Biomimetic PLGA/Strontium-Zinc Nano Hydroxyapatite Composite Scaffolds for Bone Regeneration

Construction Form and Application of Three-Dimensional Bioprinting Ink Containing Hydroxyapatite

With the increasing prevalence of bone tissue diseases, three-dimensional (3D) bioprinting applied to bone tissue engineering for treatment has received a lot of interests in recent years. The research and popularization of 3D bioprinting in bone tissue engineering require bioinks with good performance, which is closely related to ideal material and appropriate construction form. Hydroxyapatite (HAp) is the inorganic component of natural bone and has been widely used in bone tissue engineering and other fields due to its good biological and physicochemical properties. Previous studies have prepared different bioinks containing HAp and evaluated their properties in various aspects. Most bioinks showed significant improvement in terms of rheology and biocompatibility; however, not all of them had sufficiently favorable mechanical properties and antimicrobial activity. The deficiencies in properties of bioink and 3D bioprinting technology limited the applications of bioinks containing HAp in clinical trials. This review article summarizes the construction forms of bioinks containing HAp and its modifications in previous studies, as well as the 3D bioprinting techniques adopted to print bioink containing HAp. In addition, this article summarizes the advantages and underlying mechanisms of bioink containing HAp, as well as its limitations, and suggests possible improvement to facilitate the development of bone tissue engineering bioinks containing HAp in the future.

Cellular Senescence and Inflammaging in the Bone: Pathways, Genetics, Anti-Aging Strategies and Interventions

Advancing age is associated with several age-related diseases (ARDs), with musculoskeletal conditions impacting millions of elderly people worldwide. With orthopedic conditions contributing towards considerable number of patients, a deeper understanding of bone aging is the need of the hour. One of the underlying factors of bone aging is cellular senescence and its associated senescence associated secretory phenotype (SASP). SASP comprises of pro-inflammatory markers, cytokines and chemokines that arrest cell growth and development. The accumulation of SASP over several years leads to chronic low-grade inflammation with advancing age, also known as inflammaging. The pathways and molecular mechanisms focused on bone senescence and inflammaging are currently limited but are increasingly being explored. Most of the genes, pathways and mechanisms involved in senescence and inflammaging coincide with those associated with cancer and other ARDs like osteoarthritis (OA). Thus, exploring these pathways using techniques like sequencing, identifying these factors and combatting them with the most suitable approach are crucial for healthy aging and the early detection of ARDs. Several approaches can be used to aid regeneration and reduce senescence in the bone. These may be pharmacological, non-pharmacological and lifestyle interventions. With increasing evidence towards the intricate relationship between aging, senescence, inflammation and ARDs, these approaches may also be used as anti-aging strategies for the aging bone marrow (BM).

Morphological 3D Analysis of PLGA/Chitosan Blend Polymer Scaffolds and Their Impregnation with Olive Pruning Residues via Supercritical CO2

Natural extracts, such as those from the residues of the Olea europaea industry, offer an opportunity for use due to their richness in antioxidant compounds. These compounds can be incorporated into porous polymeric devices with huge potential for tissue engineering such as bone, cardiovascular, osteogenesis, or neural applications using supercritical CO2. For this purpose, polymeric scaffolds of biodegradable poly(lactic-co-glycolic acid) (PLGA) and chitosan, generated in situ by foaming, were employed for the supercritical impregnation of ethanolic olive leaf extract (OLE). The influence of the presence of chitosan on porosity and interconnectivity in the scaffolds, both with and without impregnated extract, was studied. The scaffolds have been characterized by X-ray computed microtomography, scanning electron microscope, measurements of impregnated load, and antioxidant capacity. The expansion factor decreased as the chitosan content rose, which also occurred when OLE was used. Pore diameters varied, reducing from 0.19 mm in pure PLGA to 0.11 mm in the two experiments with the highest chitosan levels. The connectivity was analyzed, showing that in most instances, adding chitosan doubled the average number of connections, increasing it by a factor of 2.5. An experiment was also conducted to investigate the influence of key factors in the impregnation of the extract, such as pressure (10-30 MPa), temperature (308-328 K), and polymer ratio (1:1-9:1 PLGA/chitosan). Increased pressure facilitated increased OLE loading. The scaffolds were evaluated for antioxidant activity and demonstrated substantial oxidation inhibition (up to 82.5% under optimal conditions) and remarkable potential to combat oxidative stress-induced pathologies.

