONCLUSIONS

A synthetic membrane comprised of type 1 collagen embedded with controlled release BMP2 improved union of critical bone defects in a preclinical nonunion model.

Harnessing the potential of dialdehyde alginate-xanthan gum hydrogels as niche bioscaffolds for tissue engineering

Biomimetic hydrogels composed of natural polysaccharides have invariably blossomed as niche biomaterials in tissue engineering applications. The prospects of creating an extracellular matrix (ECM)-like milieu from such hydrogels has garnered considerable importance. In this study, we have fabricated bioscaffolds comprising dialdehyde alginate and xanthan gum and explored their potential use in tissue regeneration. The fabricated scaffolds displayed an interconnected porous network structure that is highly desirable for the aforesaid application. The scaffolds were endowed with good mechanical properties, thermostability, protein adsorption efficacy and degradability. Curcumin-loaded hydrogels exhibited appreciable antibacterial activity against E. coli. In vitro cytocompatibility studies revealed that the scaffolds promoted adhesion and proliferation of 3T3 fibroblast cells. The Western blot analysis of p53 gene indicated no growth arrest or apoptosis in 3T3 cells thus, signifying the non-toxic nature of the scaffolds. Furthermore, the ECM formation was confirmed via SDS-PAGE analysis. The overall results clearly validated these scaffolds as effectual biomaterials for tissue engineering applications.

Coaxial 3D bioprinting of tri-polymer scaffolds to improve the osteogenic and vasculogenic potential of cells in co-culture models

The crosstalk between osteoblasts and endothelial cells is critical for bone vascularization and regeneration. Here, we used a coaxial 3D bioprinting method to directly print an osteon-like structure by depositing angiogenic and osteogenic bioinks from the core and shell regions of the coaxial nozzle, respectively. The bioinks were made up of gelatin, gelatin methacryloyl (GelMA), alginate, and hydroxyapatite (HAp) nanoparticles and were loaded with human umbilical vascular endothelial cells (HUVECs) and osteoblasts (MC3T3) in the core and shell regions, respectively. Conventional monoaxial 3D bioprinting was used as a control method, where the hydrogels, HAp nanoparticles, MC3T3 cells, and HUVECs were all mixed in one bioink and printed from the core nozzle. As a result, the bioprinted scaffolds were composed of cell-laden fibers with either a core-shell or homogenous structure, providing a non-contact (indirect) or contact (direct) co-culture of MC3T3 cells and HUVECs, respectively. Both structures supported the 3D culture of HUVECs and osteoblasts over a long period. The scaffolds also supported the expression of osteogenic and angiogenic factors. However, the gene expression was significantly higher for the core-shell structure than the homogeneous structure due to the well-defined distribution of osteoblasts and endothelial cells and the formation of vessel-like structures in the co-culture system. Our results indicated that the coaxial bioprinting technique, with the ability to create a non-contact co-culture of cells, can provide a more efficient bioprinting strategy for printing highly vascularized and bioactive bone structures.

Anti-CRISPR proteins as a therapeutic agent against drug-resistant bacteria

The continuous deployment of various antibiotics to treat multiple serious bacterial infections leads to multidrug resistance among the bacterial population. It has failed the standard treatment strategies through different antibacterial agents and serves as a significant threat to public health worldwide at devastating levels. The discovery of anti-CRISPR proteins catches the interest of researchers around the world as a promising therapeutic agent against drug-resistant bacteria. Anti-CRISPR proteins are known to inhibit bacterial CRISPR-Cas defense systems in multiple possible ways. The CRISPR-Cas nucleoprotein assembly provides adaptive immunity in bacteria against diverse categories of phage infections. Parallelly, phages also try to break the CRISPR-Cas barrier by producing anti-CRISPR proteins, leading to growth inhibition and bacterial lysis. This review begins with a brief description of the bacterial CRISPR-Cas system, followed by a detailed portrayal of anti-CRISPR proteins, including their discovery and evolution, mechanism of action, regulation of expression, and potential applications in the healthcare sector as an alternative therapeutic strategy to combat severe bacterial infections.

Recent Progress on Polysaccharide-Based Hydrogels for Controlled Delivery of Therapeutic Biomolecules

A plethora of applications using polysaccharides have been developed in recent years due to their availability as well as their frequent nontoxicity and biodegradability. These polymers are usually obtained from renewable sources or are byproducts of industrial processes, thus, their use is collaborative in waste management and shows promise for an enhanced sustainable circular economy. Regarding the development of novel delivery systems for biotherapeutics, the potential of polysaccharides is attractive for the previously mentioned properties and also for the possibility of chemical modification of their structures, their ability to form matrixes of diverse architectures and mechanical properties, as well as for their ability to maintain bioactivity following incorporation of the biomolecules into the matrix. Biotherapeutics, such as proteins, growth factors, gene vectors, enzymes, hormones, DNA/RNA, and antibodies are currently in use as major therapeutics in a wide range of pathologies. In the present review, we summarize recent progress in the development of polysaccharide-based hydrogels of diverse nature, alone or in combination with other polymers or drug delivery systems, which have been implemented in the delivery of biotherapeutics in the pharmaceutical and biomedical fields.

