In vitro and in vivo bioactivity assessment of a polylactic acid/hydroxyapatite composite for bone regeneration

Influence of polylactide coating stereochemistry on mechanical and in vitro degradation properties of porous bioactive glass scaffolds for bone regeneration

The mechanical properties of polylactide stereocomplexes (PLA SC) have been primarily studied through tensile testing, with inconsistent results, and the compressive properties of PLA SC compared to homocrystalline or amorphous PLA remain poorly understood. In this study, we coated porous bioactive glass 13-93 scaffolds with amorphous, homocrystalline, or stereocomplex PLA to investigate their mechanical and degradation properties before and after immersion in simulated body fluid. The glass scaffolds had interconnected pores and an average porosity of 76%. The PLA coatings, which were 10-100 μm thick and approximately 3% of the glass scaffold mass, covered the glass to a large extent. The compressive strength and toughness of all PLA-coated scaffolds were significantly higher than those of uncoated scaffolds, with approximately a fourfold increase before immersion and a twofold increase after immersion. The compressive strength and toughness of PLA SC-coated scaffolds were similar to those of scaffolds with homocrystalline PLA coating, and significantly higher than for scaffolds with amorphous PLA coating. All PLA coatings moderated the initial pH increase caused by the glass, which could benefit surrounding cells and bone tissue in vivo after implantation.

VEGF-modified PLA/HA nanocomposite fibrous membrane for cranial defect repair in rats

A major obstacle to bone tissue repair is the difficulty in establishing a rapid blood supply areas of bone defects. Vascular endothelial growth factor (VEGF)-infused tissue-engineered scaffolds offer a possible therapeutic option for these types of injuries. Their role is to accelerate angiogenesis and improve bone healing. In this study, we used electrostatic spinning and biofactor binding to construct polylactic acid (PLA)/hydroxyapatite (HA)-VEGF scaffold materials and clarify their pro-vascular role in bone defect areas for efficient bone defect repair. PLA/HA nanocomposite fibrous membranes were manufactured by selecting suitable electrostatic spinning parameters. Heparin and VEGF were bound sequentially, and then the VEGF binding and release curves of the fiber membranes were calculated. A rat cranial defect model was constructed, and PLA/HA fiber membranes bound with VEGF and unbound with VEGF were placed for treatment. Finally, we compared bone volume recovery and vascular recovery in different fibrous membrane sites. A VEGF concentration of 2.5 µg/mL achieved the maximum binding and uniform distribution of PLA/HA fibrous membranes. Extended-release experiments showed that VEGF release essentially peaked at 14 days. In vivo studies showed that PLA/HA fibrous membranes bound with VEGF significantly increased the number of vessels at the site of cranial defects, bone mineral density, bone mineral content, bone bulk density, trabecular separation, trabecular thickness, and the number of trabeculae at the site of defects in rats compared with PLA/HA fibrous membranes not bound with VEGF. VEGF-bound PLA/HA fibrous membranes demonstrate the slow release of VEGF. The VEGF binding process does not disrupt the morphology and structure of the fibrous membranes. The fibrous membranes could stimulate both osteogenesis and angiogenesis. Taken together, this research provides a new strategy for critical-sized bone defects repairing.

A comparative analysis of 3D printed scaffolds consisting of poly(lactic-co-glycolic) acid and different bioactive mineral fillers: aspects of degradation and cytocompatibility

Their excellent mechanical properties, degradability and suitability for processing by 3D printing technologies make the thermoplastic polylactic acid and its derivatives favourable candidates for biomaterial-based bone regeneration therapies. In this study, we investigated whether bioactive mineral fillers, which are known to promote bone healing based on their dissolution products, can be integrated into a poly(L-lactic-co-glycolic) acid (PLLA-PGA) matrix and how key characteristics of degradation and cytocompatibility are influenced. The polymer powder was mixed with particles of CaCO3, SrCO3, strontium-modified hydroxyapatite (SrHAp) or tricalcium phosphates (α-TCP, β-TCP) in a mass ratio of 90 : 10; the resulting composite materials have been successfully processed into scaffolds by the additive manufacturing method Arburg Plastic Freeforming (APF). Degradation of the composite scaffolds was investigated in terms of dimensional change, bioactivity, ion (calcium, phosphate, strontium) release/uptake and pH development during long-term (70 days) incubation. The mineral fillers influenced the degradation behavior of the scaffolds to varying degrees, with the calcium phosphate phases showing a clear buffer effect and an acceptable dimensional increase. The amount of 10 wt% SrCO3 or SrHAp particles did not appear to be appropriate to release a sufficient amount of strontium ions to exert a biological effect in vitro. Cell culture experiments with the human osteosarcoma cell line SAOS-2 and human dental pulp stem cells (hDPSC) indicated the high cytocompatibility of the composites: For all material groups cell spreading and complete colonization of the scaffolds over the culture period of 14 days as well as an increase of the specific alkaline phosphatase activity, typical for osteogenic differentiation, were observed.

Biomimetic Remineralized Three-Dimensional Collagen Bone Matrices with an Enhanced Osteostimulating Effect

Bone grafts with a high potential for osseointegration, capable of providing a complete and effective regeneration of bone tissue, remain an urgent and unresolved issue. The presented work proposes an approach to develop composite biomimetic bone material for reconstructive surgery by deposition (remineralization) on the surface of high-purity, demineralized bone collagen matrix calcium phosphate layers. Histological and elemental analysis have shown reproduction of the bone tissue matrix architectonics, and a high-purity degree of the obtained collagen scaffolds; the cell culture and confocal microscopy have demonstrated a high biocompatibility of the materials obtained. Adsorption spectroscopy, scanning electron microscopy, microcomputed tomography (microCT) and infrared spectroscopy, and X-ray diffraction have proven the efficiency of the deposition of calcium phosphates on the surface of bone collagen scaffolds. Cell culture and confocal microscopy methods have shown high biocompatibility of both demineralized and remineralized bone matrices. In the model of heterotopic implantation in rats, at the term of seven weeks, an intensive intratrabecular infiltration of calcium phosphate precipitates, and a pronounced synthetic activity of osteoblast remodeling and rebuilding implanted materials, were revealed in remineralized bone collagen matrices in contrast to demineralized ones. Thus, remineralization of highly purified demineralized bone matrices significantly enhanced their osteostimulating ability. The data obtained are of interest for the creation of new highly effective osteoplastic materials for bone tissue regeneration and augmentation.

Degradation of 3D-printed magnesium phosphate ceramics in vitro and a prognosis on their bone regeneration potential

Regenerative bone implants promote new bone formation and ideally degrade simultaneously to osteogenesis. Although clinically established calcium phosphate bone grafts provide excellent osseointegration and osteoconductive efficacy, they are limited in terms of bioresorption. Magnesium phosphate (MP) based ceramics are a promising alternative, because they are biocompatible, mechanically extremely stable, and degrade much faster than calcium phosphates under physiological conditions. Bioresorption of an implant material can include both chemical dissolution as well as cellular resorption. We investigated the bioresorption of 3D powder printed struvite and newberyite based MP ceramics in vitro by a direct human osteoclast culture approach. The osteoclast response and cellular resorption was evaluated by means of fluorescence and TRAP staining, determination of osteoclast activities (CA II and TRAP), SEM imaging as well as by quantification of the ion release during cell culture. Furthermore, the bioactivity of the materials was investigated via SBF immersion, whereas hydroxyapatite precipitates were analyzed by SEM and EDX measurements. This bioactive coating was resorbed by osteoclasts. In contrast, only chemical dissolution contributed to bioresorption of MP, while no cellular resorption of the materials was observed. Based on our results, we expect an increased bone regeneration effect of MP compared to calcium phosphate based bone grafts and complete chemical degradation within a maximum of 1.5–3.1 years.

