3D Bio Printed Implants: Combining Dosage Form with Bone Tissue Engineering

Overview Regenerative medicine and medication delivery technology have advanced significantly during the last few decades.[2] Although traditional dose forms including pills, capsules, and injectables have been used extensively to treat illnesses, these methods frequently have drawbacks such systemic toxicity, inconsistent drug levels, and inadequate site-specific action. Tissue engineering has emerged as a viable method for replacing or repairing damaged organs and tissues at the same time.  The creation of bio-printed implants that combine tissue regeneration and therapeutic drug delivery is the result of these two fields coming together, made possible by 3D bioprinting.[4]

Historical Background

When 3D printing methods like stereolithography and fused deposition modeling were first developed for industrial manufacture in the 1980s, it is when 3D bioprinting got its start.[15] These methods were modified for use in biomedicine by the early 2000s, which resulted in the creation of hydrogel-based formulations of bio-inks that could encapsulate living cells and macromolecules. After printing basic tissue constructs like skin patches and cartilage scaffolds, researchers progressively progressed to more intricate structures like organ models and vascularized tissues.[6] At the same time, drug delivery methods were changing from straightforward immediate-release formulations to targeted and regulated systems that made use of implanted devices, polymers, and nanocarriers. As the scaffold promotes regeneration, the concept of embedding medications into 3D-printed scaffolds became apparent as a natural next step, enabling therapeutic molecules to be given straight to the damaged tissue.  Bio-printed implants are now being researched in fields like wound healing, dentistry, orthopedics, and oncology.[11]

Advantages of 3D Bio printed Implants

1. Personalization: Using imaging data (CT/MRI scans), patient-specific implants can be created, guaranteeing anatomical precision and customized drug delivery.[7]

2. Localized therapy: Reduces systemic exposure and adverse effects by administering medications directly to the site of harm.[13] 

3. Sustained release: Drugs can be released gradually over a period of days, weeks, or months using bio printed hydrogels and polymers.[17]

4. Dual functionality: Implants serve as both therapeutic agent reservoirs and structural scaffolds for tissue healing.[10]

5. Fewer surgical interventions: Recurrent operations or systemic treatments can be avoided by integrating regeneration and therapy into a single implant.[3]

6. Increased bioactivity: To promote healing and enhance results, growth hormones, stem cells, and bioactive compounds can be added.[16]

Disadvantages and Challenges

This technique has significant drawbacks despite its potential:

1. Manufacturing complexity: Bioprinting calls very sophisticated machinery, sterile conditions, and exact process control.[5]

2. Material limitations: Not all biomaterials can be printed, and it's still challenging to guarantee both mechanical strength and biocompatibility.[8]

3. Regulatory obstacles: Comprehensive safety and effectiveness assessments are necessary before bio printed implants can be approved for clinical use.[12]

4. Expensive: The procedure is costly due to the need for equipment, raw materials, and trained labor.[15]

5. Problems with cell viability: It might be difficult to keep living cells viable and functional both before and after printing.[9]

6. Drug stability: Adding medications to bio-inks may change how they work or result in an early release.[4]

Ideal Characteristics of Bio printed Implants

The following characteristics are necessary for a 3D bio printed implant used for drug delivery to be successful: biocompatibility: non-toxic, non-immunogenic materials that integrate with host tissue; mechanical stability: Sufficient strength to tolerate physiological stress while promoting tissue growth; controlled degradability: The scaffold should break down at a rate that corresponds with tissue regeneration; sustained drug release: The capacity to deliver consistent, long-term release of incorporated drugs; customizability: Easily adapted to the anatomy of each patient and therapeutic needs; sterilizability: Must withstand sterilization without compromising integrity or functionality; Vascularization potential: Should permit nutrient and oxygen transport to support cell survival.[13]

Current Applications

1. Critical-Sized Bone Defect Repair: Large bone defects that cannot mend on their own, like those caused by trauma, tumor resections, or congenital deformities, can be repaired using 3D bio printed scaffolds. The implants encourage the formation of new bone while offering structural support.[2]

2. Craniofacial Reconstruction: After surgery, customized bone grafts that are printed to fit intricate cranial and facial geometries improve both the functional and aesthetic results.[8]

3. Orthopedic Implants: Unlike conventional implants, customized implants for long bones, such the femur or tibia, are made to meet the anatomical needs of each patient. This improves integration and lowers problems.[6]

4. Drug Delivery and Growth Factor Incorporation: Bio printed scaffolds can be loaded with pharmaceuticals that promote bone regeneration, osteogenic factors, or stem cells, providing a dual purpose of biological enhancement and structural repair.[14]

5. Preclinical Disease Modeling: Before being employed in clinical settings, 3D bio printed bone constructions are used in lab settings to research bone illnesses, test medications, and model the healing process of bones.[12]

6. Spinal and Vertebral Reconstruction: By offering mechanical support and encouraging bone regeneration, patient-specific bio printed implants are being investigated for the repair of injured vertebrae or intervertebral bone structures.

