In vivo evaluation of a porous hydroxyapatite/poly-DL-lactide composite for bone tissue engineering

Calcium Orthophosphate (CaPO4) Containing Composites for Biomedical Applications: Formulations, Properties, and Applications

The goal of this review is to present a wide range of hybrid formulations and composites containing calcium orthophosphates (abbreviated as CaPO4) that are suitable for use in biomedical applications and currently on the market. The bioactive, biocompatible, and osteoconductive properties of various CaPO4-based formulations make them valuable in the rapidly developing field of biomedical research, both in vitro and in vivo. Due to the brittleness of CaPO4, it is essential to combine the desired osteologic properties of ceramic CaPO4 with those of other compounds to create novel, multifunctional bone graft biomaterials. Consequently, this analysis offers a thorough overview of the hybrid formulations and CaPO4-based composites that are currently known. To do this, a comprehensive search of the literature on the subject was carried out in all significant databases to extract pertinent papers. There have been many formulations found with different material compositions, production methods, structural and bioactive features, and in vitro and in vivo properties. When these formulations contain additional biofunctional ingredients, such as drugs, proteins, enzymes, or antibacterial agents, they offer improved biomedical applications. Moreover, a lot of these formulations allow cell loading and promote the development of smart formulations based on CaPO4. This evaluation also discusses basic problems and scientific difficulties that call for more investigation and advancements. It also indicates perspectives for the future.

Biomimetic Composite Coatings for Activation of Titanium Implant Surfaces: Methodological Approach and In Vivo Enhanced Osseointegration

Innovative nanomaterials are required for the coatings of titanium (Ti) implants to ensure the activation of Ti surfaces for improved osseointegration, enhanced bone fracture healing and bone regeneration. This paper presents a systematic investigation of biomimetic composite (BC) coatings on Ti implant surfaces in a rat model of a diaphyseal femoral fracture. Methodological approaches of surface modification of the Ti implants via the usual joining methods (e.g., grit blasting and acid etching) and advanced physicochemical coating via a self-assembled dip-coating method were used. The biomimetic procedure used multi-substituted hydroxyapatite (ms-HAP) HAP-1.5 wt% Mg-0.2 wt% Zn-0.2 wt% Si nanoparticles (NPs), which were functionalized using collagen type 1 molecules (COL), resulting in ms-HAP/COL (core/shell) NPs that were embedded into a polylactic acid (PLA) matrix and finally covered with COL layers, obtaining the ms-HAP/COL@PLA/COL composite. To assess the osseointegration issue, first, the thickness, surface morphology and roughness of the BC coating on the Ti implants were determined using AFM and SEM. The BC-coated Ti implants and uncoated Ti implants were then used in Wistar albino rats with a diaphyseal femoral fracture, both in the absence and the presence of high-frequency pulsed electromagnetic shortwave (HF-PESW) stimulation. This study was performed using a bone marker serum concentration and histological and computer tomography (micro-CT) analysis at 2 and 8 weeks after surgical implantation. The implant osseointegration was evaluated through the bone–implant contact (BIC). The bone–implant interface was investigated using FE-SEM images and EDX spectra of the retrieved surgical implants at 8 weeks in the four animal groups. The obtained results showed significantly higher bone–implants contact and bone volume per tissue volume, as well as a greater amount of newly formed bone, in the BC-coated Ti implants than in the uncoated Ti implants. Direct bone–implant contact was also confirmed via histological examination. The results of this study confirmed that these biomimetic composite coatings on Ti implants were essential for a significant enhancement of osseointegration of BC-coated Ti implants and bone regeneration. This research provides a novel strategy for the treatment of bone fractures with possible orthopedic applications.

Use of Unsintered Hydroxyapatite and Poly-L-lactic Acid Composite Sheets for Management of Orbital Wall Fracture

Although unsintered hydroxyapatite and poly-L-lactic acid (u-HA/PLLA) composite sheets have various applications, such as in craniomaxillofacial fractures, orthognathic surgery, and orthopedic surgery, and have been proven to be safe and effective, no studies have reported the use of u-HA/PLLA composite sheets for orbital wall reconstruction with long-term follow-up. This study reports our preliminary results using the u-HA/PLLA composite sheet for orbital wall fractures. The SuperFIXSORB MX sheet (u-HA/PLLA composite sheet; Takiron, Tokyo, Japan), with size of 30 × 50 mm and thickness of 0.5 mm, was used in all cases of hard reconstruction of the orbital bone defect. Seventy-two patients with acute orbital wall fractures (within 2 weeks after sustaining the injury) treated at the Jikei University between January 2014 and August 2016 were included. The authors evaluated the postoperative complications and the operability of the material. The authors did not observe any postoperative complications, such as infection, postoperative diplopia, or enophthalmos, due to the use of the u-HA/PLLA composite sheet. In pure orbital fractures (orbital fractures only), the mean (±standard deviation) operation time was significantly longer with combined inferior and medial wall fractures (201.1 ± 36.6 minutes; n = 11) than with inferior wall or medial wall fractures only (135.0 ± 54.4 minutes; n = 51) (Mann-Whitney U test, P < 0.001). The U-HA/PLLA composite sheet is safe and can be used for orbital wall fracture reconstruction. Further long-term functional and aesthetic assessments for infection, ocular movement disorder, enophthalmos, and any other complication are necessary.

Shape-defined solid micro-objects from poly(d,l-lactic acid) as cell-supportive counterparts in bottom-up tissue engineering

In bottom-up tissue engineering, small modular units of cells and biomaterials are assembled toward ​larger and more complex ones. In conjunction with a new implementation of this approach, a novel method to fabricate microscale objects from biopolymers by thermal imprinting on water-soluble sacrificial layers is presented. By this means, geometrically well-defined objects could be obtained without involving toxic agents in the form of photoinitiators. The micro-objects were used as cell-adhesive substrates and cell spacers in engineered tissues created by cell-guided assembly of the objects. Such constructs can be applied both for in vitro studies and clinical treatments. Clinically relevantly sized aggregates comprised of cells and micro-objects retained their viability up to 2 weeks of culture. The aggregation behavior of cells and objects showed to depend on the type and number of cells applied. To demonstrate the micro-objects' potential for engineering vascularized tissues, small aggregates of human bone marrow stromal cells (hMSCs) and micro-objects were coated with a layer of human umbilical vein endothelial cells (HUVECs) and fused into larger tissue constructs, resulting in HUVEC-rich regions at the aggregates' interfaces. This three-dimensional network-type spatial cellular organization could foster the establishment of (premature) vascular structures as a vital prerequisite of, for example, bottom-up-engineered bone-like tissue.

