Calcium concentration dependent collagen mineralization

Human collagen sequence polypeptides mediated biomineralization and its molecular mechanism

Biotechnology provides alternatives for regenerative medicine with more controllable functions. Herein, the polypeptides encoded with human collagen I amino-acid sequences were studied for the first time to modulate biomimetic hydroxyapatite (HAP). With a length of 50-100 nm and a width of 20-30 nm, the HAP crystal formed was plate-like. The interaction of the human collagen sequence polypeptide on the (001), (100), and (211) crystal faces of HAP crystal had been studied using Molecular Dynamics (MD) simulations, respectively. Based on MD simulations, van der Waals forces and hydrogen bonds are the main interactions between polypeptides and HAP through the -NH2, -CH2-, -OH, and -COOH, respectively. According to the calculated results, der Waals forces might be the main interaction. The human collagen sequence polypeptides exhibited the highest adsorption energy on the (001) plane of HAP, significantly higher than any of the adsorption energy on the (100) and (211) planes. Therefore, the growth of the (001) would be inhibited, which kept accurate with the result of images from the Transmission Electron Microscope (TEM). Study results provide a basis for rational designing of peptides with human collagen sequences to regenerate hard tissues.

Guidelines derived from biomineralized tissues for design and construction of high-performance biomimetic materials: from weak to strong

Living organisms in nature have undergone continuous evolution over billions of years, resulting in the formation of high-performance fracture-resistant biomineralized tissues such as bones and teeth to fulfill mechanical and biological functions, despite the fact that most inorganic biominerals that constitute biomineralized tissues are weak and brittle. During the long-period evolution process, nature has evolved a number of highly effective and smart strategies to design chemical compositions and structures of biomineralized tissues to enable superior properties and to adapt to surrounding environments. Most biomineralized tissues have hierarchically ordered structures consisting of very small building blocks on the nanometer scale (nanoparticles, nanofibers or nanoflakes) to reduce the inherent weaknesses and brittleness of corresponding inorganic biominerals, to prevent crack initiation and propagation, and to allow high defect tolerance. The bioinspired principles derived from biomineralized tissues are indispensable for designing and constructing high-performance biomimetic materials. In recent years, a large number of high-performance biomimetic materials have been prepared based on these bioinspired principles with a large volume of literature covering this topic. Therefore, a timely and comprehensive review on this hot topic is highly important and contributes to the future development of this rapidly evolving research field. This review article aims to be comprehensive, authoritative, and critical with wide general interest to the science community, summarizing recent advances in revealing the formation processes, composition, and structures of biomineralized tissues, providing in-depth insights into guidelines derived from biomineralized tissues for the design and construction of high-performance biomimetic materials, and discussing recent progress, current research trends, key problems, future main research directions and challenges, and future perspectives in this exciting and rapidly evolving research field.

Polydopamine-Modified Titanium Dioxide Nanotube Arrays Doped with Calcium as a Sustained Drug Delivery System

Titanium nanotube (TNT) arrays manufactured via electrochemical anodization have been widely used as local drug carriers due to their excellent biocompatibility and customizable nanotubular structures. However, the uncontrollable and abrupt drug release at the early stage decreases the drug release duration, leading to excessive drug concentration at the implantation site. In this study, a continuous drug delivery system based on TNTs was created. Initially, a basic ultrasound-assisted approach was utilized to deposit a polydopamine (PDA) coating onto TNTs to obtain PDA-modified TNTs. Next, TNTs-PDA were submerged in a calcium chloride solution to include Ca2+ through Ca2+ coordination between the PDA layer's catechol groups. Sodium alendronate (NaAL) was used as a model drug and loaded onto TNTs-PDA-Ca2+ by immersing them in an NaAL solution. In the final step, NaAL was covalently attached to TNTs-PDA-Ca2+ through coordination bonds with Ca2+. The samples underwent characterization through the use of various techniques, including field emission scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction patterning, X-ray photoelectron spectroscopy, and inductively coupled plasma emission spectrometry. The results indicated that the bioactivity of TNTs improved, and there was an enhancement in drug loading capacity and release performance due to modification with PDA and Ca2+. Furthermore, acidic conditions can cause significant drug release due to the cleavage of coordination bonds between the drug and Ca2+ ions. Thus, the aforementioned drug delivery system represents a potentially promising approach for achieving sustained and controllable drug release.