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3D powder printing allows individual shaping of porous magnesium phosphate bone implants.

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Precipitation of amorphous hydroxyapatite confirmed the bioactivity of magnesium phosphate ceramics.

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The compatibility of magnesium phosphates with human osteoblasts and osteoclasts could be verified in a direct culture approach. Whereat, TRAP and CA II activity were in the same range or slightly increased compared to osteoclasts on β-tricalcium phosphate.

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3D powder printed magnesium phosphates showed no sign of osteoclastic resorption, but a continuous chemical degradation.

Analysis of PLA/PHB Biopolymer Material with Admixture of Hydroxyapatite and Tricalcium Phosphate for Clinical Use

One trend in tissue engineering and regenerative medicine is the development of degradable composite polymers. The aim of this study was the comprehensive analysis of Polylactic acid (PLA)/Polyhydroxybutyrate (PHB) + Hydroxyapatite (HA)/Tricalcium phosphate (TCP) material from filament production to mechanical testing of samples with different infills and the production of an implant replacement for an intervertebral disc. Filament Maker-Composer 450 (3devo; Netherlands) was used to produce filaments. Experimental samples and the implant for the intervertebral disc were made using FDM technology using a DeltiQ2 3D printer (Trilab, Czech Republic). Mechanical testing of experimental samples was performed on an Inspekt TABLE 5 kN (Hegewald & Peschke, Nossen, Germany). Microscopic analysis, cytotoxicity test, and filament diameter analysis using descriptive statistics were also part of the focus. The results of the analysis of the diameter of the filament show that the filament meets the prescribed standard. The cytotoxicity test for PLA/PHB + HA/TCP material showed no toxicity. Microscopic analysis showed an even distribution of the ceramic component in the composite polymer. Mechanical testing showed a reduction in mechanical properties with 75% and 50% of the filling of experimental samples. All experimental samples subjected to mechanical testing showed higher tensile and compressive strength values compared to the values of the mechanical properties of vertebral trabecular bones, as reported in the literature. It can therefore be concluded that the material under investigation, PLA/PHB + HA/TCP appears to be a suitable candidate for hard tissue replacement.

Angiogenic Potential of VEGF Mimetic Peptides for the Biofunctionalization of Collagen/Hydroxyapatite Composites

Currently, the focus on bioinspired concepts for the development of tissue engineering constructs is increasing. For this purpose, the combination of collagen (Coll) and hydroxyapatite (HA) comes closest to the natural composition of the bone. In order to confer angiogenic properties to the scaffold material, vascular endothelial growth factor (VEGF) is frequently used. In the present study, we used a VEGF mimetic peptide (QK) and a modified QK-peptide with a poly-glutamic acid tag (E7-QK) to enhance binding to HA, and analyzed in detail binding efficiency and angiogenic properties. We detected a significantly higher binding efficiency of E7-QK peptides to hydroxyapatite particles compared to the unmodified QK-peptide. Tube formation assays revealed similar angiogenic functions of E7-QK peptide (1µM) as induced by the entire VEGF protein. Analyses of gene expression of angiogenic factors and their receptors (FLT-1, KDR, HGF, MET, IL-8, HIF-1α, MMP-1, IGFBP-1, IGFBP-2, VCAM-1, and ANGPT-1) showed higher expression levels in HUVECs cultured in the presence of 1 µM E7-QK and VEGF compared to those detected in the negative control group without any angiogenic stimuli. In contrast, the expression of the anti-angiogenic gene TIMP-1 showed lower mRNA levels in HUVECs cultured with E7-QK and VEGF. Sprouting assays with HUVEC spheroids within Coll/HA/E7-QK scaffolds showed significantly longer sprouts compared to those induced within Coll/HA/QK or Coll/HA scaffolds. Our results demonstrate a significantly better functionality of the E7-QK peptide, electrostatically bound to hydroxyapatite particles compared to that of unmodified QK peptide. We conclude that the used E7-QK peptide represents an excellently suited biomolecule for the generation of collagen/hydroxyapatite composites with angiogenic properties.

Біоматеріал на основі полілактиду та його використання як кісткових імплантатів (аналітичний огляд літератури)

У багатьох галузях медицини широке застосування отримали імплантати з різних синтетичних та природних біоматеріалів. Серед матеріалів, що частіше використовують для створення імплантатів, полілактид (PLA), особливістю якого є біодеградація в ділянках імплантації, остеоінтеграція, здатність індукувати процеси утворення кісткової тканини та висока біосумісність з організмом. Мета огляду: проаналізувати та узагальнити дані щодо перебудови в кістці біорезорбуючих біоматеріалів на основі полілактиду та визначити тенденції розвитку проблеми. В огляді літератури подано загальну характеристику та визначено історичні віхи розвитку проблеми та використання деградуючих полімерів у кістковій хірургії. Надані дані щодо факторів, що впливають на біодеградацію в кістках цього біоматеріалу, та визначено особливості його остеоінтеграції залежно від складу. Наведено дані щодо використання PLA та співполімерів у кістковій хірургії та регенераторній медицині. Важливим напрямком майбутніх досліджень буде розробка композитних біоматеріалів на основі PLA з бажаними якостями остеоінтеграції та керованою біодеградацією. Подано нові тенденції розвитку напрямку використання в кістковій хірургії імплантатів на основі композитних матеріалів, виготовлених на основі PLA, та новітні способи створення імплантатів та композитів із використанням 3D-принтера.

Natural Drug-Loaded Bimetal-Substituted Hydroxyapatite-Polymeric Composite for Osteosarcoma-Affected Bone Repair

Repairing segmental bone deformities after resection of dangerous bone tumors is a long-standing clinical issue. The study's main objective is to synthesize a natural bioactive compound-loaded bimetal-substituted hydroxyapatite (BM-HA)-based composite for bone regeneration. The bimetal (copper and cadmium)-substituted HAs were prepared by the sol-gel method and reinforced with biocompatible polyacrylamide (BM-HA/PAA). Umbelliferone (UMB) drug was added to the BM-HA/PAA composite to enhance anticancer activity further. The composite's formation was confirmed by various physicochemical investigations, such as FT-IR, XRD, SEM, EDAX, and HR-TEM techniques. The bioactivity was assessed by immersing the sample in simulated body fluid for 1, 3, and 7 days. The zeta potential values of BM-HA/PAA and BM-HA/PAA/UMB are -36.4 mV and -49.4 mV, respectively. The in vitro viability of the prepared composites was examined in mesenchymal stem cells (MSCs). It shows the ability of the composite to produce osteogenic bone regeneration without any adverse effects. From the gene expression and PCR results, the final UMB-loaded composite induced osteogenic markers, such as Runx, OCN, and VEFG. The prepared bimetal substituted polyacrylamide reinforced HA composite loaded with UMB drug has the ability for bone repair/regenerations.

Simultaneous incorporation of PTH(1-34) and nano-hydroxyapatite into Chitosan/Alginate Hydrogels for efficient bone regeneration

Tissue regeneration based on the utilization of artificial soft materials is considered a promising treatment for bone-related diseases. Here, we report cranial bone regeneration promoted by hydrogels that contain parathyroid hormone (PTH) peptide PTH(1-34) and nano-hydroxyapatite (nHAP). A combination of the positively charged natural polymer chitosan (CS) and negatively charged sodium alginate led to the formation of hydrogels with porous structures, as shown by scanning electron microscopy. Rheological characterizations revealed that the mechanical properties of the hydrogels were almost maintained upon the addition of nHAP and PTH(1-34). In vitro experiments showed that the hydrogel containing nHAP and PTH(1-34) exhibited strong biocompatibility and facilitated osteogenic differentiation of rat bone marrow mesenchymal stem cells (rBMSCs) via the Notch signaling pathway, as shown by the upregulated expression of osteogenic-related proteins. We found that increasing the content of PTH(1-34) in the hydrogels resulted in enhanced osteogenic differentiation of BMSCs. Implantation of the complex hydrogel into a rat cranial defect model led to efficient bone regeneration compared to the rats treated with the hydrogel alone or with nHAP, indicating the simultaneous therapeutic effect of nHAP and PTH during the treatment process. Both the in vitro and in vivo results demonstrated that simultaneously incorporating nHAP and PTH into hydrogels shows promise for bone regeneration, suggesting a new strategy for tissue engineering and regeneration in the future.

