Bioactive zinc-doped sol-gel coating modulates protein adsorption patterns and in vitro cell responses

Zinc is an essential element with an important role in stimulating the osteogenesis and mineralization and suppressing osteoclast differentiation. In this study, new bioactive ZnCl₂-doped sol-gel materials were designed to be applied as coatings onto titanium. The biomaterials were physicochemically characterized and the cellular responses evaluated in vitro using MC3T3-E1 osteoblasts and RAW264.7 macrophages. The effect of Zn on the adsorption of human serum proteins onto the material surface was evaluated through nLC-MS/MS. The incorporation of Zn did not affect the crosslinking of the sol-gel network. A controlled Zn²⁺ release was obtained, reaching values below 10 ppm after 21 days. The materials were no cytotoxic and lead to increased gene expression of ALP, TGF-β, and RUNX2 in the osteoblasts. In macrophages, an increase of IL-1β, TGF-β, and IL-4 gene expression was accompanied by a reduced TNF-α liberation. Proteomic results showed changes in the adsorption patterns of proteins associated with immunological, coagulative, and regenerative functions, in a Zn dose-dependent manner. The variations in protein adsorption might lead to the downregulation of the NF-κB pathway, thus explain the observed biological effects of Zn incorporation into biomaterials. Overall, these coatings demonstrated their potential to promote bone tissue regeneration.

Proteomic analysis of calcium-enriched sol-gel biomaterials

Calcium is an element widely used in the development of biomaterials for bone tissue engineering as it plays important roles in bone metabolism and blood coagulation. The Ca ions can condition the microenvironment at the tissue-material interface, affecting the protein deposition process and cell responses. The aim of this study was to analyze the changes in the patterns of protein adsorption on the silica hybrid biomaterials supplemented with different amounts of CaCl₂, which can function as release vehicles. This characterization was carried out by incubating the Ca-biomaterials with human serum. LC-MS/MS analysis was used to characterize the adsorbed protein layers and compile a list of proteins whose affinity for the surfaces might depend on the CaCl₂ content. The attachment of pro- and anti-clotting proteins, such as THRB, ANT3, and PROC, increased significantly on the Ca-materials. Similarly, VTNC and APOE, proteins directly involved on osteogenic processes, attached preferentially to these surfaces. To assess correlations with the proteomic data, these formulations were tested in vitro regarding their osteogenic and inflammatory potential, employing MC3T3-E1 and RAW 264.7 cell lines, respectively. The results confirmed a Ca dose-dependent osteogenic and inflammatory behavior of the materials employed, in accordance with the protein attachment patterns.

The effect of strontium incorporation into sol-gel biomaterials on their protein adsorption and cell interactions

It is known strontium can both inhibit the osteoclast formation and stimulate the osteoblast maturation, so biomaterials containing this element can favour bone structure stabilisation. The addition of Sr to biomaterials could affect their interactions with proteins and cells. Here, a silica-hybrid sol-gel network doped with different amounts of SrCl₂ and applied as coatings on titanium discs was examined. in vitro analysis was performed to determine the potential effect of Sr in the coatings, showing enhanced gene expression of osteogenic markers (alkaline phosphatase and transforming growth factor-β) in MC3T3-E1 incubated with Sr-doped biomaterials. The examination of inflammatory markers (tumour necrosis factor-α and interleukin 10) in RAW 264.7 macrophages revealed an anti-inflammatory potential of these materials. Proteins adsorbed onto the coatings incubated with human serum (3 h at 37 °C) were also analysed; mass spectrometry was used to characterise the proteins adhering to materials with different Sr content. Adding Sr to the coatings increased their affinity to APOE and VTNC proteins (associated with anti-inflammatory and osteogenic functions). Moreover, the proteins involved in coagulation processes, such as prothrombin, were more abundant on the coatings containing Sr than on the base sol-gel surfaces. Correlations between gene expression and proteomic results were also examined.

