Interplay between cellular activity and three-dimensional scaffold-cell constructs with different foam structure processed by electron beam melting

Process-structure-biofunctional paradigm in cellular structured implants: an overview and perspective on the synergy between additive manufacturing, bio-mechanical behaviour and biological functions

The overview describes the synergy between biological sciences and cellular structures processed by additive manufacturing to elucidate the significance of cellular structured implants in eliminating stress shielding and in meeting the bio-mechanical property requirements of elastic modulus, impact resistance, and fatigue strength in conjunction with the biological functionality. The convergence of additive manufacturing, computer-aided design, and structure-property relationships is envisaged to provide the solution to the current day challenges in the biomedical arena. The traditional methods of fabrication of biomedical devices including casting and mechanical forming have limitations because of the mismatch in micro/microstructure, mechanical, and physical properties with the host site. Additive manufacturing of cellular structured alloys via electron beam melting and laser powder bed fusion has benefits of fabricating patient-specific design that is obtained from the computed tomography scan of the defect site. The discussion in the overview consists of two aspects - the first one describes the underlying reason that motivated 3D printing of implants from the perspective of minimising stress shielding together with the mechanical property requirements, where the mechanical properties of cellular structured implants depend on the cellular architecture and percentage cellular porosity. The second aspect focuses on the biological response of cellular structured devices.

Study of the Effect of Anodic Oxidation on the Corrosion Properties of the Ti6Al4V Implant Produced from SLM

Additive technologies allowed for the development of medicine and implantology, enabling the production of personalized and highly porous implants. Although implants of this type are used clinically, they are usually only heat treated. Surface modification using electrochemical methods can significantly improve the biocompatibility of biomaterials used for implants, including printed ones. The study examined the effect of anodizing oxidation on the biocompatibility of a porous implant made of Ti6Al4V by the SLM method. The study used a proprietary spinal implant intended for the treatment of discopathy in the c4–c5 section. As part of the work, the manufactured implant was assessed in terms of compliance with the requirements for implants (structure testing—metallography) and the accuracy of the pores produced (pore size and porosity). The samples were subjected to surface modification using anodic oxidation. The research was carried out for 6 weeks in in vitro conditions. Surface topographies and corrosion properties (corrosion potential, ion release) were compared for unmodified and anodically oxidized samples. The tests showed no effect of anodic oxidation on the surface topography and improved corrosion properties. Anodic oxidation stabilized the corrosion potential and limited the release of ions to the environment.

Clinical application of 3D-printed biodegradable lumbar interbody cage (polycaprolactone/β-tricalcium phosphate) for posterior lumbar interbody fusion

A novel 3D-printed biodegradable cage composed of polycaprolactone (PCL) and beta-tricalcium phosphate (β-TCP) in a mass ratio of 50:50, with stable resorption patterns and mechanical strength has been developed for lumbar interbody fusion. This is a prospective cohort study to evaluate the short- and mid-term safety and efficacy of this biodegradable cage in posterior lumbar interbody fusion (PLIF) surgery. This was a prospective single-arm pilot clinical trial in 22 patients with a follow-up time of 1, 3, 6, and 12 months, postoperatively. Clinical outcomes were assessed using the Japanese Orthopedic Association Back Pain Evaluation Questionnaire (JOABPEQ) and Visual analogue scale (VAS) for leg pain and low back pain. Radiological examination included X-ray, CT scan, and three-dimensional reconstruction to evaluate surgical indications, intervertebral space height (ISH), intervertebral bone fusion and cage degradation. A total of 22 patients was included, with an average age of 53.5 years. Among 22 patients, one patient lost to follow-up and one patient withdrew from the clinical trial because of cage retropulsion. The remaining 20 patients showed significant improvement in clinical and imaging outcomes compared to the preoperative period. The overall mean VAS for back decreased from 5.85 ± 0.99 preoperatively to 1.15 ± 0.86 at the 12-month follow-up (p < .001); the VAS for leg decreased from 5.75 ± 1.11 to 1.05 ± 0.76 (p < .001); the JOA score improved from 13.8 ± 2.64 to 26.45 ± 2.46 (p < .001). The mean intervertebral space height (ISH) increased from 11.01 ± 1.75 mm preoperatively to 12.67 ± 1.89 mm at the 12-month follow-up and the bone fusion reached 95.2% (20/21 disc segments). Partial resorption (inferior to 50% compared with the initial cage size) were found in all cages (21/21). The clinical and radiological assessments showed that the application of 3D-printed biodegradable PCL/β-TCP cages in PLIF yielded satisfactory results at the 12-month follow-up. In the future, long-term clinical observations and controlled clinical trials are required to further validate the safety and efficacy of this novel cage.

