Biomimetic mineralization of nanocrystalline hydroxyapatites on aminated modified polylactic acid microspheres to develop a novel drug delivery system for alendronate

Fabrication of polymeric microspheres for biomedical applications

Polymeric microspheres (PMs) have attracted great attention in the field of biomedicine in the last several decades due to their small particle size, special functionalities shown on the surface and high surface-to-volume ratio. However, how to fabricate PMs which can meet the clinical needs and transform laboratory achievements to industrial scale-up still remains a challenge. Therefore, advanced fabrication technologies are pursued. In this review, we summarize the technologies used to fabricate PMs, including emulsion-based methods, microfluidics, spray drying, coacervation, supercritical fluid and superhydrophobic surface-mediated method and their advantages and disadvantages. We also review the different structures, properties and functions of the PMs and their applications in the fields of drug delivery, cell encapsulation and expansion, scaffolds in tissue engineering, transcatheter arterial embolization and artificial cells. Moreover, we discuss existing challenges and future perspectives for advancing fabrication technologies and biomedical applications of PMs.

In vitro/ex vivo evaluation of multifunctional collagen/chitosan/hyaluronic acid hydrogel-based alendronate delivery systems

Injectable hydrogel-based materials have emerged as promising alendronate (ALN) delivery systems for the treatment of osteoporosis. However, their intrinsic permeability limits the sustained delivery of small-molecule drugs. In response to this challenge, we present the multifunctional hybrids composed of mesoporous silica particles decorated with hydroxyapatite and loaded with alendronate (MSP-NH2-HAp-ALN), which are immobilized in collagen/chitosan/hyaluronic acid-based hydrogel. We have mainly focused on the biological in vitro/ex vivo evaluation of developed composites. It was found that the extracts released from tested systems do not exhibit hemolytic properties and are safe for blood elements and the human liver cell model. The resulting materials create an environment conducive to differentiating human bone marrow mesenchymal stem cells and reduce the viability of osteoclast precursors (RAW 264.7). Importantly, even the system with the lowest concentration of ALN caused a substantial cytotoxic effect on RAW 264.7 cells; their viability decreased to 20 % and 10 % of control on 3 and 7 day of culture. Additionally, prolonged ALN release (up to 20 days) with minimized burst release was observed, while material features (wettability, swellability, degradation, mechanical properties) depended on MSP-NH2-HAp-ALN content. The obtained data indicate that developed composites establish a high-potential formulation for safe and effective osteoporosis therapy.

Low-Temperature Plasmas Improving Chemical and Cellular Properties of Poly (Ether Ether Ketone) Biomaterial for Biomineralization

Osteoblastic and chemical responses to Poly (ether ether ketone) (PEEK) material have been improved using a variety of low-temperature plasmas (LTPs). Surface chemical properties are modified, and can be used, using low-temperature plasma (LTP) treatments which change surface functional groups. These functional groups increase biomineralization, in simulated body fluid conditions, and cellular viability. PEEK scaffolds were treated, with a variety of LTPs, incubated in simulated body fluids, and then analyzed using multiple techniques. First, scanning electron microscopy (SEM) showed morphological changes in the biomineralization for all samples. Calcein staining, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) confirmed that all low-temperature plasma-treated groups showed higher levels of biomineralization than the control group. MTT cell viability assays showed LTP-treated groups had increased cell viability in comparison to non-LTP-treated controls. PEEK treated with triethyl phosphate plasma (TEP) showed higher levels of cellular viability at 82.91% ± 5.00 (n = 6) and mineralization. These were significantly different to both the methyl methacrylate (MMA) 77.38% ± 1.27, ethylene diamine (EDA) 64.75% ± 6.43 plasma-treated PEEK groups, and the control, non-plasma-treated group 58.80 ± 2.84. FTIR showed higher levels of carbonate and phosphate formation on the TEP-treated PEEK than the other samples; however, calcein staining fluorescence of MMA and TEP-treated PEEK had the highest levels of biomineralization measured by pixel intensity quantification of 101.17 ± 4.63 and 96.35 ± 3.58, respectively, while EDA and control PEEK samples were 89.53 ± 1.74 and 90.49 ± 2.33, respectively. Comparing different LTPs, we showed that modified surface chemistry has quantitatively measurable effects that are favorable to the cellular, biomineralization, and chemical properties of PEEK.

