Biologically inspired growth of hydroxyapatite nanocrystals inside self-assembled collagen fibers

Nanomaterial genotoxicity evaluation using the high-throughput p53-binding protein 1 (53BP1) assay

Toxicity evaluation of engineered nanomaterials is challenging due to the ever increasing number of materials and because nanomaterials (NMs) frequently interfere with commonly used assays. Hence, there is a need for robust, high-throughput assays with which to assess their hazard potential. The present study aimed at evaluating the applicability of a genotoxicity assay based on the immunostaining and foci counting of the DNA repair protein 53BP1 (p53-binding protein 1), in a high-throughput format, for NM genotoxicity assessment. For benchmarking purposes, we first applied the assay to a set of eight known genotoxic agents, as well as X-ray irradiation (1 Gy). Then, a panel of NMs and nanobiomaterials (NBMs) was evaluated with respect to their impact on cell viability and genotoxicity, and to their potential to induce reactive oxygen species (ROS) production. The genotoxicity recorded using the 53BP1 assay was confirmed using the micronucleus assay, also scored via automated (high-throughput) microscopy. The 53BP1 assay successfully identified genotoxic compounds on the HCT116 human intestinal cell line. None of the tested NMs showed any genotoxicity using the 53BP1 assay, except the positive control consisting in (CoO)(NiO) NMs, while only TiO2 NMs showed positive outcome in the micronucleus assay. Only Fe3O4 NMs caused significant elevation of ROS, not correlated to DNA damage. Therefore, owing to its adequate predictivity of the genotoxicity of most of the tested benchmark substance and its ease of implementation in a high throughput format, the 53BP1 assay could be proposed as a complementary high-throughput screening genotoxicity assay, in the context of the development of New Approach Methodologies.

Construction of 3D bioprinting of HAP/collagen scaffold in gelation bath for bone tissue engineering

Reconstruction of bone defects remains a clinical challenge, and 3D bioprinting is a fabrication technology to treat it via tissue engineering. Collagen is currently the most popular cell scaffold for tissue engineering; however, a shortage of printability and low mechanical strength limited its application via 3D bioprinting. In the study, aiding with a gelatin support bath, a collagen-based scaffold was fabricated via 3D printing, where hydroxyapatite (HAP) and bone marrow mesenchymal stem cells (BMSCs) were added to mimic the composition of bone. The results showed that the blend of HAP and collagen showed suitable rheological performance for 3D extrusion printing and enhanced the composite scaffold's strength. The gelatin support bath could effectively support the HAP/collagen scaffold's dimension with designed patterns at room temperature. BMSCs in/on the scaffold kept living and proliferating, and there was a high alkaline phosphate expression. The printed collagen-based scaffold with biocompatibility, mechanical properties and bioactivity provides a new way for bone tissue engineering via 3D bioprinting.

An update on hydroxyapatite/collagen composites: What is there left to say about these bioinspired materials?

Hydroxyapatite (HAp)/collagen-based composite materials have been a constant in the development of bioinspired materials for bone tissue engineering. The most fundamental research works focus on combining HAp, due to its chemical similarity with the mineral component of bones, and collagen, which is the most abundant protein in the body. Modern studies have explored different two-dimensional (2D) and 3D structures, in order to obtain biomaterials with specific physicochemical, mechanical, and biological characteristics that can be applied in distinct biomedical applications. However, as there is already so much work developed with these materials, it is crucial to question: what can still be done? What is the importance of current know-how for the future of bioinspired materials? In this paper we intend to review and update the available methodologies to synthesize HAp/collagen composites, along with their characteristics. In addition, the future of these materials in terms of applications and their potential as a cutting-edge technology is discussed.

Medicated Hydroxyapatite/Collagen Hybrid Scaffolds for Bone Regeneration and Local Antimicrobial Therapy to Prevent Bone Infections

Microbial infections occurring during bone surgical treatment, the cause of osteomyelitis and implant failures, are still an open challenge in orthopedics. Conventional therapies are often ineffective and associated with serious side effects due to the amount of drugs administered by systemic routes. In this study, a medicated osteoinductive and bioresorbable bone graft was designed and investigated for its ability to control antibiotic drug release in situ. This represents an ideal solution for the eradication or prevention of infection, while simultaneously repairing bone defects. Vancomycin hydrochloride and gentamicin sulfate, here considered for testing, were loaded into a previously developed and largely investigated hybrid bone-mimetic scaffold made of collagen fibers biomineralized with magnesium doped-hydroxyapatite (MgHA/Coll), which in the last ten years has widely demonstrated its effective potential in bone tissue regeneration. Here, we have explored whether it can be used as a controlled local delivery system for antibiotic drugs. An easy loading method was selected in order to be reproducible, quickly, in the operating room. The maintenance of the antibacterial efficiency of the released drugs and the biosafety of medicated scaffolds were assessed with microbiological and in vitro tests, which demonstrated that the MgHA/Coll scaffolds were safe and effective as a local delivery system for an extended duration therapy—promising results for the prevention of bone defect-related infections in orthopedic surgeries.

