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. 2020 Jul 14;14(7):584–589. doi: 10.1049/iet-nbt.2019.0320

CAD/CAM scaffolds for bone tissue engineering: investigation of biocompatibility of selective laser melted lightweight titanium

Hendrik Naujokat 1, Johanna Rohwedder 1, Aydin Gülses 1,✉, Oral Cenk Aktas 2, Jörg Wiltfang 1, Yahya Açil 1
PMCID: PMC8676262  PMID: 33010133

Abstract

The objective of the current in‐vitro study was to evaluate the biocompatibility of a new type of CAD/CAM scaffold for bone tissue engineering by using human cells. Porous lightweight titanium scaffolds and Bio‐Oss® scaffolds as well as their eluates were used for incubation with human osteoblasts, fibroblasts and osteosarcoma cells. The cell viability was assessed by using fluorescein diazo‐acetate propidium iodide staining. Cell proliferation and metabolism was examined by using MTT‐, WST‐Test and BrdU‐ELISA tests. Scanning electron microscope was used for investigation of the cell adhesion behaviour. The number of devitalised cells in all treatment groups did not significantly deviate from the control group. According to MTT and WST results, the number of metabolically active cells was decreased by the eluates of both test groups with a more pronounced impact of the eluate from Bio‐Oss®. The proliferation of the cells was inhibited by the addition of the eluates. Both scaffolds showed a partial surface coverage after 1 week and an extensive to complete coverage after 3 weeks. The CAD/CAM titanium scaffolds showed favourable biocompatibility compared to Bio‐Oss® scaffolds in vitro. The opportunity of a defect‐specific design and rapid prototyping by selective laser melting are relevant advantages in the field of bone tissue engineering and regenerative medicine.

Inspec keywords: calcium compounds, scanning electron microscopy, adhesion, titanium, CAD/CAM, tissue engineering, bone, biomedical materials, cellular biophysics, biomechanics, laser materials processing, melting

Other keywords: bone tissue engineering, human cells, porous lightweight titanium scaffolds, human osteoblasts, osteosarcoma cells, cell viability, fluorescein diazo‐acetate propidium iodide staining, cell proliferation, MTT tests, WST‐Test, BrdU‐ELISA tests, cell adhesion, devitalised cells, metabolically active cells, biocompatibility, selective laser melting, CAD‐CAM scaffolds, cell metabolism, scanning electron microscopy, Ti

1 Introduction

Critical‐sized bone defects, which can result from congenital diseases, trauma, or ablative tumour surgeries, are defined as those that will not heal spontaneously within a patient's lifetime [1]. Despite existing two basic management options, the use of autologous bone grafts and metallic implants, both methods have some major disadvantages. The use of autologous bone grafts is mainly associated with problems such as donor side morbidity, limited amount of available bone volume and insufficient shape and size [2, 3]. On the other hand, metallic implants do not have any functional or biological capacity and only work as a space‐holder. As metals have a different Young's modulus compared to that of bone (10–30 Gpa) [4], this might result in stress shielding and osteopenia of the adjacent bone tissues. In the long term, metallic replacements show a higher risk of infections, exposure to the oral cavity and present with a limited life span [5, 6].

In recent years, advances in the tissue engineering approaches lead to the concept of regenerative medicine. With the help of three‐dimensional scaffolds, osteoblasts or precursor cells and growth factors, engineering of bone‐like tissue has been performed successful in vitro [7] as well as in vivo [8, 9]. The clinical aim is to use engineered bone tissue for patient specific bone defect reconstruction. The mechanical, physical and biological properties of scaffold play a key role for sufficient bone regeneration. The introduction of three‐dimensional manufacturing techniques of scaffolds of different materials brought rapid progress to the reconstructive management options [10, 11]. It is well known that scaffold for enhancing tissue regeneration necessitates an interconnected porosity which has the potential to fill bone defects and improve healing [12, 13, 14]. Interconnected pore systems with pore size between 100 and 400 μm have been shown in many studies as the most appropriate option in bone tissue engineering, due to their compliance with cell penetration, tissue ingrowth, vascularisation and nutrient transport. In the past, additive manufacturing of calcium phosphate [15, 16, 17], hydroxyapatite [18, 19, 20], polymers [21] and combinations of them [22, 23, 24, 25] have been introduced.