Bone Grafts and Substitutes in Dentistry: A Review of Current Trends and Developments

After tooth loss, bone resorption is irreversible, leaving the area without adequate bone volume for successful implant treatment. Bone grafting is the only solution to reverse dental bone loss and is a well-accepted procedure required in one in every four dental implants. Research and development in materials, design and fabrication technologies have expanded over the years to achieve successful and long-lasting dental implants for tooth substitution. This review will critically present the various dental bone graft and substitute materials that have been used to achieve a successful dental implant. The article also reviews the properties of dental bone grafts and various dental bone substitutes that have been studied or are currently available commercially. The various classifications of bone grafts and substitutes, including natural and synthetic materials, are critically presented, and available commercial products in each category are discussed. Different bone substitute materials, including metals, ceramics, polymers, or their combinations, and their chemical, physical, and biocompatibility properties are explored. Limitations of the available materials are presented, and areas which require further research and development are highlighted. Tissue engineering hybrid constructions with enhanced bone regeneration ability, such as cell-based or growth factor-based bone substitutes, are discussed as an emerging area of development.

3D porous Ti6Al4V-beta-tricalcium phosphate scaffolds directly fabricated by additive manufacturing

3D Ti6Al4V-beta-tricalcium phosphate (TCP) hybrid scaffolds with interconnected porous network and controllable porosity and pore size were successfully produced by three-dimensional fiber deposition (3DF). The macrostructure of scaffolds was determined by the 3D design, whereas the micro- and submicron structure were derived from the Ti6Al4V powder sintering and the crystalline TCP powder, respectively. Ti6Al4V-TCP slurry was developed for 3DF by optimizing the TCP powder size, Ti6Al4V-to-TCP powder ratio and Ti6Al4V-TCP powder content. Moreover, the air pressure and fiber deposition rate were optimized. A maximum achievable ceramic content in the Ti6Al4V-TCP slurry that enables 3DF manufacturing was 10 wt%. The chemical analysis showed that limited contamination occurred during sintering. The compressive strength and Young's modulus of the scaffolds exhibited values between those of cancellous and cortical bone. The 3D Ti6Al4V-TCP scaffolds with 10 wt% TCP allowed deposition of a calcium phosphate layer on the surface in a simulated body fluid. Cumulative release of calcium and phosphate ions from the scaffolds was observed in a simulated physiological solution, in contrast to a cell culture medium. A pilot in vivo study, in which the scaffolds were implanted intramuscularly in dogs showed ectopic bone formation in the Ti6Al4V-TCP scaffolds with 10 wt% TCP, showing their osteoinductive potential. The porous 3D Ti6Al4V-TCP scaffolds developed here combine the mechanical properties of the metal with the bioactivity of the ceramic and are therefore likely to yield more effective strategies to control the implant-bone interface and thereby improve long-term clinical results in orthopaedics and craniomaxillofacial surgery. STATEMENT OF SIGNIFICANCE: In this work, 3D porous hybrid scaffolds made of a titanium alloy and a beta-tricalcium phosphate ceramic (Ti6Al4V-TCP) were developed using the direct additive manufacturing technique 3D fiber deposition. Upon optimization of the powders and slurry, scaffolds with up to 10 wt.% TCP with good mechanical properties and controllable porous structure at different length scales were successfully manufactured. A preliminary in vivo study in an intramuscular model demonstrated that the addition of TCP to the metal alloy improved its bioactivity. The combination of the two materials and the use of a direct additive manufacturing technique resulted in scaffolds that may lead to more effective strategies to control the implant-bone interface and thereby improve long-term clinical results in orthopaedics and craniomaxillofacial surgery.

Hexagonal pore geometry and the presence of hydroxyapatite enhance deposition of mineralized bone matrix on additively manufactured polylactic acid scaffolds

Additive manufacturing (AM) has revolutionized the design of regenerative scaffolds for orthopaedic applications, enabling customizable geometric designs and material compositions that mimic bone. However, the available evidence is contradictory with respect to which geometric designs and material compositions are optimal. There is a lack of studies that systematically compare different pore sizes and geometries in conjunction with the presence or absence of calcium phosphates. We therefore evaluated the physicochemical and biological properties of additively manufactured scaffolds based on polylactic acid (PLA) in combination with hydroxyapatite (HA). HA was either incorporated in the polymeric matrix or introduced as a coating, yielding 15 and 2% wt., respectively. Pore sizes of the scaffolds varied between 200 and 450 μm and were shaped either triangularly or hexagonally. All scaffolds supported the adhesion, proliferation and differentiation of both primary mouse osteoblasts and osteosarcoma cells up to four weeks, with only small differences in the production of alkaline phosphatase (ALP) between cells grown on different pore geometries and material compositions. However, mineralization of the PLA scaffolds was substantially enhanced in the presence of HA, either embedded in the PLA matrix or as a coating at the surface level, and by larger hexagonal pores. In conclusion, customized HA/PLA composite porous scaffolds intended for the repair of critical size bone defects were obtained by a cost-effective AM method. Our findings indicate that the analysis of osteoblast adhesion and differentiation on experimental scaffolds alone is inconclusive without the assessment of mineralization, and the effects of geometry and composition on bone matrix deposition must be carefully considered in order to understand the regenerative potential of experimental scaffolds.

Mechanical Properties and Bioactivity of Poly(Lactic Acid) Composites Containing Poly(Glycolic Acid) Fiber and Hydroxyapatite Particles

To enhance the mechanical strength and bioactivity of poly(lactic acid) (PLA) to the level that can be used as a material for spinal implants, poly(glycolic acid) (PGA) fibers and hydroxyapatite (HA) were introduced as fillers to PLA composites. To improve the poor interface between HA and PLA, HA was grafted by PLA to form HA-g-PLA through coupling reactions, and mixed with PLA. The size of the HA particles in the PLA matrix was observed to be reduced from several micrometers to sub-micrometer by grafting PLA onto HA. The tensile and flexural strength of PLA/HA-g-PLA composites were increased compared with those of PLA/HA, apparently due to the better dispersion of HA and stronger interfacial adhesion between the HA and PLA matrix. We also examined the effects of the length and frequency of grafted PLA chains on the tensile strength of the composites. By the addition of unidirectionally aligned PGA fibers, the flexural strength of the composites was greatly improved to a level comparable with human compact bone. In the bioactivity tests, the growth of apatite on the surface was fastest and most uniform in the PLA/PGA fiber/HA-g-PLA composite.

Synthesis and Modification of Hydroxyapatite Nanofiber for Poly(Lactic Acid) Composites with Enhanced Mechanical Strength and Bioactivity

To enhance the bioactivity of poly(lactic acid) (PLA), a potential bone repair material, without the lowering of mechanical strength, hydroxyapatite (HA) was introduced in the form of nanofibers as the filler for application in spinal implant materials. HA nanofibers (HANF) with aspect ratio as high as ~100 were synthesized by controlling the starting pH of the reaction. While the tensile and flexural strength of PLA/HANF composites were enhanced compared with those of PLA resin, and were higher for the composites with HANF of higher aspect ratio. To further strengthen the composites, HANF was grafted with PLA chain to form HANF-g-PLA, which could improve the interface between the HANF and matrix PLA. PLA/HANF-g-PLA composites showed even higher tensile and flexural strength than PLA/HANF composites, apparently due to the better dispersion and interfacial adhesion. The composite containing 10 wt% HANF-g-PLA showed the flexural strength of 124 MPa, which was 25% higher than that of PLA resin. In the bioactivity test using a simulated body fluid solution, the rate and uniformity of the apatite growth were observed to be higher for the composites with HANF, and were even higher for those with HANF-g-PLA. This study suggested the possibility of using the PLA/HANF-g-PLA composite in the field of spinal implant materials.