Designing of gradient scaffolds and their applications in tissue regeneration

Gradient scaffolds are isotropic/anisotropic three-dimensional structures with gradual transitions in geometry, density, porosity, stiffness, etc., that mimic the biological extracellular matrix. The gradient structures in biological tissues play a major role in various functional and metabolic activities in the body. The designing of gradients in the scaffold can overcome the current challenges in the clinic compared to conventional scaffolds by exhibiting excellent penetration capacity for nutrients & cells, increased cellular adhesion, cell viability & differentiation, improved mechanical stability, and biocompatibility. In this review, the recent advancements in designing gradient scaffolds with desired biomimetic properties, and their implication in tissue regeneration applications have been briefly explained. Furthermore, the gradients in native tissues such as bone, cartilage, neuron, cardiovascular, skin and their specific utility in tissue regeneration have been discussed in detail. The insights from such advances using gradient-based scaffolds can widen the horizon for using gradient biomaterials in tissue regeneration applications.

Design of a Novel Trabecular Acetabular Cup and Selective Laser Melting Fabrication

The acetabular cups used in total hip arthroplasty are mostly made of dense metal materials with an elastic moduli much higher than that of human bone. This leads to stress shielding after implantation, which may cause aseptic loosening of the implant. Selective laser melting (SLM) technology allows us to produce tiny and complex porous structures and to reduce the elastic moduli of dense metals, thereby avoiding stress shielding. In the present study, rhombic dodecahedron porous structures with cell sizes of 1 mm, 1.5 mm, and 2 mm were designed. The strut diameter was changed to ensure that the porosity and pore size would meet the bone ingrowth requirements. Then, porous Ti6Al4V alloy specimens were printed using SLM, and compressive tests were carried out. The results showed that the compressive strength and elastic modulus values of the specimens with a cell size of 1.5 mm were in the range of 78.16-242.94 MPa and 1.74-4.17 GPa, respectively, which are in line with the mechanical properties of human cortical bone. Finite element analysis of a total hip joint model was carried out to simulate gait, and the surface of the trabecular acetabular cup was divided into 10 regions according to the stress distribution, with the stress interval in the range of 37.44-219.24 MPa. According to the compression test results, the gradient structure of Ti6Al4V alloy with different porosity was designed for trabecular coating. The gradient porous structure meets the mechanical requirements and is closer to the natural structure of human bone than the uniformly distributed porous structure.

Sulfuretin exerts anti-depressive effects in the lipopolysaccharide-induced depressive mouse models

BACKGROUND

Herb-derived therapeutics is an attractive strategy to treat depression. Here we report the ameliorating effects of Sulfuretin, an anti-inflammatory compound in a depressive mouse model.

METHODS

Immobility times were obtained in the tail suspension test and forced swim test performed from day 14 to day 16. Quantitative real-time PCR (qRT-PCR) and Western blot were used to measure brain-derived neurotrophic factor (BDNF) and the extracellular signal-regulated kinase (ERK) pathway of the hippocampus tissue on day 17. SL327 was used to block the ERK pathway in mice to evaluate the interaction between Sulfuretin and the ERK pathway. Mice were treated with Sulfuretin for 14 days before lipopolysaccharide (LPS) injection (0.83 mg/kg/day, i.p.) for two days.

RESULTS

Behavior tests showed that Sulfuretin dose-dependently decreased immobility times correlated with depression symptoms. BDNF levels and ERK signaling were significantly restored in the Sulfuretin-treated mice, showing the improvement of brain function. Blocking the p-ERK signaling abrogated the effects of Sulfuretin in improving behaviors and levels of BDNF.

CONCLUSION

Our study suggests that Sulfuretin exhibits anti-depressive function in LPS-induced depressive mice, in which the ERK signaling plays an essential role.