Tissue-Engineered Nanomaterials Play Diverse Roles in Bone Injury Repair

Nanomaterials with bone-mimicking characteristics and easily internalized by the cell could create suitable microenvironments in which to regulate the therapeutic effects of bone regeneration. This review provides an overview of the current state-of-the-art research in developing and using nanomaterials for better bone injury repair. First, an overview of the hierarchical architecture from the macroscale to the nanoscale of natural bone is presented, as these bone tissue microstructures and compositions are the basis for constructing bone substitutes. Next, urgent clinical issues associated with bone injury that require resolution and the potential of nanomaterials to overcome them are discussed. Finally, nanomaterials are classified as inorganic or organic based on their chemical properties. Their basic characteristics and the results of related bone engineering studies are described. This review describes theoretical and technical bases for the development of innovative methods for repairing damaged bone and should inspire therapeutic strategies with potential for clinical applications.

Nano-Hydroxyapatite Composite Scaffolds Loaded with Bioactive Factors and Drugs for Bone Tissue Engineering

Nano-hydroxyapatite (n-HAp) is similar to human bone mineral in structure and biochemistry and is, therefore, widely used as bone biomaterial and a drug carrier. Further, n-HAp composite scaffolds have a great potential role in bone regeneration. Loading bioactive factors and drugs onto n-HAp composites has emerged as a promising strategy for bone defect repair in bone tissue engineering. With local delivery of bioactive agents and drugs, biological materials may be provided with the biological activity they lack to improve bone regeneration. This review summarizes classification of n-HAp composites, application of n-HAp composite scaffolds loaded with bioactive factors and drugs in bone tissue engineering and the drug loading methods of n-HAp composite scaffolds, and the research direction of n-HAp composite scaffolds in the future is prospected.

How Efficient are Alendronate-Nano/Biomaterial Combinations for Anti-Osteoporosis Therapy? An Evidence-Based Review of the Literature

Osteoporosis is defined as a systemic skeletal disease characterized by low bone mass and microarchitectural deterioration of bone tissue, with a consequent increase in bone fragility and susceptibility to fracture. Because of the systemic nature of osteoporosis, the associated escalation in fracture risk affects virtually all skeletal sites. The problem is serious since it is estimated that more than 23 million men and women are at high risk of osteoporotic-like breakages in the European Union. Alendronate (ALN) is the most commonly prescribed oral nitrogen-containing bisphosphonate (BP) for the prevention and the therapy of osteoporosis. This is also one of the most intensely studied drugs in this field. However, ALN is characterized by restricted oral absorption and bioavailability and simultaneously its administration has serious side-effects (jaw osteonecrosis, irritation of the gastrointestinal system, nausea, musculoskeletal pain, and cardiovascular risks). Therefore, delivery systems enabling controlled release and local action of this drug are of great interest, being widely researched and presented in the literature. In this review, we discuss the current trends in the design of various types of alendronate carriers. Our paper is focused on the most recent developments in the field of nano/biomaterials-based systems for ALN delivery, including nano/microformulations, synthetic/natural polymeric and inorganic materials, hydrogel-based materials, scaffolds, coated-like structures, as well as organic-inorganic hybrids. Topics related to the treatment of complex bone diseases including osteoporosis have been covered in several more general reviews; however, the systems for this particular drug have not yet been discussed in detail.