Comparison of the Bone Regenerative Capacity of Three-Dimensional Uncalcined and Unsintered Hydroxyapatite/Poly-d/l-Lactide and Beta-Tricalcium Phosphate Used as Bone Graft Substitutes

This study compared the in vivo applicability of three-dimensional uncalcined and unsintered hydroxyapatite/poly-d/l-lactide (3D-HA/PDLLA) with beta-tricalcium phosphate (β-TCP). 3D-HA/PDLLA is a newly developed bioactive, osteoconductive, bioresorbable bone regenerative composite. We performed critical-defect surgery on the mandible body of rats; the defects were filled with one of two bone graft substitutes. After a 4-week follow-up period, the mandibular specimens were examined using hematoxylin and eosin (H&E) staining, immunohistochemistry (IHC) staining and micro-computed tomography (micro-CT). The H&E staining showed an increase in newly formed bone in both groups from week 1 to 4. The difference in the Runx2 IHC optical density (OD) scores of 3D-HA/PDLLA and β-TCP was not statistically significant (p > 0.05); however, the osteocalcin IHC OD scores of the groups differed significantly (p < 0.05). Micro-CT demonstrated a similar trabecular thickness, trabecular spacing, and bone volume per total volume in the two groups (p > 0.05), indicating that bone formation in the two groups was nearly the same from a macro-perspective of bone regeneration. These results demonstrated that a different bone regeneration pattern and earlier osteoblast differentiation occurred in 3D-HA/PDLLA compared with β-TCP. In conclusion, our study demonstrates that 3D-HA/PDLLA is feasible for clinical application as a new bioactive, osteoconductive/bioresorbable bone graft substitute for maxillofacial surgery.

Application of a Bioactive/Bioresorbable Three-Dimensional Porous Uncalcined and Unsintered Hydroxyapatite/Poly-D/L-lactide Composite with Human Mesenchymal Stem Cells for Bone Regeneration in Maxillofacial Surgery: A Pilot Animal Study

A novel three-dimensional (3D) porous uncalcined and unsintered hydroxyapatite/poly-d/l-lactide (3D-HA/PDLLA) composite demonstrated superior biocompatibility, osteoconductivity, biodegradability, and plasticity, thereby enabling complex maxillofacial defect reconstruction. Mesenchymal stem cells (MSCs)-a type of adult stem cell-have a multipotent ability to differentiate into chondrocytes, adipocytes, and osteocytes. In a previous study, we found that CD90 (Thy-1, cluster of differentiation 90) and CD271 (low-affinity nerve growth factor receptor) double-positive cell populations from human bone marrow had high proliferative ability and differentiation capacity in vitro. In the present study, we investigated the utility of bone regeneration therapy using implantation of 3D-HA/PDLLA loaded with human MSCs (hMSCs) in mandibular critical defect rats. Microcomputed tomography (Micro-CT) indicated that implantation of a 3D-HA/PDLLA-hMSC composite scaffold improved the ability to achieve bone regeneration compared with 3D-HA/PDLLA alone. Compared to the sufficient blood supply in the mandibular defection superior side, a lack of blood supply in the inferior side caused delayed healing. The use of Villanueva Goldner staining (VG staining) revealed the gradual progression of the nucleated cells and new bone from the scaffold border into the central pores, indicating that 3D-HA/PDLLA loaded with hMSCs had good osteoconductivity and an adequate blood supply. These results further demonstrated that the 3D-HA/PDLLA-hMSC composite scaffold was an effective bone regenerative method for maxillofacial boney defect reconstruction.

Enhanced radiographic visualization of resorbable foils for orbital floor reconstruction: A proof of principle

PURPOSE

Despite the advantages and broad applications of alloplastic resorbable implants, postoperative radiological control is challenging due to its radiolucency. The aim of the present study was to evaluate the radiographic visibility of newly developed materials for orbital floor reconstruction.

MATERIALS AND METHODS

The radiographic visibility of four different material combinations consisting of poly-(L-lactic acid)/poly-glycolic acid (PLLA/PGA) or poly(D,L-lactic acid) (PDLLA) enriched with magnesium (Mg), hydroxyapatite (HA) or β-tricalcium phosphate (β-TCP) with various layers of thicknesses (0.3, 0.6, and 1 mm), surgically placed above the orbital floor of a human head specimen, was evaluated using computed tomography (CT) and cone beam computed tomography (CBCT). The visibility was rated on a scale of 0-10 in CT/CBCT and by Hounsfield Units in CT for each subject.

RESULTS

All of the materials were clearly detectable in CT scans. Visibility was significantly higher (p < 0.001) in the standard soft tissue window (mean score: 7.3, ranging from 2 to 10) in comparison to the standard bone window (mean score: 5.2, ranging from 1 to 10). In CBCT (mean score: 3.3, ranging from 0 to 7), there was significantly lower but still sufficient visibility of the materials compared to the CT soft tissue window (p < 0.001) and CT bone window (p < 0.001). Comparing the different materials' visibility among the group of same layer thicknesses with each other, in the majority of cases, PDLLA enriched with β-TCP appeared to be most visible in both CT and CBCT.

CONCLUSION

The incorporation of radiopaque elements to PLLA/PGA and PDLLA polymers is a promising strategy to improve their visibility in CT and CBCT. Our data suggest that the reconstruction of the orbital floor with these new materials could provide an advantageous postoperative radiographic control.

Biphasic calcium phosphate ceramics for bone reconstruction: A review of biological response

Autologous bone graft is considered as the gold standard in bone reconstructive surgery. However, the quantity of bone available is limited and the harvesting procedure requires a second surgical site resulting in severe complications. Due to these limits, scientists and clinicians have considered alternatives to autologous bone graft. Calcium phosphates (CaPs) biomaterials including biphasic calcium phosphate (BCP) ceramics have proven efficacy in numerous clinical indications. Their specific physico-chemical properties (HA/TCP ratio, dual porosity and subsequent interconnected architecture) control (regulate/condition) the progressive resorption and the bone substitution process. By describing the most significant biological responses reported in the last 30years, we review the main events that made their clinical success. We also discuss about their exciting future applications as osteoconductive scaffold for delivering various bioactive molecules or bone cells in bone tissue engineering and regenerative medicine.

