Long-term cell-mediated protein release from calcium phosphate ceramics

Enhanced effects of slowly co-released TGF-β3 and BMP-2 from biomimetic calcium phosphate-coated silk fibroin scaffolds in the repair of osteochondral defects

Bioactive agents have demonstrated regenerative potential for cell-free bone tissue engineering. Nevertheless, certain challenges persist, including ineffective delivery methods and confined therapeutic potency. Here, we demonstrated that the biomimetic calcium phosphate coating system (BioCaP) could effectively uptake and slowly release the incorporated bioactive agents compared to the surface absorption system via osteoclast-mediated degradation of BioCaP coatings. The release kinetics were determined as a function of time. The release rate was stable without remarkable burst release during the first 1 day, followed by a sustained release from day 7 to day 19. Then, we developed the bi-functional BioCaP-coated silk fibroin scaffolds enabling the effective co-delivery of TGF-β3 and BMP-2 (SFI-T/SFI-B) and the corresponding slow release of TGF-β3 and BMP-2 exhibited superior potential in promoting chondrogenesis and osteogenesis without impairing cell vitality in vitro. The SFI-T/SFI-B scaffolds could improve cartilage and bone regeneration in 5 × 4 mm rabbit osteochondral (OC) defect. These findings indicate that the biomimetic calcium-phosphate coated silk fibroin scaffolds with slowly co-released TGF-β3 and BMP-2 effectively promote the repair of OC defects, hence facilitating the future clinical translation of controlled drug delivery in tissue engineering.

Enhancement of Local Osseointegration and Implant Stability of Titanium Implant in Osteoporotic Rats by Biomimetic Multilayered Structures Containing Catalpol

This study examined the surface modification of titanium (Ti) implants to enhance early-stage osseointegration, which reduced the failure rate of internal fixation in osteoporotic fractures that inherently decrease in bone mass and strength. We employed a layer-by-layer electroassembly technique to deposit catalpol-containing hyaluronic acid/chitosan multilayers onto the surface of Ti implants. To evaluate the in vitro osteoinductive effects of catalpol-coated Ti implants, the robust osteoblast differentiation capacity of the murine preosteoblast cell line, MC3T3-E1, was employed. Furthermore, the performance of these implants was evaluated in vivo through femoral intramedullary implantation in Sprague-Dawley rats. The engineered implant effectively regulated catalpol release, promoting increased bone formation during the initial stages of implantation. The in vitro findings demonstrated that catalpol-coated Ti surfaces boosted ALP activity, cell proliferation as measured by CCK-8, and osteogenic protein expression via WB analysis, surpassing the uncoated Ti group (P < 0.05). In vivo micro-computed tomography (CT) and histological analyses revealed that catalpol-coated Ti significantly facilitated the formation and remodeling of new bone in osteoporotic rats at 14 days post-implantation. This study outlines a comprehensive and straightforward methodology for the fabrication of biofunctional Ti implants to address osteoporosis.

The bone morphogenetic protein 2 analogue L51P enhances spinal fusion in combination with BMP2 in an in vivo rat tail model