Porous hydroxyapatite scaffold orchestrated with bioactive coatings for rapid bone repair

Current bioceramic scaffolds for critical-size bone defects are still facing various challenges such as the poor capability of self-resorption, vascularization and osteogenesis. Herein, a composite scaffold (HOD) is fabricated by integrating bioactive coatings of konjac glucomannan (KGM) and deferoxamine (DFO) into porous hydroxyapatite scaffold (HA), where KGM coating induces the self-resorption of HOD after implanting and DFO promoted the vascularization at the defected bone. Porous HA scaffolds with 200-400 μm of pore sizes were prepared and these bioactive coatings were successfully deposited on the scaffold, which was confirmed by SEM. MC3T3-E1 cells could be tightly attached to the pore wall of HOD and the obvious osteogenic differentiation was clearly displayed after 14 days of co-culture. Besides, HOD displayed the potential of promoting the vascularization of HUVECs. Importantly, the accelerated degradation of HOD was observed in a macrophage-associated acidic medium, which led to the self-resorption of HOD in vivo. Micro-CT images showed that HOD was gradually replaced by newly formed bone, achieving a balance between the new bone formation and the scaffold degradation. The rapid bone repairing of the femoral defects in rats was displayed for HOD in comparison to the HA scaffold. Moreover, the therapeutic mechanism of HOD was highly associated with promoted osteogenesis and vascularization. Collectively, the porous ceramic scaffold orchestrated with bioactive coatings may be a promising strategy for repairing of the large bone defect.

Advanced materials for enamel remineralization

Dental caries, a chronic and irreversible disease caused by caries-causing bacteria, has been listed as one of the three major human diseases to be prevented and treated. Therefore, it is critical to effectively stop the development of enamel caries. Remineralization treatment can control the progression of caries by inhibiting and reversing enamel demineralization at an early stage. In this process, functional materials guide the deposition of minerals on the damaged enamel, and the structure and hardness of the enamel are then restored. These remineralization materials have great potential for clinical application. In this review, advanced materials for enamel remineralization were briefly summarized, furthermore, an outlook on the perspective of remineralization materials were addressed.

Inorganic Nanoparticles in Bone Healing Applications

Modern biomedicine aims to develop integrated solutions that use medical, biotechnological, materials science, and engineering concepts to create functional alternatives for the specific, selective, and accurate management of medical conditions. In the particular case of tissue engineering, designing a model that simulates all tissue qualities and fulfills all tissue requirements is a continuous challenge in the field of bone regeneration. The therapeutic protocols used for bone healing applications are limited by the hierarchical nature and extensive vascularization of osseous tissue, especially in large bone lesions. In this regard, nanotechnology paves the way for a new era in bone treatment, repair and regeneration, by enabling the fabrication of complex nanostructures that are similar to those found in the natural bone and which exhibit multifunctional bioactivity. This review aims to lay out the tremendous outcomes of using inorganic nanoparticles in bone healing applications, including bone repair and regeneration, and modern therapeutic strategies for bone-related pathologies.

Spatiotemporal regulation of angiogenesis/osteogenesis emulating natural bone healing cascade for vascularized bone formation

Engineering approaches for growth factor delivery have been considerably advanced for tissue regeneration, yet most of them fail to provide a complex combination of signals emulating a natural healing cascade, which substantially limits their clinical successes. Herein, we aimed to emulate the natural bone healing cascades by coupling the processes of angiogenesis and osteogenesis with a hybrid dual growth factor delivery system to achieve vascularized bone formation. Basic fibroblast growth factor (bFGF) was loaded into methacrylate gelatin (GelMA) to mimic angiogenic signalling during the inflammation and soft callus phases of the bone healing process, while bone morphogenetic protein-2 (BMP-2) was bound onto mineral coated microparticles (MCM) to mimics osteogenic signalling in the hard callus and bone remodelling phases. An Initial high concentration of bFGF accompanied by a sustainable release of BMP-2 and inorganic ions was realized to orchestrate well-coupled osteogenic and angiogenic effects for bone regeneration. In vitro experiments indicated that the hybrid hydrogel markedly enhanced the formation of vasculature in human umbilical vein endothelial cells (HUVECs), as well as the osteogenic differentiation of mesenchymal stem cells (BMSCs). In vivo results confirmed the optimal osteogenic performance of our F/G-B/M hydrogel, which was primarily attributed to the FGF-induced vascularization. This research presents a facile and potent alternative for treating bone defects by emulating natural cascades of bone healing.