Enhanced mechanic properties of calcium phosphate cements via mussel-inspired adhesive as bone substitute: Highlights of their interactions

BACKGROUND

Inspired by natural bones, many organic components were added to Calcium Phosphate Cements (CPCs) to improve their mechanical strength. However, the strength of these composite CPCs is limited by the low strength of organic components itself and the weak interaction between organic components and CPCs.

OBJECTIVE

Firstly, a composite CPC containing mussel-inspired adhesive, Poly-(Dopamine Methacrylamide-co-2-methoxy Ethylacrylate) (pDM) was developed. Secondly, the interactions between pDM and CPC and their effect on mechanical properties were investigated.

METHODS

The interactions between pDM and CPC were performed by Nuclear Magnetic Resonance, Laser Raman, X-ray Photoelectron Spectroscopy, Fourier Transform-Infrared Spectroscopy and X-ray Diffraction Analysis.

RESULTS

The toughness and compressive strength of pDM-CPC scaffold were both significantly enhanced, because of the enhanced interface binding strength among CPC and pDM due to their interaction and the improved mechanical strength of pDM owing to its self-oxidation cross-linking. The toughness of pDM-CPC scaffolds increased with the increased contents of pDM, while pDM-CPC scaffold containing 35 wt.% pDM had the highest compressive strength of all, which the latter was more than five times compared to that of CPC.

CONCLUSION

The mechanically strong pDM-CPC scaffolds has potential application in bone regeneration as well as in craniofacial and orthopedic repair.

Functionalization of biomimetic mineralized collagen for bone tissue engineering

Mineralized collagen (MC) is the basic unit of bone structure and function and is the main component of the extracellular matrix (ECM) in bone tissue. In the biomimetic method, MC with different nanostructures of neo-bone have been constructed. Among these, extra-fibrous MC has been approved by regulatory agencies and applied in clinical practice to play an active role in bone defect repair. However, in the complex microenvironment of bone defects, such as in blood supply disorders and infections, MC is unable to effectively perform its pro-osteogenic activities and needs to be functionalized to include osteogenesis and the enhancement of angiogenesis, anti-infection, and immunomodulation. This article aimed to discuss the preparation and biological performance of MC with different nanostructures in detail, and summarize its functionalization strategy. Then we describe the recent advances in the osteo-inductive properties and multifunctional coordination of MC. Finally, the latest research progress of functionalized biomimetic MC, along with the development challenges and future trends, are discussed. This paper provides a theoretical basis and advanced design philosophy for bone tissue engineering in different bone microenvironments.

Behavior of Calcium Phosphate-Chitosan-Collagen Composite Coating on AISI 304 for Orthopedic Applications

Calcium phosphate/chitosan/collagen composite coating on AISI 304 stainless steel was investigated. Coatings were realized by galvanic coupling that occurs without an external power supply because it begins with the coupling between two metals with different standard electrochemical potentials. The process consists of the co-deposition of the three components with the calcium phosphate crystals incorporated into the polymeric composite of chitosan and collagen. Physical-chemical characterizations of the samples were executed to evaluate morphology and chemical composition. Morphological analyses have shown that the surface of the stainless steel is covered by the deposit, which has a very rough surface. XRD, Raman, and FTIR characterizations highlighted the presence of both calcium phosphate compounds and polymers. The coatings undergo a profound variation after aging in simulated body fluid, both in terms of composition and structure. The tests, carried out in simulated body fluid to scrutinize the corrosion resistance, have shown the protective behavior of the coating. In particular, the corrosion potential moved toward higher values with respect to uncoated steel, while the corrosion current density decreased. This good behavior was further confirmed by the very low quantification of the metal ions (practically absent) released in simulated body fluid during aging. Cytotoxicity tests using a pre-osteoblasts MC3T3-E1 cell line were also performed that attest the biocompatibility of the coating.