STATEMENT OF SIGNIFICANCE

Nowadays, BCPs are definitely considered as the gold standard of bone substitutes in bone reconstructive surgery. Among the numerous clinical studies in literature demonstrating the performance of BCP, Passuti et al. and Randsford et al. studies largely contributed to the emergence of the BCPs. It could be interesting to come back to the main events that made their success and could explain their large adhesion from scientists to clinicians. This paper aims to review the most significant biological responses reported in the last 30years, of these BCP-based materials. We also discuss about their exciting future applications as osteoconductive scaffold for delivering various bioactive molecules or bone cells in bone tissue engineering and regenerative medicine.

PLA composites: From production to properties

Poly(lactic acid) or polylactide (PLA), a biodegradable polyester produced from renewable resources, is used for various applications (biomedical, packaging, textile fibers and technical items). Due to its inherent properties, PLA has a key-position in the market of biopolymers, being one of the most promising candidates for further developments. Unfortunately, PLA suffers from some shortcomings, whereas for the different applications specific end-use properties are required. Therefore, the addition of reinforcing fibers, micro- and/or nanofillers, and selected additives within PLA matrix is considered as a powerful method for obtaining specific end-use characteristics and major improvements of properties. This review highlights recent developments, current results and trends in the field of composites based on PLA. It presents the main advances in PLA properties and reports selected results in relation to the preparation and characterization of the most representative PLA composites. To illustrate the possibility to design the properties of composites, a section is devoted to the production and characterization of innovative PLA-based products filled with thermally-treated calcium sulfate, a by-product from the lactic acid production process. Moreover, are emphasized the last tendencies strongly evidenced in the case of PLA, i.e., the high interest to diversify its uses by moving from biomedical and packaging (biodegradation properties, "disposables") to technical applications ("durables").

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.

Cytocompatibility and biocompatibility of nanostructured carbonated hydroxyapatite spheres for bone repair

Objective

The aim of this study was to investigate the in vitro and in vivo biological responses to nanostructured carbonated hydroxyapatite/calcium alginate (CHA) microspheres used for alveolar bone repair, compared to sintered hydroxyapatite (HA).

Material and Methods

The maxillary central incisors of 45 Wistar rats were extracted, and the dental sockets were filled with HA, CHA, and blood clot (control group) (n=5/period/group). After 7, 21 and 42 days, the samples of bone with the biomaterials were obtained for histological and histomorphometric analysis, and the plasma levels of RANKL and OPG were determined via immunoassay. Statistical analysis was performed by Two-Way ANOVA with post-hoc Tukey test at 95% level of significance.

Results

The CHA and HA microspheres were cytocompatible with both human and murine cells on an in vitro assay. Histological analysis showed the time-dependent increase of newly formed bone in control group characterized by an intense osteoblast activity. In HA and CHA groups, the presence of a slight granulation reaction around the spheres was observed after seven days, which was reduced by the 42^nd day. A considerable amount of newly formed bone was observed surrounding the CHA spheres and the biomaterials particles at 42-day time point compared with HA. Histomorphometric analysis showed a significant increase of newly formed bone in CHA group compared with HA after 21 and 42 days from surgery, moreover, CHA showed almost 2-fold greater biosorption than HA at 42 days (two-way ANOVA, p<0.05) indicating greater biosorption. An increase in the RANKL/OPG ratio was observed in the CHA group on the 7^th day.

Conclusion

CHA spheres were osteoconductive and presented earlier biosorption, inducing early increases in the levels of proteins involved in resorption.

Osteoinduction of bone grafting materials for bone repair and regeneration

Regeneration of bone defects caused by trauma, infection, tumours or inherent genetic disorders is a clinical challenge that usually necessitates bone grafting materials. Autologous bone or autograft is still considered the clinical "gold standard" and the most effective method for bone regeneration. However, limited bone supply and donor site morbidity are the most important disadvantages of autografting. Improved biomaterials are needed to match the performance of autograft as this is still superior to that of synthetic bone grafts. Osteoinductive materials would be the perfect candidates for achieving this task. The aim of this article is to review the different groups of bone substitutes in terms of their most recently reported osteoinductive properties. The different factors influencing osteoinductivity by biomaterials as well as the mechanisms behind this phenomenon are also presented, showing that it is very limited compared to osteoinductivity shown by bone morphogenetic proteins (BMPs). Therefore, a new term to describe osteoinductivity by biomaterials is proposed. Different strategies for adding osteoinductivity (BMPs, stem cells) to bone substitutes are also discussed. The overall objective of this paper is to gather the current knowledge on osteoinductivity of bone grafting materials for the effective development of new graft substitutes that enhance bone regeneration.

A Comparison of the Process of Remodeling of Hydroxyapatite/Poly-D/L-Lactide and Beta-Tricalcium Phosphate in a Loading Site

Currently, the most commonly used bioresorbable scaffold is made of beta-tricalcium phosphate (β-TCP); it is hoped that scaffolds made of a mixture of hydroxyapatite (HA) and poly-D/L-lactide (PDLLA) will be able to act as novel bioresorbable scaffolds. The aim of this study was to evaluate the utility of a HA/PDLLA scaffold compared to β-TCP, at a loading site. Dogs underwent surgery to replace a section of tibial bone with a bioresorbable scaffold. After the follow-up period, the scaffold was subjected to histological analysis. The HA/PDLLA scaffold showed similar bone formation and superior cell and tissue infiltration compared to the β-TCP scaffold, as seen after Villanueva Goldner staining. Moreover, silver staining and immunohistochemistry for Von Willebrand factor and cathepsin K demonstrated better cell infiltration in the HA/PDLLA scaffold. The fibrous tissue and cells that had infiltrated into the HA/PDLLA scaffold tested positive for collagen type I and RUNX2, respectively, indicating that the tissue and cells that had infiltrated into the HA/PDLLA scaffold had the potential to differentiate into bone. The HA/PDLLA scaffold is therefore likely to find clinical application as a new bioresorbable scaffold.