Synthesis and characterization of silica-chitosan hybrid materials as antibacterial coatings for titanium implants

To avoid dental implant-related infections and to promote the osseointegration of titanium implants, the application of silicon and chitosan containing coatings is proposed. Silicon is a well-known osteogenic element and chitosan was selected to confer the antibacterial properties. The synthesis of hybrid silica-chitosan coatings using the sol-gel process is presented and the characterization using ²⁹Si-NMR to verify the correct formation of the network is discussed. The ¹³C NMR spectroscopy was used to confirm the covalent union between chitosan and the silicon network. Hydrolytic degradation and silicon release studies showed the effective silicon release from the hybrids and, hence, the possibility to promote bone formation. The introduction of different amounts of chitosan and tetraethyl orthosilicate (TEOS) modulated the Si release. The analysis of cell cultures in vitro demonstrated that the hybrid coatings were not cytotoxic and promoted cell proliferation on their surfaces. The coatings containing 5%-10% chitosan had substantial antibacterial properties.

Osseointegration mechanisms: a proteomic approach

The prime objectives in the development of biomaterials for dental applications are to improve the quality of osseointegration and to short the time needed to achieve it. Design of implants nowadays involves changes in the surface characteristics to obtain a good cellular response. Incorporating osteoinductive elements is one way to achieve the best regeneration possible post-implantation. This study examined the osteointegrative potential of two distinct biomaterials: sandblasted acid-etched titanium and a silica sol-gel hybrid coating, 70% MTMOS-30% TEOS. In vitro, in vivo, and proteomic characterisations of the two materials were conducted. Enhanced expression levels of ALP and IL-6 in the MC3T3-E1 cells cultured with coated discs, suggest that growing cells on such surfaces may increase mineralisation levels. 70M30T-coated implants showed improved bone growth in vivo compared to uncoated titanium. Complete osseointegration was achieved on both. However, coated implants displayed osteoinductive properties, while uncoated implants demonstrated osteoconductive characteristics. Coagulation-related proteins attached predominantly to SAE-Ti surface. Surface properties of the material might drive the regenerative process of the affected tissue. Analysis of the proteins on the coated dental implant showed that few proteins specifically attached to its surface, possibly indicating that its osteoinductive properties depend on the silicon delivery from the implant.

Proteomic analysis of silica hybrid sol-gel coatings: a potential tool for predicting the biocompatibility of implants in vivo

The interactions of implanted biomaterials with the host organism determine the success or failure of an implantation. Normally, their biocompatibility is assessed using in vitro tests. Unfortunately, in vitro and in vivo results are not always concordant; new, effective methods of biomaterial characterisation are urgently needed to predict the in vivo outcome. As the first layer of proteins adsorbed onto the biomaterial surfaces might condition the host response, mass spectrometry analysis was performed to characterise these proteins. Four distinct hybrid sol-gel biomaterials were tested. The in vitro results were similar for all the materials examined here. However, in vivo, the materials behaved differently. Six of the 171 adsorbed proteins were significantly more abundant on the materials with weak biocompatibility; these proteins are associated with the complement pathway. Thus, protein analysis might be a suitable tool to predict the in vivo outcomes of implantations using newly formulated biomaterials.

Preparation and characterization of injectable PMMA-strontium-substituted bioactive glass bone cement composites

In most minimally-invasive procedures used to address severe pain arising from compression fractures of the vertebral bodies, such as percutaneous vertebroplasty (PVP), a poly(methyl methacrylate) (PMMA) bone cement is used. Shortcomings of this type of cement, such as high exotherm temperature and lack of bioactivity, are well known. We prepared different formulations of a composite bone cement, whose solid constituents consisted of PMMA beads and particles of a bioactive glass (BG), where 0-20%(w/w) of the calcium component was substituted by strontium. The difference between the formulations was in the relative amounts of the solid phase constituents and in the Sr-content of BG. We determined the influence of the mixture of solid phase constituents of the cement formulation on a collection of properties, such as maximum exotherm temperature (T_max ), setting time (t_set ), and injectability (I). The selection of the PMMA beads was crucial to obtain cement composite formulations capable to be efficiently injected. Results allowed to select nine solid phase mixtures to be further tested. Then, we determined the influence of the composition of these composite bone cements on T_max , t_set , I, and cell proliferation. The results showed that the performance of various of the selected composite cements was better than that of PMMA cement reference, with lower T_max , lower t_set , and higher I. We found that incorporation of Sr-substituted BGs into these materials bestows bioactivity properties associated with the role of Sr in bone formation, leading to some composite cement formulations that may be suitable for use in PVP. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1245-1257, 2018.