In reconstructive surgery, titanium is well known as a metal with good biocompatibility to bone and soft tissue and sufficient mechanical properties [26]. However, development of titanium scaffolds in tissue engineering has been limited by production techniques [27]. But recently, advantages in three‐dimensional manufacturing of metals allow production of not only solid, but also porous titanium bodies, which might be used as scaffolds for bone tissue engineering. In order to enable the above‐mentioned porous structure and interconnectivity, various techniques have been proposed; such as powder metallurgy with or without space holders [28, 29], plasma spraying [30] or sintering of metal‐based fibres [31, 32] and selective laser melting (SLM) [33]. Among these, SLM allows a better control over the structural architecture [34], which also allows production of fine and small porous titanium structures, with pore dimensions of 100–200 µm and thereby could enable the optimisation of the structural properties of the scaffold which is required for bone and vessel ingrowth.

On the other hand, scaffolds and bone substitute materials of xenogenic origin are still in use for bone tissue regeneration. Bio‐Oss® is a bone mineral block made of the mineralised portion of bovine cancellous bone, which acts as an osteoconductive scaffold thanks to its cancellous and porous architecture. It is routinely used to fill bone defects in periodontal and maxillofacial procedures [35, 36]. The aim of the current study was to investigate the biocompatibility of selective laser melted lightweight titanium in comparison to Bio‐Oss®.

2 Material and methods

The current study was approved by the ethics committee of the University Hospital Schleswig‐Holstein, Campus Kiel under the file number D 449/17.

2.1 Scaffold materials

This study included lightweight titanium scaffolds which were produced from TiAl6V4 by SLM (Materialise, Leuven, Belgium). The scaffolds consisted of an octahedral unit‐cell which was amplified to create an outer dimension of 10 × 10 × 4 mm (see Fig. 1 a). The strut thickness was 0.5 mm which resulted in a porosity of 80%. The surface roughness resulting from SLM was Rz = 10–12 µm. The scaffolds were desinfected with ethanol 99% for 60 s and rinsed with PBS thrice before introduction into cell culture. As a control, scaffolds of commercially available processed bovine bone blocks (Bio‐Oss® block, 10 × 10 × 20 mm, Geistlich Pharma AG, Wolhusen, Switzerland) were used. The bone mineral blocks were protein free and consisted of the original trabecular architecture of the spongious (see Fig. 1 b). The scaffolds were cut to the same size (10 × 10 × 4 mm) with a diamond coated saw. The disinfection prior to introduction to cell culture was performed as described above.

Fig. 1.

Fig. 1

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Photographs of the two scaffolds. The CAD/CAM titanium scaffold was manufactured by SLM with a strut thickness of 0.5 mm and porosity of 80%

(a) Bio‐Oss® scaffold consists of the original cancellous structure, (b) Size of the scaffolds is 10 × 10 × 4 mm, respectively

2.2 Cells and cell culture

Human osteoblasts, fibroblasts and osteosarcoma cells (SaOS‐2) were used for the in‐vitro biocompatibility tests. The osteoblasts were obtained from the patients who had undergone bone graft harvesting procedures of cancellous bone from the crista iliaca anterior at the Oral and Maxillofacial Surgery Department at the Christian Albrechts University Hospital Schleswig‐Holstein, Campus Kiel. The fibroblasts were obtained from gingival samples of patients who had undergone wisdom tooth removal at the same departure. All patients were individually informed about the procedure and a written consent was obtained prior to sampling. The SaOS‐2 cells were human osteosarcoma cell lines and were commercially purchased from European Collection of Cell Cultures (No. 89050205, Salisbury, UK).

The osseous and gingival samples were transferred into the 89% Dulbecco's modified Eagle's minimum essential medium (DMEM) (PAA Laboratories, Austria), 10% foetal calf serum (FCS; Biochrom, Germany, 1% Penicillin/Streptomycin, Biochrom, Germany). Further processing took place under the laminar flow (Heraeus Instruments, Osterode, Germany). Then, they were minced into pieces ∼1–2 mm pieces and placed into cell culture flasks (Thermo‐Fisher Scientific, Waltham, USA) containing 10 ml cell culture medium. The medium was changed each 72–96 h and the cells were passaged after reaching the 80% confluence. Following aspiration of the medium and concomitant rinsing with 10 ml of phosphate buffered solution (PBS, Sigma, USA), 5 ml of PBS containing 0.05% trypsin has been added in each culture flask to detach and remove the cells from the surface, followed by the dilution of the cell suspension via DMEM enriched with 10% FCS to inhibit the action of trypsin. After that, the cell suspension was centrifuged at 3200 rounds per minute (rpm) for 180 s. The supernatant was filtered, suctioned off and remaining cell pellet was resuspended in 5 ml of medium. After that, the cells were counted in a Neubauer counting chamber (Brand, Wertheim, Germany). 105 cells were transferred into a 75 cm3 culture flask containing 10 ml of medium. The incubation has been conducted with eluates, as well as in direct contact to scaffolds.

