Osteoconductive conjugation of bone morphogenetic protein-2 onto titanium/titanium oxide surfaces coated with non-biofouling poly(poly(ethylene glycol) methacrylate)

Investigations into the effects of scaffold microstructure on slow-release system with bioactive factors for bone repair

In recent years, bone tissue engineering (BTE) has played an essential role in the repair of bone tissue defects. Although bioactive factors as one component of BTE have great potential to effectively promote cell differentiation and bone regeneration, they are usually not used alone due to their short effective half-lives, high concentrations, etc. The release rate of bioactive factors could be controlled by loading them into scaffolds, and the scaffold microstructure has been shown to significantly influence release rates of bioactive factors. Therefore, this review attempted to investigate how the scaffold microstructure affected the release rate of bioactive factors, in which the variables included pore size, pore shape and porosity. The loading nature and the releasing mechanism of bioactive factors were also summarized. The main conclusions were achieved as follows: i) The pore shapes in the scaffold may have had no apparent effect on the release of bioactive factors but significantly affected mechanical properties of the scaffolds; ii) The pore size of about 400 μm in the scaffold may be more conducive to controlling the release of bioactive factors to promote bone formation; iii) The porosity of scaffolds may be positively correlated with the release rate, and the porosity of 70%-80% may be better to control the release rate. This review indicates that a slow-release system with proper scaffold microstructure control could be a tremendous inspiration for developing new treatment strategies for bone disease. It is anticipated to eventually be developed into clinical applications to tackle treatment-related issues effectively.

Role of chitosan in titanium coatings. trends and new generations of coatings

Survival studies of dental implants currently reach high figures. However, considering that the recipients are middle-aged individuals with associated pathologies, research is focused on achieving bioactive surfaces that ensure osseointegration. Chitosan is a biocompatible, degradable polysaccharide with antimicrobial and anti-inflammatory properties, capable of inducing increased growth and fixation of osteoblasts around chitosan-coated titanium. Certain chemical modifications to its structure have been shown to enhance its antibacterial activity and osteoinductive properties and it is generally believed that chitosan-coated dental implants may have enhanced osseointegration capabilities and are likely to become a commercial option in the future. Our review provided an overview of the current concepts and theories of osseointegration and current titanium dental implant surfaces and coatings, with a special focus on the in vivo investigation of chitosan-coated implants and a current perspective on the future of titanium dental implant coatings.

Methacrylate Coatings for Titanium Surfaces to Optimize Biocompatibility

Currently, there are more than 1.5 million knee and hip replacement procedures carried out in the United States. Implants have a 10-15-year lifespan with up to 30% of revision surgeries showing complications with osteomyelitis. Titanium and titanium alloys are the favored implant materials because they are lightweight and have high mechanical strength. However, this increased strength can be associated with decreased bone density around the implant, leading to implant loosening and failure. To avoid this, current strategies include plasma-spraying titanium surfaces and foaming titanium. Both techniques give the titanium a rough and irregular finish that improves biocompatibility. Recently, researchers have also sought to surface-conjugate proteins to titanium to induce osteointegration. Cell adhesion-promoting proteins can be conjugated to methacrylate groups and crosslinked using a variety of methods. Methacrylated proteins can be conjugated to titanium surfaces through atom transfer radical polymerization (ATRP). However, surface conjugation of proteins increases biocompatibility non-specifically to bone cells, adding to the risk of biofouling which may result in osteomyelitis that causes implant failure. In this work, we analyze the factors contributing to biofouling when coating titanium to improve biocompatibility, and design an experimental scheme to evaluate optimal coating parameters.

Self-Assembled Monolayers for Dental Implants

Implant-based therapy is a mature approach to recover the health conditions of patients affected by edentulism. Thousands of dental implants are placed each year since their introduction in the 80s. However, implantology faces challenges that require more research strategies such as new support therapies for a world population with a continuous increase of life expectancy, to control periodontal status and new bioactive surfaces for implants. The present review is focused on self-assembled monolayers (SAMs) for dental implant materials as a nanoscale-processing approach to modify titanium surfaces. SAMs represent an easy, accurate, and precise approach to modify surface properties. These are stable, well-defined, and well-organized organic structures that allow to control the chemical properties of the interface at the molecular scale. The ability to control the composition and properties of SAMs precisely through synthesis (i.e., the synthetic chemistry of organic compounds with a wide range of functional groups is well established and in general very simple, being commercially available), combined with the simple methods to pattern their functional groups on complex geometry appliances, makes them a good system for fundamental studies regarding the interaction between surfaces, proteins, and cells, as well as to engineering surfaces in order to develop new biomaterials.