Three Polymers from the Sea: Unique Structures, Directional Modifications, and Medical Applications

With the increase of wounds and body damage, the clinical demand for antibacterial, hemostatic, and repairable biomaterials is increasing. Various types of biomedical materials have become research hotspots. Of these, and among materials derived from marine organisms, the research and application of alginate, chitosan, and collagen are the most common. Chitosan is mainly used as a hemostatic material in clinical applications, but due to problems such as the poor mechanical strength of a single component, the general antibacterial ability, and fast degradation speed research into the extraction process and modification mainly focuses on the improvement of the above-mentioned ability. Similarly, the research and modification of sodium alginate, used as a material for hemostasis and the repair of wounds, is mainly focused on the improvement of cell adhesion, hydrophilicity, degradation speed, mechanical properties, etc.; therefore, there are fewer marine biological collagen products. The research mainly focuses on immunogenicity removal and mechanical performance improvement. This article summarizes the source, molecular structure, and characteristics of alginate, chitosan, and collagen from marine organisms; and introduces the biological safety, clinical efficacy, and mechanism of action of these materials, as well as their extraction processes and material properties. Their modification and other issues are also discussed, and their potential clinical applications are examined.

[Study on the gelatin methacryloyl composite scaffold with exogenous transforming growth factor β 1 to promote the repair of skull defects]

Objective

To prepare a bone tissue engineering scaffold for repairing the skull defect of Sprague Dawley (SD) rats by combining exogenous transforming growth factor β ₁ (TGF-β ₁) with gelatin methacryloyl (GelMA) hydrogel.

Methods

Firstly, GelMA hydrogel composite scaffolds containing exogenous TGF-β ₁ at concentrations of 0, 150, 300, 600, 900, and 1 200 ng/mL (set to groups A, B, C, D, E, and F, respectively) were prepared. Cell counting kit 8 (CCK-8) method was used to detect the effect of composite scaffold on the proliferation of bone marrow mesenchymal stem cells (BMSCs) in SD rats. ALP staining, alizarin red staining, osteocalcin (OCN) immunofluorescence staining, and Western blot were used to explore the effect of scaffolds on osteogenic differentiation of BMSCs, and the optimal concentration of TGF-β ₁/GelMA scaffold was selected. Thirty-six 8-week-old SD rats were taken to prepare a 5 mm diameter skull bone defect model and randomly divided into 3 groups, namely the control group, the GelMA group, and the GelMA+TGF-β ₁ group (using the optimal concentration of TGF-β ₁/GelMA scaffold). The rats were sacrificed at 4 and 8 weeks after operation, and micro-CT, HE staining, and OCN immunohistochemistry staining were performed to observe the repair effect of skull defects.

Results

The CCK-8 method showed that the TGF-β ₁/GelMA scaffolds in each group had a promoting effect on the proliferation of BMSCs. Group D had the strongest effect, and the cell activity was significantly higher than that of the other groups ( P<0.05). The results of ALP staining, alizarin red staining, OCN immunofluorescence staining, and Western blot showed that the percentage of ALP positive area, the percentage of alizarin red positive area, and the relative expressions of ALP and OCN proteins in group D were significantly higher than those of the other groups ( P<0.05), the osteogenesis effect in group D was the strongest. Therefore, in vitroexperiments screened out the optimal concentration of TGF-β ₁/GelMA scaffold to be 600 ng/mL. Micro-CT, HE staining, and OCN immunohistochemistry staining of rat skull defect repair experiments showed that the new bone tissue and bone volume/tissue volume ratio in the TGF-β ₁+GelMA group were significantly higher than those in the GelMA group and control group at 4 and 8 weeks after operation ( P<0.05).

Conclusion

The TGF-β ₁/GelMA scaffold with a concentration of 600 ng/mL can significantly promote the osteogenic differentiation of BMSCs, can significantly promote bone regeneration at the skull defect, and can be used as a bioactive material for bone tissue regeneration.

Applications of oxidized alginate in regenerative medicine

Because of its ideal degradation rate and features, oxidized alginate (OA) is selected as an appropriate substitute and has been introduced into hydrogels, microspheres, 3D-printed/composite scaffolds, membranes, and electrospinning and coating materials. By taking advantage of OA, the OA-based materials can be easily functionalized and deliver drugs or growth factors to promote tissue regeneration. In 1928, it was first found that alginate could be oxidized using periodate, yielding OA. Since then, considerable progress has been made in the research on the modification and application of alginate after oxidation. In this article, we summarize the key properties and existing applications of OA and various OA-based materials and discuss their prospects in regenerative medicine.

