Surface-selective Laser Sintering Research Articles

Polylactide microparticles stabilized by chitosan graft-copolymer as building blocks for scaffold fabrication via surface-selective laser sintering

Polylactide microparticles stabilized by chitosan graft-copolymer as building blocks for scaffold fabrication via surface-selective laser sintering

The Evolution of Surface-Selective Laser Sintering: Modifying and Forming 3D Structures for Tissue Engineering

The use of surface-selective laser sintering is considered for creating and modifying the architecture of three-dimensional structures from biocompatible and bioresorbable polylactide materials. The approach allows to eliminate the thermal degradation of sintered materials by localizing heating processes on their surfaces. This is achieved via the selective absorption of mid-infrared laser radiation (1.9 μm) by a thin layer of water droplets deposited on the surfaces of polymer particles (polymer fibers) or the use of hygroscopic coatings that absorb the energy of laser radiation better than the polymer material.

Novel materials for high-resolution three-dimensional printing using surface-selective laser sintering

A new approach for high-resolution three-dimensional printing using selective laser sintering is proposed. Novel ultrafine powder is synthesized and modified to face the requirements of the laser sintering process. The effect of the powder particle size and shape on the characteristics of the sintered structures is studied.

Temperature field distribution in polymer particles during surface-selective laser sintering

The dynamics of polymer particle heating by laser irradiation during surface-selective laser sintering (SSLS) has been studied both experimentally and theoretically. Water aerosol wetting of the polymer particle surface was applied to increase the absorbance of thulium fiber laser radiation at 1.96 μm. Theoretical modeling of the laser-induced thermal processes was performed in thermolabile polylactic-co-glycolic acid powder coated with a thin water layer. Temperature gradients on the surface and inside the sintered particle volume were evaluated and analyzed. It was shown that for certain optimized SSLS parameters an effective sintering process can be achieved by delicate melting of the particle surface only, without noticeable changes in the chemical and phase compositions of the internal domains.

Optical fields in porous polylactide matrices

Optical fields induced by laser light inside porous polymer matrices (scaffolds) under stimulating effect on cells are investigated. The spectra of light scattering coefficients and anisotropy factors of porous polylactide scaffolds in the visible and near-IR ranges are determined by numerical simulation based on experimental data obtained using a double integrating sphere. Studies are conducted for dry and wet scaffolds fabricated by supercritical fluid foaming and surface-selective laser sintering. The Monte Carlo method is used to calculate the fluence rate distribution under the assumptions of the Henyey – Greenstein phase scattering function and the model phase function of scattering on spherical cavities. It is shown that th e fluence rate distribution mainly depends on the scattering coefficient and the mean cosine of the deflection angle (g-factor). The results obtained are of great practical importance for tissue engineering based on the use of polymeric porous scaffolds with cells to replace tissue defects; they can be used to determine the dose range for laser stimulation of cells.

Bioresorbable polymer matrices impregnated with BMP-2

Bioresorbable matrices from poly(lactic-co-glycolic acid) containing therapeutically significant concentrations of bone morphogenetic protein 2 (BMP-2) was formed by super-critical fluid encapsulation and surface-selective laser sintering. Biocompatibility of these matrices and the kinetics of BMP-2 release from their volume into physiological saline was investigated. It was shown experimentally that the release of BMP-2 was almost uniform for 15 days. The subsequent use of laser sintering contributed to a longer retention of BMP-2. High cytocompatibility of the obtained matrices with cultures of mesenchymal stem cells was shown in vitro.

Osteoinducing scaffolds with multi-layered biointerface

This study was aimed to design and characterise hybrid tissue-engineered constructs composed of osteoinducing polylactide-based scaffolds with multi-layered cellular biointerface for bone tissue reconstruction. Three-dimensional scaffolds with improved hydrophilic and osteoinducing properties were produced using the surface-selective laser sintering (SSLS) method. The designed scaffold pattern had dimensions of 8 × 8 × 2.5 mm and ladder-like pores (∼700 μm in width). Hyaluronic acid-coated polylactide microparticles (∼100 μm in diameter) were used as building blocks and water was used as the photosensitizer for SSLS followed by photocross-linking with Irgacure 2959 photoinitiator. Resulting scaffolds provided successful adhesion and expansion of human bone marrow mesenchymal stromal cells from a single-cell suspension. Induced calcium deposition by the cells associated with osteogenic differentiation was detected in 7–21 days of culturing in basal medium. The values were up to 60% higher on scaffolds produced at a higher prototyping speed under the experimental conditions. Innovative approach to graft the scaffolds with multi-layered cell sheets was proposed aiming to facilitate host tissue-implant integration. The sheets of murine MS-5 stromal cell line exhibited contiguous morphology and high viability in a modelled construct. Thus, the SSLS method proved to be effective in designing osteoinducing scaffolds suitable for the delivery of cell sheets.