Effect of Catechol Content in Catechol-Conjugated Dextrans on Antiplatelet Performance

The surface coating of solid substrates using dextrans has gained a great deal of attention, because dextran-coated surfaces show excellent anti-fouling property as well as biocompatibility behavior. Much effort has been made to develop efficient methods for grafting dextrans on solid surfaces. This led to the development of catechol-conjugated dextrans (Dex-C) which can adhere to a number of solid surfaces, inspired by the underwater adhesion behavior of marine mussels. The present study is a systematic investigation of the characteristics of surface coatings developed with Dex-C. Various Dex-C with different catechol contents were synthesized and used as a surface coating material. The effect of catechol content on surface coating and antiplatelet performance was investigated.

Systematic Study of Functionalizable, Non-Biofouling Agarose Films with Protein and Cellular Patterns on Glass Slides

Herein we demonstrate a systematic investigation of chemically functionalizable, non-biofouling agarose films over large-area glass surfaces. Agarose films, prepared with various concentrations of aqueous agarose, were activated by using periodate oxidation to generate aldehyde groups at the termini of the agarose chains. The non-biofouling efficacy and binding capabilities of the activated films were evaluated by using protein and cellular patterning, performed by using a microarrayer, microcontact printing, and micromolding in capillaries. Characterization by using a fluorescence slide scanner and a scanning-probe microscope revealed that the pore sizes of the agarose films played an important role in achieving desirable film performance; the 0.2 wt % agarose film exhibited the optimum efficacy in this work.

Growth factor conjugation: strategies and applications

Growth factors, first known for their essential role in the initiation of mitosis, are required for a variety of cellular processes and their localized delivery is considered as a rational approach in their therapeutic application to assure a safe and effective treatment while avoiding unwanted adverse effects. Noncovalent immobilization of growth factors as well as their covalent conjugation is amongst the most common strategies for localized delivery of growth factors. Today, immobilized and covalently conjugated growth factors are considered as a promising drug design and are widely used for protein reformulation and material design to cover the unwanted characteristics of growth factors as well as improving their functions. Selection of a suitable conjugation technique depends on the substrate chemistry and the availability of functional reactive groups in the structure of growth factor, the position of reactive groups in growth factor molecules and its relation with the receptor binding area, and the intention of creating either patterned or unpatterned conjugation. Various approaches for growth factor reformulation have been reported. This review provides an overview on chemical conjugation of growth factors and covers the relevant studies accomplished for bioconjugation of growth factors and their related application.

Ultrathin sP(EO-stat-PO) hydrogel coatings are biocompatible and preserve functionality of surface bound growth factors in vivo

Hydrogel coatings prepared from reactive star shaped polyethylene oxide based prepolymers (NCO-sP(EO-stat-PO)) minimize unspecific protein adsorption in vitro, while proteins immobilized on NCO-sP(EO-stat-PO) coatings retain their structure and biological function. The aim of the present study was to assess biocompatibility and the effect on early osseointegrative properties of a NCO-sP(EO-stat-PO) coating with additional RGD-peptides and augmentation with bone morphogenetic protein-4 (BMP) used on a medical grade high-density polyethylene (HDPE) base under in vivo circumstances. For testing of biocompatibility dishes with large amounts of bulk NCO-sP(EO-stat-PO) were implanted subcutaneously into 14 Wistar rats. In a second set-up functionalization of implants with ultrathin surface layers by coating ammonia-plasma treated HDPE with NCO-sP(EO-stat-PO), functionalization with linear RGD-peptides, and augmentation with RGD and BMP-4 was analyzed. Therefore, implants were placed subcutaneously in the paravertebral tissue and transcortically in the distal femur of another 14 Wistar rats. Both tests revealed no signs of enhanced inflammation of the surrounding tissue analyzed by CD68, IL-1ß-/TNF-α-antibody staining, nor systemic toxic reactions according to histological analysis of various organs. The mean thickness of the fibrous tissue surrounding the femoral implants was highest in native HDPE-implants and tended to be lower in all NCO-sP(EO-stat-PO) modified implants. Micro-CT analysis revealed a significant increase of peri-implant bone volume in RGD/BMP-4 coated samples. These results demonstrate that even very low amounts of surface bound growth factors do have significant effects when immobilized in an environment that retains their biological function. Hence, NCO-sP(EO-stat-PO)-coatings could offer an attractive platform to improve integration of orthopedic implants.

Peptide decorated nano-hydroxyapatite with enhanced bioactivity and osteogenic differentiation via polydopamine coating

To be better used as implant materials in bone graft substitutes, bioactivity and osteogenesis of nano-hydroxyapatite (nano-HA) need to be further enhanced. Inspired by adhesive proteins in mussels, here we developed a novel bone forming peptide decorated nano-HA material. In this study, nano-HA was coated by one-step pH-induced polymerization of dopamine, and then the peptide was grafted onto polydopamine (pDA) coated nano-HA (HA-pDA) through catechol chemistry. Our results demonstrated that the peptide-conjugated nano-HA crystals could induce the adhesion and proliferation of MG-63 cells. Moreover, the highly alkaline phosphatase activity of the functionalized nano-HA indicated that the grafted peptide could maintain its biological activity after immobilization onto the surface of HA-pDA, especially at the concentration of 100μg/mL. These modified nano-HA crystals with better bioactivity and osteogenic differentiation hold great potential to be applied as bioactive materials in bone repairing, bone regeneration and bio-implant coating applications.