Biphasic Calcium Phosphate Microparticles Mixed With Autologous Blood: Application for the Reconstruction of a Large Mandibular Bone Defect in a Dog

Large mandibular bone defects can be difficult to treat in dogs, with a high risk of mal or nonunion due to instability and risk of infection. This case report describes the use of autologous clotted blood mixed with biphasic calcium phosphate microparticles to fill a defect in a nonunion fracture and promote bone regeneration in a dog using a 2-stage surgical approach. This new method was designed and tried in a dog with a chronic, unstable mandibular fracture associated with a large sequestrum. Initial treatment involved debridement of the lesion, then the oral wound and oral vestibule were reconstructed in 2 layers. Four weeks later a second stage surgery allowed placement of a pre-contoured maxillofacial plate to bridge the defect, which was filled with a blood/biphasic calcium phosphate compound implant. Cone-beam computed tomography was used prior to the initial surgery for preoperative planning and 3-D printing of a mandibular template for plate contouring. CT was subsequently used to document the healing process, using a bone density measurement tool to assess bone regeneration. Radiographic evidence suggestive of osseointegration was observed within 6 months with effective filling of the defect and restoration of alveolar ridge continuity. A return to normal and atraumatic occlusion was considered excellent. Cone-beam computed tomography was found useful to document radiographic evidence of osseointegration, bone regrowth and remodeling. This case report is to serve as a proof-of-concept study and should be followed by a prospective evaluation.

Fabricating a novel HLC-hBMP2 fusion protein for the treatment of bone defects

Treating serious bone trauma with an osteo-inductive agent such as bone morphogenetic proteins (BMPs) has been considered as an optimized option when delivered via a collagen sponge (CS). Previous works have shown that the BMP concentration and release rate from approved CS carriers is difficult to control with precision. Here we presented the fabrication of a recombinant fusion protein from recombinant human-like collagen (HLC) and human BMP-2 (hBMP2). The fusion protein preserved the characteristic of HLC allowing the recombinant protein to be expressed in Yeast (such as Pichia pastoris GS115) and purified rapidly and easily with mass production after methanol induction. It also kept the stable properties of HLC and hBMP2 in the body fluid environment with good biocompatibility and no cytotoxicity. Moreover, the recombinant fusion protein fabricated a vertical through-hole structure with improved mechanical properties, and thus facilitated migration of bone marrow mesenchymal stem cells (MSCs) into the fusion materials. Furthermore, the fusion protein degraded and released hBMP-2 in vivo allowing osteoinductive activity and the enhancement of utilization rate and the precise control of the hBMP2 release. This fusion protein when applied to cranial defects in rats was osteoinductively active and improved bone repairing enhancing the repairing rate 3.5- fold and 4.2- fold when compared to the HLC alone and the control, respectively. There were no visible inflammatory reactions, infections or extrusions around the implantation sites observed. Our data strongly suggests that this novel recombinant fusion protein could be more beneficial in the treatment of bone defects than the simple superposition of the hBMP2/collagen sponge.

Enhancement of in vivo supraspinatus tendon-to-bone healing with an alginate-chitin scaffold and rhBMP-2

INTRODUCTION

Rotator cuff disorders present a high retear rate despite advances in surgical treatment. Tissue engineering could therefore be interesting in order to try to enhance a more biological repair. RhBMP-2 is one of the most osteogenic growth factors and it also induces the formation of collagen type I. However, it has a short half-life and in order to get a more stable release over time it could be integrated in a more slowly degradable carrier, such as an alginate-chitin scaffold. The aim of this study was to investigate the role of the alginate-chitin scaffold alone and in combination with different concentrations of rhBMP-2 when applied on chronic rotator cuff lesions in a rat model.

MATERIALS AND METHODS

We performed an experimental study with 80 Sprague-Dawley rats, 8 months old, with a chronic rupture of the supraspinatus tendon that was repaired with a modified Mason Allen suture. A scaffold was applied over the suture and 4 groups were obtained; suture (S) only suture, double control (DC) alginate and chitin scaffold, single sample (SS) scaffold of alginate with rhBMP-2 (20 µg rhBMP-2) and chitin, double sample (DS) a scaffold containing alginate with rhBMP-2 and chitin with rhBMP-2 (40 µg rhBMP-2). Macroscopic, histological and biomechanical studies were performed at 4 months after reparation.

RESULTS

The modified Åström and Rausing's histological scale (the higher the score the worse outcome, 0 points=native tendon) was applied: S got 52 points compared to DC 30 (p = 0,034), SS 22 (p = 0,009) and DS 16 (p = 0,010). Biomechanically the maximum load was highest in DC (63,05 N), followed by DS (61,60 N), SS (52,35 N) and S (51,08), p = 0,025 DS vs S. As to the elastic constant a higher value was obtained in DC (16,65), DS (12,55) and SS (12,20) compared to S (9,33), p = 0,009 DC vs S and 0,034 DS vs S.

CONCLUSIONS

The alginate-chitin scaffold seems to promote a more biological response after the reparation of a chronic rotator cuff lesion. Its effect is further enhanced by the addition of rhBMP-2 since the osteotendinous junction is more native-like and has better biomechanical properties.