Revealing the influence of electron beam melted Ti-6Al-4V scaffolds on osteogenesis of human bone marrow-derived mesenchymal stromal cells

Porous Titanium-6Aluminum-4Vanadium scaffolds made by electron beam-based additive manufacturing (AM) have emerged as state-of-the-art implant devices. However, there is still limited knowledge on how they influence the osteogenic differentiation of bone marrow-derived mesenchymal stromal cells (BMSCs). In this study, BMSCs are cultured on such porous scaffolds to determine how the scaffolds influence the osteogenic differentiation of the cells. The scaffolds are biocompatible, as revealed by the increasing cell viability. Cells are evenly distributed on the scaffolds after 3 days of culturing followed by an increase in bone matrix development after 21 days of culturing. qPCR analysis provides insight into the cells' osteogenic differentiation, where RUNX2 expression indicate the onset of differentiation towards osteoblasts. The COL1A1 expression suggests that the differentiated osteoblasts can produce the osteoid. Alkaline phosphatase staining indicates an onset of mineralization at day 7 in OM. The even deposits of calcium at day 21 further supports a successful bone mineralization. This work shines light on the interplay between AM Ti64 scaffolds and bone growth, which may ultimately lead to a new way of creating long lasting bone implants with fast recovery times.

The Marine Polysaccharide Ulvan Confers Potent Osteoinductive Capacity to PCL-Based Scaffolds for Bone Tissue Engineering Applications

Hybrid composites of synthetic and natural polymers represent materials of choice for bone tissue engineering. Ulvan, a biologically active marine sulfated polysaccharide, is attracting great interest in the development of novel biomedical scaffolds due to recent reports on its osteoinductive properties. Herein, a series of hybrid polycaprolactone scaffolds containing ulvan either alone or in blends with κ-carrageenan and chondroitin sulfate was prepared and characterized. The impact of the preparation methodology and the polysaccharide composition on their morphology, as well as on their mechanical, thermal, water uptake and porosity properties was determined, while their osteoinductive potential was investigated through the evaluation of cell adhesion, viability, and osteogenic differentiation of seeded human adipose-derived mesenchymal stem cells. The results verified the osteoinductive ability of ulvan, showing that its incorporation into the polycaprolactone matrix efficiently promoted cell attachment and viability, thus confirming its potential in the development of biomedical scaffolds for bone tissue regeneration applications.

Powder-Based 3D Printing for the Fabrication of Device with Micro and Mesoscale Features

Customized manufacturing of a miniaturized device with micro and mesoscale features is a key requirement of mechanical, electrical, electronic and medical devices. Powder-based 3D-printing processes offer a strong candidate for micromanufacturing due to the wide range of materials, fast production and high accuracy. This study presents a comprehensive review of the powder-based three-dimensional (3D)-printing processes and how these processes impact the creation of devices with micro and mesoscale features. This review also focuses on applications of devices with micro and mesoscale size features that are created by powder-based 3D-printing technology.

Pure polylysine-based foamy scaffolds and their interaction with MC3T3-E1 cells and osteogenesis

Polypeptide-derived copolymers have widely been exploited for drug/gene delivery due to their pendant functional groups and non-toxic degradation products. However, fabrication of polypeptide-based scaffolds for tissue engineering has seldom been reported. In this study, foamy poly(N _ε -benzyl formateoxycarbonyl-L-Lysine) (PZL) and poly(N _ε -benzyl formateoxycarbonyl-L-lysine-co-L-phenylalanine) (PZLP) scaffolds were successfully prepared by a combination of ring-opening polymerization of α-amino acid N-carboxyanhydride and negative porous NaCl templating approach. The physicochemical properties of these scaffolds including glass transition temperature, contact angle, compression modulus and degradation behavior were characterized. Both in vitro and in vivo biocompatibility of the scaffolds were evaluated by MC3T3-E1 cell culture and SD subcutaneous model, respectively. The results from live-dead staining, MTT and ALP activity assays indicated that PZL scaffolds were more conducive to the adhesion, proliferation and osteoblastic differentiation of MC3T3-E1 cells compared to PZLP scaffolds in the initial culture period due to their specific surface properties. While porous structure rather than surface properties of scaffolds played a decisive role in the later stage of cell culture. The results of in vivo studies including H&E, Masson's trichrome and CD34 staining further demonstrated that PZL scaffolds supported the ingrowth of microvessels than PZLP scaffolds due to their surface property difference. Collectively, PZL scaffolds displayed good biocompatibility and could be a promising candidate for tissue engineering application.