2.3 Evaluation of the eluate samples

To create the eluates of the two materials, scaffolds were incubated for seven days in the corresponding medium in order to dissolve potentially cytotoxic substances. Following the first 24 h, the culture medium was replaced by the eluate. Following 48 h, staining was performed with fluorescein diazo‐acetate propidium iodide (FDA/PI) followed by fluorescence microscopy in order to determine the viable cells. WST‐1 was performed after 4 h of incubation. MTT‐Test was carried out after an incubation period of 24 h. Bromdesoxyuridin (BrdU) assay was performed on cell dilution series after 72 h.

2.3.1 FDA/PI staining

Fluorescein diacetate (FDA, Sigma‐Aldrich, St. Louis, USA) and propidium iodide (PI, Sigma‐Aldrich, St. Louis, USA) were used for the determination of the viable and necrotic cells. Eight well plates with 1 × 104 cells per each well were supplied with standard nutrient medium. After three weeks of culture, the cells were washed with PBS and stained with the FDA solution, which consists of 30 μl of FDA stock solution (1 mg FDA/ml acetone) diluted in 10 ml PBS. After an incubation period at 37°C in the dark environment, the FDA solution was removed and replaced by 500 μl PI stock solution (1 mg PI/ml distilled water) diluted in 10 ml PBS. After an incubation of 120 s, the cells were washed with PBS. Within 60 min after staining, the cells were assessed with fluorescence microscope (Axioplan2) and documented with a digital camera (AxioCam MRc5 from ZEISS, Germany). The dyes could be excited at 488 nm (blue light, argon laser). The green fluorescence (FDA) was detected at 530 nm, whereas the red fluorescence (PI) was detected at 620 nm.

2.3.2 MTT assay

Cell proliferation was examined via the MTT Cell Proliferation Kit (#11465007001, Roche Diagnostics, Mannheim, Germany). 96‐well microtiter plates with 5 × 103 cells per well were incubated for three weeks and a sample of 100 μl eluate was obtained. After an incubation period of 24 h, cell proliferation was calculated. The optical density of the samples was carried out photometrically at 450 nm wavelength.

2.3.3 WST‐1 test

WST‐1 Cell Proliferation Reagent (Roche Diagnostics, Mannheim, Germany) was used to detect the metabolic activity of the viable cells. The scaffolds were seeded in 24‐well cell culture plates containing 100 μl of standard nutrient medium in each well with 1 × 104 cells. After three weeks of incubation, cell proliferation was assessed. In each well, 200 μl of WST‐1 reagent were added with a ratio of 1:10 (WST/nutrient medium). After incubation for 240 min, the medium was placed in a 96‐well microtiter plate. Finally, the absorption measurement was measured at 450 nm.

2.3.4 BrdU‐ELISA

Proliferating cells were examined by using the BrdU Cell Proliferation ELISA (enzyme linked immunoadsorption) kit (Roche Diagnostics, Mannheim, Germany). 96‐well microtiter plates with 5 × 103 cells in each well were incubated for three weeks and a sample of 150 μl eluate was obtained. After two days, the eluate was exchanged for standard nutrient medium, than the cells were incubated for another three days. Subsequently, 10 μl of BrdU solution was added to each well and the cells were incubated for another 24 h in order to facilitate the incorporation of BrdU into cell DNA. The optical density of the individual samples was carried out in a microplate reader (Specta Max plus 384, Molecular Devices, Sunnyvale, USA) at 450 nm wavelength.

2.4 Direct contact evaluation

For evaluation of adherence and direct contact proliferation, 1 × 104 cells/ml were incubated in wells for one week. The confluent cells then were mobilised with a cell scraper (Sigma‐Aldrich, St. Louis, USA) and diluted in 1 ml of medium. The cell suspension was drop‐seeded evenly on the scaffolds. The so prepared scaffolds were stored in the incubator for 1 h to let the cells attach and then refilled with the corresponding medium. Duration of direct contact incubation was one week and three weeks and the medium was changed every 3 days.