Biomimetic Alginate/Gelatin Cross-Linked Hydrogels Supplemented with Polyphosphate for Wound Healing Applications

In the present study, the fabrication of a biomimetic wound dressing that mimics the extracellular matrix, consisting of a hydrogel matrix composed of non-oxidized and periodate-oxidized marine alginate, was prepared to which gelatin was bound via Schiff base formation. Into this alginate/oxidized-alginate-gelatin hydrogel, polyP was stably but reversibly integrated by ionic cross-linking with Zn²⁺ ions. Thereby, a soft hybrid material is obtained, consisting of a more rigid alginate scaffold and porous structures formed by the oxidized-alginate-gelatin hydrogel with ionically cross-linked polyP. Two forms of the Zn-polyP-containing matrices were obtained based on the property of polyP to form, at neutral pH, a coacervate—the physiologically active form of the polymer. At alkaline conditions (pH 10), it will form nanoparticles, acting as a depot that is converted at pH 7 into the coacervate phase. Both polyP-containing hydrogels were biologically active and significantly enhanced cell growth/viability and attachment/spreading of human epidermal keratinocytes compared to control hydrogels without any adverse effect on reconstructed human epidermis samples in an in vitro skin irritation test system. From these data, we conclude that polyP-containing alginate/oxidized-alginate-gelatin hydrogels may provide a suitable regeneratively active matrix for wound healing for potential in vivo applications.

Therapeutics and delivery vehicles for local treatment of osteomyelitis

Osteomyelitis, or the infection of the bone, presents a major complication in orthopedics and may lead to prolonged hospital visits, implant failure, and in more extreme cases, amputation of affected limbs. Typical treatment for this disease involves surgical debridement followed by long-term, systemic antibiotic administration, which contributes to the development of antibiotic-resistant bacteria and has limited ability to eradicate challenging biofilm-forming pathogens including Staphylococcus aureus-the most common cause of osteomyelitis. Local delivery of high doses of antibiotics via traditional bone cement can reduce systemic side effects of an antibiotic. Nonetheless, growing concerns over burst release (then subtherapeutic dose) of antibiotics, along with microbial colonization of the nondegradable cement biomaterial, further exacerbate antibiotic resistance and highlight the need to engineer alternative antimicrobial therapeutics and local delivery vehicles with increased efficacy against, in particular, biofilm-forming, antibiotic-resistant bacteria. Furthermore, limited guidance exists regarding both standardized formulation protocols and validated assays to predict efficacy of a therapeutic against multiple strains of bacteria. Ideally, antimicrobial strategies would be highly specific while exhibiting a broad spectrum of bactericidal activity. With a focus on S. aureus infection, this review addresses the efficacy of novel therapeutics and local delivery vehicles, as alternatives to the traditional antibiotic regimens. The aim of this review is to discuss these components with regards to long bone osteomyelitis and to encourage positive directions for future research efforts.

Effects of alginate/chondroitin sulfate-based hydrogels on bone defects healing

Repairing bone defects remains challenging in orthopedics. Here, strontium (Sr) alginate hydrogels containing chondroitin sulfate (CS) were fabricated for enhancing bone defects repair. The effects of CS incorporation ratio on the morphology, structure, thermal stability, water uptake and mechanical performance of Sr-CS/alginate hydrogels were also evaluated. Increasing CS incorporation ratio, Sr-CS/alginate hydrogels exhibit decreasing mechanical properties and lower water retention capacity. In vitro results suggest that Sr-CS/alginate hydrogels with higher CS ratio facilitate the proliferation of osteoblasts. Additionally, the osteogenic genes expressions were investigated by real-time quantitative polymerase chain reaction (RT-qPCR). The results reveal that Sr-CS/alginate hydrogels should have positive effects on modulating the osteogenic factors. Moreover, by employing repair femoral cylindrical defects rabbit model, the efficiency of as-fabricated Sr-CS/alginate hydrogels in bone regeneration was evaluated. The animal study suggests that Sr-CS/alginate hydrogel could significantly facilitate bone defects repair and therefore should potentially be useful for osteochondral tissue engineering.

Hydroxyapatite-alginate Based Matrices for Drug Delivery

BACKGROUND

Hydroxyapatite (HAp) is a biocompatible bioceramic compound by nature and widely utilized in a broad range of biomedical applications, especially in drug delivery, tissue engineering, orthopedics, dentistry, etc. To intensify its usage, HAp is being reinforced with different biopolymer(s). In these bioceramicbiopolymeric systems, HAp crystallites have been well inviolate with the alginate molecules. The objective of this review article is to present a comprehensive discussion of different recently researched drug-releasing potential by HAp-alginate based matrices.

METHODS

During past few years, HAp particles (both synthesized and naturally derived) have been reinforced within different alginate-based systems to load a variety of drug candidates. Most of the reported drug-releasing HAp-alginate based matrices were prepared by the methodology of ionic-gelation of sodium alginate followed by air-drying/spray drying process.

RESULTS

HAp-alginate systems have already been proved as useful for loading a variety of drugs and also resulting sustained drug delivery with minimizing the drawbacks of pure alginate matrices (such as burst drug-releasing and low mechanical property in the alkaline pH).

CONCLUSION

HAp-alginate composites loaded with different kinds of drugs have already been reported to exhibit sustained releasing of loaded drugs over a longer period.