Direct comparison of 3D and 2D cultivation reveals higher osteogenic capacity of elderly osteoblasts in 3D

Background

The aim of this study was the investigation of the osteogenic potential of human osteoblasts of advanced donor age in 2D and 3D culture.

Methods

Osteoblasts were induced to osteogenic differentiation and cultivated, using the same polystyrene material in 2D and 3D culture for 2 weeks. Samples were taken to evaluate alkaline phosphatase (ALP) activity, mineralization and gene expression.

Results

Osteoprotegerin (OPG) levels were significantly increased (8.2-fold) on day 7 in 3D compared to day 0 (p < 0.0001) and 11.6-fold higher in 3D than in 2D (p < 0.0001). Both culture systems showed reduced osteocalcin (OC) levels (2D 85% and 3D 50% of basic value). Collagen type 1 (Col1) expression was elevated in 3D on day 7 (1.4-fold; p = 0.009). Osteopontin (OP) expression showed 6.5-fold higher levels on day 7 (p = 0.002) in 3D than in 2D. Mineralization was significantly higher in 3D on day 14 (p = 0.0002).

Conclusion

Advanced donor age human primary osteoblasts reveal significantly higher gene expression levels of OPG, Col1 and OP in 3D than in monolayer. Therefore, it seems that a relatively high potential of bone formation in a natural 3D arrangement is presumably still present in osteoblasts of elderly people.

Trial registration

5217/11 on the 22nd of Dec. 2011.

Fabrication of nanoparticles for bone regeneration: new insight into applications of nanoemulsion technology

Introducing synthetic bone substitutes into the clinic was a major breakthrough in the regenerative medicine of bone. Despite many advantages of currently available bone implant materials such as biocompatiblity and osteoconductivity, they still suffer from relatively poor bioactivity, osteoinductivity and osteointegration. These properties can be effectively enhanced by functionalization of implant materials with nanoparticles such as osteoinductive hydroxyapatite nanocrystals, resembling inorganic part of the bone, or bioactive polymer nanoparticles providing sustained delivery of pro-osteogenic agents directly at implantation site. One of the most widespread techniques for fabrication of nanoparticles for bone regeneration applications is nanoemulsification. It allows manufacturing of nanoscale particles (<100 nm) that are injectable, 3D-printable, offer high surface-area-to-volume-ratio and minimal mass transport limitations. Nanoparticles obtained by this technique are of particular interest for biomedical engineering due to fabrication procedures requiring low surfactant concentrations, which translates into reduced risk of surfactant-related in vivo adverse effects and improved biocompatibility of the product. This review discusses nanoemulsion technology and its current uses in manufacturing of nanoparticles for bone regeneration applications. In the first section, we introduce basic concepts of nanoemulsification including nanoemulsion formation, properties and preparation methods. In the next sections, we focus on applications of nanoemulsions in fabrication of nanoparticles used for delivery of drugs/biomolecules facilitating osteogenesis and functionalization of bone implants with special emphasis on biomimetic hydroxyapatite nanoparticles, synthetic polymer nanoparticles loaded with bioactive compounds and bone-targeting nanoparticles. We also highlight key challenges in formulation of nanoparticles via nanoemulsification and outline potential further improvements in this field.

Biomimetic Mineralization on 3D Printed PLA Scaffolds: On the Response of Human Primary Osteoblasts Spheroids and In Vivo Implantation

This study aimed to assess the response of 3D printed polylactic acid (PLA) scaffolds biomimetically coated with apatite on human primary osteoblast (HOb) spheroids and evaluate the biological response to its association with Bone Morphogenetic Protein 2 (rhBMP-2) in rat calvaria. PLA scaffolds were produced via 3D printing, soaked in simulated body fluid (SBF) solution to promote apatite deposition, and characterized by physical-chemical, morphological, and mechanical properties. PLA-CaP scaffolds with interconnected porous and mechanical properties suitable for bone repairing were produced with reproducibility. The in vitro biological response was assessed with human primary osteoblast spheroids. Increased cell adhesion and the rise of in vitro release of growth factors (Platelet-Derived Growth Factor (PDGF), Basic Fibroblast Growth Factor (bFGF), Vascular Endothelial Growth Factor (VEGF) was observed for PLA-CaP scaffolds, when pre-treated with fetal bovine serum (FBS). This pre-treatment with FBS was done in a way to enhance the adsorption of serum proteins, increasing the number of bioactive sites on the surface of scaffolds, and to partially mimic in vivo interactions. The in vivo analysis was conducted through the implantation of 3D printed PLA scaffolds either alone, coated with apatite (PLA-CaP) or PLA-CaP loaded with rhBMP-2 on critical-sized defects (8 mm) of rat calvaria. PLA-CaP+rhBMP2 presented higher values of newly formed bone (NFB) than other groups at all in vivo experimental periods (p < 0.05), attaining 44.85% of NFB after six months. These findings indicated two new potential candidates as alternatives to autogenous bone grafts for long-term treatment: (i) 3D-printed PLA-CaP scaffold associated with spheroids, since it can reduce the time of repair in situ by expression of biomolecules and growth factors; and (ii) 3D-printed PLA-CaP functionalized rhBMP2 scaffold, a biocompatible, bioactive biomaterial, with osteoconductivity and osteoinductivity.

Effect of donor age and 3D-cultivation on osteogenic differentiation capacity of adipose-derived mesenchymal stem cells

Background and Purpose: Age and co-morbidities compromise healing tendencies of traumatic fractures in geriatric patients. Non-healing fractures may need regenerative medicine techniques involving autologous mesenchymal stem cells (MSCs). Donor age may affect the viability and differentiation capacity of MSCs. We investigated age-related differences in adipose-derived MSCs (AMSCs) concerning osteogenic potential in 2D and 3D cultivation. Materials and Methods: AMSCs were harvested from young (mean age: 37.5 ± 8.6 years) and old (mean age: 75.8 ± 9.2 years) patients. Cells were induced to osteogenic differentiation and cultivated in 2D and 3D for 14 days. Alkaline phosphatase (ALP) activity, mineralization and gene expression were investigated. Results: ALP activity revealed highest levels in 3D of old AMSCs after 14 days. ALP expression showed significant rises in old vs. young cells in 2D (p = 0.0024). Osteoprotegerin revealed the highest levels in old AMSCs in 2D. Highest osteocalcin levels presented in young cells compared to old cells in 2D (p = 0.0258) and young cells in 3D (p = 0.0014). Conclusion: 3D arrangement of old AMSCs without growth factors is not ensuring superior osteogenesis in vitro. AMSCs, especially cells from older patients, reveal higher osteogenic potential in 2D than in 3D. 3D arrangement favors osteogenic potential of young cells.