Nano-hydroxyapatite as a delivery system: overview and advancements

Nano-hydroxyapatite is being investigated as vital components of implants and dental and tissue engineering devices. It is found as a bone replacement due to its non-toxicity and cytocompatibility with dental tissues and bone. The reality that nanocrystalline hydroxyapatite can be made of porous granules and scaffolds. Additionally, it has a massive loading potential indicating its use as a transporter for drugs or a regulated drug release mechanism in pharmaceutical research. This review aims to present existing nano-hydroxyapatite research developments as a drug carrier employed in bone tissue disorders locally and deliver poorly soluble drugs with reduced bioavailability. We have discussed the nano-hydroxyapatite role in the delivery of drugs (i.e. anti-resorptive, anti-cancer, and antibiotics), proteins, genetic material, and radionuclides.

Mechanistically Scoping Cell-Free and Cell-Dependent Artificial Scaffolds in Rebuilding Skeletal and Dental Hard Tissues

Rebuilding mineralized tissues in skeletal and dental systems remains costly and challenging. Despite numerous demands and heavy clinical burden over the world, sources of autografts, allografts, and xenografts are far limited, along with massive risks including viral infections, ethic crisis, and so on. Per such dilemma, artificial scaffolds have emerged to provide efficient alternatives. To date, cell-free biomimetic mineralization (BM) and cell-dependent scaffolds have both demonstrated promising capabilities of regenerating mineralized tissues. However, BM and cell-dependent scaffolds have distinctive mechanisms for mineral genesis, which makes them methodically, synthetically, and functionally disparate. Herein, these two strategies in regenerative dentistry and orthopedics are systematically summarized at the level of mechanisms. For BM, methodological and theoretical advances are focused upon; and meanwhile, for cell-dependent scaffolds, it is demonstrated how scaffolds orchestrate osteogenic cell fate. The summary of the experimental advances and clinical progress will endow researchers with mechanistic understandings of artificial scaffolds in rebuilding hard tissues, by which better clinical choices and research directions may be approached.

Cryogenic 3D printing of modified polylactic acid scaffolds with biomimetic nanofibrous architecture for bone tissue engineering

The individualized polylactic acid (PLA) scaffolds fabricated by 3D printing technique have a good application prospect in the bone tissue engineering field. However, 3D printed PLA scaffold mainly manufactured by using a Fused Deposition Modelling fabrication technique (FDM) has some disadvantages, such as having smooth surface, strong hydrophobicity, poor cell adhesion, undesirable bioactivity, the degradation and deterioration at a high temperature triggering an inflammatory response. In this work, the aminated modified polylactic acid nanofibrous scaffold prepared by cryogenic 3D printing technology is designed to provide a feasible countermeasure to solve the key problems existing at present. The prepared scaffolds were fully characterized in terms of physico-chemical and morphological analyses, and the collected results revealed that the using of the cryogenic 3D printing technology can effectively avoid the degradation and deterioration of PLA at a high temperature required by FDM technique and promote the formation of nanofibrous structures. The in vitro tests with MC3T3-E1 cells confirmed that the cell-responsive biomimetic fibrous architecture and improved hydrophilicity due to the introduction of hydrophilic active amino groups provided a bioactive interface for cell adhesion and growth. Meanwhile, the active amino groups introduced by ammonolysis reaction can act as active sites for biomineralization. Thus, the as-prepared scaffolds may hold great potential for bone tissue engineering applications.