Calcium Orthophosphate-Containing Biocomposites and Hybrid Biomaterials for Biomedical Applications

The state-of-the-art on calcium orthophosphate (CaPO4)-containing biocomposites and hybrid biomaterials suitable for biomedical applications is presented. Since these types of biomaterials offer many significant and exciting possibilities for hard tissue regeneration, this subject belongs to a rapidly expanding area of biomedical research. Through the successful combinations of the desired properties of matrix materials with those of fillers (in such systems, CaPO4 might play either role), innovative bone graft biomaterials can be designed. Various types of CaPO4-based biocomposites and hybrid biomaterials those are either already in use or being investigated for biomedical applications are extensively discussed. Many different formulations in terms of the material constituents, fabrication technologies, structural and bioactive properties, as well as both in vitro and in vivo characteristics have been already proposed. Among the others, the nano-structurally controlled biocomposites, those containing nanodimensional compounds, biomimetically fabricated formulations with collagen, chitin and/or gelatin, as well as various functionally graded structures seem to be the most promising candidates for clinical applications. The specific advantages of using CaPO4-based biocomposites and hybrid biomaterials in the selected applications are highlighted. As the way from a laboratory to a hospital is a long one and the prospective biomedical candidates have to meet many different necessities, the critical issues and scientific challenges that require further research and development are also examined.

In Vitro and in Vivo Studies of Novel Poly(D,L-lactic acid), Superhydrophilic Carbon Nanotubes, and Nanohydroxyapatite Scaffolds for Bone Regeneration

Poly(D,L-lactide acid, PDLLA) has been researched for scaffolds in bone regeneration. However, its hydrophobocity and smooth surface impedes its interaction with biological fluid and cell adhesion. To alter the surface characteristics, different surface modification techniques have been developed to facilitate biological application. The present study compared two different routes to produce PDLLA/superhydrophilic vertically aligned carbon nanotubes:nanohydroxyapatite (PDLLA/VACNT-O:nHAp) scaffolds. For this, we used electrodeposition and immersion in simulated body fluid (SBF). Characterization by goniometry, scanning electron microscopy, X-ray diffraction, and infrared spectroscopy confirmed the polymer modifications, the in vitro bioactivity, and biomineralization. Differential scanning calorimetry and thermal gravimetric analyses showed that the inclusion of VACNT-O:nHA probably acts as a nucleating agent increasing the crystallization rate in the neat PDLLA without structural alteration. Our results showed the formation of a dense nHAp layer on all scaffolds after 14 days of immersion in SBF solution; the most intense carbonated nHAp peaks observed in the PDLLA/VACNT-O:nHAp samples suggest higher calcium precipitation compared to the PDLLA control. Both cell viability and alkaline phosphatase assays showed favorable results, because no cytotoxic effects were present and all produced scaffolds were able to induce detectable mineralization. Bone defects were used to evaluate the bone regeneration; the confocal Raman and histological results confirmed high potential for bone applications. In vivo study showed that the PDLLA/VACNT-O:nHAp scaffolds mimicked the immature bone and induced bone remodeling. These findings indicate surface improvement and the applicability of this new nanobiomaterial for bone regenerative medicine.

Biomimetic nanocomposites to control osteogenic differentiation of human mesenchymal stem cells

The design of biomimetic nanomaterials that can directly influence the behavior of cells and facilitate the regeneration of tissues and organs has become an active area of research. Here, the production of materials based on nano-hydroxyapatite composites in scaffolds with nanofibrous and nanoporous topographies, designed to mimic the native bone matrix for applications in bone tissue engineering, is reported. Human mesenchymal stem cells grown on these nanocomposites are stimulated to rapidly produce bone minerals in situ, even in the absence of osteogenic supplements in the cell-culture medium. Nanocomposites comprising type I collagen and nano-hydroxyapatite are found to be especially efficient at inducing mineralization. When subcutaneously implanted into nude mice, this biomimetic nanocomposite is able to form a new bone matrix within only two weeks. Furthermore, when the nanocomposite is enriched with human mesenchymal stem cells before implantation, development of the bone matrix is accelerated to within one week. To the best of the authors' knowledge, this study provides the first clear in vitro and in vivo demonstration of osteoinduction controlled by the material characteristics of a biomimetic nanocomposite. This approach can potentially facilitate the translation of de novo bone-formation technologies to the clinic.

Preparation, characterization, and in vitro cytotoxicity evaluation of a novel anti-tuberculosis reconstruction implant

Background

Reconstruction materials currently used in clinical for osteoarticular tuberculosis (TB) are unsatisfactory due to a variety of reasons. Rifampicin (RFP) is a well-known and highly effective first-line anti-tuberculosis (anti-TB) drug. Poly-DL-lactide (PDLLA) and nano-hydroxyapatite (nHA) are two promising materials that have been used both for orthopedic reconstruction and as carriers for drug release. In this study we report the development of a novel anti-TB implant for osteoarticular TB reconstruction using a combination of RFP, PDLLA and nHA.

Methods

RFP, PDLLA and nHA were used as starting materials to produce a novel anti-TB activity implant by the solvent evaporation method. After manufacture, the implant was characterized and its biodegradation and drug release profile were tested. The in vitro cytotoxicity of the implant was also evaluated in pre-osteoblast MC3T3-E1 cells using multiple methodologies.

Results

A RFP/PDLLA/nHA composite was successfully synthesized using the solvent evaporation method. The composite has a loose and porous structure with evenly distributed pores. The production process was steady and no chemical reaction occurred as proved by Fourier Transform Infrared Spectroscopy (FTIR) and X-Ray Diffraction (XRD). Meanwhile, the composite blocks degraded and released drug for at least 12 weeks. Evaluation of in vitro cytotoxicity in MC3T3-E1 cells verified that the synthesized composite blocks did not affect cell growth and proliferation.

Conclusion

It is feasible to manufacture a novel bioactive anti-TB RFP/PDLLA/nHA composite by the solvent evaporation method. The composite blocks showed appropriate properties such as degradation, drug release and biosafety to MC3T3-E1 cells. In conclusion, the novel composite blocks may have great potential for clinical applications in repairing bone defects caused by osteoarticular TB.