In vivo studies on osteoinduction: A systematic review on animal models, implant site, and type and postimplantation investigation

Musculoskeletal diseases involving loss of tissue usually require management with bone grafts, among which autografts are still the gold standard. To overcome autograft disadvantages, the development of new scaffolds is constantly increasing, as well as the number of in vivo studies evaluating their osteoinductivity in ectopic sites. The aim of the present systematic review is to evaluate the last 10 years of osteoinduction in vivo studies. The review is focused on: (a) which type of animal model is most suitable for osteoinduction evaluation; (b) what are the most used types of scaffolds; (c) what kind of post-explant evaluation is most used. Through three websites (www.pubmed.com, www.webofknowledge.com and www.embase.com), 77 in vivo studies were included. Fifty-eight studies were conducted in small animal models (rodents) and 19 in animals of medium or large size (rabbits, dogs, goats, sheep, and minipigs). Despite the difficulty in establishing the most suitable animal model for osteoinductivity studies, small animals (in particular mice) are the most utilized. Intramuscular implantation is more frequent than subcutis, especially in large animals, and synthetic scaffolds (especially CaP ceramics) are preferred than natural ones, also in combination with cells and growth factors. Paraffin histology and histomorphometric evaluations are usually employed for postimplantation analyses.

3D-Printing of Hierarchically Designed and Osteoconductive Bone Tissue Engineering Scaffolds

In Bone Tissue Engineering (BTE), autologous bone-regenerative cells are combined with a scaffold for large bone defect treatment (LBDT). Microporous, polylactic acid (PLA) scaffolds showed good healing results in small animals. However, transfer to large animal models is not easily achieved simply by upscaling the design. Increasing diffusion distances have a negative impact on cell survival and nutrition supply, leading to cell death and ultimately implant failure. Here, a novel scaffold architecture was designed to meet all requirements for an advanced bone substitute. Biofunctional, porous subunits in a load-bearing, compression-resistant frame structure characterize this approach. An open, macro- and microporous internal architecture (100 µm-2 mm pores) optimizes conditions for oxygen and nutrient supply to the implant's inner areas by diffusion. A prototype was 3D-printed applying Fused Filament Fabrication using PLA. After incubation with Saos-2 (Sarcoma osteogenic) cells for 14 days, cell morphology, cell distribution, cell survival (fluorescence microscopy and LDH-based cytotoxicity assay), metabolic activity (MTT test), and osteogenic gene expression were determined. The adherent cells showed colonization properties, proliferation potential, and osteogenic differentiation. The innovative design, with its porous structure, is a promising matrix for cell settlement and proliferation. The modular design allows easy upscaling and offers a solution for LBDT.

Establishment of Collagen: Hydroxyapatite/BMP-2 Mimetic Peptide Composites

Extensive efforts were undertaken to develop suitable biomaterials for tissue engineering (TE) applications. To facilitate clinical approval processes and ensure the success of TE applications, bioinspired concepts are currently focused on. Working on bone tissue engineering, we describe in the present study a method for biofunctionalization of collagen/hydroxyapatite composites with BMP-2 mimetic peptides. This approach is expected to be fundamentally transferable to other tissue engineering fields. A modified BMP-2 mimetic peptide containing a negatively charged poly-glutamic acid residue (E7 BMP-2 peptide) was used to bind positively charged hydroxyapatite (HA) particles by electrostatic attraction. Binding efficiency was biochemically detected to be on average 85% compared to 30% of BMP-2 peptide without E7 residue. By quartz crystal microbalance (QCM) analysis, we could demonstrate the time-dependent dissociation of the BMP-2 mimetic peptides and the stable binding of the E7 BMP-2 peptides on HA-coated quartz crystals. As shown by immunofluorescence staining, alkaline phosphatase expression is similar to that detected in jaw periosteal cells (JPCs) stimulated with the whole BMP-2 protein. Mineralization potential of JPCs in the presence of BMP-2 mimetic peptides was also shown to be at least similar or significantly higher when low peptide concentrations were used, as compared to JPCs cultured in the presence of recombinant BMP-2 controls. In the following, collagen/hydroxyapatite composite materials were prepared. By proliferation analysis, we detected a decrease in cell viability with increasing HA ratios. Therefore, we chose a collagen/hydroxyapatite ratio of 1:2, similar to the natural composition of bone. The following inclusion of E7 BMP-2 peptides within the composite material resulted in significantly elevated long-term JPC proliferation under osteogenic conditions. We conclude that our advanced approach for fast and cost-effective scaffold preparation and biofunctionalization is suitable for improved and prolonged JPC proliferation. Further studies should prove the functionality of composite scaffolds in vivo.

Elaboration and Biocompatibility of an Eggshell-Derived Hydroxyapatite Material Modified with Si/PLGA for Bone Regeneration in Dentistry

Hydroxyapatite (HAp) is the most commonly used biomaterial in modern bone regeneration studies because of its chemical similarity to bone, biocompatibility with different polymers, osteoconductivity, low cost, and lack of immune response. However, to overcome the disadvantages of HAp, which include fragility and low mechanical strength, current studies typically focus on property modification through the addition of other materials. Objective. To develop and evaluate the biocompatibility of a HAp material extracted from eggshells and modified with silicon (Si) and poly(lactic-co-glycolic) acid (PLGA). Materials and Methods. An in vitro experimental study in which a HAp material prepared from eggshells was synthesized by wet chemical and conventional chemical precipitation. Subsequently, this material was reinforced with Si/PLGA using the freezing/lyophilization method, and then osteoblast cells were seeded on the experimental material (HAp/Si/PLGA). To analyse the biocompatibility of this composite material, scanning electron microscopy (SEM) and fluorescence confocal microscopy (FCM) techniques were used. PLGA, bovine bone/PLGA (BB/PLGA), and HAp/PLGA were used as controls. Results. A cellular viability of 96% was observed for the experimental HAp/Si/PLGA material as well as for the PLGA. The viability for the BB/PLGA material was 90%, and the viability for the HAp/PLGA was 86%. Cell adhesion was observed on the exterior surface of all materials. However, a continuous monolayer and the presence of filopodia were observed over both external and internal surface of the experimental materials. Conclusions. The HAp/Si/PLGA material is highly biocompatible with osteoblastic cells and can be considered promising for the construction of three-dimensional scaffolds for bone regeneration in dentistry.

Nanocomposite scaffold seeded with mesenchymal stem cells for bone repair

The mechanical property of bone tissue scaffolds is one of the most important aspects in bone tissue engineering that has remained problematic. In our previous study, we fabricated a three-dimensional scaffold from nano-hydroxyapatite/gelatin (nHA/Gel) and investigated its efficiency in promoting bone regeneration both in vitro and in vivo. In the present study, the effect of adding silicon carbide (SiC) on the mechanical and biological behaviors of the nHA/Gel/SiC and bone regeneration in vivo were determined. nHA and SiC were synthesized and characterized by the X-ray diffraction pattern and transmission electron microscope image. Layer solvent casting, freeze drying, and lamination techniques were applied to prepare these scaffolds. Then, the biocompatibility and cell adhesion behavior of the synthesized nHA/Gel/SiC scaffolds were investigated. For in vivo studies, rats were categorized into three groups: blank defect, blank scaffold, and rat bone marrow mesenchymal stem cells (rBM-MSCs)/scaffold. After 1, 4, and 12 weeks post-injury, the rats were sacrificed and the calvaria were harvested. Sections with a thickness of 5 µm thickness were prepared and stained with hematoxylin-eosin and Masson's Trichrome, and immunohistochemistry was performed. Our results showed that SiC effectively increased the mechanical properties of the nHA/Gel/SiC scaffold. No significant differences were observed in biocompatibility, cell adhesion, and cytotoxicity of the nHA/Gel/SiC in comparison with the nHA/Gel nanocomposite. Based on histological and immunohistochemical studies, both osteogenesis and collagenization were significantly higher in the rBM-MSCs/scaffold group, quantitatively and qualitatively. The present study strongly suggests the potential of SiC as an alternative strategy to improve the mechanical and biological properties of bone tissue engineering scaffolds, and shows that the pre-seeded nHA/Gel/SiC scaffold with rBM-MSCs improves osteogenesis in the engineered bone implant.