Biomechanics and mechanobiology of the bone matrix

The bone matrix plays an indispensable role in the human body, and its unique biomechanical and mechanobiological properties have received much attention. The bone matrix has unique mechanical anisotropy and exhibits both strong toughness and high strength. These mechanical properties are closely associated with human life activities and correspond to the function of bone in the human body. None of the mechanical properties exhibited by the bone matrix is independent of its composition and structure. Studies on the biomechanics of the bone matrix can provide a reference for the preparation of more applicable bone substitute implants, bone biomimetic materials and scaffolds for bone tissue repair in humans, as well as for biomimetic applications in other fields. In providing mechanical support to the human body, bone is constantly exposed to mechanical stimuli. Through the study of the mechanobiology of the bone matrix, the response mechanism of the bone matrix to its surrounding mechanical environment can be elucidated and used for the health maintenance of bone tissue and defect regeneration. This paper summarizes the biomechanical properties of the bone matrix and their biological significance, discusses the compositional and structural basis by which the bone matrix is capable of exhibiting these mechanical properties, and studies the effects of mechanical stimuli, especially fluid shear stress, on the components of the bone matrix, cells and their interactions. The problems that occur with regard to the biomechanics and mechanobiology of the bone matrix and the corresponding challenges that may need to be faced in the future are also described.

Osteogenic and angiogenic bioactive collagen entrapped calcium/zinc phosphates coating on biodegradable Zn for orthopedic implant applications

Zinc is becoming one of the leading candidate materials for biodegradable orthopedic implants owing to its attractive properties in terms of degradation behavior and mechanical properties. However, the insufficient surface bio-activities postpone its clinical application. In this study, an organic-inorganic collagen entrapped calcium/zinc phosphates coating was constructed on Zn surface to lessen Zn²⁺ releasing rate and to leverage the surface osteogenic and angiogenic properties. Collagen molecules were immobilized onto Zn substrate and subsequently coordinated with calcium and zinc ions to promote the CaZnP inorganic phase growth, ensuing an intertwined collagen-CaZnP hybrid system. Consequently, the hybrid coating was highly coalesced and compact. Such high quality warranted the contained Zn²⁺ releasing in a tolerable rate favorable for cells viability. The collagen-CaZnP coated Zn showed remarkedly stronger osteogenicity as compared to the untreated Zn, ascertained by the MC3T3-E1 osteoblast cell proliferation and differentiation assays, such as alkaline phosphatase expression and calcium nodule formation results. In addition, this hybrid coating supported human umbilical vein endothelial cells (HUVECs) migration and tube formation. The enhanced osteogenic and angiogenic properties could be ascribed to the nature of collagen and calcium/zinc phosphate components, the hybrid micro/nano-structure as well as the ability of controlling the Zn²⁺ release of Zn substrate into a suitable concentration range. Our strategy provides a new avenue to surface modification of biodegradable metals for bone regenerative perspective.

Orthophosphate and alkaline phosphatase induced the formation of apatite with different multilayered structures and mineralization balance

Mineralized collagen is a natural organic-inorganic composite. The combination of organic collagen and inorganic apatite to form different nanostructures is the key to producing bone substitutes with biomechanical properties that are as identical to normal bone as possible. However, the formation of apatite with different nanostructures during collagen mineralization is unexplored. Here, pyrophosphate (Pyro-P), as an important hydrolysate of adenosine triphosphate in the body, was introduced to prepare mineralized collagen under the regulation of alkaline phosphatase (ALP) and orthophosphate (Ortho-P). Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results showed that mineralized collagen, which combined with different crystallinities and multilayered structured apatite, was successfully prepared. A combination of ion chromatography (IC), Fourier transform infrared (FTIR) spectroscopy, circular dichroism (CD), and thermogravimetry (TG) analyses revealed the crucial role of Ortho-P in the formation of multilayered flower-shaped apatite with different crystallinities and in the maintenance of mineralization balance. Mineralization balance is of great significance for maintaining normal bone morphology during bone regeneration. Overall, our results provide a promising method to produce new bone substitute materials for the repair of large bone defects and a deeper insight into the mechanisms of biomineralization.