Degradation behavior, cytotoxicity, hemolysis, and antibacterial properties of electro-deposited Zn-Cu metal foams as potential biodegradable bone implants

Zinc (Zn) alloys have attracted much attention for biomedical applications due to their biodegradability, biocompatibility, and biological functionalities. Zn alloy foams have high potential to be used as regenerative medical implants by virtue of their porous structure, which allows new bone tissue ingrowth, their low elastic modulus approximating that of natural bone, and their biodegradation, which eliminates the need for follow-up surgery to remove the implants after bone tissue healing. In this context, a biodegradable Zn-Cu foam was fabricated by electrochemical deposition on a foamed Cu template and given a subsequent diffusion heat treatment. The microstructure, mechanical properties, degradation behavior, toxicity, hemolysis percentages, and antibacterial effects of the Zn-Cu foams were assessed for biomedical applications. The Zn-Cu foams exhibited a yield strength of ~12.1 MPa, a plateau strength of 16.8 MPa, and a strain over 50% under compression tests. The corrosion rate of the Zn-Cu foams measured by electrochemical polarization testing was 0.18 mm/y. The Zn-Cu foams showed good blood compatibility with a hemolysis percentage of less than 5%. Cytotoxicity assessment indicated that a 100% concentration of the Zn-Cu foam extract showed clear cytotoxicity against MC3T3-E1 osteoblast cells, but a 12.5% concentration of the extract showed > 90% cell viability. Moreover, the Zn-Cu foams showed good antibacterial effects. STATEMENT OF SIGNIFICANCE: This work reportsa biodegradable Zn-Cu foam with high mechanical strength and ductility, suitable degradation rate, good antibacterial capacity, and good hemolysis property and biocompatibility. The Zn-Cu foam exhibited a yield strength of ~12.1 MPa, a plateau strength of 16.8 MPa, and a strain over 50% under compression tests. The corrosion rate of the Zn-Cu foam measured by electrochemical polarization testing was 0.18 mm/y in Hanks' Solutions. The Zn-Cu foam showed good blood compatibility with a hemolysis percentage of less than 5%. Cytotoxicity assessment indicated that a 12.5% concentration of the foam extract showed > 90% cell viability. Moreover, the Zn-Cu foam showed good antibacterial effects against S. aureus.

3D printed porous titanium cages filled with simvastatin hydrogel promotes bone ingrowth and spinal fusion in rhesus macaques

Sustainable release of simvastatin from poloxamer 407 hydrogel in 3D-printed porous Ti6Al4V for spinal fusion in rhesus macaques.

Manual polishing of 3D printed metals produced by laser powder bed fusion reduces biofilm formation

Certain 3D printed metals and surface finishes may be better suited for canine patient specific orthopedic implants on the basis of minimizing potential bacterial biofilm growth. Thirty disks each of titanium alloy, stainless steel, and cobalt chromium alloy were 3D printed via laser powder bed fusion. Fifteen disks of each metal were subsequently polished. After incubation with a robust biofilm-forming methicillin-resistant Staphylococcus pseudintermedius isolate, disks were rinsed and sonicated to collect biofilm bacteria. Serial dilutions were plated on blood agar, and colony forming units were counted log (ln) transformed for analysis of variance. Interference microscopy quantified surface roughness for comparison to biofilm growth. Scanning electron microscopy on both pre- and post-sonicated disks confirmed biofilm presence and subsequent removal, and visualized surface features on cleaned disks. Significantly more bacteria grew on rough versus polished metal preparations (p < 0.0001). Titanium alloy had more bacterial biofilm growth compared to cobalt chromium alloy (p = 0.0001) and stainless steel (p < 0.0001). There were no significant growth differences between cobalt chromium alloy and stainless steel (p = 0.4737). Relationships between biofilm growth and surface roughness varied: positive with the rough preparations and negative with the smooth. Polished preparations had increased variance in surface roughness compared to rough preparations, and within disk variance predominated over between disk variance for all preparations with the exception of rough cobalt chromium alloy and rough stainless steel. Using scanning electron microscopy, bacterial biofilms tended to form in crevices. Overall, manual polishing of 3D printed surfaces significantly reduced biofilm growth, with preparation-specific relationships between surface roughness and biofilm growth. These results suggest that metallic implants produced by laser powder bed fusion should be polished. Further research will elucidate the optimal surface roughness per preparation to reduce potential biofilm formation and implant associated infection.