2.5 Scanning electron microscope (SEM)

After one week and three weeks of direct contact incubation, the scaffolds were prepared for SEM (XL30CP, Philips Electron Optics GmbH, Kassel, Germany). The medium was removed and fixation with glutaraldehyde 3% in PBS was performed at a pH value of 7.4 for one day. Cells were dehydrated in an ascending alcohol dilution for 5 min for each series following removal of the glutaraldehyde solution. Subsequently, drying with hexamethyldisilazane for 1 min (Sigma‐Aldrich, St. Louis, USA) and the gold vapour deposition with the thickness of 15 nm (SCD 500, CAL‐Tec, Ashford, UK) was conducted. SEM analysis was performed at a voltage between 10 and 15 kV.

2.6 Statistical analysis

Descriptive statistical analysis was conducted by using univariate ANOVA test. The level of significance was set at p <0.05, a significant deviation is marked with a star (*) in the graphs.

3 Results

3.1 FDA/PI staining

The FDA/PI staining shows a small number of devitalised cells in all study groups. Representative images can be seen in Fig. 2. In the control group are 3.1–4.6% avital cells.

Fig. 2.

Fig. 2

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Fluorescence microscopy of the human cells cultured in the eluates (three weeks) from

(a), (d), (g) CAD/CAM titanium (left column), (b), (e), (h) Bio‐Oss® (median column), (c), (f), (i) Control (right column)

The first row shows osteoblasts, the second fibroblasts and the third osteosarcoma cells. Cell vitality staining was performed with fluorescin diacetate (FDA) and propidium iodide (PI). Green staining indicates living cells in contrast to red staining which appears in avital cells. Sporadic avital cells were found in every treatment group (white arrows)

The amount of avital cells increases to 4.5–5.2% when incubated with the eluate of the titanium and 6.7–8.3% when incubated with the eluate of the Bio‐Oss® (Table 1). However, the number of devitalised cells does not show any significant impact of the eluates. No evidence for cytotoxicity at any cell type was found. In general, the fibroblasts and the osteosarcoma cells present a higher cell count than the osteoblasts.

Table 1.

Number of devitalised cells is slightly but not significantly increased when incubated with the eluate from Bio‐Oss® but not from the titanium scaffold

Titanium Bio‐Oss® Control
osteoblasts 4.5% 6.7% 3.3%
fibroblasts 5.2% 8.3% 3.1%
SaOS‐2 4.9% 7.6% 4.6%
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3.2 MTT and WST‐1 tests

In MTT‐test, the metabolic activity of the osteoblasts is lowered by 34% by addition of the eluate of the titanium and 44% by addition of the eluate of the Bio‐Oss® scaffold. The metabolic activity of the fibroblasts decreases by 32% when incubated with the titanium eluate and by 46% by addition of the eluate of the Bio‐Oss® scaffold. The SaOs‐2 cells present a metabolic activity lowered by 12% with the titanium eluate and 21% with the Bio‐Oss® eluate in comparison to the control group (Fig. 3).

Fig. 3.

Fig. 3

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MTT‐Test with human osteoblasts, fibroblasts and osteosarcoma cells (SaOS‐2). The metabolic activity is lowered by addition of the eluates of the titanium as well as the Bio‐Oss® scaffold. The effect is more pronounced with the Bio‐Oss®. However, there is no significant difference between the materials. The respective control groups were set 100%

In the WST‐test, the metabolic activity of the osteoblasts, fibroblasts and osteosarcoma‐cells is lowered by addition of the eluates of the titanium to 65, 65 and 87%, respectively. The metabolic activity when incubating with the eluate of the Bio‐Oss® is 53, 53 and 84% of the control group (Fig. 4). Although the effect of metabolic decrease is more pronounced with the eluate of the Bio‐Oss®, there is no significant difference between the two scaffold materials.

Fig. 4.

Fig. 4

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WST‐Test with human osteoblasts, fibroblasts and osteosarcoma cells (SaOS‐2). The metabolic activity is lowered by addition of the eluates of the titanium to 65, 65 and 87%, respectively. The metabolic activity when incubating with the eluate of the Bio‐Oss® is 53, 53 and 84% of the control group. There is no significant difference between the tested materials. The respective control groups were set 100%

3.3 BrdU‐ELISA

The BrdU‐assay shows a decrease of the proliferation of the osteoblasts to 49 and 39% of the control when incubated with the eluates. The proliferation of the fibroblasts is lowered to 51 and 39% by the addition of the eluates of the titanium and Bio‐Oss® scaffolds, respectively. The proliferation of the SaOS‐2 is 98 and 83% when incubated with the eluates (Fig. 5). Although there is a relevant impact of the two eluates, no significant difference between the eluate of the titanium and the Bio‐Oss® appeared.