Nanoindentation for Monitoring the Time-Variant Mechanical Strength of Drug-Loaded Collagen Hydrogel Regulated by Hydroxyapatite Nanoparticles

Hydroxyapatite nanoparticle-complexed collagen (HAP/Col) hydrogels have been widely used in biomedical applications as a scaffold for controlled drug release (DR). The time-variant mechanical properties (Young's modulus, E) of HAP/Col hydrogels are highly relevant to the precise and efficient control of DR. However, the correlation between the DR and the E of hydrogels remains unclear because of the lack of a nondestructive and continuous measuring system. To reveal the correlations, herein, we investigate the time-variant behavior of E for HAP/Col hydrogels during 28 days using the atomic force microscopy (AFM) nanoindentation technique. The initial E of hydrogels was controlled from 200 to 9000 Pa by the addition of HAPs. Subsequently, we analyzed the relationship between the DR of the hydrogels and the changes in their mechanical properties (ΔE) during hydrogel degradation. Interestingly, the higher the initial E value of HAP/Col hydrogels is, the higher is the rate of hydrogel degradation over time. However, the DR of hydrogels with higher initial E appeared to be significantly delayed by up to 40% at a maximum. The results indicate that adding an appropriate amount of HAPs into hydrogels plays a crucial role in determining the initial E and their degradation rate, which can contribute to the properties that prolong DR. Our findings may provide insights into designing hydrogels for biomedical applications such as bone regeneration and drug-delivery systems.

Self-assembly study of type I collagen extracted from male Wistar Hannover rat tail tendons

BACKGROUND

Collagen, the most abundant protein in the animal kingdom, represents a promising biomaterial for regenerative medicine applications due to its structural diversity and self-assembling complexity. Despite collagen's widely known structural and functional features, the thermodynamics behind its fibrillogenic self-assembling process is still to be fully understood. In this work we report on a series of spectroscopic, mechanical, morphological and thermodynamic characterizations of high purity type I collagen (with a D-pattern of 65 nm) extracted from Wistar Hannover rat tail. Our herein reported results can be of help to elucidate differences in self-assembly states of proteins using ITC to improve the design of energy responsive and dynamic materials for applications in tissue engineering and regenerative medicine.

METHODS

Herein we report the systematic study on the self-assembling fibrillogenesis mechanism of type I collagen, we provide morphological and thermodynamic evidence associated to different self-assembly events using ITC titrations. We provide thorough characterization of the effect of pH, effect of salts and protein conformation on self-assembled collagen samples via several complementary biophysical techniques, including circular dichroism (CD), Fourier Transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), atomic force microscopy (AFM), scanning electron microscopy (SEM), dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA).

RESULTS

Emphasis was made on the use of isothermal titration calorimetry (ITC) for the thermodynamic monitoring of fibrillogenesis stages of the protein. An overall self-assembly enthalpy value of 3.27 ± 0.85 J/mol was found. Different stages of the self-assembly mechanism were identified, initial stages take place at pH values lower than the protein isoelectric point (pI), however, higher energy release events were recorded at collagen's pI. Denatured collagen employed as a control exhibited higher energy absorption at its pI, suggesting different energy exchange mechanisms as a consequence of different aggregation routes.

Calcium Phosphate Based Bioactive Ceramic Layers on Implant Materials Preparation, Properties, and Biological Performance

Calcium phosphate based bioactive ceramics (CPCs) can be successfully applied as implant coatings since they are chemically similar to the inorganic constituent of hard tissues (bones, teeth). Nowadays, in orthopedic surgeries, it is still common to use metallic implants. However, the biological response of the human body to these foreign materials can be adverse, causing the failure of implant materials. This disadvantage can be avoided by bioactive coatings on the surface of implants. CPCs can be prepared by different routes that provide coatings of different quality and properties. In our paper, we compared the morphological, chemical, and biological properties of CPC coatings prepared by the pulse current electrochemical method. The size and thickness of the pulse current deposited platelets largely depended on the applied parameters such as the length of ton and the current density. The decrease in the ton/toff ratio resulted in thinner, more oriented platelets, while the increase in current density caused a significant decrease in grain size. The higher pH value and the heat treatment favored the phase transformation of CPCs from monetite to hydroxyapatite. The contact angle measurements showed increased hydrophilicity of the CPC sample as well as better biocompatibility compared to the uncoated implant material.

Mimicking Natural Microenvironments: Design of 3D-Aligned Hybrid Scaffold for Dentin Regeneration

Tooth loss is a common consequence of a huge number of causes and can decrease the quality of humans’ life. Tooth is a complex organ composed of soft connective tissues and mineralized tissues of which dentin is the most voluminous component whose formation is regulated by a very complex process displaying several similarities with osteogenesis. Calcium phosphates, in particular hydroxyapatite (HA), is the phase present in higher amount into the structure of dentin, characterized by microscopic longitudinal dentinal tubules. To address the challenge of dental tissue regeneration, here we propose a novel biomimetic approach, to design hybrid scaffolds resembling the physico-chemical features of the natural mineralized tissues, suitable to recreate an appropriate microenvironment that stimulates cell colonization and proliferation, therefore effective for improving regenerative approach in dental applications. Biomineralization is the adopted synthesis as a nature inspired process consisting in the nucleation of magnesium-doped-hydroxyapatite (MgHA) nanocrystals on the gelatin (Gel) matrix generating hybrid flakes (Gel/MgHA) featured by a Gel:MgHA weight ratio close to 20:80 and size of 50–70 μm. Chemical and topotactic constrains affect the formation of MgHA mineral phase on the organic template, generating quasi-amorphous MgHA as revealed by XRD analysis and Ca/P ratio lower than 1.67, resembling the chemical and biological features of the natural apatite. The Gel/MgHA was then merged into the polymeric blend made of chitosan (Chit) and Gel to obtain a 3D porous scaffold with polymers: MgHA weight ratio of 40:60 and featured by an aligned porous structure as obtained by controlled freeze-drying process. The overall composite shows a swelling ratio of about 15 times after 6 h in PBS. The chemical stability was assured by means of a dehydrothermal cross-linking treatment (DHT) keeping the degradation lower than 20% after 28 days, while cell adhesion and proliferation were evaluated using a mouse fibroblast cell line.