7. Integration with Joint Implants: To promote osseointegration, lessen implant loosening, and increase long-term stability, 3D bio printed bone scaffolds are utilized in conjunction with joint replacements (such as hip or knee prosthesis).[7]

Applications of 3D Bioprinted Implants in Bone Tissue Engineering

1. Customized Repair for Bone: Defects  Scaffolds customized for each patient that fit the dimensions, form, and geometry of bone deformities can be made using 3D bioprinted implants.  Especially in intricate craniofacial, maxillofacial, and long bone restorations, this personalization improves implant integration and lowers surgical difficulties.[11]

2. Encouragement of Vascularization and Osteogenesis: To promote bone formation and vascularization, bioprinted constructions can be loaded with angiogenic and osteoinductive growth factors, including bone morphogenetic proteins (BMPs).  The scaffold's precise cell and bioactive molecule placement maximizes the local microenvironment, facilitating quicker and more effective bone regeneration.[8]

3. Delivery of Biomaterials and Stem Cells: Mesenchymal stem cells (MSCs) and other stem cells can be added to bioprinted scaffolds to help the creation of bone tissue by differentiating into osteoblasts.  The gradual integration with native bone tissue is facilitated and cell viability is guaranteed by the combination of biocompatible hydrogels and bioinks.[6]

4. Mechanical and load-bearing assistance: Implants with mechanical characteristics that can be adjusted to resemble natural bone can be created using sophisticated 3D bioprinting processes.  In some situations, these implants can replace metal implants by temporarily supporting physiological stresses and encouraging tissue regeneration.[13]

5. Drug-Eluting Bone Implants: Bioprinted scaffolds can serve as local drug delivery systems, releasing antibiotics, anti-inflammatory agents, or osteogenic drugs directly at the defect site. This dual function supports bone healing while minimizing systemic side effects.[17]

6. Disease Modeling and Preclinical Testing: 3D bioprinted bone constructs provide physiologically relevant in vitro models for studying bone diseases, testing drug efficacy, and optimizing scaffold designs before clinical application. This reduces reliance on animal models and accelerates translational research.[9]

7. Complex Bone Tissue Reconstruction: Multi-material and multi-cell bioprinting allow the creation of heterogeneous structures that mimic the composition of native bone, including cortical and cancellous regions. This capability is particularly useful for reconstructing complex anatomical structures, such as the jaw or vertebrae.[14]

Fig – Applications of 3d bioprinting implants bone tissue.

Drug selection criteria for Dexamethasone:

The long-acting synthetic glucocorticoid dexamethasone has drawn interest in bone tissue engineering because of its dual osteogenic and anti-inflammatory qualities.[13] Its weak water solubility (~0.089 mg/mL) and moderate lipophilicity (LogP ~1.83) enable regulated, localized release when added to biodegradable scaffolds such hydroxyapatite composites, PCL, GelMA, or PLGA. Dexamethasone decreases inflammation and encourages mesenchymal stem cell development into osteoblasts by modifying gene expression via glucocorticoid receptors.  If the dosage is carefully managed to avoid cytotoxicity or systemic side effects, its chemical stability within scaffolds, lengthy half-life (36–54 hours), and potential for sustained release make it an excellent choice for 3D-printed bone implants.[8]

Composition and Excipient Used in 3D bioprinting bone tissue implants:

Methods for Preparation of 3D Bioprinted Bone Tissue Implants

1. Bioprinting using inkjet: This method involves carefully applying bioinks that include growth stimulants and osteogenic cells as tiny droplets onto a substrate.  Although the variety of printable biomaterials is limited by viscosity restrictions, it enables high printing speeds and the incorporation of multiple cell types.[9]

2. Based on Extrusion: The process of bioprinting  Extrusion bioprinting, the most popular technique for creating bone tissue constructions, extrudes continuous filaments of bioink using mechanical or pneumatic force.  In order to simulate the mineral phase of bone, it promotes the use of hydrogels mixed with ceramic nanoparticles (such as hydroxyapatite and β-tricalcium phosphate).  The technique makes it possible to build bigger scaffolds that are mechanically stable.[16]

3. Bioprinting with Laser Assistance (LAB):  LAB transfers cell-rich bioinks onto a collector surface using concentrated laser pulses.  This method avoids direct nozzle contact and provides good resolution and cell survival. It is especially useful for precisely positioning mesenchymal stem cells or osteoblasts within intricate bone morphologies.[11] 