Peptide-Decorated DNA Nanostructures Promote Site-Specific Hydroxyapatite Growth

The guiding principle for mineralized tissue formation is that mineral growth occurs through the interaction of Ca²⁺ and phosphate ions with extracellular matrix (ECM) proteins. Recently, nanoengineered DNA structures have been proposed as mimics to ECM scaffolds. However, these principles have not been applied to mineralized tissues. Here, we describe DNA nanostructures, namely, a DNA nanotube and a DNA origami rectangle that are site specifically functionalized with a mineral-promoting "SSEE" peptide derived from ECM proteins present in mineralized tissues. In the presence of Ca²⁺ and phosphate ions (mineralizing conditions), site-specific calcium phosphate formation occurred on the DNA nanostructures. Amorphous calcium phosphate or hydroxyapatite was formed depending on the incubation time, shape of the DNA nanostructure, and amount of Ca²⁺ and phosphate ions present. The ability to design and control the growth of hydroxyapatite through nanoengineered scaffolds provides insights into the mechanisms that may occur during crystal nucleation and growth of mineralized tissues and can inspire mineralized tissue regeneration strategies.

Bioinspired mineralized collagen scaffolds for bone tissue engineering

Successful regeneration of large segmental bone defects remains a major challenge in clinical orthopedics, thus it is of important significance to fabricate a suitable alternative material to stimulate bone regeneration. Due to their excellent biocompatibility, sufficient mechanical strength, and similar structure and composition of natural bone, the mineralized collagen scaffolds (MCSs) have been increasingly used as bone substitutes via tissue engineering approaches. Herein, we thoroughly summarize the state of the art of MCSs as tissue-engineered scaffolds for acceleration of bone repair, including their fabrication methods, critical factors for osteogenesis regulation, current opportunities and challenges in the future. First, the current fabrication methods for MCSs, mainly including direct mineral composite, in-situ mineralization and 3D printing techniques, have been proposed to improve their biomimetic physical structures in this review. Meanwhile, three aspects of physical (mechanics and morphology), biological (cells and growth factors) and chemical (composition and cross-linking) cues are described as the critical factors for regulating the osteogenic feature of MCSs. Finally, the opportunities and challenges associated with MCSs as bone tissue-engineered scaffolds are also discussed to point out the future directions for building the next generation of MCSs that should be endowed with satisfactorily mimetic structures and appropriately biological characters for bone regeneration.

Highly aligned hierarchical intrafibrillar mineralization of collagen induced by periodic fluid shear stress

Periodic fluid shear stress (FSS) is one of the main mechanical microenvironments in mineralization of bone matrix. To elucidate the mechanism of periodic FSS in collagen mineralization, a mechanical loading induced mineralization system is developed and compared with traditional polyacrylic acid (PAA) induced mineralization. Fourier transform infrared (FTIR) spectroscopy, calcium-to-phosphorus molar ratio and transmission electron microscopy (TEM) demonstrate that both periodic FSS and PAA can control the size of amorphous calcium phosphate (ACP) to avoid aggregation and help the formation of intrafibrillar mineralization. Differently, periodic FSS under a proper cycle and range can accelerate the conversion of ACP to apatite crystals and alleviate the reduced transformation caused by PAA. Under the action of template analogues, periodic FSS can also promote the formation of highly oriented hierarchical intrafibrillar mineralized (HIM) collagen. These findings are helpful for understanding the mechanism of collagen mineralization in natural bone matrix and contribute to the design of novel bone substitute materials with hierarchical structures.