Recent developments in biomaterials for long-bone segmental defect reconstruction: A narrative overview

Reconstruction of long-bone segmental defects (LBSDs) has been one of the biggest challenges in orthopaedics. Biomaterials for the reconstruction are required to be strong, osteoinductive, osteoconductive, and allowing for fast angiogenesis, without causing any immune rejection or disease transmission. There are four main types of biomaterials including autograft, allograft, artificial material, and tissue-engineered bone. Remarkable progress has been made in LBSD reconstruction biomaterials in the last ten years.

THE TRANSLATIONAL POTENTIAL OF THIS ARTICLE

Our aim is to summarize recent developments in the divided four biomaterials utilized in the LBSD reconstruction to provide the clinicians with new information and comprehension from the biomaterial point of view.

Segmental long bone regeneration guided by degradable synthetic polymeric scaffolds

Recent developments in synthetic bone grafting materials and adjuvant therapeutic agents have opened the door to the regenerative reconstruction of critical-size long bone segmental defects resulting from trauma, osteoporotic fractures or tumour resections. Polymeric scaffolds with controlled macroporosities, degradability, useful surgical handling characteristics, and the ability to deliver biotherapeutics to promote new bone ingrowth have been developed for this challenging orthopaedic application. This review highlights major classes of degradable synthetic polymers and their biomineral composites, including conventional and amphiphilic polyesters, polyanhydrides, polycarbonates, and polyethylene glycol-based hydrogels, that have been explored for the regenerative reconstruction of critical-size long bone segmental defects over the past two decades. The pros and cons of these synthetic scaffold materials are presented in the context of enabling or impeding the functional (mechanical and radiographic) repair of a long bone segmental defect, with the long bone regeneration outcomes compared with healthy long bone controls or results achieved with current grafting standards.

Development of a Small Animal Ankle Arthrodesis Model

BACKGROUND

Our understanding of the biology of ankle arthrodesis is based largely on work in spine and long bone animal models. However, the local soft tissue and vascular anatomy of the foot and ankle is different from that of the spine. Accordingly, the objective of this study was to develop a small animal ankle arthrodesis model.

METHODS

A total of 12 Lewis rats successfully underwent ankle arthrodesis with stabilization consisting of a single Kirschner wire across the prepared tibiotalar joint. Based on high nonunion rates with this initial procedure, a modification was made consisting of a second pin crossing the joint. A total of 6 rats underwent the second procedure. Radiographs were taken postoperatively and in 2-week intervals up to 10 weeks. Micro computed tomography (µCT) and histological analysis was conducted at 10 weeks to assess the fusion mass. Osseous bridging of greater than 50% across the tibiotalar joint was deemed a successful fusion.

RESULTS

µCT analysis determined that 11 of the 12 rats in the single-pin cohort developed nonunions (8.3% fusion rate). In the dual-pin cohort, all 6 animals successfully fused (100% fusion rate). Histological analysis supported the radiographic imaging conclusions.

CONCLUSION

While the initial procedure had a high nonunion rate, enhancing the stability of the fixation greatly increased the union rate.

CLINICAL RELEVANCE

The present work demonstrates the first reliable small animal ankle arthrodesis model. We believe that this model can be used in the development of novel therapies aimed at decreasing complications and increasing fusion rates.

CRISPR-Cas9 modified bacteriophage for treatment of Staphylococcus aureus induced osteomyelitis and soft tissue infection

Osteomyelitis, or bone infection, is often induced by antibiotic resistant Staphylococcus aureus strains of bacteria. Although debridement and long-term administration of antibiotics are the gold standard for osteomyelitis treatment, the increase in prevalence of antibiotic resistant bacterial strains limits the ability of clinicians to effectively treat infection. Bacteriophages (phages), viruses that in a lytic state can effectively kill bacteria, have gained recent attention for their high specificity, abundance in nature, and minimal risk of host toxicity. Previously, we have shown that CRISPR-Cas9 genomic editing techniques could be utilized to expand temperate bacteriophage host range and enhance bactericidal activity through modification of the tail fiber protein. In a dermal infection study, these CRISPR-Cas9 phages reduced bacterial load relative to unmodified phage. Thus we hypothesized this temperate bacteriophage, equipped with the CRISPR-Cas9 bactericidal machinery, would be effective at mitigating infection from a biofilm forming S. aureus strain in vitro and in vivo. In vitro, qualitative fluorescent imaging demonstrated superiority of phage to conventional vancomycin and fosfomycin antibiotics against S. aureus biofilm. Quantitative antibiofilm effects increased over time, at least partially, for all fosfomycin, phage, and fosfomycin-phage (dual) therapeutics delivered via alginate hydrogel. We developed an in vivo rat model of osteomyelitis and soft tissue infection that was reproducible and challenging and enabled longitudinal monitoring of infection progression. Using this model, phage (with and without fosfomycin) delivered via alginate hydrogel were successful in reducing soft tissue infection but not bone infection, based on bacteriological, histological, and scanning electron microscopy analyses. Notably, the efficacy of phage at mitigating soft tissue infection was equal to that of high dose fosfomycin. Future research may utilize this model as a platform for evaluation of therapeutic type and dose, and alternate delivery vehicles for osteomyelitis mitigation.

