The main aim of bone tissue engineering is to fabricate highly biocompatible, osteoconductive and/or osteoinductive biomaterials for tissue regeneration. Bone implants should support bone growth at the implantation site via promotion of osteoblast adhesion, proliferation, and formation of bone extracellular matrix. Moreover, a very desired feature of biomaterials for clinical applications is their osteoinductivity, which means the ability of the material to induce osteogenic differentiation of mesenchymal stem cells toward bone-building cells (osteoblasts). Nevertheless, the development of completely biocompatible biomaterials with appropriate physicochemical and mechanical properties poses a great challenge for the researchers. Thus, the current trend in the engineering of biomaterials focuses on the surface modifications to improve biological properties of bone implants. This review presents the most recent findings concerning surface modifications of biomaterials to improve their osteoconductivity and osteoinductivity. The article describes two types of surface modifications: (1) Additive and (2) subtractive, indicating biological effects of the resultant surfaces in vitro and/or in vivo. The review article summarizes known additive modifications, such as plasma treatment, magnetron sputtering, and preparation of inorganic, organic, and composite coatings on the implants. It also presents some common subtractive processes applied for surface modifications of the biomaterials (i.e., acid etching, sand blasting, grit blasting, sand-blasted large-grit acid etched (SLA), anodizing, and laser methods). In summary, the article is an excellent compendium on the surface modifications and development of advanced osteoconductive and/or osteoinductive coatings on biomaterials for bone regeneration.

Background: Nanocomposites produced by reinforcement of polysaccharide matrix with nanoparticles are widely used in engineering of biomaterials. However, clinical applications of developed novel biomaterials are often limited due to their poor biocompatibility. Purpose: The aim of this work was to comprehensively assess biocompatibility of highly macroporous chitosan/agarose/nanohydroxyapatite bone scaffolds produced by a novel method combining freeze-drying with a foaming agent. Within these studies, blood plasma protein adsorption, osteoblast (MC3T3-E1 Subclone 4 and hFOB 1.19) adhesion and proliferation, and osteogenic differentiation of mesenchymal stem cells derived from bone marrow and adipose tissue were determined. The obtained results were also correlated with materials’ surface chemistry and wettability to explain the observed protein and cellular response. Results: Obtained results clearly showed that the developed nanocomposite scaffolds were characterized by high biocompatibility and osteoconductivity. Importantly, the scaffolds also revealed osteoinductive properties since they have the ability to induce osteogenic differentiation (Runx2 synthesis) in undifferentiated mesenchymal stem cells. The surface of biomaterials is extremely hydrophilic, prone to protein adsorption with the highest affinity toward fibronectin binding, which allows for good osteoblast adhesion, spreading, and proliferation. Conclusion: Produced by a novel method, macroporous nanocomposite biomaterials have great potential to be used in regenerative medicine for acceleration of the bone healing process.

Chitosan/1,3-β-D-glucan matrices have been recently used in various biomedical applications. Within this study, the structural changes in hybrid polysaccharide chitosan/1,3-β-D-glucan matrices cross-linked at 70 °C and 80 °C were detected with Attenuated Total Reflection Fourier Transform Infrared spectroscopy (ATR FT-IR) and Raman spectroscopy enabled thorough insights into molecular structure of studied biomaterials, whereas X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) provided their surface characteristics with confirmation of their effective and non-destructive properties. There are temperature-dependent differences in the chemical interactions between 1,3-β-D-glucan units and N-glucosamine in chitosan, resulting in surface polarity changes. The second order derivatives and deconvolution revealed the alterations in the secondary structure of studied matrices, along with different sized grain-like structures revealed by AFM. Since surface physicochemical properties of biomaterials have great impact on cell behavior, abovementioned techniques may allow to optimize and modify the preparation of polymeric matrices with desired features.

The cross-linking temperature of polymers may affect the surface characteristics and molecular arrangement, which are responsible for their mechanical and physico-chemical properties. The aim of this research was to determine and explain in detail the mechanism of unit interlinkage of two-component chitosan/1,3-β-d-glucan matrices gelled at 90 °C. This required identifying functional groups interacting with each other and assessing surface topography providing material chemical composition. For this purpose, various spectroscopic and microscopic approaches, such as attenuated total reflection Fourier transform infrared spectroscopy (ATR FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), were applied. The results indicate the involvement mainly of the C-C and C-H groups and C=O⋯HN moieties in the process of biomaterial polymerization. Strong chemical interactions and ionocovalent bonds between the N-glucosamine moieties of chitosan and 1,3-β-d-glucan units were demonstrated, which was also reflected in the uniform surface of the sample without segregation. These unique properties, hybrid character and proper cell response may imply the potential application of studied biomaterial as biocompatible scaffolds used in regenerative medicine, especially in bone restoration and/or wound healing.

Modification of implantable scaffolds with magnesium and zinc for improvement of bone regeneration is a growing trend in the engineering of biomaterials. The aim of this study was to synthesize nano-hydroxyapatite substituted with magnesium (Mg²⁺) (HA-Mg) and zinc (Zn²⁺) (HA-Zn) ions in order to fabricate chitosan-agarose-hydroxyapatite (HA) scaffolds (chit/aga/HA) with improved biocompatibility. Fabricated biomaterials containing Mg²⁺ or Zn²⁺ were tested using osteoblasts and mesenchymal stem cells to determine the effect of incorporated metal ions on cell adhesion, spreading, proliferation, and osteogenic differentiation. The study was conducted in direct contact with the scaffolds (cells were seeded onto the biomaterials) and using fluid extracts of the materials. It demonstrated that incorporation of Mg²⁺ ions into chit/aga/HA structure increased spreading of the osteoblasts, promoted cell proliferation on the scaffold surface, and enhanced osteocalcin production by mesenchymal stem cells. Although biomaterial containing Zn²⁺ did not improve cell proliferation, it did enhance type I collagen production by mesenchymal stem cells and extracellular matrix mineralization as compared to cells cultured in a polystyrene well. Nevertheless, scaffolds made of pure HA gave better results than material with Zn²⁺. Results of the experiments clearly showed that modification of the chit/aga/HA scaffold with Zn²⁺ did not have any positive impact on cell behavior, whereas, incorporation of Mg²⁺ ions into its structure may significantly improve biocompatibility of the resultant material, increasing its potential in biomedical applications.