Bone morphogenic protein 2 (BMP2) is known to induce osteogenesis and is applied clinically to enhance spinal fusion despite adverse effects. BMP2 needs to be used in high doses to be effective due to the presence of BMP2 inhibitors. L51P is a BMP2 analogue that acts by inhibition of BMP2 inhibitors. Here, we hypothesized that mixtures of BMP2 and L51P could achieve better spinal fusion outcomes regarding ossification. To test whether mixtures of both cytokines are sufficient to improve ossification, 45 elderly Wistar rats (of which 21 were males) were assigned to seven experimental groups, all which received spinal fusion surgery, including discectomy at the caudal 4-5 level using an external fixator and a porous β-tricalcium phosphate (βTCP) carrier. These βTCP carriers were coated with varying concentrations of BMP2 and L51P. X-rays were taken immediately after surgery and again six and twelve weeks post-operatively. Histological sections and µCT were analyzed after twelve weeks. Spinal fusion was assessed using X-ray, µCT and histology according to the Bridwell scale by voxel-based quantification and a semi-quantitative histological score, respectively. The results were congruent across modalities and revealed high ossification for high-dose BMP2 (10 µg), while PBS induced no ossification. Low-dose BMP2 (1 µg) or 10 µg L51P alone did not induce relevant bone formation. However, all combinations of low-dose BMP2 with L51P (1 µg + 1/5/10 µg) were able to induce similar ossificationas high-dose BMP2. These results are of high clinical relevance, as they indicate L51P is sufficient to increase the efficacy of BMP2 and thus lower the required dose for spinal fusion. STATEMENT OF SIGNIFICANCE: Spinal fusion surgery is frequently applied to treat spinal pathologies. Bone Morphogenic Protein-2 (BMP2) has been approved by the U .S. Food and Drug Administration (FDA-) and by the "Conformité Européenne" (CE)-label. However, its application is expensive and high concentrations cause side-effects. This research targets the improvement of the efficacy of BMP2 in spinal fusion surgery.

BMP2-Functionalized Biomimetic Calcium Phosphate Graft Promotes Alveolar Defect Healing During Orthodontic Tooth Movement in Beagle Dogs

Background: Grafting of biomaterial in alveolar defect facilitates bone healing and orthodontic treatment. BMP2-functionalized biomimetic calcium phosphate (BioCaP) graft had shown excellent bone defect healing potential in many preclinical studies. In this study, we aimed to investigate the influence of BioCaP graft on surgical alveolar bone defect healing during orthodontic tooth movement (OTM) in beagle dogs.

Methods: Nine Beagle dogs were randomly assigned to three groups: control, deproteinized bovine bone (DBB), and BioCaP. The maxillary second premolars were protracted into the defects of the extracted maxillary first premolar for 8 weeks. The rate of OTM, alveolar remodeling and bone defect healing were evaluated by histology, histomorphometry, and cone beam computed tomography (CBCT) imaging. Periodontal probing depth was analyzed. Gingival cervicular fluid was collected at week 4 and 8, and the IL-1β level was measured by ELISA.

Results: The histological sections of the bone defect showed more newly formed bone in the BioCaP group. The percentage of new bone formation in the BioCaP group was 1.61-, and 1.25-fold higher compared to the control and DBB group, respectively. After 8 weeks of OTM, the resorption rate of BioCaP was 1.42-fold higher compared to DBB. The root resorption index in the DBB group was 1.87-, and 1.39-fold higher compared to the control and BioCaP group, respectively. CBCT images showed 1.92-, and 1.36-fold higher bone mineral density in the BioCaP group compared to the control and DBB group, respectively. There was no significant difference in OTM among the three groups. The distance between the enamel cementum and the crest of the alveolar ridge in the control group was 1.45-, and 1.69-fold higher compared to DBB and BioCaP group, respectively. Periodontal probing depth at week 8 was reduced in the BioCaP group compared to the control. IL-1β concentration in the gingival cervicular fluid was significantly lower in the BioCaP group compared to the control group at week 4 and 8.

Conclusion: BioCaP graft robustly promoted bone regeneration and alveolar bone defect healing without affecting OTM. BioCaP graft caused less alveolar bone recession and root resorption of traction tooth with favorable periodontal attachment level indicating that BioCaP as a bioactive and functional bone filling material for alveolar bone defects during orthodontic treatment.