Biomimetic Membranes of Methacrylated Gelatin/Nanohydroxyapatite/Poly(l-Lactic Acid) for Enhanced Bone Regeneration

Nanofibrous poly(l-lactic acid) (PLLA) membrane-simulated extracellular matrices (ECMs) can be used in the biomedical field. However, the hydrophobic nature and poor osteoinductive property of PLLA limit its application in guided bone regeneration (GBR). In this work, a methacrylated gelatin/nano-HA (GelMA/nHA) complex was first synthesized in situ and then introduced into PLLA to fabricate biomimetic GelMA/nHA/PLLA membranes, mimicking the nanofibrous architecture and composition of ECMs by electrospinning and photocrosslinking. Compared to PLLA and GelMA/PLLA membranes, the novel GelMA/nHA/PLLA membranes demonstrated better tensile, hydrophilic, water sorption, and degradation properties. An in vitro biological evaluation indicated that the membranes promoted human bone marrow-derived mesenchymal stem cell (hBMSC) proliferation, adhesion, and osteogenic differentiation. Critical-sized defects in rat models were used to evaluate the bone regeneration performances of the three kinds of membranes in vivo, and the GelMA/nHA/PLLA membranes demonstrated excellent osteogenic regeneration potential. Therefore, GelMA/nHA/PLLA membranes have wide application prospects in bioengineering applications such as GBR treatment.

Alginate-Assisted Mineralization of Collagen by Collagen Reconstitution and Calcium Phosphate Formation

The understanding of the mineralization of collagen for bone formation is a current key theme in bone tissue engineering and is of great relevance to the fabrication of novel biomimetic bone grafting materials. The noncollagenous proteins (NCPs) play a vital role in bone formation and are considered to be responsible for regulating intrafibrillar penetration of minerals into collagen fibrils by means of their abundant polyanionic domains. In this study, alginate, as a NCPs analogue, was introduced in the mineralization of collagen to mediate the collagen self-assembly with simultaneous hydroxyapatite (HA) synthesis. The biomimetic systems were based upon the self-assembly of collagen (Col) or collagen-alginate (CA) in the absence or presence of a varying content of HA. The alginate-mediated effects were found to include the lateral aggregation of small fibrils into the extremely large bundles and the assisted deposition of HA for a larger mineralized fibril. This alginate-assisted mineralization of collagen gave rise to an exquisite 3D mineralized architecture with enhanced mechanical property. The cell viability experiments showed the excellent proliferation and spreading morphologies of rat bone mesenchymal stem cells (MSCs) on the assembled products, and a higher expression of osteogenic differentiation related transcription factor was obtained in the alginate-assisted mineralization of collagen. This study indicated that the selection of an appropriate substance, e.g., alginate as an anionic polyelectrolyte with Ca-capturing property, could be a convenient, simple solution to achieve a mineralized collagen scaffold with the reinforced mechanical property for potential applications in bone regeneration.

Apatite minerals derived from collagen phosphorylation modification induce the hierarchical intrafibrillar mineralization of collagen fibers

Collagen is the critical organic component of bone matrix, which is the template for bone biomineralization. Phosphorylation modification of collagen plays an important role in the process of biomineralization in vivo, but its mechanism on in vitro biomimetic mineralization of bone matrix remains unclear at the molecular level. Sodium tripolyphosphate is used to phosphorylate collagen in this study and new phosphate groups appear on collagen fibrils after phosphorylation modification. The chelating amount of calcium is improved linearly with increasing the phosphorylation degree of collagen fibrils, which demonstrates that the introduced phosphate groups serve as new nucleation sites and participate in the formation of apatite minerals inside the collagen fibers. Stabilized nanosized amorphous calcium phosphate by polyacrylic acid can also permeate into collagen fibers and further transform into another layer of hydroxyapatite minerals. Both layers of apatite minerals eventually induce the formation of hierarchical intrafibrillar mineralization structure within the phosphorylated collagen fibers. The present research enriches the previous biomineralization mechanism of bone matrix, provides a facile strategy for biomimetic mineralization of collagen, and offers the basis for future investigation of the advanced bone substitute materials.