Nanocrystals: A perspective on translational research and clinical studies

Poorly soluble small molecules typically pose translational hurdles owing to their low solubility, low bioavailability, and formulation challenges. Nanocrystallization is a versatile method for salvaging poorly soluble drugs with the added benefit of a carrier-free delivery system. In this review, we provide a comprehensive analysis of nanocrystals with emphasis on their clinical translation. Additionally, the review sheds light on clinically approved nanocrystal drug products as well as those in development.

Mesenchymal Stromal Cell-Seeded Biomimetic Scaffolds as a Factory of Soluble RANKL in Rankl-Deficient Osteopetrosis

Biomimetic scaffolds are extremely versatile in terms of chemical composition and physical properties, which can be defined to accomplish specific applications. One property that can be added is the production/release of bioactive soluble factors, either directly from the biomaterial, or from cells embedded within the biomaterial. We reasoned that pursuing this strategy would be appropriate to setup a cell‐based therapy for RANKL‐deficient autosomal recessive osteopetrosis, a very rare skeletal genetic disease in which lack of the essential osteoclastogenic factor RANKL impedes osteoclast formation. The exogenously administered RANKL cytokine is effective in achieving osteoclast formation and function in vitro and in vivo, thus, we produced murine Rankl^−/− mesenchymal stromal cells (MSCs) overexpressing human soluble RANKL (hsRL) following lentiviral transduction (LVhsRL). Here, we described a three‐dimensional (3D) culture system based on a magnesium‐doped hydroxyapatite/collagen I (MgHA/Col) biocompatible scaffold closely reproducing bone physicochemical properties. MgHA/Col‐seeded murine MSCs showed improved properties, as compared to two‐dimensional (2D) culture, in terms of proliferation and hsRL production, with respect to LVhsRL‐transduced cells. When implanted subcutaneously in Rankl^−/− mice, these cell constructs were well tolerated, colonized by host cells, and intensely vascularized. Of note, in the bone of Rankl^−/− mice that carried scaffolds with either WT or LVhsRL‐transduced Rankl^−/− MSCs, we specifically observed formation of TRAP⁺ cells, likely due to sRL released from the scaffolds into circulation. Thus, our strategy proved to have the potential to elicit an effect on the bone; further work is required to maximize these benefits and achieve improvements of the skeletal pathology in the treated Rankl^−/− mice. Stem Cells Translational Medicine2019;8:22–34

Evaluation of different crosslinking agents on hybrid biomimetic collagen-hydroxyapatite composites for regenerative medicine

This study focuses on the development of novel bone-like scaffolds by bio-inspired, pH-driven, mineralization of type I collagen matrix with magnesium-doped hydroxyapatite nanophase (MgHA/Coll). To this aim, this study evaluates the altered modifications in the obtained composite due to different crosslinkers such as dehydrothermal treatment (DHT), 1,4-butanediol diglycidyl ether (BDDGE) and ribose in terms of morphological, physical-chemical and biological properties. The physical-chemical properties of the composites evaluated by XRD, FTIR, ICP and TGA demonstrated that the chemical mimesis of bone was effectively achieved using the in-lab biomineralization process. Furthermore, the presence of various crosslinkers greatly promoted beneficial enzymatic resistivity and swelling ability. The morphological results revealed highly porous and fibrous micro-architecture with total porosity above 85% with anisotropic pore size within the range of 50-200μm in all the analysed composites. The mechanical behaviour in response to compressive forces demonstrated enhanced compressive modulus in all crosslinked composites, suggesting that mechanical behaviour is largely dependent on the type of crosslinker used. The biomimetic compositional and morphological features of the composites elicited strong cell-material interaction. Therefore, the results showed that by activating specific crosslinking mechanisms, hybrid composites can be designed and tailored to develop tissue-specific biomimetic biomaterials for hard tissue engineering.

* Biomineralized Recombinant Collagen-Based Scaffold Mimicking Native Bone Enhances Mesenchymal Stem Cell Interaction and Differentiation