Evaluation of Bone Sialoprotein Coating of Three-Dimensional Printed Calcium Phosphate Scaffolds in a Calvarial Defect Model in Mice

The bioactive coating of calcium phosphate cement (CPC) is a promising approach to enhance the bone-healing properties of bone substitutes. The purpose of this study was to evaluate whether coating CPCs with bone sialoprotein (BSP) results in increased bone formation. Forty-five female C57BL/6NRj mice with an average age of six weeks were divided into three groups. Either a BSP-coated or an uncoated three-dimensional plotted scaffold was implanted into a drilled 2.7-mm diameter calvarial defect, or the defect was left empty (control group; no CPC). Histological analyses revealed that BSP-coated scaffolds were better integrated into the local bone stock eight weeks after implantation. Bone volume/total volume (BV/TV) ratios and bone thickness at the bone–implant contact were analyzed via micro computed tomography (µCT) after eight weeks. BSP-coated scaffolds and uncoated CPC scaffolds increased bone thickness in comparison to the control (CPC + BSP: 691.1 ± 253.5 µm, CPC: 603.1 ± 164.4 µm, no CPC: 261.7 ± 37.8 µm, p < 0.01). Accordingly, BV/TV was enhanced in both scaffold groups (CPC + BSP: 1.3 ± 0.5%, CPC: 0.9 ± 0.5%, no CPC: 0.2 ± 0.3%, p < 0.01). The BSP coating showed a tendency towards an increased bone thickness (p = 0.18) and BV/TV (p = 0.18) in comparison to uncoated CPC scaffolds. However, a significant increase in bone formation through BSP coating was not found.

Improving long-term subcutaneous drug delivery by regulating material-bioenvironment interaction

Subcutaneous long-acting release (LAR) formulations have been extensively developed in the clinic to increase patient compliance and reduce treatment cost. Despite preliminary success for some LAR systems, a major obstacle limiting the therapeutic effect remains on their interaction with surrounding tissues. In this review, we summarize how living bodies respond to injected or implanted materials, and highlight some typical strategies based on smart material design, which may significantly improve long-term subcutaneous drug delivery. Moreover, possible strategies to achieve ultra-long (months, years) subcutaneous drug delivery systems are proposed. Based on these discussions, we believe the well-designed subcutaneous long-acting formulations will hold great promise to improve patient quality of life in the clinic.

How does the pathophysiological context influence delivery of bone growth factors?

"Orthobiologics" represents an important category of therapeutics for the regeneration of bone defects caused by injuries or diseases, and bone growth factors are a particularly rapidly growing sub-category. Clinical application of bone growth factors has accelerated in the last two decades with the introduction of BMPs into clinical bone repair. Optimal use of growth factor-mediated treatments heavily relies on controlled delivery, which can substantially influence the local growth factor dose, release kinetics, and biological activity. The characteristics of the surrounding environment, or "context", during delivery can dictate growth factor loading efficiency, release and biological activity. This review discusses the influence of the surrounding environment on therapeutic delivery of bone growth factors. We specifically focus on pathophysiological components, including soluble components and cells, and how they can actively influence the therapeutic delivery and perhaps efficacy of bone growth factors.

A review paper on biomimetic calcium phosphate coatings

Biomimetic calcium phosphate coatings have been developed for bone regeneration and repair because of their biocompatibility, osteoconductivity, and easy preparation. They can be rendered osteoinductive by incorporating an osteogenic agent, such as bone morphogenetic protein 2 (BMP-2), into the crystalline lattice work in physiological situations. The biomimetic calcium phosphate coating enables a controlled, slow and local release of BMP-2 when it undergoes cell mediated coating degradation induced by multinuclear cells, such as osteoclasts and foreign body giant cells, which mimics a physiologically similar release mode, to achieve sustained ectopic or orthotopic bone formation. Therefore, biomimetic calcium phosphate coatings are considered to be a promising delivery vehicle for osteogenic agents. In this review, we present an overview of biomimetic calcium phosphate coatings including their preparation techniques, physico-chemical properties, potential as drug carrier, and their pre-clinical application both in ectopic and orthotopic animal models. We briefly review some features of hydroxyapatite coatings and their clinical applications to gain insight into the clinical applications of biomimetic calcium phosphate coatings in the near future.