An in vitro study on dentin demineralization and remineralization: Collagen rearrangements and influence on the enucleated phase

Dentin remineralization is of clinical relevance in the therapy of caries and dentin hypersensitivity. This study is aimed at gaining more insights on a molecular scale, through IR spectroscopy, into dentin demineralization and remineralization. The dentin demineralization by ethylenediaminetetraacetic acid, EDTA (17%, 2 h) significantly altered the secondary structure distribution of collagen, upon loss of interaction with calcium ions. To investigate dentin remineralization, previously demineralized human dentin slices were soaked in Dulbecco's Phosphate Buffered Saline (DPBS) or Hank's Balanced Salt Solution HBSS, in close contact with three commercial cements used as sustained releasing sources of Ca²⁺ and OH^- ions (i.e. calcium hydroxide- and calcium silicate-based cements). IR spectroscopy showed the occurrence of remineralization under these conditions. Collagen did not lose its ability to chelate Ca²⁺, and these interactions allowed collagen to rearrange into a conformation similar to that of sound dentin. This process appeared slower in HBSS than DPBS, as also shown by the lower degree of maturation of the inorganic phase enucleated in the former medium (amorphous calcium phosphate versus B-type carbonated apatite). Collagen appeared to act as a spatial constraint to crystal deposition, affecting crystallinity and carbonate content of the enucleated phase. Remineralization was found to strongly depend on the calcium releasing ability of the cements. The fast formation of a rough apatite biocoating may represent a favorable clinical condition in the context of mineralized tissue regeneration.

Keratin nanoparticles-coating electrospun PVA nanofibers for potential neural tissue applications

Keratin has the potential to improve biocompatibility and bioactivity of polymeric nanofibers. However, the addition of keratin into the blend nanofiber would decrease the mechanical properties of nanofibers due to the poor spinnability of keratin, and caused inhomogeneous distribution of keratin inside the nanofibers. Therefore, polymeric nanofibers surface-modified with keratin nanoparticles would improve the hydrophility and mechanical property. In this study, keratose (oxidative keratin, KOS) nanoparticles-coating PVA nanofibers (KNPs/PVA) were fabricated by electrospray deposition after electrospinning and acted on neural cells. The chemical conformation, mechanical properties and wettability of KNPs/PVA nanofibers were characterized. The KNPs/PVA nanofibers provided better wettability and stronger mechanical properties compared to KOS/PVA blend nanofibers at the same mass ratio of KOS to PVA. Furthermore, KNPs/PVA nanofibers displayed better cyto-biocompatibility in terms of cell morphology, adhesion and proliferation compared with PVA nanofibers and KOS/PVA blend nanofibers. These results suggested that polymeric nanofibers surface-modified with KOS nanoparticles can provide superior wettability, mechanical properties and biocompatibility by comparison with the blend nanofibers.

Biomimetic delivery of signals for bone tissue engineering

Bone tissue engineering is an exciting approach to directly repair bone defects or engineer bone tissue for transplantation. Biomaterials play a pivotal role in providing a template and extracellular environment to support regenerative cells and promote tissue regeneration. A variety of signaling cues have been identified to regulate cellular activity, tissue development, and the healing process. Numerous studies and trials have shown the promise of tissue engineering, but successful translations of bone tissue engineering research into clinical applications have been limited, due in part to a lack of optimal delivery systems for these signals. Biomedical engineers are therefore highly motivated to develop biomimetic drug delivery systems, which benefit from mimicking signaling molecule release or presentation by the native extracellular matrix during development or the natural healing process. Engineered biomimetic drug delivery systems aim to provide control over the location, timing, and release kinetics of the signal molecules according to the drug's physiochemical properties and specific biological mechanisms. This article reviews biomimetic strategies in signaling delivery for bone tissue engineering, with a focus on delivery systems rather than specific molecules. Both fundamental considerations and specific design strategies are discussed with examples of recent research progress, demonstrating the significance and potential of biomimetic delivery systems for bone tissue engineering.

Biomimetic mineralization of a hydroxyapatite crystal in the presence of a zwitterionic polymer

The biomimetic mineralization of nano-hydroxyapatite using a zwitterionic polymer as a template to cognize the biomineralization of natural bone in vivo.

Shear-mediated orientational mineralization of bone apatite on collagen fibrils

Intrafibrillar mineralization of collagen under a 1.5 Pa FSS environment versus the serious extrafibrillar mineralization of collagen under no FSS.

Spatial charge manipulated set-selective apatite deposition on micropatterned piezoceramic

Apatite was selectively deposited with the manipulation of spatial charge on the micropatterned piezoelectric K_0.5Na_0.5NbO₃.