Fig. 5.

Fig. 5

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BrdU‐assay with human osteoblasts, fibroblasts and osteosarcoma cells (SaOS‐2). The proliferation of the osteoblasts is inhibited to 49 and 39%, the proliferation of the fibroblasts to 51 and 39% by the addition of the eluates, respectively. The proliferation of the SaOS‐2 is 98 and 83% when incubated with the eluates. No significant difference between the eluate of the titanium and the Bio‐Oss® appeared. The respective control groups were set 100%

3.4 Scanning electron microscopy

Scanning electron microscopy was performed after one week and three weeks incubation of the scaffolds with human osteoblasts, fibroblasts and osteosarcoma‐cells. Representative images can be seen in Fig. 6.

Fig. 6.

Fig. 6

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Scanning electron microscopy of the scaffolds after incubation with human osteoblasts, fibroblasts and osteosarcoma‐cells

(a) Upper row presents a titanium scaffold with osteoblasts after 1 week in magnification times 100, (b) times 500, (c), (d) In the middle row is a Bio‐Oss® scaffold with complete surface coverage of fibroblasts after 3 weeks, (e), (f) Osteosarcoma cells covering the surface of a titanium scaffold after 3 weeks present a more compact and massive geometry without long cell protrusions. The white boxes in (a), (c) and (e) indicate the magnifications in (b), (d) and (f)

The number of attached cells depends on the scaffold material, type of cells and the duration of incubation (Table 2).

Table 2.

Number of attached cells detected by scanning electron microscopy depends on the scaffold material, type of cells and the duration of incubation

Titanium Bio‐Oss®
1 week 3 weeks 1 week 3 weeks
osteoblast + + + + +  + + + + + 
fibroblast + + + + + + + + + + + 
SaOS‐2 + + + + + + + + + + + 
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0 = no cells,  + = sporadic surface coverage,  + + = partial surface coverage,  + + + = extensive surface coverage,  + + + + = complete surface coverage.

Osteoblasts and fibroblasts present a well‐spread morphology on both materials and form a nearly complete coverage of the scaffold surfaces after three weeks. In contrast to that, the surface coverage is partially after one week on both materials. The osteosarcoma cells present a more compact and flat geometry without cell protrusions on both materials. These morphological findings are in accordance with the morphology detected in the FDA/PI staining. The scaffold surface coverage is partial after 1 week at both materials and extensive on Bio‐Oss® and complete on titanium after 3 weeks.

4 Discussion

Current study aimed to clarify the biocompatibility of a novel architecture and production technique of a lightweight titanium scaffold manufactured by SLM. There are no indications for cytotoxicity. The proliferation and metabolic activity of all three cell types is reduced when incubated with the eluates, with a more pronounced impact of the eluate from Bio‐Oss®. These findings are in accordance with other studies, indicating lower biocompatibility of Bio‐Oss® in vitro than in vivo [37, 38, 39]. The scaffold made of TiAl6V4 shows higher proliferation rate and metabolic activity of the tested human cells. This titanium alloy has an excellent and well‐known biocompatibility, which is not lowered by the laser melting procedure [40]. In the literature, the structure of osteoconductive scaffolds is well defined in terms of pore size, interconnectivity and porosity. Generally, the increase in bone regeneration in the defects treated with scaffolds is related to the scaffold structure and its mechanical properties, thus the pore sizes play a key role in bone and vessel ingrowth. Moreover, according to the existing literature, pore dimensions which allow cell ingrowth could range from 100 to 500 µm [41]. In the current study, the pore sizes of titanium and Bio‐Oss® scaffolds were estimated to be 600 µm and 150 ± 50 µm, respectively. As shown in SEM analysis, the surfaces of the struts of the titanium scaffolds are completely covered by ingrown cells (Fig. 6). The physical and chemical surface properties and the roughness of Rz = 10–12 µm seem to be well suitable for attachment and proliferation of human osteoblasts, fibroblasts and osteosarcoma cells. This leads to a lining of the struts, but the spaces in between are not completely filled after three weeks incubation in vitro. It can be expected that in an in‐vivo environment, the large spaces would be advantageous for vascular ingrowth and deposition of extracellular matrix [42, 43]. In contrast to the titanium, the Bio‐Oss® consists of a significant smaller pore size and more detailed cancellous anatomy of the trabecula. The SEM analysis shows coverage of the surface of the trabecula as well as areas of confluent cells that span and cover the porosities. It can be expected that in an in‐vivo environment, the Bio‐Oss® scaffold might by fulfilled with cells, but by spanning the porosities, the ingrowth of blood vessels might be delayed or impaired. However, further studies might also be useful to examine the biocompatibility by using in‐vitro and/or ex‐vivo models. As suggested by Liu et al. [44, 45], assessment of the interaction of novel biomaterials with blood via haemolysis testing could be a simple tool in understanding the clinical applicability of the material.