Newly Designed Human-Like Collagen to Maximize Sensitive Release of BMP-2 for Remarkable Repairing of Bone Defects

Designing the “ideal” hydrogel/matrix which can load bone morphogenetic protein-2 (BMP-2) in a low dose and with a sustained release is the key for its successful therapeutic application to enhance osteogenesis. The current use of natural collagen sponges as hydrogel/matrix is limited due to the collagen matrix showing weak mechanical strength and unmanageable biodegradability. Furthermore, the efficiency and safe dose usage of the BMP-2 has never been seriously considered other than purely chasing the lowest dose usage and extended-release time. In this paper, we customized a novel enzymatically cross-linked recombinant human-like collagen (HLC) sponge with low immunogenicity, little risk from hidden viruses, and easy production. We obtained a unique vertical pore structure and the porosity of the HLC, which are beneficial for Mesenchymal stem cells (MSCs) migration into the HLC sponge and angiopoiesis. This HLC sponge loading with low dose BMP-2 (1 µg) possessed high mechanical strength along with a burst and a sustained release profile. These merits overcome previous limitations of HLC in bone repair and are safer and more sensitive than commercial collagens. For the first time, we identified that a 5 µg dose of BMP-2 can bring about the side effect of bone overgrowth through this sensitive delivery system. Osteoinduction of the HLC-BMP sponges was proved by an in vivo mouse ectopic bone model and a rat cranial defect repair model. The method and the HLC-BMP sponge have the potential to release other growth factors and aid other tissue regeneration. Additionally, the ability to mass-produce HLC in our study overcomes the current supply shortage, which limits bone repair in the clinic.

Multifunctional scaffolds for facile implantation, spontaneous fixation, and accelerated long bone regeneration in rodents

Graft-guided regenerative repair of critical long bone defects achieving facile surgical delivery, stable graft fixation, and timely restoration of biomechanical integrity without excessive biotherapeutics remains challenging. Here, we engineered hydration-induced swelling/stiffening and thermal-responsive shape-memory properties into scalable, three-dimensional–printed amphiphilic degradable polymer-osteoconductive mineral composites as macroporous, non–load-bearing, resorbable synthetic grafts. The distinct physical properties of the grafts enabled straightforward surgical insertion into critical-size rat femoral segmental defects. Grafts rapidly recovered their precompressed shape, stiffening and swelling upon warm saline rinse to result in 100% stable graft fixation. The osteoconductive macroporous grafts guided bone formation throughout the defect as early as 4 weeks after implantation; new bone remodeling correlated with rates of scaffold composition-dependent degradation. A single dose of 400-ng recombinant human bone morphogenetic protein-2/7 heterodimer delivered via the graft accelerated bone regeneration bridging throughout the entire defect by 4 weeks after delivery. Full restoration of torsional integrity and complete scaffold resorption were achieved by 12 to 16 weeks after surgery. This biomaterial platform enables personalized bone regeneration with improved surgical handling, in vivo efficacy and safety.

Sustained Release of Two Bioactive Factors from Supramolecular Hydrogel Promotes Periodontal Bone Regeneration

Intact and stable bone reconstruction is ideal for the treatment of periodontal bone destruction but remains challenging. In research, biomaterials are used to encapsulate stem cells or bioactive factors for periodontal bone regeneration, but, to the best of our knowledge, using a supramolecular hydrogel to encapsulate bioactive factors for their sustained release in bone defect areas to promote periodontal bone regeneration has not been reported. Herein, we used a well-studied hydrogelator, NapFFY, to coassemble with SDF-1 and BMP-2 to prepare a supramolecular hydrogel, SDF-1/BMP-2/NapFFY. In vitro and in vivo results indicated that these two bioactive factors were ideally, synchronously, and continuously released from the hydrogel to effectively promote the regeneration and reconstruction of periodontal bone tissues. Specifically, after the bone defect areas were treated with our SDF-1/BMP-2/NapFFY hydrogel for 8 weeks using maxillary critical-sized periodontal bone defect model rats, a superior bone regeneration rate of 56.7% bone volume fraction was achieved in these rats. We anticipate that our SDF-1/BMP-2/NapFFY hydrogel could replace bone transplantation in the clinic for the repair of periodontal bone defects and periodontally accelerated osteogenic orthodontics in the near future.