Wear Behaviour of the Pair Ti–6Al–4V–UHMWPE of Acrylic Bone Cements Containing Different Radiopaque Agents

The objective of this study was to improve the wear behaviour of acrylic bone cements by substituting the conventional inorganic radiopaque agents (BaSO4, ZrO2) for different iodinated radiopaque monomers which can co-polymerize with the methyl methacrylate monomer, MMA. To this aim, the wear behaviour of the pair Ti–6Al–4V–UHMWPE (ultra high molecular weight polyethylene) was studied in the absence and in the presence of cement particles (the third body).

Biological characterization of a new silicon based coating developed for dental implants

Taking into account the influence of Si in osteoblast cell proliferation, a series of sol-gel derived silicon based coating was prepared by controlling the process parameters and varying the different Si-alkoxide precursors molar rate in order to obtain materials able to release Si compounds. For this purpose, methyltrimethoxysilane (MTMOS) and tetraethyl orthosilicate (TEOS) were hydrolysed together and the sol obtained was used to dip-coat the different substrates. The silicon release ability of the coatings was tested finding that it was dependent on the TEOS precursor content, reaching a Si amount value around ninefolds higher for coatings with TEOS than for the pure MTMOS material. To test the effect of this released Si, the in vitro performance of developed coatings was tested with human adipose mesenchymal stem cells finding a significantly higher proliferation and mineralization on the coating with the higher TEOS content. For in vivo evaluation of the biocompatibility, coated implants were placed in the tibia of the rabbit and a histological analysis was performed. The evaluation of parameters such as the bone marrow state, the presence of giant cells and the fibrous capsule proved the biocompatibility of the developed coatings. Furthermore, coated implants seemed to produce a qualitatively higher osteoblastic activity and a higher number of bone spicules than the control (uncoated commercial SLA titanium dental implant).

Synthesis of hybrid sol-gel materials and their biological evaluation with human mesenchymal stem cells

Surface engineering of biomaterials could promote the osseointegration of implants. In this work, two types of hybrid sol-gel materials were developed to stimulate cell attachment, proliferation and differentiation of osteogenic cells. One type was synthesised from vinyl triethoxysilane (VTES) and tetraethyl-orthosilicate (TEOS) at different molar ratios, while the other from VTES and hydroxyapatite particles (HAp). Hybrid materials were systematically investigated using nuclear magnetic resonance, Fourier transform infrared spectroscopy and contact angle metrology. The biocompatibility and osseoinduction of the coatings were evaluated by measuring mesenchymal stem cell proliferation using MTT assays and analysing the mineralised extracellular matrix production by quantifying calcium-rich deposits. The results highlighted the versatility of these coatings in obtaining different properties by changing the molar ratio of the VTES:TEOS precursors. Thus, mineralisation was stimulated by increasing TEOS content, while the addition of HAp improved cell proliferation but worsened mineralisation.