The need of synthetic bone grafts that recreate from macro- to nanoscale level the biochemical and biophysical cues of bone extracellular matrix has been a major driving force for the development of new generation of biomaterials. In this study, synthetic bone substitutes have been synthesized via biomimetic mineralization of a recombinant collagen type I-derived peptide (RCP), enriched in tri-amino acid sequence arginine-glycine-aspartate (RGD). Three-dimensional (3D) isotropic porous scaffolds of three different compositions are developed by freeze-drying: non-mineralized (RCP, as a control), mineralized (Ap/RCP), and mineralized scaffolds in the presence of magnesium (MgAp/RCP) that closely imitate bone composition. The effect of mineral phase on scaffold pore size, porosity, and permeability, as well as on their in vitro kinetic degradation, is evaluated. The ultimate goal is to investigate how chemical (i.e., surface chemistry and ion release from scaffold) together with physical signals (i.e., surface nanotopography) conferred via biomimetic mineralization can persuade and guide mesenchymal stem cell (MSC) interaction and fate. The three scaffold compositions showed optimum pore size and porosity for osteoconduction, without significant differences between them. The degradation tests confirmed that MgAp/RCP scaffolds presented higher reactivity under physiological condition compared to Ap/RCP ones. The in vitro study revealed an enhanced cell growth and proliferation on MgAp/RCP scaffolds at day 7, 14, and 21. Furthermore, MgAp/RCP scaffolds potentially promoted cell migration through the inner areas reaching the bottom of the scaffold after 14 days. MSCs cultured on MgAp/RCP scaffolds displayed higher gene and protein expressions of osteogenic markers when comparing them with the results of those MSCs grown on RCP or Ap/RCP scaffolds. This work highlights that mineralization of recombinant collagen mimicking bone mineral composition and morphology is a versatile approach to design smart scaffold interface in a 3D model guiding MSC fate.

Recombinant DNA technology and click chemistry: a powerful combination for generating a hybrid elastin-like-statherin hydrogel to control calcium phosphate mineralization

Understanding the mechanisms responsible for generating different phases and morphologies of calcium phosphate by elastin-like recombinamers is supreme for bioengineering of advanced multifunctional materials. The generation of such multifunctional hybrid materials depends on the properties of their counterparts and the way in which they are assembled. The success of this assembly depends on the different approaches used, such as recombinant DNA technology and click chemistry. In the present work, an elastin-like recombinamer bearing lysine amino acids distributed along the recombinamer chain has been cross-linked via Huisgen [2 + 3] cycloaddition. The recombinamer contains the SNA15 peptide domains inspired by salivary statherin, a peptide epitope known to specifically bind to and nucleate calcium phosphate. The benefit of using click chemistry is that the hybrid elastin-like-statherin recombinamers cross-link without losing their fibrillar structure. Mineralization of the resulting hybrid elastin-like-statherin recombinamer hydrogels with calcium phosphate is described. Thus, two different hydroxyapatite morphologies (cauliflower- and plate-like) have been formed. Overall, this study shows that crosslinking elastin-like recombinamers leads to interesting matrix materials for the generation of calcium phosphate composites with potential applications as biomaterials.

A Biomimetic Material with a High Bio-responsibility for Bone Reconstruction and Tissue Engineering

A biomimetic composite was prepared using type-I collagen as the matrix, and particles of sol-gel-derived bioactive glass (58S), hyaluronic acid and phosphatidylserine as additives. The material has an interconnected 3-D porous structure with a porosity > 85%. When incubated in simulated body fluid (SBF), the composite induced the formation of microcrystals of bone-like hydroxyapatite (HA), suggesting good bioactive properties. During the in vitro cell-culture experiment, MC3T3-E1 cells adhered to, migrated and spread on the surface of the porous composite. The material was employed to repair a 10-mm defect in a rabbit's radius. The composite was gradually degraded within 8 weeks and replaced by new bone. After 12 weeks, the bone marrow cavity was restored and the Haversian canal was noted from the histological observation. The biomimetic composite is a potential scaffold material for bone reconstruction and bone tissue engineering.

Rapid biomimetic mineralization of collagen fibrils and combining with human umbilical cord mesenchymal stem cells for bone defects healing

Collagen biomineralization is regulated by complicated interactions between the collagen matrix and non-collagenous extracellular proteins. Here, the use of sodium tripolyphosphate to simulate the templating functional motif of the C-terminal fragment of non-collagenous proteins is reported, and a low molecular weight polyacrylic acid served as a sequestration agent to stabilize amorphous calcium phosphate into nanoprecursors. Self-assembled collagen fibrils served as a fixed template for achieving rapid biomimetic mineralization in vitro. Results demonstrated that, during the mineralization process, intrafibrillar and extrafibrillar hydroxyapatite mineral with collagen fibrils formed and did so via bottom-up nanoparticle assembly based on the non-classical crystallization approach in the presence of these dual biomimetic functional analogues. In vitro human umbilical cord mesenchymal stem cell (hUCMSC) culture found that the mineralized scaffolds have a better cytocompatibility in terms of cell viability, adhesion, proliferation, and differentiation into osteoblasts. A rabbit femoral condyle defect model was established to confirm the ability of the n-HA/collagen scaffolds to facilitate bone regeneration and repair. The images of gross anatomy, MRI, CT and histomorphology taken 6 and 12weeks after surgery showed that the biomimetic mineralized collagen scaffolds with hUCMSCs can promote the healing speed of bone defects in vivo, and both of the scaffolds groups performing better than the bone defect control group. As new bone tissue formed, the scaffolds degraded and were gradually absorbed. All these results demonstrated that both of the scaffolds and cells have better histocompatibility.

Synthesis of Biocompatible Hydroxyapatite Using Chitosan Oligosaccharide as a Template

In this study, a novel biocompatible hydroxyapatite (HA) was synthesized by using chitosan oligosaccharide (COS) as a template. These HA samples were studied by Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The biocompatibility of HA samples was evaluated via cell viability, cell morphology and alkaline phosphatase staining of MG-63 cell lines. The results show that HA synthesized in the presence of COS was favorable to proliferation and osteogenic differentiation of MG-63 cells. These hydroxyapatites are potentially attractive biomaterials for bone tissue engineering applications.