Features of Polymeric Structures By Surface—Selective Laser Sintering of Polymer Particles Using Water as Sensitizer

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Тканеинженерные конструкции для регенеративной медицины на основе мезенхимальных клеток пульпы молочного зуба и полимерных матриксов нового поколения

The aim of the present work was to develop an approach for producing tissue engineered constructs based on mesenchymal stromal cell culture and new-generation biodegradable synthetic polymer matrices obtained by the technology of surface-selective laser sintering. Primary mesenchymal stromal cells were derived from the pulp of naturally shed deciduous teeth. Following seeding, the cells were cultured on matrices for ten days. Cell viability was quantitatively assessed using CytoTox Assay (Promega) based on the colorimetric measurement of mitochondrial dehydrogenase activity. Cellular structure and spatial arrangement within a tissue-engineered matrix was visualized by scanning electron microscopy (SEM), using supravital lanthanoid staining. The results obtained showed that matrices under development enable good cell adhesion and proliferation, and hence can be used as a cell carrier in tissue engineering. Thus, the techniques of surface-selective laser sintering, which was developed by us, could find wide use in regenerative medicine.

Study of the involvement of allogeneic MSCs in bone formation using the model of transgenic mice

ABSTRACTMesenchymal stem cells (MSCs) are thought to be the most attractive type of cells for bone repair. However, much still remains unknown about MSCs and needs to be clarified before this treatment can be widely applied in the clinical practice. The purpose of this study was to establish the involvement of allogeneic MSCs in the bone formation in vivo, using a model of transgenic mice and genetically labeled cells. Polylactide scaffolds with hydroxyapatite obtained by surface selective laser sintering were used. The scaffolds were sterilized and individually seeded with MSCs from the bone marrow of 5-week-old GFP(+) transgenic C57/Bl6 or GFP(−)C57/Bl6 mice. 4-mm-diameter critical-size defects were created on the calvarial bone of mice using a dental bur. Immediately after the generation of the cranial bone defects, the scaffolds with or without seeded cells were implanted into the injury sites. The cranial bones were harvested at either 6 or 12 weeks after the implantation. GFP(+) transgenic mice having scaffolds with unlabeled MSCs were used for the observation of the host cell migration into the scaffold. GFP(−) mice having scaffolds with GFP(+)MSCs were used to assess the functioning of the seeded MSCs. The obtained data demonstrated that allogeneic MSCs were found on the scaffolds 6 and 12 weeks post-implantation. By week 12, a newly formed bone tissue from the seeded cells was observed, without an osteogenic pre-differentiation. The host cells did not appear, and the control scaffolds without seeded cells remained empty. Besides, a possibility of vessel formation from seeded MSCs was shown, without a preliminary cell cultivation under controlled conditions.

Surface-selective laser sintering of thermolabile polymer particles using water as heating sensitizer

We report the implementation of a novel scheme for surface-selective laser sintering (SSLS) of polymer particles, based on using water as a sensitizer of laser heating and sintering of particles as well as laser radiation at a wavelength of , corresponding to the strong absorption band of water. A method of sintering powders of poly(lactide-co-glycolide), a hydrophobic bioresorbable polymer, after modifying its surface with an aqueous solution of hyaluronic acid is developed. The sintering thresholds for wetted polymer are by lower than those for sintering in air. The presence of water restricts the temperature of the heated polymer, preventing its thermal destruction. Polymer matrices with a developed porous structure are obtained. The proposed SSLS method can be applied to produce bioresorbable polymer matrices for tissue engineering.

Selective laser sintering of bioactive composite matrices for bone tissue engineering

A method for surfaceselective laser sintering which produces mineralpolymeric materials based on calcium phosphates and aliphatic polyesters was developed. Threedimensional matrices of the given architectonics for replacement of bone defects and bone tissue engineering were obtained. The microstruc� ture of the experimental samples obtained and their surface morphology and internal structure were investi� gated by scanning electron microscopy (SEM). The characteristic values of the compressive strength and rel� ative deformation of the mineral-polymer composite samples obtained by surfaceselective laser sintering of fine powders consisting of 80 wt % ceramic granules based on tricalcium phosphate and 20 wt % D,Lpoly� lactide PDL04 corresponded to the characteristic indices of the similar parameters for the trabecular bone tissue. As a result of the initial study of the biological properties of mineral-polymer composite scaffolds made by surfaceselective laser sintering, it was shown that they had low cytotoxicity and no adverse effects on the proliferative potential of mesenchymal stem cells. The technology of surfaceselective laser sintering suggested could be effectively used to create scaffolds for bone tissue engineering.

Formation of a bioactive material for selective laser sintering from a mixture of powdered polylactide and nano-hydroxyapatite in supercritical carbon dioxide

Supercritical carbon dioxide (SC-CO2) is used to prepare bioactive composites from powdered polylactide and nanosized hydroxyapatite for surface-selective laser sintering of three-dimensional tissue engineering structures. The mixture of powdered polylactide and nanosized hydroxyapatite and cannot be directly laser-sinter because of the impossibility of forming continuous filaments from sintered polymer particles. The use of composite particles for sintering formed in SC-CO2 medium makes it possible to eliminate this shortcoming and to form continuous structures. Analysis of the composition and mechanical tests of such structures showed that the sintered composite obtained is fairly uniform, without destruction centers, capable of withstanding the same mechanical loads as the pure polymer, and therefore, suitable for use in tissue scaffold engineering.