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

Synthetic bone graft substitutes based on composites consisting of a polymer and a calcium-phosphate (CaP) ceramic are developed with the aim to satisfy both mechanical and bioactivity requirements for successful bone regeneration. In the present study, we have employed extrusion to produce a composite consisting of 50 wt.% poly(D,L-lactic acid) (PLA) and 50 wt.% nano-sized hydroxyapatite (HA) powder, achieving homogeneous distribution of the ceramic within the polymeric phase. In vitro, in both a simulated physiological saline (SPS) and a simulated body fluid (SBF), a greater weight loss was observed for PLA/HA than for PLA particles upon 12-week immersion. Furthermore, in SPS, a continuous release of calcium and phosphate from the composite was measured, whereas in SBF, decrease of the amount of the two ions in the solution was observed both for PLA and PLA/HA accompanied with the formation of a CaP layer on the surface. In vitro characterization of the composite bioactivity was performed by culturing human mesenchymal stromal cells (hMSCs) and assessing proliferation and osteogenic differentiation, with PLA as a control. Both PLA/HA composite and PLA control were shown to support hMSCs proliferation over a period of two weeks. In addition, the composite significantly enhanced alkaline phosphatase (ALP) activity of hMSCs in osteogenic medium as compared with the polymer control. A novel implant design was employed to develop implants from dense, extruded materials, suitable for testing osteoinductivity in vivo. In a preliminary study in dogs, PLA/HA composite implants induced heterotopic bone formation upon 12-week intramuscular implantation in all animals, in contrast to PLA control, which was not osteoinductive. Unlike in vitro, a more pronounced degradation of PLA was observed in vivo as compared with PLA/HA composite.

Influence of polymer molecular weight in osteoinductive composites for bone tissue regeneration

In bone tissue regeneration, certain polymer and calcium-phosphate-based composites have been reported to enhance some biological surface phenomena, facilitating osteoinduction. Although the crucial role of inorganic fillers in heterotopic bone formation by such materials has been shown, no reports have been published on the potential effects the polymer phase may have. The present work starts from the assumption that the polymer molecular weight regulates the fluid uptake, which determines the hydrolysis rate and the occurrence of biological surface processes. Here, two composites were prepared by extruding two different molecular weight L/D,L-lactide copolymers with calcium phosphate apatite. The lower molecular weight copolymer allowed larger fluid uptake in the composite thereof, which was correlated with a higher capacity to adsorb proteins in vitro. Further, the large fluid absorption led to a quicker composite degradation that generated rougher surfaces and enhanced ion release. Following intramuscular implantation in sheep, only the composite with the lower molecular weight polymer could induce heterotopic bone formation. Besides influencing the biological potential of composites, the molecular weight also regulated their viscoelastic behaviour under cyclic stresses. The results lead to the conclusion that designing biomaterials with appropriate physico-chemical characteristics is crucial for bone tissue regeneration in mechanical load-bearing sites.

An overview of recent advances in designing orthopedic and craniofacial implants

Great deal of research is still going on in the field of orthopedic and craniofacial implant development to resolve various issues being faced by the industry today. Despite several disadvantages of the metallic implants, they continue to be used, primarily because of their superior mechanical properties. In order to minimize the harmful effects of the metallic implants and its by-products, several modifications are being made to these materials, for instance nickel-free stainless steel, cobalt-chromium and titanium alloys are being introduced to eliminate the toxic effects of nickel being released from the alloys, introduce metallic implants with lower modulus, reduce the cost of these alloys by replacing rare elements with less expensive elements etc. New alloys like tantalum, niobium, zirconium, and magnesium are receiving attention given their satisfying mechanical and biological properties. Non-oxide ceramics like silicon nitride and silicon carbide are being currently developed as a promising implant material possessing a combination of properties such as good wear and corrosion resistance, increased ductility, good fracture and creep resistance, and relatively high hardness in comparison to alumina. Polymer/magnesium composites are being developed to improve mechanical properties as well as retain polymer's property of degradation. Recent advances in orthobiologics are proving interesting as well. This paper thus deals with the latest improvements being made to the existing implant materials and includes new materials being introduced in the field of biomaterials.

Bone tissue engineering: recent advances and challenges

The worldwide incidence of bone disorders and conditions has trended steeply upward and is expected to double by 2020, especially in populations where aging is coupled with increased obesity and poor physical activity. Engineered bone tissue has been viewed as a potential alternative to the conventional use of bone grafts, due to their limitless supply and no disease transmission. However, bone tissue engineering practices have not proceeded to clinical practice due to several limitations or challenges. Bone tissue engineering aims to induce new functional bone regeneration via the synergistic combination of biomaterials, cells, and factor therapy. In this review, we discuss the fundamentals of bone tissue engineering, highlighting the current state of this field. Further, we review the recent advances of biomaterial and cell-based research, as well as approaches used to enhance bone regeneration. Specifically, we discuss widely investigated biomaterial scaffolds, micro- and nano-structural properties of these scaffolds, and the incorporation of biomimetic properties and/or growth factors. In addition, we examine various cellular approaches, including the use of mesenchymal stem cells (MSCs), embryonic stem cells (ESCs), adult stem cells, induced pluripotent stem cells (iPSCs), and platelet-rich plasma (PRP), and their clinical application strengths and limitations. We conclude by overviewing the challenges that face the bone tissue engineering field, such as the lack of sufficient vascularization at the defect site, and the research aimed at functional bone tissue engineering. These challenges will drive future research in the field.

Controlling dynamic mechanical properties and degradation of composites for bone regeneration by means of filler content

Bone tissue is a dynamic composite system that adapts itself, in response to the surrounding daily (cyclic) mechanical stimuli, through an equilibrium between growth and resorption processes. When there is need of synthetic bone grafts, the biggest issue is to support bone regeneration without causing mechanically-induced bone resorption. Apart from biological properties, such degradable materials should initially support and later leave room to bone formation. Further, dynamic mechanical properties comparable to those of bone are required. In this study we prepared composites comprising calcium phosphate and L-lactide/D-lactide copolymer in various content ratios using the extrusion method. We evaluated the effect of the inorganic filler amount on the polymer phase (i.e. on the post-extrusion intrinsic viscosity). We then studied their in vitro degradation and dynamic mechanical properties (in dry and humid conditions). By increasing the filler content, we observed significant decrease of the intrinsic viscosity of the polymer phase during the extrusion process. Composites containing higher amounts of apatite had faster degradation, and were also mechanically stiffer. But, due to the lower intrinsic viscosity of their polymer phase, they had larger damping properties. Besides this, higher amounts of apatite also rendered the composites more hydrophilic letting them absorb more water and causing them the largest decrease in stiffness. These results show the importance of filler content in controlling the properties of such composites. Further, in this study we observed that the viscoelastic properties of the composite containing 50wt% apatite were comparable to those of dry human cortical bone.