Hydroxyapatite/silver electrospun fibers for anti-infection and osteoinduction

Bone implant materials cause the most common complication of bone infections in orthopedic surgery, resulting in implant failure. Antibiotic treatment of bone infections leads to problems such as bacterial resistance and reduced osteogenic capacity. In this study, dopamine (DA) was self-polymerized on the surface of Polylactic acid (PLLA)/Hydroxyapatite (HA) nanowire composite fibers to form an adhesive polydopamine (PDA) membrane, and a stable silver-nanoparticles (Ag-NPs) coating layer was constructed on it by electrochemically driven Ag⁺ coordination and chelation through Polypyrrole (PPy) mediation, achieving steady and slow release of Ag-NPs. With optimized DA soaking time of 24 h and soaking concentration of 0.5 g·L^-1, nanoparticles were uniformly distributed on PLLA/HA/PDA/PPy/Ag composite fibers and the hydrophilicity of the composite fibers was well-behaved. Besides, the composite fibers possessed good physiological stability and 100% antibacterial rate against Escherichia coli (E. coli) as well as Staphylococcus aureus (S. aureus). In addition, the composite fibers had promoted apatite nucleation and growth on surface and good cytocompatibility with osteoblasts, indicating ability of inducing osteogenic differentiation. In summary, a multi-functional PLLA/HA/PDA/PPy/Ag composite fiber with long-term antibacterial property, bioactivity and osteoinductivity was successfully constructed by electrospinning and electrochemical deposition.

Comparison of the Efficacy of Three Different Bone Regeneration Materials: An Animal Study

Objective The proposed study aimed to evaluate and compare the bone regeneration between commercially available hydroxyapatite–β-tricalcium phosphate (Ossifi; Equinox, the Netherlands), powdered polylactic acid (powdered PLA; Sigma-Aldrich, United States), and three-dimensionally printed PLA (3D-printed PLA; Cubex, SC, United States) using 3D printer (Cube X trio) in an animal model.

Materials and Methods Eighteen New Zealand rabbits were divided into three groups with six animals each. Platelet-rich fibrin (PRF) was collected from the venous blood and preserved. Bone defect (4 mm × 2 mm) without disturbing the bone marrow was created and filled with bone graft material (group 1–Ossifi, group 2–powdered PLA, and group 3–3D-printed PLA), over which PRF membranes were placed. The graft material and the barrier were stabilized using resorbable sutures, and all the animals were maintained for 4, 8, and 12 weeks, after which they were euthanized, and bone samples were retrieved. Retrieved bone samples were subjected to radiological and histological analysis.

Results The radiographic and histological changes of 3D-printed PLA in comparison with other two materials (Ossifi and powdered PLA) seemed to have a significant difference.

Conclusion 3D-printed PLA scaffolds showed positive signs of bone regeneration around the material in continuity defects. PLA material can be a promising alternative bone regenerative material.

Biological Compatibility of a Polylactic Acid Composite Reinforced with Natural Chitosan Obtained from Shrimp Waste

The aim of this work is to evaluate the effect of chitosan content (1, 3 and 5 wt %) dispersed in polylactic acid (PLA) on the structure and properties of composites. Also, the hydrolytic degradation, and the cell viability and adhesion of human MG-63 osteoblasts are analyzed to determine the composites’ suitability for use in tissue engineering. For the manufacture of the materials, natural chitosan was extracted chemically from shrimp exoskeleton. The composites were fabricated by extrusion, because it is a low-cost process, it is reproducible, and it does not compromise the biocompatibility of the materials. FT-IR and XRD show that the chitosan does not change the polymer structure, and interactions between the composite components are discarded. In vitro degradation tests show that the composites do not induce significant pH changes in phosphate buffer solution due to their low susceptibility to hydrolytic degradation. The adhesion and morphological characteristics of the osteoblasts are evaluated using confocal microscopy and scanning electron microscopy. The cell viability is determined by the MTT assay. Osteoblasts adhesion is observed on the surface of PLA and composites. A higher amount of chitosan, higher number of cells with osteoblastic morphology, and mineralized nodules are observed on the composite surface. The highest metabolic activity is evidenced at 21 days. The results suggest that the Polylactic acid/chitosan composites are potentially suitable for use as a biomaterial.

Hydroxyapatite nanobelt/polylactic acid Janus membrane with osteoinduction/barrier dual functions for precise bone defect repair

Controllable osteoinduction maintained in the original defect area is the key to precise bone repair. To meet the requirement of precise bone regeneration, a hydroxyapatite (HAp) nanobelt/polylactic acid (PLA) (HAp/PLA) Janus membrane has been successfully prepared in this study by coating PLA on a paper-like HAp nanobelt film by a casting-pervaporation method. The Janus membrane possesses dual functions: excellent osteoinduction from the hydrophilic HAp nanobelt side and barrier function originating from the hydrophobic PLA film. The cell viability and osteogenic differentiation ability of human adipose-derived stem cells (hADSCs) on the Janus membrane were assessed. The in vitro experimental results prove that the HAp nanobelt side presents high cell viability and efficient osteoinduction without any growth factor and that the PLA side can prohibit cell attachment. The in vivo repair experiments on a rat mandible defect model prove that the PLA side can prevent postoperative adhesion between bone and adjacent soft tissues. Most importantly, the HAp side has a strong ability to promote defect repair and bone regeneration. Therefore, the HAp/PLA Janus membrane will have wide applications as a kind of tissue engineering material in precise bone repair because of its unique dual osteoinduction/barrier functions, biocompatibility, low cost, and its ability to be mass-produced.

STATE OF SIGNIFICANCE

Precise bone defect repair to keeping tissue integrity and original outline shape is a very important issue for tissue engineering. Here, we have designed and prepared a novel HAp/PLA Janus membrane using a casting-pervaporation method to form a layer of PLA film on paper-like HAp nanobelt film. HAp nanobelt side of the Janus membrane can successfully promote osteogenic differentiation. PLA side of the Janus membrane exhibits good properties as a barrier for preventing the adhesion of cells in vitro. Mandible repair experiments in vivo have shown that the HAp/PLA Janus membrane can promote rat mandible repair on the HAp side and can successfully prevent postoperative adhesion on the PLA side at the same time. Therefore, the HAp/PLA Janus membrane with its osteoinduction/barrier dual functions can be applied to repair bone defect precisely.

Polymer-mineral scaffold augments in vivo equine multipotent stromal cell osteogenesis

Background

Use of bioscaffolds to direct osteogenic differentiation of adult multipotent stromal cells (MSCs) without exogenous proteins is a contemporary approach to bone regeneration. Identification of in vivo osteogenic contributions of exogenous MSCs on bioscaffolds after long-term implantation is vital to understanding cell persistence and effect duration.

Methods

This study was designed to quantify in vivo equine MSC osteogenesis on synthetic polymer scaffolds with distinct mineral combinations 9 weeks after implantation in a murine model. Cryopreserved, passage (P)1, equine bone marrow-derived MSCs (BMSC) and adipose tissue-derived MSCs (ASC) were culture expanded to P3 and immunophenotyped with flow cytometry. They were then loaded by spinner flask on to scaffolds composed of tricalcium phosphate (TCP)/hydroxyapatite (HA) (40:60; HT), polyethylene glycol (PEG)/poly-l-lactic acid (PLLA) (60:40; GA), or PEG/PLLA/TCP/HA (36:24:24:16; GT). Scaffolds with and without cells were maintained in static culture for up to 21 days or implanted subcutaneously in athymic mice that were radiographed every 3 weeks up to 9 weeks. In vitro cell viability and proliferation were determined. Explant composition (double-stranded (ds)DNA, collagen, sulfated glycosaminoglycan (sGAG), protein), equine and murine osteogenic target gene expression, microcomputed tomography (μCT) mineralization, and light microscopic structure were assessed.