Materials Science and Design Principles of Growth Factor Delivery Systems in Tissue Engineering and Regenerative Medicine

Growth factors (GFs) are signaling molecules that direct cell development by providing biochemical cues for stem cell proliferation, migration, and differentiation. GFs play a key role in tissue regeneration, but one major limitation of GF-based therapies is dosage-related adverse effects. Additionally, the clinical applications and efficacy of GFs are significantly affected by the efficiency of delivery systems and other pharmacokinetic factors. Hence, it is crucial to design delivery systems that provide optimal activity, stability, and tunable delivery for GFs. Understanding the physicochemical properties of the GFs and the biomaterials utilized for the development of biomimetic GF delivery systems is critical for GF-based regeneration. Many different delivery systems have been developed to achieve tunable delivery kinetics for single or multiple GFs. The identification of ideal biomaterials with tunable properties for spatiotemporal delivery of GFs is still challenging. This review characterizes the types, properties, and functions of GFs, the materials science of widely used biomaterials, and various GF loading strategies to comprehensively summarize the current delivery systems for tunable spatiotemporal delivery of GFs aimed for tissue regeneration applications. This review concludes by discussing fundamental design principles for GF delivery vehicles based on the interactive physicochemical properties of the proteins and biomaterials.

In situ bone regeneration enabled by a biodegradable hybrid double-network hydrogel

The biodegradable hybrid double-network hydrogel for stem cell-enhanced bone regeneration.

Alginate Matrices for Protein Delivery – a Short Review

Growth factors are powerful molecules that regulate cellular growth, proliferation, healing, and cellular differentiation. A delivery matrix that incorporates growth factors with high loading efficiencies, controls their release, and maintains bioactivity would be a powerful tool for regenerative medicine. Alginate has several unique properties that make it an excellent platform for the delivery of proteins. Mild gelling conditions can minimize the risk of protein denaturation; moreover, alginate can serve as protection from degradation until protein release. Various modifications have been proposed to tune alginate binding and release proteins, simultaneously adjusting alginate degradability, mechanical stiffness, swelling, gelation properties and cell affinity. The primary objective of this article is to review the literature related to recent advances in the application of alginate matrices in protein delivery in regenerative medicine. A special emphasis is put on the relevance of delivery of growth factors and chemokine.

Hydrolytically-degradable click-crosslinked alginate hydrogels

Degradable biomaterials aim to recapitulate the dynamic microenvironment that cells are naturally exposed to. By oxidizing the alginate polymer backbone, thereby rendering it susceptible to hydrolysis, and crosslinking it via norbornene-tetrazine click chemistry, we can control rheological, mechanical, and degradation properties of resulting hydrogels. Chemical modifications were confirmed by nuclear magnetic resonance (NMR) and the resulting mechanical properties measured by rheology and unconfined compression testing, demonstrating that these are both a function of norbornene coupling and oxidation state. The degradation behavior was verified by tracking mechanical and swelling behavior over time, showing that degradation could be decoupled from initial mechanical properties. The cell compatibility was assessed in 2D and 3D using a mouse pre-osteoblast cell line and testing morphology, proliferation, and viability. Cells attached, spread and proliferated in 2D and retained a round morphology and stable number in 3D, while maintaining high viability in both contexts over 7 days. Finally, oxidized and unoxidized control materials were implanted subcutaneously into the backs of C57/Bl6 mice, and recovered after 8 weeks. Histological staining revealed morphological differences and fibrous tissue infiltration only in oxidized materials. These materials with tunable and decoupled mechanical and degradation behavior could be useful in many tissue engineering applications.

A rapid method for determining protein diffusion through hydrogels for regenerative medicine applications

Hydrogels present versatile platforms for the encapsulation and delivery of proteins and cells for regenerative medicine applications. However, differences in hydrogel cross-linking density, polymer weight content, and affinity for proteins all contribute to diverse diffusion rates of proteins through hydrogel networks. Here, we describe a simple method to accurately measure protein diffusion through hydrogels, within a few hours and without the use of large amounts of protein. We tracked the diffusion of several proteins of varying molecular weights along the axial direction of capillary tubes filled with alginate, collagen, or poly(ethylene glycol) hydrogels. The rate of protein diffusion decreased with increasing molecular weight. A computational model of protein diffusion through capillary tubes was also created to predict and verify experimental protein diffusion coefficients. This in vitro capillary tube-based method of measuring protein diffusion represents a simple strategy to interrogate protein diffusion through natural and synthetic hydrogels and aid in the design of better biomaterial-based delivery vehicles that can effectively modulate protein release.

Three dimensional cell printing with sulfated alginate for improved bone morphogenetic protein-2 delivery and osteogenesis in bone tissue engineering

Three-dimensional (3D) cell printing is a unique technique that enables free-form fabrication of cell-laden hydrogel scaffolds with controllable features and interconnected pores for tissue engineering applications. To this end, bioink materials able to offer good printability and favorable cellular interaction are highly required. Herein, we synthesized alginate sulfate, which is a structural mimic of heparin that can strongly bind with growth factors to prolong their activities, and studied its feasibility for cell printing applications. Several bio-inks composed of alginate and alginate-sulfate were studied to characterize their material properties and their utilities in 3D printing. The inclusion of alginate-sulfate in bio-inks (alginate/alginate-sulfate) did not significantly influence their rheological properties and allowed for a good 3D printing processibility with distinct pores and features. Moreover, alginate/alginate-sulfate bio-inks exhibited an improved retention of bone morphogenetic protein 2 in 3D-printed scaffolds. Osteoblastic proliferation and differentiation in vitro were promoted by alginate/alginate-sulfate 3D-printed constructs with an optimal composition of 3% alginate and 2% alginate-sulfate. We envision that bio-inks displaying prolonged interactions with growth factors will be useful for tissue engineering applications including bone regeneration.