Harnessing the Potential of PLGA Nanoparticles for Enhanced Bone Regeneration

Recently, nanotechnologies have become increasingly prominent in the field of bone tissue engineering (BTE), offering substantial potential to advance the field forward. These advancements manifest in two primary ways: the localized application of nanoengineered materials to enhance bone regeneration and their use as nanovehicles for delivering bioactive compounds. Despite significant progress in the development of bone substitutes over the past few decades, it is worth noting that the quest to identify the optimal biomaterial for bone regeneration remains a subject of intense debate. Ever since its initial discovery, poly(lactic-co-glycolic acid) (PLGA) has found widespread use in BTE due to its favorable biocompatibility and customizable biodegradability. This review provides an overview of contemporary advancements in the development of bone regeneration materials using PLGA polymers. The review covers some of the properties of PLGA, with a special focus on modifications of these properties towards bone regeneration. Furthermore, we delve into the techniques for synthesizing PLGA nanoparticles (NPs), the diverse forms in which these NPs can be fabricated, and the bioactive molecules that exhibit therapeutic potential for promoting bone regeneration. Additionally, we addressed some of the current concerns regarding the safety of PLGA NPs and PLGA-based products available on the market. Finally, we briefly discussed some of the current challenges and proposed some strategies to functionally enhance the fabrication of PLGA NPs towards BTE. We envisage that the utilization of PLGA NP holds significant potential as a potent tool in advancing therapies for intractable bone diseases.

Towards the Clinical Translation of 3D PLGA/β-TCP/Mg Composite Scaffold for Cranial Bone Regeneration

Recent years have witnessed the rapid development of 3D porous scaffolds with excellent biocompatibility, tunable porosity, and pore interconnectivity, sufficient mechanical strength, controlled biodegradability, and favorable osteogenesis for improved results in cranioplasty. However, clinical translation of these scaffolds has lagged far behind, mainly because of the absence of a series of biological evaluations. Herein, we designed and fabricated a composite 3D porous scaffold composed of poly (lactic-co-glycolic) acid (PLGA), β-tricalcium phosphate (β-TCP), and Mg using the low-temperature deposition manufacturing (LDM) technique. The LDM-engineered scaffolds possessed highly porous and interconnected microstructures with a porosity of 63%. Meanwhile, the scaffolds exhibited mechanical properties close to that of cancellous bone, as confirmed by the compression tests. It was also found that the original composition of scaffolds could be maintained throughout the fabrication process. Particularly, two important biologic evaluations designed for non-active medical devices, i.e., local effects after implantation and subchronic systemic toxicity tests, were conducted to evaluate the local and systemic toxicity of the scaffolds. Additionally, the scaffolds exhibited significant higher mRNA levels of osteogenic genes compared to control scaffolds, as confirmed by an in vitro osteogenic differentiation test of MC3T3-E1 cells. Finally, we demonstrated the improved cranial bone regeneration performance of the scaffolds in a rabbit model. We envision that our investigation could pave the way for translating the LDM-engineered composite scaffolds into clinical products for cranial bone regeneration.

Zinc-based biomaterials for bone repair and regeneration: mechanism and applications

Zinc (Zn) is one of the most important trace elements in the human body and plays a key role in various physiological processes, especially in bone metabolism. Zn-containing materials have been reported to enhance bone repair through promoting cell proliferation, osteogenic activity, angiogenesis, and inhibiting osteoclast differentiation. Therefore, Zn-based biomaterials are potential substitutes for traditional bone grafts. In this review, the specific mechanisms of bone formation promotion by Zn-based biomaterials were discussed, and recent developments in their application in bone tissue engineering were summarized. Moreover, the challenges and perspectives of Zn-based biomaterials were concluded, revealing their attractive potential and development directions in the future.