Injectable acrylic bone cements for vertebroplasty based on a radiopaque hydroxyapatite. Formulation and rheological behaviour

The utilization of injectable acrylic bone cement is crucial to the outcome of vertebroplasty and kyphoplasty. However, only a few cements that are in clinical use today are formulated specifically for use in these procedures and even these formulations are not regarded as "ideal" injectable bone cements. The aim of this work is to prepare bioactive bone cements by adding strontium hydroxyapatite (SrHA) to a cement formulation based on polymethylmethacrylate. Thus, the cement combines the immediate mechanical support given by the setting of the acrylic matrix with optimum radiopacity and bioactivity due to the incorporation of the SrHA. Formulations of bioactive cement were prepared with 10 and 20 wt% of SrHA as synthesised and after a surface treatment with the monomer. Cements loaded with treated particles showed an enhancement of their handling properties, and hence, an improvement on their rheological behaviour, injectabilities and compressive parameters. Further experiments were also carried out to determine their bioactivity and biocompatibility and results appear in other publication.

Acrylic bone cements with bismuth salicylate: Behavior in simulated physiological conditions

In a previous work, we reported the development of acrylic bone cement formulations for application in percutaneous vertebroplasty, by using bismuth salicylate (BS) as the radiopaque agent. Our objective was to obtain high radiopacity along with a therapeutical effect produced by the release of salicylic acid in situ. To follow that study, the setting kinetics and static and dynamical mechanical properties of the BS cements were studied in simulated physiological conditions. Moreover, radiopacity after various times of immersion in saline and the wettability of the cements surfaces were determined. The study finished with the analysis of the biological response. From the results, it can be concluded that physiological conditions did not affect negatively to the cements performance, since all BS-loaded cements fulfilled the ISO standard requirements. Radiopacity of the formulations was maintained over time and cements with BS were found to be biocompatible.

Propagation of fatigue cracks in acrylic bone cements containing different radiopaque agents

In this work three iodine-containing monomers were proposed as new radiopaque agents for acrylic bone cements. In previous studies the addition of iodine-containing methacrylate monomers provided a statistically significant increase in tensile stress, fracture toughness and ductility, with respect to the barium sulphate(BaSO4)-containing cement. However, since fatigue resistance is one of the main properties required to ensure a good long-term performance of permanent prostheses, it is important to compare the fatigue properties of these new bone cement formulations with the radiolucent and BaSO4-containing bone cements. Because the acrylic cements have initial cracks, fatigue crack propagation studies were performed. It can be observed that these acrylic cements followed the Paris-Erdogan model. The results showed that the addition of some organic radiopacifiers (DISMA, TIBMA) increased the fatigue crack propagation resistance as compared to the radiolucent cement, being similar to the BaSO4-containing cement. The radiolucent cement showed a low crack propagation resistance.

Elimination of barium sulphate from acrylic bone cements. Use of two iodine-containing monomers

The aim of this work is to present a new approach to joint arthroplasty failure related to bone cement mantle. As barium sulphate is considered one of the main causes of mechanical weakness in the cement, we substituted this inorganic radiopacifier of the solid component for radiopaque monomers in the liquid component. We obtained two different cements, one containing 5 vol% 2-[2',3',5'-triiodobenzoyl] ethyl methacrylate (TIBMA) and the other containing 3,5-diiodine salicylic methacrylate (DISMA). In both cases, the mechanical properties of these new cements were better than those of the barium sulphate-containing cement. The radiopacity obtained was comparable to that of the aforementioned cement and all the samples showed good biocompatibility.

A radiopaque polymeric matrix for acrylic bone cements

As part of the search for an alternative to inorganic radiopaque agents, this work studies the possibility of modifying bone cement formulations by incorporating a radiopaque monomer, that is, 4-iodophenol methacrylate (IPMA), in the liquid phase. The monomer was synthesized in the laboratory, and cements were prepared by the standard method. The influence on the different cement characteristics of various monomer concentrations was studied. It was seen that the setting time decreased as the percentage of monomer increased. The radiopacity attained in the 15 vol.% IPMA formulations was about the same as that for a cement containing 10 wt.% barium sulphate. Dynamic and static mechanical properties were measured. The materials did not show significant differences in the glass transition temperature. However, static mechanical properties showed enhanced compressive strength, tensile strength, and elastic modulus with respect to conventional cements formulated with barium sulphate. Histological studies showed a good response of muscular tissue to implanted specimens.