Biodegradable Materials for Bone Repair and Tissue Engineering Applications

This review discusses and summarizes the recent developments and advances in the use of biodegradable materials for bone repair purposes. The choice between using degradable and non-degradable devices for orthopedic and maxillofacial applications must be carefully weighed. Traditional biodegradable devices for osteosynthesis have been successful in low or mild load bearing applications. However, continuing research and recent developments in the field of material science has resulted in development of biomaterials with improved strength and mechanical properties. For this purpose, biodegradable materials, including polymers, ceramics and magnesium alloys have attracted much attention for osteologic repair and applications. The next generation of biodegradable materials would benefit from recent knowledge gained regarding cell material interactions, with better control of interfacing between the material and the surrounding bone tissue. The next generations of biodegradable materials for bone repair and regeneration applications require better control of interfacing between the material and the surrounding bone tissue. Also, the mechanical properties and degradation/resorption profiles of these materials require further improvement to broaden their use and achieve better clinical results.

Calcium Orthophosphate-Containing Biocomposites and Hybrid Biomaterials for Biomedical Applications

The state-of-the-art on calcium orthophosphate (CaPO4)-containing biocomposites and hybrid biomaterials suitable for biomedical applications is presented. Since these types of biomaterials offer many significant and exciting possibilities for hard tissue regeneration, this subject belongs to a rapidly expanding area of biomedical research. Through the successful combinations of the desired properties of matrix materials with those of fillers (in such systems, CaPO4 might play either role), innovative bone graft biomaterials can be designed. Various types of CaPO4-based biocomposites and hybrid biomaterials those are either already in use or being investigated for biomedical applications are extensively discussed. Many different formulations in terms of the material constituents, fabrication technologies, structural and bioactive properties, as well as both in vitro and in vivo characteristics have been already proposed. Among the others, the nano-structurally controlled biocomposites, those containing nanodimensional compounds, biomimetically fabricated formulations with collagen, chitin and/or gelatin, as well as various functionally graded structures seem to be the most promising candidates for clinical applications. The specific advantages of using CaPO4-based biocomposites and hybrid biomaterials in the selected applications are highlighted. As the way from a laboratory to a hospital is a long one and the prospective biomedical candidates have to meet many different necessities, the critical issues and scientific challenges that require further research and development are also examined.

Transformation of amorphous calcium carbonate to rod-like single crystal calcite via "copying" collagen template

Collagen Langmuir films were prepared by spreading the solution of collagen over deionized water, CaCl2 solution and Ca(HCO3)2 solution. Resultant collagen Langmuir monolayers were then compressed to a lateral pressure of 10 mN/m and held there for different duration, allowing the crystallization of CaCO3. The effect of crystallization time on the phase composition and microstructure of CaCO3 was investigated. It was found that amorphous calcium carbonate (ACC) was obtained at a crystallization time of 6 h. The amorphous CaCO3 was transformed to rod-like single crystal calcite crystals at an extended crystallization time of 12 h and 24 h, via "copying" the symmetry and dimensionalities of collagen fibers. Resultant calcite crystallites were well oriented along the longitudinal axis of collagen fibers. The ordered surface structure of collagen fibers and electrostatic interactions played key roles in tuning the oriented nucleation and growth of the calcite crystallites. The mineralized collagen possessing both desired mechanical properties of collagen fiber and good biocompatibility of calcium carbonate may be assembled into an ideal biomaterial for bone implants.

Jellyfish collagen scaffolds for cartilage tissue engineering

Porous scaffolds were engineered from refibrillized collagen of the jellyfish Rhopilema esculentum for potential application in cartilage regeneration. The influence of collagen concentration, salinity and temperature on fibril formation was evaluated by turbidity measurements and quantification of fibrillized collagen. The formation of collagen fibrils with a typical banding pattern was confirmed by atomic force microscopy and transmission electron microscopy analysis. Porous scaffolds from jellyfish collagen, refibrillized under optimized conditions, were fabricated by freeze-drying and subsequent chemical cross-linking. Scaffolds possessed an open porosity of 98.2%. The samples were stable under cyclic compression and displayed an elastic behavior. Cytotoxicity tests with human mesenchymal stem cells (hMSCs) did not reveal any cytotoxic effects of the material. Chondrogenic markers SOX9, collagen II and aggrecan were upregulated in direct cultures of hMSCs upon chondrogenic stimulation. The formation of typical extracellular matrix components was further confirmed by quantification of sulfated glycosaminoglycans.