Hydroxyapatite bioactivated bacterial cellulose promotes osteoblast growth and the formation of bone nodules

The goal of this study was to investigate the feasibility of bacterial cellulose (BC) scaffold to support osteoblast growth and bone formation. BC was produced by culturing Acetobacter xylinum supplemented with hydroxyapatite (HA) to form BC membranes (without HA) and BC/HA membranes. Membranes were subjected to X-ray photoelectron spectroscopy (XPS) analysis to determine surface element composition. The membranes were further used to evaluate osteoblast growth, alkaline phosphatase activity and bone nodule formation. BC was free of calcium and phosphate. However, XPS analysis revealed the presence of both calcium (10%) and phosphate (10%) at the surface of the BC/HA membrane. Osteoblast culture showed that BC alone was non-toxic and could sustain osteoblast adhesion. Furthermore, osteoblast adhesion and growth were significantly (p ≤0.05) increased on BC/HA membranes as compared to BC alone. Both BC and BC/HA membranes improved osteoconductivity, as confirmed by the level of alkaline phosphatase (ALP) activity that increased from 2.5 mM with BC alone to 5.3 mM with BC/HA. BC/HA membranes also showed greater nodule formation and mineralization than the BC membrane alone. This was confirmed by Alizarin red staining (ARS) and energy dispersive X-ray spectroscopy (EDX). This work demonstrates that both BC and BC/HA may be useful in bone tissue engineering.

Poly(lactide-co-glycolide)-Hydroxyapatite Composites: The Development of Osteoinductive Scaffolds for Bone Regenerative Engineering

Regenerative engineering represents a new multidisciplinary paradigm to engineer complex tissues, organs, or organ systems through the integration of tissue engineering with advanced materials science, stem cell science and developmental biology. While possessing elements of tissue engineering, regenerative medicine, and morphogenesis, regenerative engineering is distinct from these individual disciplines since it specifically focuses on the integration and subsequent response of stem cells to biomaterials. One goal of regenerative engineering is the design of materials capable of inducing associated cells toward highly specialized functions. For example, the interaction of cells with calcium phosphate surfaces has proven to be an important signaling modality in promoting osteogenic differentiation. A biodegradable polymer-ceramic composite system has been developed from poly(lactide-co-glycolide) and in situ synthesized hydroxyapatite based on the three-dimensional sintered microsphere matrix platform. We have systematically optimized scaffold physico-chemical, mechanical, and structural properties for bone tissue regeneration applications by varying several parameters such as solution pH, polymer:ceramic ratio, sintering time and sintering temperature. The bioactivity of composite scaffolds is attributed to their ability to deliver calcium ions to surrounding medium and allow for reprecipitation of calcium phosphate on the scaffold surface. Furthermore, the composite scaffolds have demonstrated increased loading capacity of osteoinductive growth factor (BMP-2) and a more sustained release profile due to a greater number of adsorption sites provided by the ionic calcium and phosphate groups as well as a larger matrix surface area. In vitro cell studies were performed to investigate the efficacy of this composite system to induce osteogenic differentiation of human adipose-derived stem cells. Cells cultured on the ceramic containing scaffolds exhibited significantly higher expression of osteoblastic markers and greater extracellular matrix mineralization than non-ceramic containing scaffolds, indicating the potential for the ceramic phase to promote osteogenic differentiation. In addition, loaded BMP-2 retained its bioactivity as a mitogen and osteoinductive agent during the differentiation of adipose-derived stem cells into mature osteoblasts. In vivo evaluation using a critical-sized ulnar defect model in New Zealand white rabbits demonstrated the ability of composite scaffolds to support cellular infiltration throughout the scaffold pore structure and vascularization of new tissue, as well as facilitate formation of newly mineralized bone tissue. The work described herein provides strong evidence for the potential of polymer-ceramic composite scaffolds to function as osteoinductive bone graft substitutes, and paves the way for future development of advanced tissue-inducing materials.

Fabrication and in vivo osteogenesis of biomimetic poly(propylene carbonate) scaffold with nanofibrous chitosan network in macropores for bone tissue engineering

A biomimetic poly(propylene carbonate) (PPC) porous scaffold with nanofibrous chitosan network within macropores (PPC/CSNFs) for bone tissue engineering was fabricated by a dual solid-liquid phase separation technique. PPC scaffold with interconnected solid pore wall structure was prepared by the first phase separation, which showed a high porosity of 91.9% and a good compressive modulus of 14.2 ± 0.56 MPa, respectively. By the second phase separation, nanofibrous chitosan of 50-500 nm in diameter was formed in the macropores with little influence on the pore structure and the mechanical properties of PPC scaffold. The nanofibrous chitosan content was calculated to be 9.78% by elemental analysis. After incubation in SBF for 14 days, more apatite crystals were deposited on the pore surface as well as the nanofibrous chitosan surface of PPC/CSNFs scaffold compared with PPC scaffold. The in vitro culture of bone mesenchymal stem cells showed that PPC/CSNFs scaffold exhibited a better cell viability than PPC scaffold. After implantation in rabbits for 16 weeks, the defect was entirely repaired by PPC/CSNFs scaffold, as opposed to the incomplete healing for PPC scaffold. It indicated that PPC/CSNFs scaffold showed a faster in vivo osteogenesis rate than PPC scaffold. Hereby, PPC/CSNFs scaffold will be a potential candidate for bone tissue engineering.

Osteopontin functionalization of hydroxyapatite nanoparticles in a PDLLA matrix promotes bone formation

We studied the osteoconductive tissue response of hydroxyapatite (HA) nanoparticles functionalized with osteopontin (OPN) in a matrix of poly-D,L-lactic-acid (PDLLA). In a canine endosseus 0.75-mm gap implant model, we tested the osteointegrative impact of the OPN functionalized composite as an implant coating, and a non-functionalized composite was used as reference control. During the four weeks of observation, the OPN functionalized composite coating significantly increased the formation of new bone in the porosities of the implant, but no differences were observed in the gap. The study provides evidence of its potential use either alone or in combination with other osteoconductive compounds.