Sulfuretin promotes osteoblastic differentiation in primary cultured osteoblasts and in vivo bone healing

Although sulfuretin, the major flavonoid of Rhus verniciflua Stokes, has a variety of biological actions, its in vitro and in vivo effects on osteogenic potential remain poorly understood. The objective of the present study was to investigate the effects of sulfuretin on in vitro osteoblastic differentiation and the underlying signal pathway mechanisms in primary cultured osteoblasts and on in vivo bone formation using critical-sized calvarial defects in mice. Sulfuretin promoted osteogenic differentiation of primary osteoblasts, with increased ALP activity and mineralization, and upregulated differentiation markers, including ALP, osteocalcin, and osteopontin, in a concentration-dependent manner. The expression levels of Runx2, BMP-2, and phospho-Smad1/5/8 were upregulated by sulfuretin. Moreover, sulfuretin increased phosphorylation of Akt, mTOR, ERK, and JNK. Furthermore, sulfuretin treatment increased mRNA expression of Wnt ligands, phosphorylation of GSK3, and nuclear β-catenin protein expression. In vivo studies with calvarial bone defects revealed that sulfuretin significantly enhanced new bone formation by micro-computed tomography and histologic analysis. Collectively, these data suggest that sulfuretin acts through the activation of BMP, mTOR, Wnt/β-catenin, and Runx2 signaling to promote in vitro osteoblast differentiation and facilitate in vivo bone regeneration, and might be have therapeutic benefits in bone disease and regeneration.

Sulfuretin Attenuates MPP⁺-Induced Neurotoxicity through Akt/GSK3β and ERK Signaling Pathways

Parkinson's disease (PD) is the second most common neurodegenerative disease. It is caused by the death of dopaminergic neurons in the substantia nigra pars compacta. Oxidative stress and mitochondrial dysfunction contribute to the loss of dopaminergic neurons in PD. Sulfuretin is a potent antioxidant that is reported to be beneficial in the treatment of neurodegenerative diseases. In this study, we examined the protective effect of sulfuretin against 1-methyl-4-phenyl pyridinium (MPP⁺)-induced cell model of PD in SH-SY5Y cells and the underlying molecular mechanisms. Sulfuretin significantly decreased MPP⁺-induced apoptotic cell death, accompanied by a reduction in caspase 3 activity and polyADP-ribose polymerase (PARP) cleavage. Furthermore, it attenuated MPP⁺-induced production of intracellular reactive oxygen species (ROS) and disruption of mitochondrial membrane potential (MMP). Consistently, sulfuretin decreased p53 expression and the Bax/Bcl-2 ratio. Moreover, sulfuretin significantly increased the phosphorylation of Akt, GSK3β, and ERK. Pharmacological inhibitors of PI3K/Akt and ERK abolished the cytoprotective effects of sulfuretin against MPP⁺. An inhibitor of GSK3β mimicked sulfuretin-induced protection against MPP⁺. Taken together, these results suggest that sulfuretin significantly attenuates MPP⁺-induced neurotoxicity through Akt/GSK3β and ERK signaling pathways in SH-SY5Y cells. Our findings suggest that sulfuretin might be one of the potential candidates for the treatment of PD.

Additive manufacturing of titanium alloys in the biomedical field: processes, properties and applications

The mechanical properties and biocompatibility of titanium alloy medical devices and implants produced by additive manufacturing (AM) technologies – in particular, selective laser melting (SLM), electron beam melting (EBM) and laser metal deposition (LMD) – have been investigated by several researchers demonstrating how these innovative processes are able to fulfil medical requirements for clinical applications. This work reviews the advantages given by these technologies, which include the possibility to create porous complex structures to improve osseointegration and mechanical properties (best match with the modulus of elasticity of local bone), to lower processing costs, to produce custom-made implants according to the data for the patient acquired via computed tomography and to reduce waste.

Alkaline poly(ethylene glycol)-based hydrogels for a potential use as bioactive wound dressings

