Page 24 - IJB-9-4

International Journal of Bioprinting Lattice-Solid hybrid 3D printing for artificial implant

are the most common methods for replacing bone defects to the longitudinal axis have been studied to optimize
after wide excision [1-4] . There are limitations on using orthopedic implants. For instance, a fully lattice implant
allografts or conventional implants as a treatment for a with cross-sectional symmetry has been studied to achieve
malignant tumor, which can occur anywhere in the body the desired light weight and compatible mechanical
and in various sizes. Consequently, using a customized properties compared to bone structures . In addition,
[27]
implant in patients undergoing extensive tissue removal a fully lattice implant with a gradient macrostructure is
can be an alternative method. utilized in bone implants, and the mechanical properties
of these structures have been reported [27-29] . Bone tissue
Additive manufacturing (AM) technology has in nature has a structural gradient. If the lattice structure
been extensively developed in various fields [5-9] . The implant does not mimic these gradients, stress shielding
development of AM has allowed for the innovative design occurs owing to uneven load distribution, resulting
of patient-specific orthopedic implants for bone sarcoma in resorption and bone failure of host tissues. In most
patients [10-15] . This current technology can replace the orthopedic surgeries using 3D-printed implants, hybrid
allograft with a 3D-printed implant and combine an implants, rather than fully lattice implants, are utilized.
endoprosthesis with an implant in limb salvage surgery . Several studies have also been conducted to control the
[16]
Conventional modular-type tumor implants often require porosity, pore size, and shape of hybrid implants using
total replacement of the whole joint with an artificial joint compressive and tensile tests . While these studies
[30]
to fix the implant, resulting in disability for the patient. In have been conducted on specimens with cross-sectional
contrast, AM can preserve the patient’s joint if the tumor symmetry, in actual surgical cases, implants have complex
does not erode the adjacent joint [17,18] . surfaces with an asymmetric section, as shown in Figure 1,

Despite the advantages mentioned above, the for the purpose of ensuring sufficient mechanical strength
mechanical performance of the implant produced by AM and avoiding damage major neurovascular structure. Thus,
must meet the rigid endurance and safety criteria. The studies on such hybrid implants, including pizza types
load direction and magnitude of the implant depend on (P-type) and shell types (S-type), should be carried out.
the surgical site; the lower limb has to withstand repeated Common mixing patterns with lattice and solid
weight loads more than the upper limb. Moreover, to structures can be categorized into two types. One mixing
regenerate bone and soft tissues and ensure strong adhesion pattern was a lattice coating with a solid core in the
to the bone tissues, the implant should be composed of center (Figure 1a). In another pattern, the two structures
hybrid structures that combine solid and lattice structures. occupy a certain volume without a central core structure
The lattice structure with an open porosity inside the (Figure 1b). The S-type is often utilized in limb salvage
structure has biological advantages in orthopedic implants: surgery for long bones, while the P-type is applied for flat
it has a lightweight design, provides a scaffold for bone bones, such as pelvic bones. However, there are no specific
ingrowth, and reduces metal artifacts during postoperative mechanical analyses or guidelines for combining lattice
surveillance for local recurrence [16,19] . Providing an and solid structures to design a mechanically durable
appropriate pore structure is the most important factor megaprosthesis.
when using mesh structures to enhance osteointegration.
A few animal studies have reported the osteoinductive Before limb salvage surgery, the mechanical properties
effect of 3D-printed titanium alloy implants [20-24] , and one of the 3D-printed implant, including the hybrid structure
human case study reported 8%–10% bone integration into with solid and lattice structures, should be evaluated
the mesh structure . The mesh structure is commonly preoperatively experimentally to ensure that it will last
[25]
mentioned in previous literature on 3D-printed custom- for the entire lifetime of the patient, given the diverse
made implants in orthopedic oncology, particularly at the shapes and proportions of hybrid structures in each
bone and implant junctions, because it provides a scaffold surgery. However, it is practically impossible to evaluate
for bone ingrowth [11,15,16,19] . However, the lattice structure the personalized types of implants experimentally owing
shows mechanical weakness compared to the solid to the absence of standard design criteria for the implant
structure, and the roughness of the lattice structure may and time limitation that inevitably arise because bone
cause irreparable damage to neurovascular structures . tumors are progressing over time. Therefore, finite element
[26]
Therefore, a lattice structure is combined with a solid analysis (FEA) is required to replace the experiment.
structure rather than used alone.
The present study entailed mechanical and
Various specimens have been studied to optimize microstructural analyses for Ti-6Al-4V solid-mesh
implant structures. Nevertheless, to our knowledge, only hybrid structures produced by electron beam melting
specimens with cross-sectional symmetry with respect (EBM). Different types of hybrid structures with various

Volume 9 Issue 4 (2023) 16 https://doi.org/10.18063/ijb.716