Comparison of Three Different Aqueous Microenvironments for Enhancing Oral Bioavailability of Sildenafil: Solid Self-Nanoemulsifying Drug Delivery System, Amorphous Microspheres and Crystalline Microspheres

Background

The purpose of this study was to screen various drug delivery systems for improving the aqueous solubility and oral bioavailability of sildenafil. Three representative techniques, solid self-nanoemulsifying drug delivery systems (SNEDDS), amorphous microspheres and crystalline microspheres, were compared.

Methods

Both microspheres systems contained sildenafil:Labrasol:PVP at a weight ratio of 1:1:6. The amorphous microspheres were manufactured using ethanol, while crystalline microspheres were generated using distilled water. Liquid SNEDDS was composed of sildenafil:Labrasol:Transcutol HP:Captex 300 in the ratio of 1:70:15:15 (w:w:w:w). The solidification process in SNEDDS was performed using HDK N20 Pharma as a solid carrier.

Results

The amorphous microspheres appeared spherical with significantly decreased particle size compared to the drug powder. The crystalline microspheres exhibited a rough surface with no major particle-size difference compared with sildenafil powder, indicating that the hydrophilic excipients adhered to the sildenafil crystal. Solid SNEDDS presented a smooth surface, assuming that the oily liquid was adsorbed to the porous solid carrier. According to the physicochemical evaluation, the crystalline state maintained in crystalline microspheres, whereas the crystal state changed to amorphous state in other formulations. Amorphous microspheres, crystalline microspheres and solid SNEDDS produced about 79, 55, 82-fold increased solubility, compared to drug powder. Moreover, the prepared formulations provided a higher dissolution rate (%) and plasma concentration than did the drug powder (performance order; solid SNEDDS ≥ amorphous microspheres ≥ crystalline microspheres > drug powder). Among the formulations, solid SNEDDS demonstrated the highest improvement in oral bioavailability (AUC; 1508.78 ± 343.95 h·ng/mL).

Conclusion

Therefore, solid SNEDDS could be recommended as an oral dosage form for enhancing the oral bioavailability of sildenafil.

New method for the protection and restoration of calcareous cultural heritage stones by polyelectrolytes and hydroxyapatite nanocrystals

We have investigated the feasibility of a new two-step protocol for the restoration of marbles. The process employs a polyelectrolyte multilayer film that enhances the chemical affinity between the treated stone and restorative material (hydroxyapatite nanocrystals), through functionalization, while at the same time it attributes an acid resistant property to the resulting system. Surface functionalization and material deposition is achieved through spraying; a simple and versatile application method suitable for objects of various sizes and geometries. Polyelectrolyte (polyethylenimine and polyacrylic acid) deposition was examined through Attenuated Total Reflection Fourier-Transform Infrared Spectroscopy (ATR-FTIR) and Atomic Force Microscopy (AFM), and tested through contact angle, water absorption and dissolution experiments. The hydroxyapatite nanocrystals were studied by ATR-FTIR, z-potential, AFM and Scanning Electron Microscopy (SEM), and characterized via contact angle and color alteration measurements. Our results show that the polyelectrolyte multilayer was stable in an aqueous environment with increased acid resistance (up to 46% decrease in mass weight loss when compared with untreated samples) and decreased water absorption (up to 39%). Color measurements of the outer hydroxyapatite layer showed a minimal color alteration for one type of the tested substrates showing low color difference values (ΔΕ* < 5). The results suggest that the proposed method holds great potential for marble restoration as it attributes multi-functionality and is easy to apply.

An overview of polyester/hydroxyapatite composites for bone tissue repairing

Objectives

The polyester/hydroxyapatite (polyester/HA) composites play an important role in bone tissue repairing, mostly because they mimic the composition and structure of naturally mineralized bone tissue. This review aimed to discuss commonly used geometries of polyester/HA composites, including microspheres, membranes, scaffolds and bulks, and their applications in bone tissue repairing and to discuss existed restrictions and developing trends of polyester/HA.