BMP-functionalised coatings to promote osteogenesis for orthopaedic implants

The loss of bone integrity can significantly compromise the aesthetics and mobility of patients and can be treated using orthopaedic implants. Over the past decades; various orthopaedic implants; such as allografts; xenografts and synthetic materials; have been developed and widely used in clinical practice. However; most of these materials lack intrinsic osteoinductivity and thus cannot induce bone formation. Consequently; osteoinductive functionalisation of orthopaedic implants is needed to promote local osteogenesis and implant osteointegration. For this purpose; bone morphogenetic protein (BMP)-functionalised coatings have proven to be a simple and effective strategy. In this review; we summarise the current knowledge and recent advances regardingBMP-functionalised coatings for orthopaedic implants.

Strategies for controlled delivery of growth factors and cells for bone regeneration

The controlled delivery of growth factors and cells within biomaterial carriers can enhance and accelerate functional bone formation. The carrier system can be designed with pre-programmed release kinetics to deliver bioactive molecules in a localized, spatiotemporal manner most similar to the natural wound healing process. The carrier can also act as an extracellular matrix-mimicking substrate for promoting osteoprogenitor cellular infiltration and proliferation for integrative tissue repair. This review discusses the role of various regenerative factors involved in bone healing and their appropriate combinations with different delivery systems for augmenting bone regeneration. The general requirements of protein, cell and gene therapy are described, with elaboration on how the selection of materials, configurations and processing affects growth factor and cell delivery and regenerative efficacy in both in vitro and in vivo applications for bone tissue engineering.

Biomimetic coatings for bone tissue engineering of critical-sized defects

The repair of critical-sized bone defects is still challenging in the fields of implantology, maxillofacial surgery and orthopaedics. Current therapies such as autografts and allografts are associated with various limitations. Cytokine-based bone tissue engineering has been attracting increasing attention. Bone-inducing agents have been locally injected to stimulate the native bone-formation activity, but without much success. The reason is that these drugs must be delivered slowly and at a low concentration to be effective. This then mimics the natural method of cytokine release. For this purpose, a suitable vehicle was developed, the so-called biomimetic coating, which can be deposited on metal implants as well as on biomaterials. Materials that are currently used to fill bony defects cannot by themselves trigger bone formation. Therefore, biological functionalization of such materials by the biomimetic method resulted in a novel biomimetic coating onto different biomaterials. Bone morphogenetic protein 2 (BMP-2)-incorporated biomimetic coating can be a solution for a large bone defect repair in the fields of dental implantology, maxillofacial surgery and orthopaedics. Here, we review the performance of the biomimetic coating both in vitro and in vivo.

Cell-mediated BMP-2 liberation promotes bone formation in a mechanically unstable implant environment

The flexible alloplastic materials that are used in bone-reconstruction surgery lack the mechanical stability that is necessary for sustained bone formation, even if this process is promoted by the application of an osteogenic agent, such as BMP-2. We hypothesize that if BMP-2 is delivered gradually, in a cell-mediated manner, to the surgical site, then the scaffolding material's lack of mechanical stability becomes a matter of indifference. Flexible discs of Ethisorb were functionalized with BMP-2, which was either adsorbed directly onto the material (rapid release kinetics) or incorporated into a calcium-phosphate coating (slow release kinetics). Unstabilized and titanium-plate-stabilized samples were implanted subcutaneously in rats and retrieved up to 14 days later for a histomorphometric analysis of bone and cartilage volumes. On day 14, the bone volume associated with titanium-plate-stabilized discs bearing an adsorbed depot of BMP-2 was 10-fold higher than that associated with their mechanically unstabilized counterparts. The bone volume associated with discs bearing a coating-incorporated depot of BMP-2 was similar in the mechanically unstabilized and titanium-plate-stabilized groups, and comparable to that associated with the titanium-plate-stabilized discs bearing an adsorbed depot of BMP-2. Hence, if an osteogenic agent is delivered in a cell-mediated manner (via coating degradation), ossification can be promoted even within a mechanically unstable environment.