Synthesis of hydroxypropyl methacrylate/polysaccharide graft copolymers as matrices for controlled release tablets

Hydrophilic matrices are an interesting option when developing drug delivery systems. With this aim, hydroxypropyl methacrylate was grafted onto hydroxypropyl starch and hydroxypropyl cellulose substrates by following the Ce(IV) redox initiation method. Different amounts of ethyleneglycol' dimethacrylate, 7 and 34 mol%, as the crosslinking monomer, were also added. The drying of grafted products was carried out by lyophilization, obtaining white powders. Reaction yields (percent grafting, grafting efficiency, etc.) and some physical characteristics of the powders (particle size, moisture uptake, density, morphology, etc.) were determined. These parameters indicate how useful these products may be as potential matrices for direct compressed tablets. In this light, the powder flowability and the binding properties of each copolymer were determined. The graft copolymers can be considered of great interest as direct compression excipients. Due to their different chemical structure and composition, they showed differences in viscoelastic properties that revealed an interesting range of possibilities for use in drug delivery formulations. Tablets formulated with conventional excipients were also tested. Dissolution tests of various tablets were carried out. In 12 hr, 60-80% of the model drugs was released.

Synthetic PMMA-grafted polysaccharides as hydrophilic matrix for controlled-release forms

This paper describes the rheological behavior of starch and cellulose acrylic graft copolymers synthesized with the aim of obtaining controlled-release excipients. The rheological characteristics determine the final release properties of matrix tablets. The study of the storage and loss moduli (G' and G", respectively) and the viscosity allowed us to know if the polymer behavior was that of a gel and, hence, if it could act as a barrier to drug diffusion. Since dynamic measurements showed a storage modulus higher than the loss modulus, we assessed that all the polymers were gels. Thus, knowing that all the graft copolymers had acceptable properties for compression, the release of theophylline as a model drug at different pH was studied. Polymers with higher absorption capacity, viscosity, and compactibility allowed formulations with slower release rates.

Characterization of new acrylic bone cement based on methyl methacrylate/1-hydroxypropyl methacrylate monomer

New formulations of acrylic bone cement based on methyl methacrylate/1-hydroxypropyl methacrylate (MMA/HPMA) monomers were developed with the purpose of obtaining more ductile materials with reduced polymerization shrinkage. In this way, the ductility of such materials increased, but the introduction of high percentages of the hydrophilic component produced an important decrease in Young's modulus and strength. To ascertain the reason for the deterioration of the tensile parameters, an analysis by scanning electron microscopy of these formulations was carried out; it revealed poor adhesion between the matrix and poly(MMA) beads. We also observed that the polymerization shrinkage increased as the amount of hydrophilic monomer in the formulation decreased, and the 50% (v/v) HPMA modified bone cement compensated for this volume reduction with its water uptake swelling. Measurements taken on the setting time and polymerization exotherm showed a decrease in the former and an increase in the latter, because of the introduction of a more reactive monomer in the bone cement formulation.

Modified acrylic bone cement with high amounts of ethoxytriethyleneglycol methacrylate

One cause of arthroplasty failure is the brittle mechanical behavior of bone cements. However, the improvement of cement formulations must also be accompanied by the maintenance of a wide variety of characteristics. New bone cements were obtained by the substitution of high percentages, up to 60% (v/v), of methyl methacrylate (MMA) by a higher molecular weight and more hydrophilic monomer, ethoxytriethyleneglycol methacrylate (TEG). The essential advantages of these materials were the decrease of maximum temperature together with a decrease in the residual monomer content with respect to conventional cement formulations. The water absorption process obeyed diffusion laws and the equilibrium water content increased by the introduction of higher percentages of the hydrophilic component. This characteristic had an appreciable effect on the viscoelastic behavior analyzed by DMTA. These modified bone cements had reduced polymerization shrinkage and similar levels of porosity. Tensile test revealed that the introduction of TEGMA gave rise to an important modification of the mechanical behavior, with a noticeable increase in the fracture strain. This fact was also confirmed by means of the analysis of the fracture surfaces by SEM.