Specific inductive potential of a novel nanocomposite biomimetic biomaterial for osteochondral tissue regeneration

Osteochondral lesions require treatment to restore the biology and functionality of the joint. A novel nanostructured biomimetic gradient scaffold was developed to mimic the biochemical and biophysical properties of the different layers of native osteochondral structure. The present results show that the scaffold presents important physicochemical characteristics and can support the growth and differentiation of mesenchymal stromal cells (h-MSCs), which adhere and penetrate into the cartilaginous and bony layers. H-MSCs grown in chondrogenic or osteogenic medium decreased their proliferation during days 14-52 on both scaffold layers and in medium without inducing factors used as controls. Both chondrogenic and osteogenic differentiation of h-MSCs occurred from day 28 and were increased on day 52, but not in the control medium. Safranin O staining and collagen type II and proteoglycans immunostaining confirmed that chondrogenic differentiation was specifically induced only in the cartilaginous layer. Conversely, von Kossa staining, osteocalcin and osteopontin immunostaining confirmed that osteogenic differentiation occurred on both layers. This study shows the specific potential of each layer of the biomimetic scaffold to induce chondrogenic or osteogenic differentiation of h-MSCs. These processes depended mainly on the media used but not the biomaterial itself, suggesting that the local milieu is fundamental for guiding cell differentiation. Copyright © 2013 John Wiley & Sons, Ltd.

The influence of transition metal ions on collagen mineralization

The ions in body fluid play an important role in bone formation besides being a synthesizing material. Transition metal ions Co(2+), Ni(2+), Zn(2+), Fe(3+), Mn(2+), Cu(2+), Cd(2+) and Hg(2+) doped hydroxyapatite (HAP)/collagen composites were synthesized successfully in the presence of collagen traces at mild acidic pH for the first time. However, the amount of doped Hg(2+) and Cd(2+) was relatively low. Meanwhile, through soaking the collagen sponge as a template in simulated body fluid (SBF) which contains different transition metal ions (Mn(2+), Cu(2+), Ni(2+), Co(2+), Cd(2+), Hg(2+)), bone-like HAP/collagen composites were synthesized. Hg(2+) had a certain inhibitory effect on the formation of HAP crystals on the surface of the collagen sponge while Co(2+) can promote the formation of HAP on the collagen sponge. For both HAP/collagen composites and HAP/collagen sponge, it was found that transition metal ions Mn(2+) had a significant effect on the morphology of HAP particles and could induce to form floc-like HAP particle aggregates.

Effects of different crosslinking conditions on the chemical-physical properties of a novel bio-inspired composite scaffold stabilised with 1,4-butanediol diglycidyl ether (BDDGE)

Serious cartilage lesions (Outerbridge III, IV) may be successfully treated with a three-layered gradient scaffold made by magnesium-doped hydroxyapatite and type I collagen, manufactured through a bio-inspired process and stabilised by a reactive bis-epoxy (1,4-butanediol diglycidyl ether, BDDGE). Each layer was analysed to elucidate the effects of crosslinking variables (concentration, temperature and pH). The chemical stabilisation led to an homogeneous and aligned collagenous matrix: the fibrous structures switched to a laminar foils-based arrangement and organic phases acquired an highly coordinated 3D-organization. These morphological features were strongly evident when crosslinking occurred in alkaline solution, with BDDGE concentration of at least 1 wt%. The optimised crosslinking conditions did not affect the apatite nano-crystals nucleated into self-assembling collagen fibres. The present work allowed to demonstrate that acting on BDDGE reaction parameters might be an useful tool to control the chemical-physical properties of bio-inspired scaffold suitable to heal wide osteochondral defects, even through arthroscopic procedure.

Optimized conditions for mesenchymal stem cells to differentiate into osteoblasts on a collagen/hydroxyapatite matrix

Collagen/hydroxyapatite (HA) composite scaffolds are known to be suitable scaffolds for seeding with mesenchymal stem cells (MSCs) differentiated into osteoblasts and for the in vitro production of artificial bones. However, the optimal collagen/HA ratio remains unclear. Our study confirmed that a higher collagen content increased scaffold stiffness but that a greater stiffness was not sufficient for bone tissue formation, a complex process evidently also dependent on scaffold porosity. We found that the scaffold pore diameter was dependent on the concentration of collagen and HA and that it could play a key role in cell seeding. In conclusion, the optimal scaffold for new bone formation and cell proliferation was found to be a composite scaffold formed from 50 wt % HA in 0.5 wt % collagen I solution.

Biocomposites and hybrid biomaterials based on calcium orthophosphates

The state-of-the-art of biocomposites and hybrid biomaterials based on calcium orthophosphates that are suitable for biomedical applications is presented in this review. Since these types of biomaterials offer many significant and exciting possibilities for hard tissue regeneration, this subject belongs to a rapidly expanding area of biomedical research. Through successful combinations of the desired properties of matrix materials with those of fillers (in such systems, calcium orthophosphates might play either role), innovative bone graft biomaterials can be designed. Various types of biocomposites and hybrid biomaterials based on calcium orthophosphates, either those already in use or being investigated for biomedical applications, are extensively discussed. Many different formulations, in terms of the material constituents, fabrication technologies, structural and bioactive properties as well as both in vitro and in vivo characteristics, have already been proposed. Among the others, the nanostructurally controlled biocomposites, those containing nanodimensional compounds, biomimetically fabricated formulations with collagen, chitin and/or gelatin as well as various functionally graded structures seem to be the most promising candidates for clinical applications. The specific advantages of using biocomposites and hybrid biomaterials based on calcium orthophosphates in the selected applications are highlighted. As the way from the laboratory to the hospital is a long one, and the prospective biomedical candidates have to meet many different necessities, this review also examines the critical issues and scientific challenges that require further research and development.

Hydroxyapatite-collagen composites. Part I: can the decrease of the interactions between the two components be a physicochemical component of osteoporosis in aged bone?