Results

The ASC and BMSC number increased significantly in HT constructs between 7 and 21 days of culture, and BMSCs increased similarly in GT constructs. Radiographic opacity increased with time in GT-BMSC constructs. Extracellular matrix (ECM) components and dsDNA increased significantly in GT compared to HT constructs. Equine and murine osteogenic gene expression was highest in BMSC constructs with mineral-containing scaffolds. The HT constructs with either cell type had the highest mineral deposition based on μCT. Regardless of composition, scaffolds with cells had more ECM than those without, and osteoid was apparent in all BMSC constructs.

Conclusions

In this study, both exogenous and host MSCs appear to contribute to in vivo osteogenesis. Addition of mineral to polymer scaffolds enhances equine MSC osteogenesis over polymer alone, but pure mineral scaffold provides superior osteogenic support. These results emphasize the need for bioscaffolds that provide customized osteogenic direction of both exo- and endogenous MSCs for the best regenerative potential.

In vitro and in vivo biological characterization of poly(lactic acid) fiber scaffolds synthesized by air jet spinning

Poly(lactic acid) (PLA) is one of the most promising renewable and biodegradable polymers for mimic extracellular matrix for tissue engineering applications. In this work, PLA spun membrane scaffold were successfully prepared by air jet spinning technology. Morphology, mechanical properties, in vitro biocompatibility, and in vitro and in vivo degradation of PLA fibrous scaffold were characterized by X-ray diffraction, Fourier Transform Infrared, and scanning electron microscope (SEM). Morphological results assessed by SEM analyses indicated that PLA scaffolds possessed an average fiber diameter of approximately 0.558 ± 0.141 µm for 7% w/v of PLA and approximately 0.647 ± 0.137 µm for 10% w/v. Interestingly, our results showed that the nanofiber size of PLA scaffold allow structural stability after 100 days of in vitro degradation in Ringer solution where the average fiber diameter were of approximately 0.633 ± 0.147 µm for 7% w/v and approximately 0.645 ± 0.140 µm for 10% w/v of PLA. Mechanical properties of PLA fibers scaffold after in vitro degradation showed decrease in terms of flexibility elongation, and less energy was needed to achieve maximal elastic deformation. The fiber size exerts an influence on the biological response of human Bone Marrow Mesenchymal Stromal Cells as confirmed by MTT assay after 9 days of cell culture and the in vivo degradation assay of 7% w/v and 10% w/v of PLA scaffold, did not demonstrate evidence of toxicity with a mild inflammatory respond. In conclusion, airbrushing technology promises to be a viable and attractive alternative technique for producing a biocompatible PLA nanofiber scaffold that could be considered for tissue engineering regeneration. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2435-2446, 2018.

* In Vivo Models for the Evaluation of the Osteogenic Potency of Bone Substitutes Seeded with Mesenchymal Stem Cells of Human Origin: A Concise Review

Research concerning bone substitutes is one of the most challenging fields in orthopedic research and has a high clinical relevance, especially since the currently available bone substitutes are limited in their osteostimulative capabilities. In vitro models for the evaluation of the properties of bone substitutes allow the use of human mesenchymal stem cells (hMSCs) seeded onto scaffolds, but suffer from the lack of a physiological environment for those cells. Most in vivo models include the use of non-hMSC and are therefore lacking in clinical relevance. To overcome these issues, in vivo models were created that allow the evaluation of hMSC-seeded bone substitutes, combining the advantages of the use of human cells with the physiological conditions of an organism in vivo. In brief, models usually aim for bone formation in immunocompromised rodents. The subcutaneous implantation of scaffolds is most widely performed, showing low complication rates along with good results, but suffering from inferior vascularization of the implants and the absence of the realistic structural and mechanical conditions of bone. Orthotopic implantation, for example in calvarian or long bone defects, provides the most appropriate surrounding for hMSC-seeded scaffolds. However, parallel host-induced bone formation is a major limitation. This review summarizes in vivo models for the evaluation of the osteogenic potency of bone substitutes seeded with mesenchymal stem cells of human origin.

Surface-enrichment with hydroxyapatite nanoparticles in stereolithography-fabricated composite polymer scaffolds promotes bone repair

Fabrication of composite scaffolds using stereolithography (SLA) for bone tissue engineering has shown great promises. However, in order to trigger effective bone formation and implant integration, exogenous growth factors are commonly combined to scaffold materials. In this study, we fabricated biodegradable composite scaffolds using SLA and endowed them with osteopromotive properties in the absence of biologics. First we prepared photo-crosslinkable poly(trimethylene carbonate) (PTMC) resins containing 20 and 40wt% of hydroxyapatite (HA) nanoparticles and fabricated scaffolds with controlled macro-architecture. Then, we conducted experiments to investigate how the incorporation of HA in photo-crosslinked PTMC matrices improved human bone marrow stem cells osteogenic differentiation in vitro and kinetic of bone healing in vivo. We observed that bone regeneration was significantly improved using composite scaffolds containing as low as 20wt% of HA, along with difference in terms of osteogenesis and degree of implant osseointegration. Further investigations revealed that SLA process was responsible for the formation of a rich microscale layer of HA corralling scaffolds. To summarize, this work is of substantial importance as it shows how the fabrication of hierarchical biomaterials via surface-enrichment of functional HA nanoparticles in composite polymer stereolithographic structures could impact in vitro and in vivo osteogenesis.

STATEMENT OF SIGNIFICANCE

This study reports for the first time the enhance osteopromotion of composite biomaterials, with controlled macro-architecture and microscale distribution of hydroxyapatite particles, manufactured by stereolithography. In this process, the hydroxyapatite particles are not only embedded into an erodible polymer matrix, as reported so far in the literature, but concentrated at the surface of the structures. This leads to robust in vivo bone formation at low concentration of hydroxyapatite. The reported 3D self-corralling composite architecture provides significant opportunities to develop functional biomaterials for bone repair and tissue engineering.

Linking the Transcriptional Landscape of Bone Induction to Biomaterial Design Parameters

New engineering possibilities allow biomaterials to serve as active orchestrators of the molecular and cellular events of tissue regeneration. Here, the molecular control of tissue regeneration for calcium phosphate (CaP)-based materials is established by defining the parameters critical for tissue induction and those are linked to the molecular circuitry controlling cell physiology. The material properties (microporosity, ion composition, protein adsorption) of a set of synthesized osteoinductive and noninductive CaP ceramics are parameterized and these properties are correlated to a transcriptomics profile of osteogenic cells grown on the materials in vitro. Using these data, a genetic network controlling biomaterial-induced bone formation is built. By isolating the complex material properties into single-parameter test conditions, it is verified that a subset of these genes is indeed controlled by surface topography and ions released from the ceramics, respectively. The gene network points to a decisive role for extracellular matrix deposition in osteoinduction by genes such as tenascin C and hyaluronic acid synthase 2, which are controlled by calcium and phosphate ions as well as surface topography. This work provides insight into the biomaterial composition and material engineering aspects of bone void filling and can be used as a strategy to explore the interface between biomaterials and tissue regeneration.

Poly(lactic acid)-based particulate systems are promising tools for immune modulation

Poly(lactic acid) (PLA) is one of the most successful and versatile polymers explored for controlled delivery of bioactive molecules. Its attractive properties of biodegradability and biocompatibility in vivo have contributed in a meaningful way to the approval of different products by the FDA and EMA for a wide range of biomedical and pharmaceutical applications, in the past two decades. This polymer has been widely used for the preparation of particles as delivery systems of several therapeutic molecules, including vaccines. These PLA vaccine carriers have shown to induce a sustained and targeted release of different bacterial, viral and tumor-associated antigens and adjuvants in vivo, triggering distinct immune responses. The present review intends to highlight and discuss the major advantages of PLA as a promising polymer for the development of potent vaccine delivery systems against pathogens and cancer. It aims to provide a critical discussion based on preclinical data to better understand the major effect of PLA-based carrier properties on their interaction with immune cells and thus their role in the modulation of host immunity.