Influence of the modification of P/L ratio on a new formulation of acrylic bone cement

The use of smaller powder/liquid (P/L) ratio favours the handling and wetting of poly(methyl methacrylate) (PMMA) beads in bone cement formulations. In this paper a P/L ratio of 1.86 is tested to overcome adhesion problems found in hydroxypropyl methacrylate (HPMA) modified bone cements and the influence on bone cement characteristics was analysed. The reduction of the P/L ratio leads to higher temperature peaks and shorter setting times, whereas the residual monomer content increases slightly. Water uptake obeys the diffusion laws, and the introduction of a more hydrophilic monomer gives rise to an increase of this parameter, which does not present significant changes with modification of the P/L ratio. Polymerization shrinkage is slightly greater because of the introduction of higher proportions of monomer in the formulation. Mechanical properties are similar to those obtained with conventional P/L ratios. The analysis of scanning electron microscopy (SEM) reveals an improvement of the adhesion between phases with respect to P/L = 2 formulations.

pH-sensitive hydrogels based on non-ionic acrylic copolymers

Hydrogels based on ethoxytriethyleneglycol monomethacrylate/methyl methacrylate copolymers were prepared by free radical polymerization at 70 degrees C in bulk with 2,2'-azobisisobutyronitrile as initiator. The swelling behaviour of the hydrogels was studied by immersion of the films in water and in buffered solutions at various pHs. The hydration process was followed gravimetrically measuring the water uptake of the films with the time of treatment. The kinetics fit adequately a Fickian law for reduced sorption coefficients, Mt/M infinity, lower than 0.6. The values of the diffusion coefficient were lower at neutral pH than at acidic or alkaline pHs, and they seemed to be independent of the copolymer composition. The results obtained were consistent with the stress relaxation model of polymer chains predicted for a relatively fast hydration process. The swelling process is reversible and the polymeric films are stable after repeating cycles of hydration and desorption promoted by the change of pH in appropriate buffered solutions.

Application of tertiary amines with reduced toxicity to the curing process of acrylic bone cements

4-Dimethylaminobenzyl alcohol (DMOH) and 4-dimethylaminobenzyl methacrylate (DMMO) were used as the activators in the benzoyl peroxide initiated redox polymerization for the preparation of acrylic bone cement based on poly(methylmethacrylate) beads of different particle size. The residual monomer content of the cured cements was about 2 wt %, independent of the redox system used in the polymerization, indicating that the activating effect of the tertiary aromatic amines DMOH or DMMO was sufficient to reach a polymerization conversion similar to that obtained with the benzoyl peroxide (BPO) N,N-dimethyl-4-toluidine (DMT) system. The BPO/DMOH and BPO/DMMO redox systems provided exotherms of decreasing peak temperature and increasing setting time, and the cured materials presented higher average molecular weight and similar glass transition temperatures in comparison with those obtained when DMT was used as the activator. In addition, these activators are three times less toxic than the classical DMT.

New aspects of the effect of size and size distribution on the setting parameters and mechanical properties of acrylic bone cements

The effect of the size and the size distribution of poly(methyl methacrylate) (PMMA) beads on the classical kinetic parameters, peak temperature and setting time, for acrylic bone cement formulations prepared with PMMA particles in the range 10-60 microns of average diameter and a relatively wide size distribution is analysed. In addition, the combined effects of the concentration of the free radical initiator benzoyl peroxide and the activator N, N-dimethyl-4-toluidine for the different particle sizes are studied and compared with those commercially available formulations like CMW or Rostal. The results obtained indicated that the use of PMMA particles with average diameter of 50-60 microns, and a relatively wide size distribution (10-140 microns diameter), significantly changes the curing parameters (peak temperature and setting time) of the cement formulations in comparison with the classical behaviour of the commercial systems of CMW and Rostal, without any noticeable loss in the mechanical properties, such as tensile strength, elastic moduli, and compressive strength and plastic strain.