Simple, mild, and area-specific calcium phosphate (CaP) coating techniques are useful for the production and surface modification of biomaterials. In this study, an area-specific CaP coating technique for polymer substrates was successfully developed using a liquid-phase laser process. In the proposed method, Nd-YAG laser light (355 nm, 30 Hz, and 1-3 W) irradiated an ethylene-vinyl alcohol copolymer (EVOH) substrate immersed in a supersaturated CaP solution for various periods of time (up to 30 min). The CaP-forming ability increased with an increase in the laser power and irradiation period. At the optimal laser power (3 W), a continuous CaP layer formed within 30 min on the laser-irradiated surface of the EVOH substrate. The formation of CaP was attributed to laser absorption by the EVOH substrate, which promoted the surface modification of EVOH and an increase in the temperature of the solution near the surface of the substrate. The resulting CaP coating showed better cell adhesion property than the naked EVOH substrate. The proposed CaP coating technique is simple (quick and single step) and area specific. Furthermore, the present process is carried out under mild conditions, that is, at normal pressures and temperatures in a safe aqueous medium. These are significant advantages of the proposed CaP coating technique.

Three-dimensional (3D) porous scaffolds for supporting cell adhesion and growth play a vital role in tissue engineering applications. In the present study, three different collagen-based 3D sponges were functionalized by apatite coating. The sponges were coated with apatite on their outer and inner surfaces while retaining their interconnecting pores. To achieve this, we employed a vacuum degassing system in our plasma- and precursor-assisted biomimetic process using a supersaturated calcium phosphate solution. The resulting apatite-coated sponges (mineralized sponges) showed better cell adhesion properties in vitro for osteoblast-like MC3T3-E1 cells compared to that of uncoated sponges. The three mineralized sponges were implanted in the subcutaneous tissue of rats. Upon histological evaluation after 10 days, the mineralized sponges showed cell in-growth rates that were approximately 4-fold greater than those of the untreated sponges without any notable inflammatory reactions. As these sponges are composed of clinically approved collagen-based frameworks and possess a 3D porous structure with a mineralized surface appropriate for cell adhesion and internalization, further in vitro and in vivo studies should be conducted regarding tissue engineering applications.

In this paper, we have further developed our simple (one-pot) and rapid (short irradiation time) laser fabrication process of submicrometer spheres composed of amorphous calcium iron phosphate. In our previous process, laser irradiation was applied to a calcium phosphate (CaP) reaction mixture supplemented with ferric ions (Fe(3+)) as a light-absorbing agent. Because the intention of the present study was to fabricate magnetite-encapsulated CaP-based submicrometer spheres, ferrous ions (Fe(2+)) were used as a light-absorbing agent rather than ferric ions. The ferrous ions served as a light-absorbing agent and facilitated the fabrication of submicrometer and micrometer spheres of amorphous calcium iron phosphate. The sphere formation and growth were better promoted by the use of ferrous ions as compared with the use of ferric ions. The chemical composition of the spheres was controllable through adjustment of the experimental conditions. By the addition of sodium hydroxide to the CaP reaction mixture supplemented with ferrous ions, fabrication of CaP-based magnetic submicrometer spheres was successfully achieved. Numerous magnetite and wüstite nanoparticles were coprecipitated or segregated into the CaP-based spherical amorphous matrix via light-material interaction during the CaP precipitation process. The magnetic properties of the magnetite and wüstite formed in the CaP-based spheres were investigated by magnetization measurements. The present process and the resulting CaP-based spheres are expected to have great potential for biomedical applications.

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Calcium phosphate (CaP) coating is an effective method for surface-functionalization of bioinert materials and for production of osteoconductive implants. Recently, we developed a laser-assisted biomimetic process (LAB process) for facile and area-specific CaP coating. In this study, the LAB process was applied to chemically stable and mechanically durable poly(etheretherketone) (PEEK), which has become widely used as an orthopedic and dental implant material. The LAB process was carried out by irradiating pulsed Nd:YAG laser light (355 nm) onto a PEEK substrate that was immersed in supersaturated CaP solution. The CaP coating applicability depended on laser fluence, i.e., CaP successfully formed on PEEK surface after the LAB process at 2 W/cm2. Further increase in laser fluence did not result in the successful formation. At the optimal fluence of 2 W/cm2, the laser-irradiated PEEK surface was modified and heated to induce heterogeneous CaP precipitation within 10 min in CaP solution, followed by further CaP growth over the irradiation time (tested up to 30 min). The LAB process improved the cytocompatibility of PEEK surface with osteoblastic MC3T3-E1 cells. Furthermore, the LAB-processed CaP-coated PEEK substrate formed a dense hydroxyapatite layer on its surface in the simulated body fluid, suggesting the osteoconductivity of this material. The present LAB process can be a useful new tool to produce osteoconductive PEEK-based implants.

Calcium phosphate (CaP) deposition was induced on optically semitransparent polymers irradiated with laser in a supersaturated CaP solution, but not on a transparent polymer.

We developed a simple and quick physicochemical process for fabricating calcium iron phosphate submicrometre spheres. Here, pulsed laser irradiation was performed to a calcium phosphate reaction mixture supplemented with ferric ions as a light-absorbing agent. The size and chemical composition of the spheres were controllable through the experimental conditions.Certain types of calcium phosphates (CaPs) show good biocompatibility and osteoconductivity owing to the similarity in the mineral components of vertebrate hard tissues. Submicrometre spheres of CaPs are potentially safe and biocompatible delivery carriers for drugs, genes and imaging agents. 1-3 Among the conventional fabrication methods of CaP spheres, 2,3 physical processes such as plasma-spraying, solid-state reaction, milling and laser ablation in liquid 4-6 are easy and practical. However, the control of the size and/or shape of the spheres in the submicrometre range is generally weak. Chemical precipitation processes using supersaturated and labile CaP solutions are valid for fabricating submicrometre spheres of CaP. However, for precise size control of the spheres, the precipitation process oen requires special additives such as synthetic surfactants, biomolecules and growth-inhibitory ions. 3,7 Recently, the process of pulsed laser melting in liquid has attracted increasing attention as a simple, quick and additivefree process for fabricating submicrometre spheres of semiconductor, metal and metal oxide. [8][9][10][11][12] In this process, source nanoparticles dispersed in liquid are irradiated with much weaker pulsed laser light compared with that used in the

The present authors recently developed a new calcium phosphate (CaP) coating technique on an ethylene-vinyl alcohol copolymer substrate utilizing a laser-assisted biomimetic (LAB) process. In the present study, the LAB process was applied to a sintered hydroxyapatite (sHA) substrate for CaP coating. The LAB process was carried out by irradiating the sHA substrate immersed in a supersaturated CaP solution with a low-energy Nd-YAG pulsed laser. Within 30 min of irradiation, contiuous CaP layers with different morphologies were successfully formed on the laser-irradiated sHA surface. A submicron cavernous structure of the CaP layer was developed into a micron flake-like structure as the laser power increased from 1 to 3 W. This result suggests that the secondary nucleation and growth of CaP crystals were accelerated by laser irradiation in a power-dependent manner. Laser absorption by the sHA substrate and the resulting increase in ambient temperature locally near the surface should be responsible for the accelerated CaP nucleation and growth. The present CaP coating technique using the LAB process is simple and quick, hence it would be useful in orthopedic and dental applications as an on-demand surface-functionalization method for biomaterials consisting of sHA.