The number of patients with chronic wounds is increasing constantly in today's aging society. However, little work is done so far tackling the associated disadvantageous shift of the wound pH. In our study, we developed two different approaches on pH-modulating wound dressing materials, namely, bioactive interpenetrating polymer network hydrogels based on poly(ethylene glycol) diacrylate/N-vinylimidazole/alginate (named VI_x ) and poly(ethylene glycol) diacrylate/2-dimethylaminoethyl methacrylate/N-carboxyethylchitosan (named DMAEMA_x ). Both formulations showed a good cytocompatibility and wound healing capacity in vitro. The developed dressing materials significantly increased the cell ingrowth in wounded human skin constructs; by 364% and 313% for the VI_x and the DMAEMA_x hydrogel formulation, respectively. Additionally, VI_x hydrogels were found to be suitable scaffolds for superficial cell attachment. Our research on the material properties suggests that ionic interactions and hydrogen bonds are the driving forces for the mechanical and swelling properties of the examined hydrogels. High amounts of positively charged amino groups in DMAEMA_x hydrogels caused increased liquid uptake (around 190%), whereas VI_x hydrogels showed a 10-fold higher maximum compressive stress in comparison to hydrogels without ionizable functional groups. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 3360-3368, 2017.

Investigation of silk fibroin nanoparticle-decorated poly(l-lactic acid) composite scaffolds for osteoblast growth and differentiation

Attempts to reflect the physiology of organs is quite an intricacy during the tissue engineering process. An ideal scaffold and its surface topography can address and manipulate the cell behavior during the regeneration of targeted tissue, affecting the cell growth and differentiation significantly. Herein, silk fibroin (SF) nanoparticles were incorporated into poly(l-lactic acid) (PLLA) to prepare composite scaffolds via phase-inversion technique using supercritical carbon dioxide (SC-CO2). The SF nanoparticle core increased the surface roughness and hydrophilicity of the PLLA scaffolds, leading to a high affinity for albumin attachment. The in vitro cytotoxicity test of SF/PLLA scaffolds in L929 mouse fibroblast cells indicated good biocompatibility. Then, the in vitro interplay between mouse preosteoblast cell (MC3T3-E1) and various topological structures and biochemical cues were evaluated. The cell adhesion, proliferation, osteogenic differentiation and their relationship with the structures as well as SF content were explored. The SF/PLLA weight ratio (2:8) significantly affected the MC3T3-E1 cells by improving the expression of key players in the regulation of bone formation, ie, alkaline phosphatase (ALP), osteocalcin (OC) and collagen 1 (COL-1). These results suggest not only the importance of surface topography and biochemical cues but also the potential of applying SF/PLLA composite scaffolds as biomaterials in bone tissue engineering.

In vitro and in vivo study of additive manufactured porous Ti6Al4V scaffolds for repairing bone defects

Metallic implants with a low effective modulus can provide early load-bearing and reduce stress shielding, which is favorable for increasing in vivo life-span. In this research, porous Ti6Al4V scaffolds with three pore sizes (300~400, 400~500, and 500~700 μm) were manufactured by Electron Beam Melting, with an elastic modulus range of 3.7 to 1.7 GPa. Cytocompatibility in vitro and osseointegration ability in vivo of scaffolds were assessed. hBMSCs numbers increased on all porous scaffolds over time. The group with intended pore sizes of 300 to 400 μm was significantly higher than that of the other two porous scaffolds at days 5 and 7. This group also had higher ALP activity at day 7 in osteogenic differentiation experiment. The scaffold with pore size of 300 to 400 μm was implanted into a 30-mm segmental defect of goat metatarsus. In vivo evaluations indicated that the depth of bone ingrowth increased over time and no implant dislocation occurred during the experiment. Based on its better cytocompatibility and favorable bone ingrowth, the present data showed the capability of the additive manufactured porous Ti6Al4V scaffold with an intended pore size of 300 to 400 μm for large segmental bone defects.

Long-term osseointegration of 3D printed CoCr constructs with an interconnected open-pore architecture prepared by electron beam melting

In orthopaedic surgery, cobalt chromium (CoCr) based alloys are used extensively for their high strength and wear properties, but with concerns over stress shielding and bone resorption due to the high stiffness of CoCr. The structural stiffness, principally related to the bulk and the elastic modulus of the material, may be lowered by appropriate design modifications, to reduce the stiffness mismatch between metal/alloy implants and the adjacent bone. Here, 3D printed CoCr and Ti6Al4V implants of similar macro-geometry and interconnected open-pore architecture prepared by electron beam melting (EBM) were evaluated following 26week implantation in adult sheep femora. Despite higher total bone-implant contact for Ti6Al4V (39±4%) than CoCr (27±4%), bone formation patterns were similar, e.g., densification around the implant, and gradual ingrowth into the porous network, with more bone in the outer half (periphery) than the inner half (centre). Raman spectroscopy revealed no major differences in mineral crystallinity, the apatite-to-collagen ratio, or the carbonate-to-phosphate ratio. Energy dispersive X-ray spectroscopy showed similar Ca/P ratio of the interfacial tissue adjacent to both materials. Osteocytes made direct contact with CoCr and Ti6Al4V. While osteocyte density and distribution in the new-formed bone were largely similar for the two alloys, higher osteocyte density was observed at the periphery of the porous network for CoCr, attributable to slower remodelling and a different biomechanical environment. The results demonstrate the possibility to achieve bone ingrowth into open-pore CoCr constructs, and attest to the potential for fabricating customised osseointegrated CoCr implants for load-bearing applications.