Biocomposites and hybrid biomaterials based on calcium orthophosphates

The state-of-the-art of biocomposites and hybrid biomaterials based on calcium orthophosphates that are suitable for biomedical applications is presented in this review. Since these types of biomaterials offer many significant and exciting possibilities for hard tissue regeneration, this subject belongs to a rapidly expanding area of biomedical research. Through successful combinations of the desired properties of matrix materials with those of fillers (in such systems, calcium orthophosphates might play either role), innovative bone graft biomaterials can be designed. Various types of biocomposites and hybrid biomaterials based on calcium orthophosphates, either those already in use or being investigated for biomedical applications, are extensively discussed. Many different formulations, in terms of the material constituents, fabrication technologies, structural and bioactive properties as well as both in vitro and in vivo characteristics, have already been proposed. Among the others, the nanostructurally controlled biocomposites, those containing nanodimensional compounds, biomimetically fabricated formulations with collagen, chitin and/or gelatin as well as various functionally graded structures seem to be the most promising candidates for clinical applications. The specific advantages of using biocomposites and hybrid biomaterials based on calcium orthophosphates in the selected applications are highlighted. As the way from the laboratory to the hospital is a long one, and the prospective biomedical candidates have to meet many different necessities, this review also examines the critical issues and scientific challenges that require further research and development.

Biomedical Applications of Biodegradable Polymers

Utilization of polymers as biomaterials has greatly impacted the advancement of modern medicine. Specifically, polymeric biomaterials that are biodegradable provide the significant advantage of being able to be broken down and removed after they have served their function. Applications are wide ranging with degradable polymers being used clinically as surgical sutures and implants. In order to fit functional demand, materials with desired physical, chemical, biological, biomechanical and degradation properties must be selected. Fortunately, a wide range of natural and synthetic degradable polymers has been investigated for biomedical applications with novel materials constantly being developed to meet new challenges. This review summarizes the most recent advances in the field over the past 4 years, specifically highlighting new and interesting discoveries in tissue engineering and drug delivery applications.

A model for tissue engineering applications: femoral critical size defect in immunodeficient mice

Animal models for preclinical functionality assays lie midway between in vitro systems such as cell culture and actual clinical trials. We have developed a novel external fixation device for femoral critical size defect (CSD) in the femurs of immunodeficient mice as an experimental model for studying bone regeneration and bone tissue engineering. The external fixation device comprises four pointed rods and dental acrylic paste. A segmental bone defect (2 mm) was created in the midshaft of the mouse femur. The CSD in the femur of the mice were either left untreated or treated with a bone allograft, a cell-scaffold construct, or a scaffold-only construct. The repair and healing processes of the CSD were monitored by digital x-ray radiography, microcomputed tomography, and histology. Repair of the femoral CSD was achieved with the bone allografts, and partial repair of the femoral CSD was achieved with the cell scaffold and the scaffold-only constructs. No repair of the nongrafted femoral CSD was observed. Our results establish the feasibility of this new mouse femoral model for CSD repair of segmental bone using a simple stabilized external fixation device. The model should prove especially useful for in vivo preclinical proof-of-concept studies that involve cell therapy-based technologies for bone tissue engineering applications in humans.

A bioactive and bioresorbable porous cubic composite scaffold loaded with bone marrow aspirate: a potential alternative to autogenous bone grafting

STUDY DESIGN

Experimental animal study.

OBJECTIVE

To investigate the osteogenic properties of a particulate uncalcined, unsintered hydroxyapatite/polydllactide (u-HA/PdlLA) composite scaffold loaded with bone marrow aspirate (BMA).

SUMMARY OF BACKGROUND DATA

Because of the high morbidity associated with bone graft harvesting, current research in spine surgery has largely focused on bone graft alternatives involving a combination of scaffolds and osteogenic substances. BMA is obtained by a simple and relatively noninvasive method and can easily be clinically applied as an osteogenic material. However, few studies have reported successful posterolateral spinal fusion (PLF) with BMA-loaded synthetic materials.

METHODS

Porous u-HA/PdlLA composites loaded with BMA were used as bone graft substitutes. In experiment 1, porous u-HA/PdlLA cylinders containing or lacking BMA were implanted in rabbit muscles. They were retrieved 4, 8, and 12 weeks after implantation, and ectopic bone formation was histologically evaluated. In experiment 2, 48 rabbits underwent PLF with 1 of 4 bone grafts: autogenous bone (group 1); single-strip u-HA/PdlLA alone (group 2); morselized u-HA/PdlLA + BMA (group 3); or single-strip u-HA/PdlLA + BMA (group 4). After 12 weeks, fusion was assessed by manual palpation, microcomputed tomography, mechanical tests, and histologic examination.

RESULTS

In experiment 1, ectopic bone formation was observed in BMA-loaded u-HA/PdlLA, and the new bone area increased until 12 weeks after implantation. In experiment 2, the fusion rates in groups 1, 2, 3, and 4 were 58.3%, 16.7%, 66.7%, and 91.7%, respectively, as determined by manual palpation, and 66.7%, 16.7%, 75.0%, and 91.7%, respectively, as determined by microcomputed tomography. The mechanical strength was significantly greater in group 4 than in the other groups (P < 0.05).

CONCLUSION

Conclusion. Our results indicate that BMA-loaded porous μ-HA/PdlLA is an effective alternative to autogenous bone grafts. The structure and composition of porous u-HA/PdlLA render it an effective scaffold for BMA.

Hydroxyapatite nanoparticles in poly-D,L-lactic acid coatings on porous titanium implants conducts bone formation

It is well established in the field of biomaterials that hydroxyapatite (HA) may provide interesting osteoconductive properties. In this study, we investigated the osseointegrational effect of a 50/50 vol % composite of HA nanoparticles and poly-D,L-lactic acid (PDLLA) coated on model titanium bone implants in an in vivo animal model. The aim is to evaluate how the addition of HA to PDLLA may improve the bone formation and initial fixation of the implant. Two titanium implants coated with the PDLLA/HA composite and pure PDLLA, respectively, were implanted bilaterally in proximal part of humeri with a 2-mm peri-implant gap in 10 sheep. After 12 weeks, the remains of the coatings were present on 20.3 and 19.8% of PDLLA/HA composite- and PDLLA-coated implants, respectively. It was observed that newly formed bone (39.3%) and fibrous tissue (58.3%) had replaced the PDLLA/HA composite, whereas pure PDLLA was replaced almost completely by fibrous tissue (96.2%). Consequently, the PDLLA/HA composite-coated implants were better fixated as confirmed by push-out tests. Using quantification of peri-implant tissue and implant fixation as parameters, the present findings, therefore, clearly reveal that the addition of nanoparticulate HA to a PDLLA coating on titanium implants increases osseointegration.

