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Materials Science in Additive Manufacturing Preparation and modification of porous Ti

4.2.1. Chemical molecular dipping better antimicrobial properties than the pristine surface, as

In the chemical molecular dipping method, the scaffold shown in Figure 10.
is immersed in a solution containing active ingredients, Chemical molecular dipping has played an important
and the solution adheres to the surface of the material role in the field of surface modification of early medical
through chemical reaction or drying to form a coating so materials; its preparation conditions are simple, and the
as to improve the material performance of porous implants cost involved is low. However, given an array of pitfalls, such
whose performance is mainly affected by the chemical as the weak binding force between the prepared coating
composition. At present, components that are added to and the substrate, the poor surface wear resistance of the
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its surface are primarily Ca/P inorganic salt materials such scaffold, and the susceptibility to fatigue fracture, it proves
as hydroxyapatite and organic materials. to be difficult to use in a complex stress environment.
Calcium phosphate and hydroxyapatite are the main 4.2.2. Vapor deposition
inorganic components of human bone and the most
common additive components, which can participate in The vapor deposition method refers to vaporizing the
metabolism, stimulate or induce regeneration of bone component to be added, contacting porous titanium, and
tissue, and accelerate the repair of damaged parts. Because forming a film on the surface, as shown in Figure 11A.
of its brittleness, hydroxyapatite is generally coated by According to the principle of gasification and reaction, it
thermal spraying, laser cladding, and hydrothermal can be divided into physical vapor deposition (PVD) and
treatment. In addition, to promote the deposition of chemical vapor deposition (CVD).
inorganic materials, its adsorption can also be promoted PVD is a method in which the target material is
by alkali heat treatment in advance. Wang et al. immersed transferred by evaporation or sputtering in atomic,
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TiNbZr alloy in sodium hydroxide solution and heated it molecular, or ion states and aggregated on the surface of
at 60℃ in an autoclave for 24 h. The treated scaffold was the substrate to form a film in a vacuum environment.
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immersed in simulated body fluid (SBF) for a week so that This method primarily encompasses vacuum evaporation,
Ca/P elements were uniformly deposited on the material’s sputtering coating, and ion coating. Escudero et al.
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surface. Cell experiments showed that synthetic calcium used PVD to deposit silver coating with a thickness of
and phosphorus materials significantly enhanced cell 4.5 ± 1.5 μm on the surface of porous Ti6Al4V alloy.
fixation and osseointegration, and enhanced phenotypic Compared with the blank group, the silver-coated
osteogenic lineages (osteopontin and osteonectin) and scaffold reduced the adhesion of Staphylococcus aureus
osteoblast synthesis activities of human bone marrow- on the porous sample and inhibited the formation of
derived mesenchymal cells. Staphylococcus biofilm on the material’s surface within
The organic polymer coating is conducted mainly 72 h. In addition, the maximum cumulative silver release
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by preparing a solution containing the expected load measured within 28 days was <3.5 × 10 ppm, which did
components, and soaking the modified porous titanium not cause significant damage to osteoblasts’ adhesion,
alloy in the solution, a step through which the substrate proliferation, and differentiation, highlighting good
binds to the surface through electrostatic adsorption or compatibility and antibacterial effects.
chemical reaction with the functional group of active CVD refers to depositing a metal inorganic coating
molecules, to achieve a firm bond between the substrate or solid film on the substrate by chemical reaction with
and the load material. Chudinova et al. coated chitosan/ one or several compounds containing film elements after
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hydroxyapatite composite (CS/HA) on a porous titanium gasification. Wang et al. used the CVD method to prepare
surface to prepare biomaterials with good bone integration tantalum coating on the surface of a porous TC4 scaffold,
ability. It was shown that CS/HA composites are novel as shown in Figure 11B. The healing and fusion effect of
materials for treating bone defects in diabetic patients by the scaffold in rabbits with lumbar vertebrae resection was
reactivating the Wnt/b-catenin pathway. evaluated. The results showed that bone marrow-derived

Chemical conjugation between the substrate surface and mesenchymal stem cells (BMSCs) increased on the surface
grafted molecules is vital to stable covalent modification. of Ta-coated scaffolds by a larger margin than those in the
Compared with electrostatic interaction, chemical grafting blank group (Figure 11C).
with polydopamine (PDA) as a binder can achieve more Due to the rapid gas diffusion, the gas deposition
multi-functional component loading. Jiao et al. method can be used to modify the surface of complex
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utilized PDA combined with Ag particles to modify the porous structures, producing a deposited coating with high
porous titanium surface. PDA achieved tunability of silver purity. However, the problem with this process is that the
adsorption and release, and the modified surface had thickness of the deposited coating is small. Compared with

Volume 3 Issue 1 (2024) 13 https://doi.org/10.36922/msam.2753