STATEMENT OF SIGNIFICANCE

Although cobalt chromium (CoCr) based alloys are used extensively in orthopaedic surgery, stress shielding due to the high stiffness of CoCr is of concern. To reduce the stiffness mismatch between CoCr and bone, CoCr and Ti6Al4V implants having an interconnected open-pore architecture were prepared by electron beam melting (EBM). After six months of submerged healing in sheep, both alloys showed similar patterns of bone formation, with densification around the implant and gradual ingrowth into the porous network. The molecular and elemental composition of the interfacial tissue was similar for both alloys. Osteocytes made direct contact with both alloys, with similar overall osteocyte density and distribution. The work attests to the potential for achieving osseointegration of EBM manufactured porous CoCr implants.

Osteoblast functions in functionally graded Ti-6Al-4 V mesh structures

We describe here the combined efforts of engineering and biological sciences as a systemic approach to fundamentally elucidate osteoblast functions in functionally graded Ti-6Al-4 V mesh structures in relation to uniform/monolithic mesh arrays. First, the interconnecting porous architecture of functionally graded mesh arrays was conducive to cellular functions including attachment, proliferation, and mineralization. The underlying reason is that the graded fabricated structure with cells seeded from the large pore size side provided a channel for efficient transfer of nutrients to other end of the structure (small pore size), leading to the generation of mineralized extracellular matrix by differentiating pre-osteoblasts. Second, a comparative and parametric study indicated that gradient mesh structure had a pronounced effect on cell adhesion and mineralization, and strongly influenced the proliferation phase. High intensity and near-uniform distribution of proteins (actin and vinculin) on struts of the gradient mesh structure (cells seeded from large pore side) implied signal transduction during cell adhesion and was responsible for superior cellular activity, in comparison to the uniform mesh structure and non-porous titanium alloy. Cells adhered to the mesh struts by forming a sheet, bridging the pores through numerous cytoplasmic extensions, in the case of porous mesh structures. Intercellular interaction in porous structures provided a pathway for cells to communicate and mature to a differentiated phenotype. Furthermore, the capability of cells to migrate through the interconnecting porous architecture on mesh structures led to colonization of the entire structure. Cells were embedded layer-by-layer in the extracellular matrix as the matrix mineralized. The outcomes of the study are expected to address challenges associated with the treatment of segmental bone defects and bone-remodeling through favorable modulation of cellular response. Moreover, the study provides a foundation for a new branch of functionally graded materials with interconnected porous architecture.

Interplay between self-assembled structure of bone morphogenetic protein-2 (BMP-2) and osteoblast functions in three-dimensional titanium alloy scaffolds: Stimulation of osteogenic activity

Three-dimensional cellular scaffolds are receiving significant attention in bone tissue engineering to treat segmental bone defects. However, there are indications of lack of significant osteoinductive ability of three-dimensional cellular scaffolds. In this regard, the objective of the study is to elucidate the interplay between bone morphogenetic protein (BMP-2) and osteoblast functions on 3D mesh structures with different porosities and pore size that were fabricated by electron beam melting. Self-assembled dendritic microstructure with interconnected cellular-type morphology of BMP-2 on 3D scaffolds stimulated osteoblast functions including adhesion, proliferation, and mineralization, with prominent effect on 2-mm mesh. Furthermore, immunofluorescence studies demonstrated higher density and viability of osteoblasts on lower porosity mesh structure (2 mm) as compared to 3- and 4-mm mesh structures. Enhanced filopodia cellular extensions with extensive cell spreading was observed on BMP-2 treated mesh structures, a behavior that is attributed to the unique self-assembled structure of BMP-2 that effectively communicates with the cells. The study underscores the potential of BMP-2 in imparting osteoinductive capability to the 3D printed scaffolds.