The recombinant human dentin matrix protein 1-coated titanium and its effect on the attachment, proliferation and ALP activity of MG63 cells

The aim of the present work was to design a bio-interactive implant surface by coating recombinant human dentin matrix protein 1 (hDMP1) onto titanium and to investigate the biological function of this material. Firstly, the plasmid containing the hDMP1 cDNA was constructed and hDMP1 was expressed, purified and characterized. Then, hDMP1 was coated onto the surface of Ti substrates via a biochemical technique and the procedure was divided into three steps: in the beginning, titanium was treated by regular polishing and denoted as Cp-Ti; then, Cp-Ti received alkaline and water treatment and was nominated as AW-Ti; finally, AW-Ti was coated with hDMP1 and referred to as hDMP1-Ti. The inserts of hDMP1 genes were detected by enzyme digestion as well as gel electrophoresis, and the complete nucleotide sequence of hDMP1 was tested. The purified recombinant hDMP1 was electrophoresed on a 10 % SDS-PAGE gel. Cp-Ti, AW-Ti and hDMP1-Ti were characterized by X-ray photoelectron spectroscope and water contact angles tests. The biological activity of MG63 cells cultured in the three groups was investigated by the cell attachment, proliferation and alkaline phosphatase activity assays. The results show that hDMP1 was successfully constructed and coated onto the titanium surface, and hDMP1-Ti had higher hydrophilicity than Cp-Ti. Compared with Cp-Ti and AW-Ti, hDMP1-Ti showed better in vitro bioactivity.

Strategies for controlled delivery of growth factors and cells for bone regeneration

The controlled delivery of growth factors and cells within biomaterial carriers can enhance and accelerate functional bone formation. The carrier system can be designed with pre-programmed release kinetics to deliver bioactive molecules in a localized, spatiotemporal manner most similar to the natural wound healing process. The carrier can also act as an extracellular matrix-mimicking substrate for promoting osteoprogenitor cellular infiltration and proliferation for integrative tissue repair. This review discusses the role of various regenerative factors involved in bone healing and their appropriate combinations with different delivery systems for augmenting bone regeneration. The general requirements of protein, cell and gene therapy are described, with elaboration on how the selection of materials, configurations and processing affects growth factor and cell delivery and regenerative efficacy in both in vitro and in vivo applications for bone tissue engineering.

Fibronectin and bone morphogenetic protein-2-decorated poly(OEGMA-r-HEMA) brushes promote osseointegration of titanium surfaces

To be better used as medical implants in orthopedic and dental clinical applications, titanium and titanium-based alloys need to be capable of inducing osteogenesis. Here we describe a method that allows the facile decoration of titanium surfaces to impart an osteogenesis capacity. A Ti surface was first deposited on a poly(OEGMA-r-HEMA) film using surface-initiated atom-transfer radical polymerization (SI-ATRP) with the further step of carboxylation. The modified surfaces were resistant to cell adhesion. Fibronectin (FN) and recombinant human bone morphogenetic protein-2 (rhBMP-2) were further immobilized onto p(OEGMA-r-HEMA) matrices. Our results demonstrate that the FN- and rhBMP-2-conjugated polymer surfaces could induce the adhesion of MC3T3 cells on Ti surfaces. Moreover, the protein-tethered surface exhibited enhanced cell differentiation in terms of alkaline phosphatase activity compared to that of the pristine Ti surface at similar cell proliferation rates. This research establishes a simple modification method of Ti surfaces via Ti-thiolate self-assembled monolayers (SAMs) and SI-ATRP and identifies a dual-functional Ti surface that combines antifouling and osseointegration promotion.

Anti-fouling bioactive surfaces

Bioactive surfaces refer to surfaces with immobilized bioactive molecules aimed specifically at promoting or supporting particular interactions. Such surfaces are of great importance for various biomedical and biomaterials applications. In the past few years, considerable effort has been made to create bioactive surfaces by forming specific biomolecule-modified surfaces on a non-biofouling "base" or "background". Hydrophilic and bioinert polymers have been widely used as anti-fouling layers that resist non-specific protein interactions. They can also serve as "spacers" to effectively move the immobilized biomolecule away from the surface, thus enhancing its bioactivity. In this review we summarize several successful approaches for the design and preparation of bioactive surfaces based on different types of anti-fouling/spacer materials. Some perspectives on future research in this area are also presented.