In recent years, there is a growing interest in the use of additive manufacturing methods for rapid prototyping and production of various scaffolds in tissue engineering [46]. Among these techniques, SLM has been shown to be one of the most popular and commercially‐available powder in bed additive manufacturing option [47]. It has been suggested that SLM allows an excellent control over the architecture of a titanium scaffold and enables production of fine and small porous titanium structures with thinner struts, and thereby optimising the structural and mechanical properties, which is basically required for cellular ingrowth [27]. Spoerke et al. have proclaimed that increasing elastic and plastic deformation via thinner struts could reduce stress shielding inside the scaffold and may provide a biomechanical stimulus for the bone‐forming cells [41]. On the other hand, scaffolds with thinner struts prone to undergo elastic and plastic deformation which might cause a reduction in both mechanical strength and fatigue resistance [48]. Further in‐vivo studies could be beneficial in understanding the exact relation between strut size, plastic deformation and osteogenesis. But in vivo, bone architecture is much more complex and specific to its locations than scaffolds can be manufactured today. Bone is a dynamic tissue always remodelling and adapting to the current biomechanical requirements according to Wolf's law. In a clinical setting, a workflow would be advantageous that first analysis of the bone defect and the biomechanical forces related to the defect. On the basis of the biomechanical requirements, a defect‐specific scaffold could be designed and manufactured patient‐specific by CAD/CAM technique [43]. The titanium scaffolds were mainly designed for bony reconstruction in orthopaedic [49] and cranio‐maxillofacial applications [48]. As some years before, the SLM technique did not allow to manufacture lightweight structures with thin struts and a high porosity, a solid outer titanium cage was loaded with osteoconductive bone mineral scaffolds for reconstruction of a mandibular defect. The titanium cage defined the shape, gave mechanical strength and allowed fixation to the adjacent bone tissue. But the titanium cage did not support bone tissue regeneration. In contrast to that, the brittle bone mineral blocks were unable to give any mechanical support at a load bearing bone defect [9, 50]. But after the initial stabilisation, the outer titanium cage led to complications concerning soft tissue dehiscence, impaired blood supply and stress shielding. The development of lightweight titanium seems to be advantageous, as an osteoconductive titanium scaffold allows bone tissue regeneration, provides sufficient stability and the ability of fixation to the adjacent bone without an additional outer cage [33]. Therefore, in addition to its biocompatibility, the load bearing capacity of the scaffold is of great importance in clinical applications. However, as mentioned above, the mechanical resistance has to be adapted to avoid stress shielding and bone resorption in the course of time. The strut thickness and its distribution play a key role in elastic modulus of a scaffold. By reducing the strut diameter, a decrease of the homogenised elastic modulus could be obtained [26]. It has been suggested that an implantable and load bearing scaffold should have a compressive strength of higher then 70 Mpa [51]. However, it has been also proclaimed that, human trabecular bone has a modulus ranging from 0.01–2 Gpa [52] and the modulus of a scaffold should be within the range of trabecular bone. It should be kept in mind that different bones and even different areas of a bone can have different mechanical properties. Additionally, load bearing and load sharing concepts [53] should also be taken into account in selecting the most appropriate scaffold/strut size. The assessment of the mechanical properties of this novel scaffold was outside of the purpose and settings of the current research. However, future studies might focus on the mechanical properties such as compressive strength and stress shielding and the determination of the strut size related optimal elastic moduli according to recipient sites would be beneficial in optimising clinical results.

5 Conclusion

Lightweight titanium scaffolds manufactured by SLM present sufficient biocompatibility and suitable pore design. The mechanical stability is of advantage when reconstruction of load bearing bone defects is demanded. It has to be taken into consideration that the high stability of the titanium struts is a risk of stress shielding and consecutive bone resorption. However, CAD/CAM titanium scaffolds are a suitable material for bone tissue regeneration, but further studies are needed to determine the required biomechanical properties.

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