Metal Ion-Doped Hydroxyapatite-Based Materials for Bone Defect Restoration

Hydroxyapatite (HA)-based materials are widely used in the bone defect restoration field due to their stable physical properties, good biocompatibility, and bone induction potential. To further improve their performance with extra functions such as antibacterial activity, various kinds of metal ion-doped HA-based materials have been proposed and synthesized. This paper offered a comprehensive review of metal ion-doped HA-based materials for bone defect restoration based on the introduction of the physicochemical characteristics of HA followed by the synthesis methods, properties, and applications of different kinds of metal ion (Ag+, Zn2+, Mg2+, Sr2+, Sm3+, and Ce3+)-doped HA-based materials. In addition, the underlying challenges for bone defect restoration using these materials and potential solutions were discussed.

Advances in Biodegradable Polymers and Biomaterials for Medical Applications-A Review

The introduction of new materials for the production of various types of constructs that can connect directly to tissues has enabled the development of such fields of science as medicine, tissue, and regenerative engineering. The implementation of these types of materials, called biomaterials, has contributed to a significant improvement in the quality of human life in terms of health. This is due to the constantly growing availability of new implants, prostheses, tools, and surgical equipment, which, thanks to their specific features such as biocompatibility, appropriate mechanical properties, ease of sterilization, and high porosity, ensure an improvement of living. Biodegradation ensures, among other things, the ideal rate of development for regenerated tissue. Current tissue engineering and regenerative medicine strategies aim to restore the function of damaged tissues. The current gold standard is autografts (using the patient's tissue to accelerate healing), but limitations such as limited procurement of certain tissues, long operative time, and donor site morbidity have warranted the search for alternative options. The use of biomaterials for this purpose is an attractive option and the number of biomaterials being developed and tested is growing rapidly.

3D printed strontium-zinc-phosphate bioceramic scaffolds with multiple biological functions for bone tissue regeneration

Calcium phosphate (CaP) bioceramics are broadly employed for bone regeneration due to their excellent biocompatibility and osteoconductivity. However, they are not capable of repairing healing-impaired bone defects such as defects with conditions of ischemia or infection due to restricted bioactivities. In this study, we synthesized single-phased strontium-zinc-phosphate (SZP, SrZn2(PO4)2) bioceramics via a solution combustion method and further fabricated SZP scaffolds using a three-dimensional (3D) printing technique. Compared to 3D printed β-tricalcium phosphate (β-TCP) scaffolds, the 3D printed SZP scaffolds presented comparable porosity, compressive strength, and Young's modulus, but increased ability of osteogenesis, angiogenesis, immunomodulation and anti-bacterial activity. Specifically, 3D printed SZP scaffolds not only led to significantly higher osteogenic differentiation of MC3T3-E1 cells and pro-angiogenesis of human umbilical vein endothelial cells (HUVECs) directly or through macrophage-mediated immunomodulation, but also inhibited the growth of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli). The in vivo study of the rat cranial bone defect model further confirmed better vascularized bone regeneration in 3D-printed SZP scaffolds. These findings indicate that the proposed 3D-printed SZP scaffolds might be a versatile candidate for bone tissue engineering.

Influence of strontium containing fluorophosphate glass onto structural and mechanical behavior of MTA network

OBJECTIVE

This study aimed to evaluate the effect of incorporation of strontium based fluoro phosphate glass (SrFPG) 48P₂O₅-29CaO-14NaO-3CaF₂-6SrO on physico chemical and biological properties of mineral trioxide aggregate (MTA).

METHODS

Optimized SrFPG glass powder were prepared using planetary ball mill and incorporated into MTA in varying proportion (1, 5, 10 wt%) to obtain SrMT1, SrMT5, SrMT10 bio-composite respectively. The bio-composites were characterized using XRD, FTIR and SEM-EDAX before and after soaking for 28 days in stimulated body fluid (SBF) solution. To assess the mechanical properties and biocompatibility of the prepared bio-composite, density, pH analysis, compressive strength and cytotoxicity evaluation using MTT assay were done before and after soaking for 28 days in SBF solution.