Double-layered microsphere based dual growth factor delivery system for guided bone regeneration

Microsphere based drug delivery systems show great advantages for tissue engineering. However, it is still a big challenge to fabricate microspheres with capability in delivering and controlled releasing multiple growth factors. In the present study, double-layered microspheres consisting of an inner-layer of small core particles and an outer-layer of big shell particles were developed to sequentially release cell homing factors (SDF-1) and osteoinductive growth factors (BMP-2) for bone regeneration. In vitro release testing showed that bioactivity of both growth factors retained within the microspheres and differential release of SDF-1 and BMP-2 was achieved. Microspheres with both growth factors showed an obvious chemotaxis effect on preosteoblasts by inducing more cell migration. In osteoinductive ability tests, the microspheres with both growth factors showed higher ALP activity and more mineralized modules than control groups after culturing for 2 weeks. The expression of bone development transcription factors (Runx2, OCN, Osterix) as well as Smad signals (Smad 1, 5, 8) showed higher gene expression in the dual growth factor group. Our results suggest that a double-layered microsphere system enhances the recruitment of osteogenic cells and osteoinduction, which provides a promising platform for bone regeneration.

Polysaccharide-Based Controlled Release Systems for Therapeutics Delivery and Tissue Engineering: From Bench to Bedside

Polysaccharides or polymeric carbohydrate molecules are long chains of monosaccharides that are linked by glycosidic bonds. The naturally based structural materials are widely applied in biomedical applications. This article covers four different types of polysaccharides (i.e., alginate, chitosan, hyaluronic acid, and dextran) and emphasizes their chemical modification, preparation approaches, preclinical studies, and clinical translations. Different cargo fabrication techniques are also presented in the third section. Recent progresses in preclinical applications are then discussed, including tissue engineering and treatment of diseases in both therapeutic and monitoring aspects. Finally, clinical translational studies with ongoing clinical trials are summarized and reviewed. The promise of new development in nanotechnology and polysaccharide chemistry helps clinical translation of polysaccharide-based drug delivery systems.

Application of alginate microbeads as a carrier of bone morphogenetic protein-2 for bone regeneration

Bone morphogenetic protein-2 (BMP-2) is commonly used to enhance bone regeneration. The potential of BMP-2 for bone regeneration varies according to the concentration and release kinetics on the implanted site. Therefore, it is important to determine appropriate carriers of BMP-2. However, no optimal delivery vehicles have been identified. In the present study, we used alginate microbeads as a delivery vehicle for BMP-2. Alginate microbeads can be implanted onto the disease site through surgery or injection. The objective of this study was to evaluate that the osteoinductive properties of BMP-2 are effective in alginate microbeads as a carrier. In this study, the release kinetics of BMP-2 in alginate microbeads was evaluated using an enzyme-linked immunosorbent assay. BMP-2 released from alginate microbeads induced high alkaline phosphatase activity in canine adipose tissue-derived mesenchymal stem cells. Injection of alginate microbeads with BMP-2 into mouse subcutaneous tissue, as well as surgical implantation into the 5-mm circular calvarial defects in rats, was conducted and the results showed extensive new bone formation. In conclusion, alginate microbeads can be utilized as an effective BMP-2 delivery vehicle for use in orthopedic surgery and as an injectable vehicle for a minimally invasive therapy. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 107B: 286-294, 2019.

3D printed microchannel networks to direct vascularisation during endochondral bone repair

Bone tissue engineering strategies that recapitulate the developmental process of endochondral ossification offer a promising route to bone repair. Clinical translation of such endochondral tissue engineering strategies will require overcoming a number of challenges, including the engineering of large and often anatomically complex cartilage grafts, as well as the persistence of core regions of avascular cartilage following their implantation into large bone defects. Here 3D printing technology is utilized to develop a versatile and scalable approach to guide vascularisation during endochondral bone repair. First, a sacrificial pluronic ink was used to 3D print interconnected microchannel networks in a mesenchymal stem cell (MSC) laden gelatin-methacryloyl (GelMA) hydrogel. These constructs (with and without microchannels) were next chondrogenically primed in vitro and then implanted into critically sized femoral bone defects in rats. The solid and microchanneled cartilage templates enhanced bone repair compared to untreated controls, with the solid cartilage templates (without microchannels) supporting the highest levels of total bone formation. However, the inclusion of 3D printed microchannels was found to promote osteoclast/immune cell invasion, hydrogel degradation, and vascularisation following implantation. In addition, the endochondral bone tissue engineering strategy was found to support comparable levels of bone healing to BMP-2 delivery, whilst promoting lower levels of heterotopic bone formation, with the microchanneled templates supporting the lowest levels of heterotopic bone formation. Taken together, these results demonstrate that 3D printed hypertrophic cartilage grafts represent a promising approach for the repair of complex bone fractures, particularly for larger defects where vascularisation will be a key challenge.