4. Digital Light Processing (DLP) and Stereolithography (SLA): Both techniques use UV or visible light to photo-crosslink light-sensitive bioresins. High-resolution bone scaffolds with complex internal channels that assist vascularization can be produced using SLA and DLP. Osteoconductivity is increased by adding growth factors or nanoceramics to photo-curable resins.[12]

5. Bioprinting that is hybrid: To take use of their complementing advantages, this tactic blends two or more printing methods.  For example, the mechanical framework can be formed by extrusion, and cells or growth factors can be precisely seeded using inkjet or laser techniques. These combinations show promise for replicating native bone's biological milieu and load-bearing capacity.[8] 

6. Maturation and Post-Processing: Constructs usually go through crosslinking, mineralization, and culture in bioreactors after printing. Functional bone regeneration requires osteogenic differentiation and the development of vascular networks, both of which are facilitated by dynamic culture conditions.[17]

Evaluation Methods of 3D Bioprinted Bone Tissue Implants

1. Analysis of Structure and Morphology:  Microscopy methods including confocal microscopy and scanning electron microscopy (SEM) are used to analyze the printed constructions' layer-by-layer fidelity, pore size, and surface shape.  In order to evaluate the internal structure, porosity, and interconnectivity of scaffolds—all of which are essential for vascular ingrowth and nutrient diffusion—micro-computed tomography, or micro-CT, offers high-resolution three-dimensional imaging.[10]

2. Mechanical Description: Compression testing, tensile testing, and nanoindentation are used to determine the strength, stiffness, and elastic modulus of bone implants because they must endure physiological loads. Viscoelastic characteristics are assessed using dynamic mechanical analysis (DMA) in settings that mimic those found in vivo.[14]

3. Assessment by Physicochemical  FTIR and XRD: are examples of spectroscopic techniques that verify the mineral distribution, crystallinity, and chemical composition of structures.  Studies on water absorption, swelling ratio, and degradation rate aid in forecasting implant stability and resorption patterns inside the body.[2] 

4. Biological Evaluation in Vitro  Assays: like MTT, Alamar Blue, or Live/Dead staining are used to assess cell viability and proliferation in order to ascertain the bioink's cytocompatibility.  Alkaline phosphatase activity, calcium deposition tests, and gene expression indicators (RUNX2, osteocalcin, and osteopontin) are used to assess osteogenic differentiation.  Co-culture research involving osteogenic and endothelial cells sheds light on their angiogenic potential.[11]

5. Preclinical Assessment in Vivo: The ability to regenerate bone, vascularization, and immune response are evaluated using animal models (e.g., rabbit femur defect, rat calvarial defect).  Micro-CT measures the volume and density of bone, whereas histological staining (H&E, Masson's trichrome) verifies the creation of new bone. Biodegradation rate and functional integration with host bone are demonstrated by long-term implantation investigations.[15]

6. Testing for Functional Performance: After implantation, the load-bearing capability and resistance to mechanical stress are evaluated. To assess implant viability over time, vascular network development and nutrient delivery are evaluated.[7]

RESULTS AND DISCUSSION

The creation of bone tissue implants with exact geometry, repeatable architecture, and regulated medication distribution has shown great promise thanks to 3D bioprinting.  Research continuously shows that interconnected-pore bioprinted scaffolds promote osteogenic differentiation, cell adhesion, and proliferation.[8] Incorporating bioactive substances like growth hormones, BMP-2, and dexamethasone (Dex) improves integration into host tissue by promoting osteogenesis and angiogenesis.  Successful bone regeneration depends on sustained drug release from hydrogels or microspheres inside the scaffold, which has been demonstrated to lower local inflammation and sustain therapeutic levels for prolonged periods of time.[13]

Optimized polymer blends, such as PLGA, PCL, and gelatin, can produce enough compressive strength to temporarily support physiological loads while gradually deteriorating to allow for natural bone regeneration, according to mechanical

tests of printed structures.  Furthermore, by demonstrating higher cell proliferation and upregulation of bone-specific markers like osteocalcin, osteonectin, and collagen type I, in vitro tests like Alamar Blue and RT-PCR validate the bioactivity of printed scaffolds.[15]

There are still difficulties in spite of these developments.  Ongoing research priorities include vascularization throughout big implants, managing the spatial distribution of various cell types, and guaranteeing mechanical stability over the long term.  In order to facilitate clinical translation, future research will concentrate on multi-material printing, the integration of smart biomaterials that are sensitive to the local microenvironment, and scalable manufacturing methodologies.[14]

Marketed Examples