The interactions of Type I acid soluble collagen (Col) with both carbonate-free hydroxyapatite (HA(1100)) and carbonate-rich one (CHA) were investigated. The aim was to ascertain whether the increase of bone CO(3) (2-) with ageing could relate to the disease known as osteoporosis. HA(1100)-Col and CHA-Col composites with various ratios were prepared and examined. Scanning electron microscopy and differential scanning calorimetry showed a stronger adhesion of the Col matrix to the granules of HA(1100) than to those of CHA. FT-IR spectroscopy showed that with HA(1100) both multiple hydrogen bonds of Col peptide -NH groups with HA PO(4) (3-), and electrochemical interactions between Col peptide -C=O groups and HA Ca(2+) were present. In the presence of CO(3) (2-), the interactions between -NH and phosphate were diminished, and Ca(2+) interacted more strongly with CO(3) (2-) than with peptide -C=O, so causing a separation between the two components of the bone extra-cellular matrix. The results obtained strengthen the hypothesis that the substitution of PO(4) (3-) ions by CO(3) (2-) ions in the HA lattice might be a significant component of osteoporosis, although further investigation is needed.

Formation of calcium deficient HAp/collagen composites by hydrolysis of alpha-TCP

Bone-like composites containing calcium deficient hydroxyapatite (CDHAp) were formed by the hydrolysis of alpha-tricalcium phosphate (alpha-TCP) in the presence of type I collagen. CDHAp-collagen composites were synthesized using two techniques. In one technique alpha-TCP was mixed with non-milled (as-received) collagen prior to the addition of the aqueous solution. In the second, the collagen was milled with alpha-TCP in heptane at room temperature prior to its conversion to CDHAp. The effect of milling strongly facilitates the formation of CDHAp at physiological temperature. The proportion of milled collagen between 5 and 20 wt% present in the alpha-TCP/collagen composites has no significant effect on the rate of CDHAp formation. Variations in pH and in calcium and phosphate concentrations were determined as a function of collagen processing and variations specific to the presence of collagen were discerned. Compared to CDHAp or to composites containing non-milled collagen, diametrical and compressive strengths of CDHAp increased in the presence of milled collagen. Lack of collagen dispersion and incomplete formation of CDHAp during 48 h were the bases for reduced strengths of composites containing non-milled collagen.

Gradient structural bone-like apatite induced by chitosan hydrogel via ion assembly

Polymers with negatively charged groups (-COOH, -OH or -PO(4)H(2)) were frequently adopted to induce or promote apatite deposition through electrostatic interaction. However, chitosan with positively charged groups (-NH(2)) was ignored, although it could bind most of metal ions through chelation. Based on the chelation properties of the amino group, a chitosan hydrogel obtained via physical cross-linking was used as template for ion assembly. Gradient structural bone-like apatite induced by chitosan hydrogel was achieved via ion assembly within a few hours under ambient conditions, in which amino groups of chitosan acted as anchors between chitosan and apatite nucleation. The phase and component of bone-like apatite were similar to apatite in rabbit ribs according to XRD patterns and FT-IR spectra. XRD results revealed that bone-like apatite was carbonated apatite and preferred growth orientation in the direction of c-axis. The profile of elements distribution in chitosan suggested that the content of calcium and phosphorous elements decreased with the increase of depth along the radius direction, which was accompanied by the formation of apatite-rich regions near the outer layer. When chitosan was dipped in calcium ions solution, Ca(2+) ions bound amino groups of chitosan and formed chitosan/calcium ions complexes (CS-NH(2)…Ca(2+)). CS-NH(2)…Ca(2+) subsequently attracted negatively-charged phosphate ions through electrostatic interaction. When ion assembly finished, Ca and P ions in the chitosan hydrogel converted into ACP with Ca/P ratio of 1.19. ACP converted into bone-like apatite with Ca/P ratio of 2.01 after alkali treatment.

Enzymatically crosslinked porous composite matrices for bone tissue regeneration

Three-dimensional porous hydroxyapatite/collagen (HA/Coll) composites with a random pore structure were obtained by freeze-drying and crosslinked by an enzymatic treatment using microbial transglutaminase (mTGase). The procedure resulted in improved mechanical strength and thermal stability of the scaffolds. The scaffolds were characterized in terms of their stability (Coll release, swelling, collagenase-mediated degradation), thermal properties (thermogravimetric analysis, differential scanning calorimetry), mechanical behavior under compression and cell compatibility. Enzymatic treatment stabilized the sponges to water vapors, with measurable swelling ratio between 100% for HA/Coll/mTGase 0/100 to 5% for HA/Coll/mTGase 80/20. Weight loss in water due to Coll release was between 2 and 10% in mTGase-crosslinked samples and decreased with increasing HA content. Cultures of MG63 osteoblast-like cells and human umbilical vein endothelial cells (HUVEC) showed good adhesion and proliferation on the scaffolds, good viability (through MTT test, 100-150% of control), and good differentiation (alkaline phosphatase, up to 40 UI/L with respect to 35 UI/L for control).

An organic matrix-mediated processing methodology to fabricate hydroxyapatite based nanostructured biocomposites

An amorphous calcium phosphate precursor phase, which forms by adding orthophosphoric acid to a calcium hydroxide suspension, is transformed into crystalline hydroxyapatite by introducing polymer solutions. The nanostructured composite films formed by a solvent casting technique from the concentrated hybrid suspension are characterised for structure and mechanical properties.