Cell-scaffold transplant of hydrogel seeded with rat bone marrow progenitors for bone regeneration

Bone is the second most frequently transplanted tissue in humans and efforts are focused on developing cell-scaffold constructs which can be employed for autologous implantation in place of allogenic transplants. The objective of the present study was to examine the efficacy of a gelatin-based hydrogel scaffold to support osteogenic differentiation of rat bone marrow-derived mesenchymal stem cells (MSCs) and its application in a cranial defect model. MSCs which were cultured on hydrogel under osteogenic conditions demonstrated typical osteogenic differentiation which included cluster formation with positive Alizarin Red S staining, sedimentation of calcium phosphate as defined by SEM and EDS spectroscopy and expression of mRNA osteogenic markers. Empty scaffolds or those containing either differentiated cells or naïve cells were implanted into cranial defects of athymic nude mice and the healing process was followed by μCT. Substantial bone formation (65%) was observed with osteogenic cell-scaffold constructs when compared to the naïve cell construct (25%) and the cell free scaffold (10%). Results demonstrated the potential of hydrogel scaffolds to serve as a supportive carrier for bone marrow-derived MSCs.

Hematopoiesis in regenerated bone marrow within hydroxyapatite scaffold

We examined whether regenerated bone marrow (BM) with BM-derived stromal cells (BMSCs) on hydroxyapatite (HA) scaffolds can reconstitute the functional niche. Ly5.2 BMSCs on HA scaffolds were implanted s.c. onto the backs of Ly5.2 recipient mice. Lineage negative Ly5.1 BM cells expressing luciferase (luc) were i.v. administered into the recipient mice. Eight weeks after primary transplantation, secondary implantation was performed; the scaffolds removed from the first recipient mice were s.c. implanted into secondary recipient mice. Luc+ cells were detected in the scaffolds for 6 mo after secondary implantation. Injection of G-CSF resulted in wide distribution of bioluminescence from the original scaffolds to the whole body. Even after removing the scaffolds from the secondary recipient mice, luc+ cells were emitted by G-CSF stimulation, indicating that regenerated BM is capable of supporting hematopoietic stem cells (HSCs) and delivering HSCs to native BM in vivo. These data suggest that the functional niche is reconstituted at least partly and that regenerated BM on the scaffold may be used as a portable source of HSCs.

Material properties and osteogenic differentiation of marrow stromal cells on fiber-reinforced laminated hydrogel nanocomposites

The fibrils in the bone matrix are glued together by extracellular matrix proteins to form laminated structures (osteons) to provide elasticity and a supportive substrate for osteogenesis. The objective of this work was to investigate material properties and osteogenic differentiation of bone marrow stromal (BMS) cells seeded on osteon-mimetic fiber-reinforced hydrogel/apatite composites. Layers of electrospun poly(l-lactide) fiber mesh coated with a poly(lactide-co-ethylene oxide fumarate) (PLEOF) hydrogel precursor solution were stacked and pressed together, and crosslinked to produce a laminated fiber-reinforced composite. Hydroxyapatite (HA) nanocrystals were added to the precursor solution to produce an osteoconductive matrix for BMS cells. Acrylamide-terminated Arg-Gly-Asp (RGD) peptide (Ac-GRGD) was conjugated to the PLEOF/HA hydrogel phase to promote focal point adhesion of BMS cells. Laminates were characterized with respect to the Young's modulus, degradation kinetics and osteogenic differentiation of BMS cells. The moduli of the laminates under dry and wet conditions were significantly higher than those of the fiber mesh and PLEOF/HA hydrogel, and within the range of values reported for wet human cancellous bone. At days 14 and 21, alkaline phosphatase (ALPase) activity of the laminates was significantly higher than those of the fiber mesh and hydrogel. Lamination significantly increased the extent of mineralization of BMS cells and laminates with HA and conjugated with RGD (Lam-RGD-HA) had 2.7-, 3.5- and 2.8-fold higher calcium content (compared to laminates without HA or RGD) after 7, 14 and 21days, respectively. The Lam-RGD-HA group had significantly higher expression of osteopontin and osteocalcin compared to the hydrogel or laminates without HA or RGD, consistent with the higher ALPase activity and calcium content of Lam-RGD-HA. Laminated osteon-mimetic structures have the potential to provide mechanical strength to the regenerating region as well as supporting the differentiation of progenitor cells to the osteogenic lineage.

A tissue-like construct of human bone marrow MSCs composite scaffold support in vivo ectopic bone formation

Biocompatible and osteoconductive cell-scaffold constructs comprise the first and most important step towards successful in vivo bone repair. This study reports on a new cell-scaffold construct composed of gelatin-based hydrogel and ceramic (CaCO(3)/beta-TCP) particles loaded with human MSCs producing a tissue-like construct applied as a transplant for in vivo bone formation. Bone marrow-derived human MSCs were cultured in osteogenic induction medium. 5 x 10(5) (P(2)) cells were loaded on a mixture of hydrogel microspheres and ceramic particles, cultured in a rotating dynamic culture for up to 3 weeks. Both hydrogel microspheres and ceramic particles coalesced together to form a tissue-like construct, shown by histology to contain elongated spindle-like cells forming the new tissue between the individual particles. Cell proliferation and cell viability were confirmed by Alamar blue assay and by staining with CFDA, respectively. FACS analysis conducted before loading the cells, and after formation of the construct, revealed that the profile of cell surface markers remained unchanged throughout the dynamic culture. The osteogenic potential of the cells composing the tissue-like construct was further validated by subcutaneous transplants in athymic nude mice. After 8 weeks a substantial amount of new bone formation was observed in the cell-construct transplants, whereas no bone formation was observed in transplants containing no cells. This new cell construct provides a system for in vivo bone transplants. It can be tailored for a specific size and shape as needed for various transplant sites and for all aspects of regenerative medicine and biomaterial science.

Hybrid structure in PCL-HAp scaffold resulting from biomimetic apatite growth

Polymer-ceramic composites are favourite candidates when aiming to replace bone tissue. We present here scaffolds made of polycaprolactone-hydroxyapatite (PCL-HAp) composites, and investigate in vitro mineralisation of the scaffolds in SBF after or without a nucleation treatment. In vitro bioactivity is enhanced by HAp incorporation as well as by nucleation treatment, as demonstrated by simulated body fluid (SBF) mineralization. Surprisingly, we obtained a hybrid interconnected organic-inorganic structure, as a result of micropore invasion by biomimetic apatite, which results in a mechanical strengthening of the material after two weeks of immersion in SBF92. The presented scaffolds, due to their multiple qualities, are expected to be valuable supports for bone tissue engineering.