RESULTS

A nonlinear variation in compressive strength and pH values was noted. Of the bio-composites, SrMT10 was evidenced with rich apatite formation in XRD, FTIR and SEM with EDAX analysis. MTT assay showed increased cell viability in all the samples before and after in vitro studies.

Bacterial Inhibition and Osteogenic Potentials of Sr/Zn Co-Doped Nano-Hydroxyapatite-PLGA Composite Scaffold for Bone Tissue Engineering Applications

Bacterial infection associated with bone grafts is one of the major challenges that can lead to implant failure. Treatment of these infections is a costly endeavor; therefore, an ideal bone scaffold should merge both biocompatibility and antibacterial activity. Antibiotic-impregnated scaffolds may prevent bacterial colonization but exacerbate the global antibiotic resistance problem. Recent approaches combined scaffolds with metal ions that have antimicrobial properties. In our study, a unique strontium/zinc (Sr/Zn) co-doped nanohydroxyapatite (nHAp) and Poly (lactic-co-glycolic acid) -(PLGA) composite scaffold was fabricated using a chemical precipitation method with different ratios of Sr/Zn ions (1%, 2.5%, and 4%). The scaffolds’ antibacterial activity against Staphylococcus aureus were evaluated by counting bacterial colony-forming unit (CFU) numbers after direct contact with the scaffolds. The results showed a dose-dependent reduction in CFU numbers as the Zn concentration increased, with 4% Zn showing the best antibacterial properties of all the Zn-containing scaffolds. PLGA incorporation in Sr/Zn-nHAp did not affect the Zn antibacterial activity and the 4% Sr/Zn-nHAp-PLGA scaffold showed a 99.7% bacterial growth inhibition. MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) cell viability assay showed that Sr/Zn co-doping supported osteoblast cell proliferation with no apparent cytotoxicity and the highest doping percentage in the 4% Sr/Zn-nHAp-PLGA was found to be ideal for cell growth. In conclusion, these findings demonstrate the potential for a 4% Sr/Zn-nHAp-PLGA scaffold with enhanced antibacterial activity and cytocompatibility as a suitable candidate for bone regeneration.

Promotion of In Vitro Osteogenic Activity by Melt Extrusion-Based PLLA/PCL/PHBV Scaffolds Enriched with Nano-Hydroxyapatite and Strontium Substituted Nano-Hydroxyapatite

Bone tissue engineering has emerged as a promising strategy to overcome the limitations of current treatments for bone-related disorders, but the trade-off between mechanical properties and bioactivity remains a concern for many polymeric materials. To address this need, novel polymeric blends of poly-L-lactic acid (PLLA), polycaprolactone (PCL) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) have been explored. Blend filaments comprising PLLA/PCL/PHBV at a ratio of 90/5/5 wt% have been prepared using twin-screw extrusion. The PLLA/PCL/PHBV blends were enriched with nano-hydroxyapatite (nano-HA) and strontium-substituted nano-HA (Sr-nano-HA) to produce composite filaments. Three-dimensional scaffolds were printed by fused deposition modelling from PLLA/PCL/PHBV blend and composite filaments and evaluated mechanically and biologically for their capacity to support bone formation in vitro. The composite scaffolds had a mean porosity of 40%, mean pores of 800 µm, and an average compressive modulus of 32 MPa. Polymer blend and enriched scaffolds supported cell attachment and proliferation. The alkaline phosphatase activity and calcium production were significantly higher in composite scaffolds compared to the blends. These findings demonstrate that thermoplastic polyesters (PLLA and PCL) can be combined with polymers produced via a bacterial route (PHBV) to produce polymer blends with excellent biocompatibility, providing additional options for polymer blend optimization. The enrichment of the blend with nano-HA and Sr-nano-HA powders enhanced the osteogenic potential in vitro.