Problem of hydroxyapatite dispersion in polymer matrices: a review

This review summarizes recent work on manufacturing biocomposites suitable for bone tissue engineering. There is a great need to engineer multi-phase (i.e. composite) materials that combine the advantages exhibited by each component of the material, with a structure and composition similar to that of natural bone. The discussion concentrates on the preparation of nanocomposites containing hydroxyapatite particles (one of the most widely used bioceramics materials) with polymer matrices. Special attention is paid to the preparation of nanocomposites with individual (non-aggregated) nanoparticles because this is a key problem in nanotechnology industrialization. Controlling the mixing between so two dissimilar phases is a critical challenge in the design of these inorganic-organic systems. Several approaches that may be applied to overcome this problem will be described in this review.

Gradient collagen/nanohydroxyapatite composite scaffold: development and characterization

This paper reports an in situ diffusion method for the fabrication of compositionally graded collagen/nanohydroxyapatite (HA) composite scaffold. The method is diffusion based and causes the precipitation of nano-HA crystallites in situ. A collagen matrix acts as a template through which calcium ions (Ca(2+)) and phosphate ions (PO4(3-)) diffuse and precipitate a non-stoichiometric HA. It was observed that needle-like prismatic nano-HA crystallites (about 2 x 2 x 20 nm) precipitated in the interior of the collagen template onto the collagen fibrils. Chemical and microstructural analysis revealed a gradient of the Ca to P ratio across the width of the scaffold template, resulting in the formation of a Ca-rich side and a Ca-depleted side of scaffold. The Ca-rich side featured low porosity and agglomerates of the nano-HA crystallites, while the Ca-depleted side featured higher porosity and nano-HA crystallites integrated with collagen fibrils to form a porous network structure.

Design of graded biomimetic osteochondral composite scaffolds

With the ultimate goal to generate suitable materials for the repair of osteochondral defects, in this work we aimed at developing composite osteochondral scaffolds organized in different integrated layers, with features which are biomimetic for articular cartilage and subchondral bone and can differentially support formation of such tissues. A biologically inspired mineralization process was first developed to nucleate Mg-doped hydroxyapatite crystals on type I collagen fibers during their self-assembling. The resulting mineral phase was non-stoichiometric and amorphous, resembling chemico-physical features of newly deposited, natural bone matrix. A graded material was then generated, consisting of (i) a lower layer of the developed biomineralized collagen, corresponding to the subchondral bone, (ii) an upper layer of hyaluronic acid-charged collagen, mimicking the cartilaginous region, and (iii) an intermediate layer of the same nature as the biomineralized collagen, but with a lower extent of mineral, resembling the tidemark. The layers were stacked and freeze-dried to obtain an integrated monolithic composite. Culture of the material for 2 weeks after loading with articular chondrocytes yielded cartilaginous tissue formation selectively in the upper layer. Conversely, ectopic implantation in nude mice of the material after loading with bone marrow stromal cells resulted in bone formation which remained confined within the lower layer. In conclusion, we developed a composite material with cues which are biomimetic of an osteochondral tissue and with the capacity to differentially support cartilage and bone tissue generation. The results warrant testing of the material as a substitute for the repair of osteochondral lesions in orthotopic animal models.

Controlled release of vancomycin from cross-linked gelatine

This paper explores the possibility of using biodegradable cross-linked gelatines as antibiotic devices for a long-term elution (80 days). Capillary electrophoresis (CE) has been utilized to evaluate the mass percentage of vancomycin and gelatine contemporary released from differently cross-linked vancomycin loaded gelatine samples in an elution time ranging from 24 to 1920 h. While the solubilization kinetic of gelatine samples differently cross-linked can be very close described by the simplified Higuchi model, the vancomycin release kinetic is contemporary governed by both the Fickian diffusion process trough the gelatine matrix network and the dissolution process of the matrix due to its degradation. Comparing the antibiotic eluting kinetics from gelatine at diverse cross-linking degree we observed that the degradation of the proteic matrix appears to have a minor influence in the drug release control. Vancomycin released from all the gelatine partially cross-linked samples results active against Staphylococcus aureus and Streptococcus faecalis which represent the most pathogens commonly isolated in orthopaedic infections. Vancomycin overcomes the minimum inhibitory concentration for both the bacteria in the whole range of elution time. Cross-linked gelatine devices appear to represent a useful biodegradable delivery system for local anti-infective therapy in arthoplasty.

Oriented nucleation of hydroxylapatite crystals on spider dragline silks

Spider dragline silk as a protein fiber can be pictured as the oriented organization of protein nanocrystals along the long axis with their spacing filled by amorphous protein domains. We used the surface of the spider dragline silk as a biological template to nucleate bone mineral hydroxylapatite (HAP) site-specifically from a HAP-supersaturated solution. HAP crystals were found to be nucleated on the surface of silks with their c axis preferentially oriented at an average angle of 72.9 degrees with respect to the long axis of the silks. The preferred orientation is nearly identical among the different mineralized silks that we studied. Other materials such as Au and CdS could be nucleated on the silks but did not show any preferred orientation. We believe that the oriented nucleation of HAP is directly related to the structures of silks and HAP. The mineralized silks will combine the good mechanical properties of the spider silks and the biocompatibility of HAP and may be assembled into ideal biomaterials as bone implants.