Composite bilayered scaffolds with bio-functionalized ceramics for cranial bone defects: An in vivo evaluation

Enhanced healing of critical-sized bone defects using degradable scaffolds with tailored composition through immunomodulation and angiogenesis

The impact of orthopedic scaffolds on bone defect healing, particularly the late-stage bone remodeling process, is pivotal for the therapeutic outcome. This study applies fadditively manufactured scaffolds composed of hydroxyapatite-doped poly(lactide-co-glycolide)-b-poly(ethylene glycol)-b-poly(lactide-co-glycolide) (HA-PELGA) with varying properties to treat rat calvarial defects, elucidating their significant role in bone remodeling by modulating physiological responses. We engineered two scaffolds with different polylactic acid (PLA) to polyglycolic acid (PGA) ratio (9/1 and 18/1) to vary in hydrophobicity, degradation rate, mechanical properties, and structural stability. These variations influenced physiological responses, including osteogenesis, angiogenesis, and immune reactions, thereby guiding bone remodeling. Our findings show that the HA-PELGA(18/1) scaffold, with a slower degradation rate, supported bulk bone formation due to a stable microenvironment. Conversely, the HA-PELGA(9/1) scaffold, with a faster degradation rate and more active interfaces, facilitated the formation of a thin bone layer and higher bone infiltration. This study demonstrates these degradable scaffolds help to promote bone healing and reveals how scaffold properties influence the bone remodeling process, offering a potential strategy to optimize scaffold design aiming at late-stage bone defect healing.

Periosteum-Mimicking Tissue-Engineered Composite for Treating Periosteum Damage in Critical-Sized Bone Defects

The periosteum is an indispensable part of the bone that nourishes the cortical bone and acts as a repertoire of osteoprogenitor cells. Periosteal damage as a result of traumatic injuries, infections, or surgical assistance in bone surgeries is often associated with a high incidence of delayed bone healing (union or nonunion) compounded with severe pain and a risk of a secondary fracture. Developing bioengineered functional periosteal substitutes is an indispensable approach to augment bone healing. In this study, we have developed a biomimetic periosteum membrane consisting of electrospun oxygen-releasing antioxidant polyurethane on collagen membrane (polyurethane-ascorbic acid-calcium peroxide containing fibers on collagen (PUAOCC)). Further, to assist bone formation, we have developed a bioactive inorganic-organic composite cryogel (bioglass-collagen-gelatin-nanohydroxyapatite (BCGH)) as a bone substitute. In an in vitro simulated oxidative stress model, PUAOCC supported the primary periosteal cell survival. Moreover, in an in vivo, critical-sized (5.9 mm × 3.2 mm × 1.50 mm) unicortical rat tibial bone defect, implantation of PUAOCC along with the functionalized BCGH led to significant improvement in bone formation along with periosteal regeneration. The periosteal regeneration was confirmed by expression of periosteum-specific periostin and neuronal regulation-related protein markers. Our study demonstrates the development of a periosteum-mimicking membrane with promising applications to facilitate periosteal regeneration, thus assisting bone formation when used in combination with bone composites and mimicking the natural bone repair process.

Improved Bone Regeneration in Rabbit Bone Defects Using 3D Printed Composite Scaffolds Functionalized with Osteoinductive Factors

Large critical size bone defects are complicated to treat, and in many cases, autografts become a challenge due to size and availability. In such situations, a synthetic bone implant that can be patient-specifically designed and fabricated with control over parameters such as porosity, rigidity, and osteogenic cues can act as a potential synthetic bone substitute. In this study, we produced photocuring composite resins with poly(trimethylene carbonate) containing high ratios of bioactive ceramics and printed porous 3D composite scaffolds to be used as bone grafts. To enhance the overall surface area available for cell infiltration, the scaffolds were also filled with a macroporous cryogel. Furthermore, the scaffolds were functionalized with osteoactive factors: bone morphogenetic protein and zoledronic acid. The scaffolds were evaluated in vitro for biocompatibility and for functionality in vivo in critical bone defects (∼8 mm) in two clinically relevant rabbit models. These studies included a smaller study in rabbit tibia and a larger study in the rabbit cranium. It was observed that the bioactive molecule-functionalized 3D printed porous composite scaffolds provide an excellent conductive surface inducing higher bone formation and improved defect healing in both critical size long bones and cranial defects. Our findings provide strong evidence in favor of these composites as next generation synthetic bone substitutes.

Orthobiologics with phytobioactive cues: A paradigm in bone regeneration

Bone injuries occur due to various traumatic and disease conditions. Healing of bone injury occurs via a multi-stage intricate process. Body has the potential to rectify most of the bone injuries but some severe traumatic cases with critical size defects may require interventions. Autografts are still considered the "gold standard" for fracture healing but due to limitations associated with it, new alternatives are warranted. The field of orthobiologics has provided novel approaches using scaffolds, bioactive molecules, stem cells for the treatment of bone defects. Phyto-bioactives have been widely used in alternative medicine and folklore practices for curing bone ailments. It is believed that different bioactive constituents in plants work synergistically to give the therapeutic efficacy. Bioactives in plants extracts act upon different signal transduction pathways aiding in bone healing. The present review focuses on the use, chemical composition, mode of delivery, mechanism of action, and possible future strategies of three medicinal plants popularly used in traditional medicine for bone healing: Cissus quadrangularis, Withania somnifera and Tinospora cordifolia. Plants extracts seem to be a natural and non-toxic therapeutic alternative in treating bone injuries. Most of the studies on bone healing for these plants have reported oral administration of the extracts and presented them as a safe alternative without any side effects despite giving higher doses. Forthcoming studies could be directed towards the local delivery of extracts at the defect site. Unification of herbal extracts and orthobiologics could be an interesting direction in the field of bone healing in future. The present review intends to provide a bird's eye view of different strategies used in bone healing, mechanisms involved and future direction of advancements using phytobioactives and orthobiologics.