STATEMENT OF SIGNIFICANCE

During the last decades, vaccination has had a great impact on global health with the control of many severe diseases. Polymeric nanosystems have emerged as promising strategies to stabilize vaccine antigens, promoting their controlled release to phagocytic cells, thus avoiding the need for multiple administrations. One of the most promising polymers are the aliphatic polyesters, which include the poly(lactic acid). This is a highly versatile biodegradable and biocompatible polymer. Products containing this polymer have already been approved for all food and some biomedical applications. Despite all favorable characteristics presented above, PLA has been less intensively discussed than other polymers, such as its copolymer PLGA, including regarding its application in vaccination and particularly in tumor immunotherapy. The present review discusses the major advantages of poly(lactic acid) for the development of potent vaccine delivery systems, providing a critical view on the main properties that determine their effect on the modulation of immune cells.

Poly (lactic acid)-based biomaterials for orthopaedic regenerative engineering

Regenerative engineering converges tissue engineering, advanced materials science, stem cell science, and developmental biology to regenerate complex tissues such as whole limbs. Regenerative engineering scaffolds provide mechanical support and nanoscale control over architecture, topography, and biochemical cues to influence cellular outcome. In this regard, poly (lactic acid) (PLA)-based biomaterials may be considered as a gold standard for many orthopaedic regenerative engineering applications because of their versatility in fabrication, biodegradability, and compatibility with biomolecules and cells. Here we discuss recent developments in PLA-based biomaterials with respect to processability and current applications in the clinical and research settings for bone, ligament, meniscus, and cartilage regeneration.

ELABORATION AND EVALUATION OF A COMPOSITE BONE SUBSTITUTE BASED ON β-TCP/DCPD AND PHBV, PRELIMINARY RESULTS

Objective: In the present study, we investigate the biological performance of a calcium phosphate ceramics (CPC) bone substitute combined with poly-hydroxybutyrate-co-hydroxyvalerate (PHBV). Materials and Methods: A particulate CPC [45% beta-tricalcium phosphate ([Formula: see text]-TCP) and 55% of dihydrated dicalcium phosphate (DCPD)] was incorporated into a biodegradable copolymer PHBV. Two series of the composite, 1 and 2, with CPC–PHBV weight ratios of (40%–60% and 60%–40%), respectively, were prepared using chloroform for dissolving the polymer and a pressure molding process for shaping the composite samples. After particle size analysis, the two composites were characterized by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). In a second step, a 10[Formula: see text]mm bony segmental defect created in the tibias of 20 New Zealand White Rabbits was filled randomly with either composite 1 for group 1 or composite 2 for group 2. There were 10 animals in each group. Clinical, radiological and histological assessments were then carried out to evaluate the biological properties of developed CPC–PHBV composites. Results: For both variants of the developed CPC–PHBV biocomposite, there was evidence of osseous consolidation within three months. An in vivo investigation revealed the biological properties of the biocomposite, namely, biocompatibility, bioactivity, biodegradability and osteoconductivity. The morphological characteristics, granule size and chemical composition, were indeed found to be favorable for osseous cell development. This study likewise showed lower mortality for the variant with weight ratio (40%CPC–60%PHBV). Conclusion: An in vivo investigation revealed that the new biomaterial composed of CPC and PHBV exhibits manifest osteoconductivity and bioactivity with better degradation kinetics than the CPC. Moreover, the variant with 40%CPC/60%PHBV appeared more resistant to infection than the 60%CPC/40%PHBV which is an indicator of biocompatibility.

Independent effects of the chemical and microstructural surface properties of polymer/ceramic composites on proliferation and osteogenic differentiation of human MSCs

Within the general aim of finding affordable and sustainable regenerative solutions for damaged and diseased tissues and organs, significant efforts have been invested in developing synthetic alternatives to natural bone grafts, such as autografts. Calcium phosphate (CaP) ceramics are among widely used synthetic bone graft substitutes, but their mechanical properties and bone regenerative capacity are still outperformed by their natural counterparts. In order to improve the existing synthetic bone graft substitutes, it is imperative to understand the effects of their individual properties on a biological response, and to find a way to combine the desired properties into new, improved functional biomaterials. To this end, we studied the independent effects of the chemical composition and surface microstructure of a poly(lactic acid)/hydroxyapatite (PLA/HA) composite material on the proliferation and osteogenic differentiation of clinically relevant bone marrow-derived human mesenchymal stromal cells (hMSCs). While the molecular weight of the polymer and presence/absence of the ceramic phase were used as the chemical variables, a soft embossing technique was used to pattern the surfaces of all materials with either pits or pillars with identical microscale dimensions. The results indicated that, while cell morphology was affected by both the presence and availability of HA and by the surface microstructure, the effect of the latter parameter on cell proliferation was negligible. The osteogenic differentiation of hMSCs, and in particular the expression of bone morphogenetic protein 2 (BMP-2) and osteopontin (OP) were significantly enhanced when cells were cultured on the composite based on low-molecular-weight PLA, as compared to the high-molecular-weight PLA-based composite and the two pure polymers. The OP expression on the low-molecular-weight PLA-based composite was further enhanced when the surface was patterned with pits. Taken together, within this experimental set up, the individual effect of the chemistry, and in particular of the presence of CaP, was more pronounced than the individual effect of the surface microstructure, although their combined effects were, in some cases, synergistic. The approach presented here opens new routes to study the interactions of biomaterials with the biological environment in greater depths, which can serve as a starting point for developing biomaterials with improved bioactivity.

STATEMENT OF SIGNIFICANCE

The aim of the this study was to obtain insight into independent effects of the chemical composition and surface microstructure of a poly(lactic acid)/hydroxyapatite (PLA/HA) composite material on the morphology, proliferation and osteogenic differentiation of clinically relevant bone marrow-derived human mesenchymal stromal cells (hMSCs). While the need for synthetic alternatives for natural bone in bone regenerative strategies is rapidly increasing, the clinical performance of synthetic biomaterials needs to be further improved. To do this successfully, we believe that a better understanding of the relationship between a property of a material and a biological response is imperative. This study is a step forward in this direction, and we are therefore convinced that it will be of interest to the readers of Acta Biomaterialia.

Man as a Living Bioreactor: Prefabrication of a Custom Vascularized Bone Graft in the Gastrocolic Omentum

Reconstruction of critical-size jaw defects still remains challenging. The standard treatment today is transplantation of autologous bone grafts, which is associated with high donor-site morbidity and unsatisfactory outcomes. We aimed to reconstruct a mandibular discontinuity defect after ablative surgery using the gastrocolic omentum as a bioreactor for heterotopic ossification. Three-dimensional computed tomography data were used to produce an ideal virtual replacement for the mandibular defect. A titanium mesh cage was filled with bone mineral blocks, infiltrated with 12 mg of recombinant human bone morphogenetic protein 2, and enriched with bone marrow aspirate. The scaffold was implanted into the gastrocolic omentum, and 3 months later, a free flap was harvested to reconstruct the mandibular defect. In vivo single photon emission computed tomography/computed tomography revealed bone remodeling and mineralization inside the mandibular transplant during prefabrication and after transplantation. Reconstruction was possible without any further modifications of the graft. A histological evaluation revealed that large sections of the Bio-Oss material were covered with osteoid matrix 3 months after transplantation. The quality of life of the patient significantly increased with acquisition of the ability to masticate and the improvement in pronunciation and aesthetics. Heterotopic bone induction to form a mandibular replacement inside the gastrocolic omentum is possible in human subjects. Heterotopic prefabrication is associated with many advantages, like allowing a reduced operative burden compared with conventional techniques and good three-dimensional outcomes.