Methods

The current review was conducted by searching Web of Science, and Google Scholar for relevant studies published related with polyester/HA composites. Selected studies were analyzed with a focus on the fabrication techniques, properties (mechanical properties, biodegradable properties and biological properties) and applications of polyester/HA composites in bone repairing.

Results

A total of 111 articles were introduced to discuss the review. Different geometries of polyester/HA composites were discussed. In addition, properties and applications of polyester/HA composites were evaluated. The addition of HA into polyester can adjust the mechanical and biodegradability of composites. Besides, the addition of HA into polyester can improve its osteogenic abilities. The results showed that polyester/HA composites can ideal candidate for bone tissue repairing.

Conclusion

Polyester/HA composites have many remarkable properties, such as appropriate mechanical strength, biodegradability, favorable biological properties. Diverse geometries of polyester/HA composites have been used in bone repairing, drug delivery and implant fixation. Further work needs to be done to investigate existed restrictions, including the controlled degradation rate, controlled drug release performance, well-matched mechanical properties, and novel fabrication techniques.

The translational potential of this article

The present review reveals the current state of the polyester/HA composites used in bone tissue repairing, contributing to future trends of polyester/HA composites in the forthcoming future.

Nanopharmaceutical-based regenerative medicine: a promising therapeutic strategy for spinal cord injury

Spinal cord injury (SCI) is a neurological disorder that can lead to loss of perceptive and athletic function due to the severe nerve damage. To date, pieces of evidence detailing the precise pathological mechanisms in SCI are still unclear. Therefore, drug therapy cannot effectively alleviate the SCI symptoms and faces the limitations of systemic administration with large side effects. Thus, the development of SCI treatment strategies is urgent and valuable. Due to the application of nanotechnology in pharmaceutical research, nanopharmaceutical-based regenerative medicine will bring colossal development space for clinical medicine. These nanopharmaceuticals (i.e. nanocrystalline drugs and nanocarrier drugs) are designed using different types of materials or bioactive molecules, so as to improve the therapeutic effects, reduce side effects, and subtly deliver drugs, etc. Currently, an increasing number of nanopharmaceutical products have been approved by drug regulatory agencies, which has also prompted more researchers to focus on the potential treatment strategies of SCI. Therefore, the purpose of this review is to summarize and elaborate the research progress as well as the challenges and future of nanopharmaceuticals in the treatment of SCI, aiming to promote further research of nanopharmaceuticals in SCI.

Programmed antibacterial and mineralization therapy for dental caries based on zinc-substituted hydroxyapatite/ alendronate-grafted polyacrylic acid hybrid material

The domination of cariogenic bacteria in dental plaque biofilms is the primary cause of dental caries. In view of this, for the purpose of an effective treatment of dental caries, it is of great importance to inhibit the activity of acidogenic bacteria and promote the remineralization of damaged teeth simultaneously. However, the expensive antibacterial agents and poor mineralization ability of materials limit the practical applications. Biomineralization regulated by non-collagenous proteins (NCPs) gives hints to combine the remineralization ability of NCPs with accessible antibacterial property effectively. In this work, we propose a programmed antibacterial and remineralization strategy for the therapy of dental caries based on zinc-substituted hydroxyapatite/ alendronate-grafted polyacrylic acid hybrid nanoneedles (ZHA@ALN-PAA). This hybrid material dissolves in the acidic caries environment and regulate the pH to nearly neutral (6.5). Abundant calcium/ phosphate ions are supplemented and the ALN-PAA embedded in it has also been released, which assists the biomineralization on tooth defect. It has been revealed that the inhibition ratio of ZHA@ALN-PAA against Streptococcus mutans is the highest (11.25 folds that of HA), which originates from the highest zinc ions released (132.9 mg/L). Besides, the interspace of etched enamel is fully filled with regenerated nanorods and the surface microhardness (SMH) is significantly improved (3.68 folds that of etched enamel) after only 3 days of mineralization in vitro. This strategy developed here is simple and cost-effective, which can be referred to design the effective anti-caries materials applied for clinic treatment and daily oral care.