Biocompatibility of Tissue Engineering Constructions from Porous Polylactide Carriers Obtained by the Method of Selective Laser Sintering and Bone Marrow-Derived Multipotent Stromal Cells

We studied the biocompatibility of porous polylactide carrier matrices obtained by means of surface selective laser sintering. Carrier matrices had no cytotoxic activity, but maintained adhesion and proliferation of cells. Subcutaneous transplantation of tissue engineering constructions from these carriers and bone marrow-derived multipotent stromal cells did not cause the inflammatory response and pathological changes in rats. The conditions for organotypic regeneration were provided at the site of transplantation (high degree of blood supply and considerable amount of immature precursor cells).

Biocompatibility and osteogenic potential of human fetal femur-derived cells on surface selective laser sintered scaffolds

For optimal bone regeneration, scaffolds need to fit anatomically into the requisite bone defects and, ideally, augment cell growth and differentiation. In this study we evaluated novel computationally designed surface selective laser sintering (SSLS) scaffolds for their biocompatibility as templates, in vitro and in vivo, for human fetal femur-derived cell viability, growth and osteogenesis. Fetal femur-derived cells were successfully cultured on SSLS-poly( d, l)-lactic acid (SSLS-PLA) scaffolds expressing alkaline phosphatase activity after 7 days. Cell proliferation, ingrowth, Alcian blue/Sirius red and type I collagen positive staining of matrix deposition were observed for fetal femur-derived cells cultured on SSLS-PLA scaffolds in vitro and in vivo. SSLS-PLA scaffolds and SSLS-PLA scaffolds seeded with fetal femur-derived cells implanted into a murine critical-sized femur segmental defect model aided the regeneration of the bone defect. SSLS techniques allow fabrication of biocompatible/biodegradable scaffolds, computationally designed to fit any defect, providing a template for cell osteogenesis in vitro and in vivo.

Laser technologies for fabricating individual implants and matrices for tissue engineering

This paper presents the results of work on the development and modification of laser methods of rapid prototyping and fabrication of individual implants and matrices for tissue engineering. A technology has been developed for shaping mineral-polymer bioactive structures, based on laser photopolymerization of a liquid mixture of polyfunctional acrylic oligomers with microparticles of hydroxyapatite. A method is proposed and developed for surface-selective laser sintering, making it possible to sinter polymeric microparticles without melting them completely, but only submelting their surface. This made it possible to obtain bioactive polymeric matrices based on bioresorbable aliphatic polyesters.

Fabrication of polymer scaffolds for tissue engineering using surface selective laser sintering

A new approach to the fabrication of individual implants and scaffolds for tissue engineering—surface selective laser sintering (SSLS)—is proposed and realized. In contrast to the conventional selective laser sintering, the SSLS method makes it possible to sinter polymer microparticles and melt the near-surface layer rather than the microparticle as a whole. The effect of the laser radiation parameters and the structure and composition of the raw products on the structure and properties of the biomaterials sintered by the laser radiation is analyzed. This approach makes possible both the application of thermally unstable polymers (e.g., polylactides or polylactoglycolides) and the fabrication of scaffolds with incorporated bioactive proteins. The results obtained yield a regular physical basis for a new technology of the fabrication of various polymer scaffolds that represent important materials and elements of modern tissue engineering. The flexibility of the SSLS method is especially important at the stage of investigation of the cell and tissue responses needed for the optimization of the material for a specific application in tissue engineering.

Three‐Dimensional Bioactive and Biodegradable Scaffolds Fabricated by Surface‐Selective Laser Sintering

A new method of surface-selective laser sintering (SSLS) leads to the fabrication of three-dimensional (3D) composite scaffolds (spatial resolution ∼200 μm) that are both bioactive and biodegradable. Moreover, the scaffolds can have very precise dimensions and intricate structure. Conventionally, in selective laser sintering (SLS), the polymer absorbs infrared (λ=10.6 μm) radiation and this leads to a volumetric absorption by the whole polymer particle. In other words, each particle of polymer is completely melted and fuses to the next in order to form the desired morphology. In our experiments we have used near-infrared (λ=0.97 μm) laser radiation, which polymer particles do not absorb at all. To initiate the sintering process a small quantity (< 0.1 wt.-%) of carbon microparticles were homogeneously distributed on the surfaces of the polymer particles. Thus, the melting process was limited to only the surfaces of each particle. The carbon microparticles are strong absorbers of laser radiation, and this opens up the technique to a range of polymers that up till now could not be processed by laser sintering. More importantly, since the laser melts only the surfaces of the particles, delicate bioactive species trapped within each particle retain their activity throughout the processing. We have demonstrated the application of this technique by the incorporation of the enzyme ribonuclease A into particles of poly(d,l-lactic) acid (PLA) and the assembly of 3D matrices at three different laser intensities, using a 0.97 μm wavelength continuous wave (CW) diode laser.