Enhanced In Vitro Biocompatible Polycaprolactone/Nano-Hydroxyapatite Scaffolds with Near-Field Direct-Writing Melt Electrospinning Technology

Polycaprolactone (PCL) scaffold is a common biological material for tissue engineering, owing to its good biocompatibility, biodegradability and plasticity. However, it is not suitable for osteoblast adhesion and regeneration of bone tissue due to its non-biological activity, poor mechanical strength, slow degradation speed, smooth surface and strong hydrophobicity. To improve the mechanical properties and biocompatibility of PCL scaffold, the PCL/nHA scaffolds were prepared by melting and blending different proportions of nano-hydroxyapatite (nHA) with PCL by the near-field direct-writing melt electrospinning technology in this study. The morphology, porosity, mechanical properties and in vitro biocompatibility of the PCL/nHA scaffolds were studied. The results showed that when the proportion of nHA was less than or equal to 25%, PCL/nHA composite scaffolds were easily formed in which bone marrow mesenchymal stem cells proliferated successfully. When the proportion of nHA was 15%, the PCL/nHA composite scaffolds had excellent structural regularity, good fiber uniformity, outstanding mechanical stability and superior biocompatibility. The PCL/nHA composite scaffolds were ideal scaffold materials, which would broaden their applications for bone tissue engineering.

Bioactive Composite for Orbital Floor Repair and Regeneration

In the maxillofacial area, specifically the orbital floor, injuries can cause bone deformities in the head and face that are difficult to repair or regenerate. Treatment methodologies include use of polymers, metal, ceramics on their own and in combinations mainly for repair purposes, but little attention has been paid to identify suitable materials for orbital floor regeneration. Polyurethane (PU) and hydroxyapatite (HA) micro- or nano- sized with different percentages (25%, 40% & 60%) were used to fabricate bioactive tissue engineering (TE) scaffolds using solvent casting and particulate leaching methods. Mechanical and physical characterisation of TE scaffolds was investigated by tensile tests and SEM respectively. Chemical and structural properties of PU and PU/HA scaffolds were evaluated by infrared (IR) spectroscopy and Surface properties of the bioactive scaffold were analysed using attenuated total reflectance (ATR) sampling accessory coupled with IR. Cell viability, collagen formed, VEGF protein amount and vascularisation of bioactive TE scaffold were studied. IR characterisation confirmed the integration of HA in composite scaffolds, while ATR confirmed the significant amount of HA present at the top surface of the scaffold, which was a primary objective. The SEM images confirmed the pores' interconnectivity. Increasing the content of HA up to 40% led to an improvement in mechanical properties, and the incorporation of nano-HA was more promising than that of micro-HA. Cell viability assays (using MG63) confirmed biocompatibility and CAM assays confirmed vascularization, demonstrating that HA enhances vascularization. These properties make the resulting biomaterials very useful for orbital floor repair and regeneration.

Physical and Chemical Characterization of Biomineralized Collagen with Different Microstructures

Mineralized collagen is the basic unit in hierarchically organized natural bone with different structures. Polyacrylic acid (PAA) and periodic fluid shear stress (FSS) are the most common chemical and physical means to induce intrafibrillar mineralization. In the present study, non-mineralized collagen, extrafibrillar mineralized (EM) collagen, intrafibrillar mineralized (IM) collagen, and hierarchical intrafibrillar mineralized (HIM) collagen induced by PAA and FSS were prepared, respectively. The physical and chemical properties of these mineralized collagens with different microstructures were systematically investigated afterwards. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) showed that mineralized collagen with different microstructures was prepared successfully. The pore density of the mineralized collagen scaffold is higher under the action of periodic FSS. Fourier transform infrared spectroscopy (FTIR) analysis showed the formation of the hydroxyapatite (HA) crystal. A significant improvement in the pore density, hydrophilicity, enzymatic stability, and thermal stability of the mineralized collagen indicated that the IM collagen under the action of periodic FSS was beneficial for maintaining collagen activity. HIM collagen fibers, which are prepared under the co-action of periodic FSS and sodium tripolyphosphate (TPP), may pave the way for new bone substitute material applications.