Comparison of cation and anion-mediated resolution enhancement of bioprinted hydrogels for membranous tissue fabrication.

Fabrication of engineered thin membranous tissues (TMTs) presents a significant challenge to researchers, as these structures are small in scale, but present complex anatomies containing multiple stratified cell layers. While numerous methodologies exist to fabricate such tissues, many are limited by poor mechanical properties, need for post-fabrication, or lack of cytocompatibility. Extrusion bioprinting can address these issues, but lacks the resolution necessary to generate biomimetic, microscale TMT structures. Therefore, our goal was to develop a strategy that enhances bioprinting resolution below its traditional limit of 150 µm and delivers a viable cell population. We have generated a system to effectively shrink printed gels via electrostatic interactions between anionic and cationic polymers. Base hydrogels are composed of gelatin methacrylate type A (cationic), or B (anionic) treated with anionic alginate, and cationic poly-L-lysine, respectively. Through a complex coacervation-like mechanism, the charges attract, causing compaction of the base GelMA network, leading to reduced sample dimensions. In this work, we evaluate the role of both base hydrogel and shrinking polymer charge on effective print resolution and cell viability. The alginate anion-mediated system demonstrated the ability to reach bioprinting resolutions of 70 µm, while maintaining a viable cell population. To our knowledge, this is the first study that has produced such significant enhancement in extrusion bioprinting capabilities, while also remaining cytocompatible.

Extracorporealization of the Mandibular Condyle: Effects on Viability and Function.

Study Design: For certain condylar fractures, extracorporealization of the condylar segment may be performed via extra-oral vertical ramus osteotomy (EVRO) to facilitate reduction and fixation. This approach can similarly be used for condyle-sparing resection of osteochondromas of the condyle. Due to controversy regarding long-term health of the condyle after extracorporealization, we conducted a retrospective analysis of surgical outcomes. Objective: For certain condylar fractures, extracorporealization of the condylar segment may be performed via extra-oral vertical ramus osteotomy (EVRO) to facilitate reduction and fixation. This approach can similarly be used for condyle-sparing resection of osteochondromas of the condyle. Due to controversy regarding long-term health of the condyle after extracorporealization, we investigated the viability of this technique through a retrospective analysis of outcomes. Methods: Twenty-six patients were treated using EVRO with extracorporealization of the condyle for both condylar fractures (18 patients) and osteochondroma (8 patients). Of the 18 trauma patients, 4 were excluded due to limited follow-up. Clinical outcomes were measured, including occlusion, maximum interincisal opening (MIO), facial asymmetry, incidence of infection, and temporomandibular joint (TMJ) pain. Radiographic signs of condylar resorption were investigated, quantified, and categorized using panoramic imaging. Results: Average follow-up was 15.9 months. Average maximum interincisal opening was 36.8 mm. Four patients demonstrated mild resorption and one patient demonstrated moderate resorption. Two cases of malocclusion were attributed to failed repairs of other concurrent facial fractures. Three patients reported TMJ pain. Conclusions: Extracorporealization of the condylar segment with EVRO to facilitate open treatment of condylar fractures is a viable treatment option when more conventional approaches prove unsuccessful.

A randomized prospective comparison of maxillomandibular fixation (MMF) techniques: "SMARTLock" hybrid MMF versus MMF screws.

OBJECTIVE: The aim of this study was to assess the efficacy of the "SMARTLock" hybrid system and determine whether it results in fewer intraoperative and postoperative complications compared with placement of intermaxillary fixation (IMF) screws in trauma patients. STUDY DESIGN: This prospective study, which was approved by the institutional review board, compared the results of MMF in mandibular fractures by using the Stryker "SMARTLock" hybrid system versus traditional IMF screws. Patients were recruited and assigned randomly to either group. The 2 groups were compared for placement time, intraoperative complications, loosening of hardware, postoperative complications, and time to device removal. RESULTS: We enrolled 32 patients in the study, with 13 patients randomized to the group receiving hybrid MMF (HMMF) with the SMARTLock system and 19 to the group of patients receiving MMF with traditional IMF screws. The mean application time for HMMF was 25.92 minutes compared with 18.28 minutes for IMF screws. After removal, the HMMF was associated with gingival overgrowth and gingival edema. CONCLUSIONS: This is the first study to compare HMMF with MMF with the use of IMF screws. Hybrid arch bars do require more manipulation for ideal placement compared with individually placed bone screws to achieve ideal MMF. Compared with IMF screws, the hybrid device was associated with gingival edema and overgrowth, but there was decreased incidence of loosening in the postoperative period.

Self-Retained Voice Prosthesis in the Decompression of the Odontogenic Keratocyst: A Technical Note.

Decompression of the odontogenic keratocyst has been a long-standing treatment modality in the armamentarium of oral-maxillofacial surgeons. Many different types of effective decompression tubes have been described in the literature. They reduce the size of the cystic lesion by decreasing the intraluminal pressure, induce histologic structural changes in the epithelial lining of the cyst, and allow for bone deposition to occur from the periphery of the cystic cavity. However, many of these have pitfalls including tube dislodgement, traumatization of the oral mucosa, and mucosal overgrowth. We describe a novel technique using an indwelling voice prosthesis (Inhealth Technologies, Carpinteria, CA) to decompress odontogenic keratocysts. We found that our method provides effective decompression using appropriate-length prostheses fit to the cyst dimensions. It provides improved comfort in patients, with less mucosal irritation or overgrowth, improved ease of irrigation, and improved retention that often does not require sutures.

Melanotic Neuroectodermal Tumor of Infancy: Case Report and Review of Management.

Melanotic neuroectodermal tumor of infancy (MNTI) is a rare pigmented tumor of the head and neck, which most commonly presents during the first year of life. Most cases present in the bones of the craniofacial region, including the maxilla (60.3%), skull (18.1%), and mandible (10.3%). The alveolar crest of the anterior maxilla is the most common site. MNTIs are locally aggressive, but benign, lesions derived from neural crest cells. However, they have a high rate of recurrence, and ≤6.5% of cases will demonstrate metastasis to lymph nodes or distant organs. They present clinically as an expansile pigmented mass. Radiographically, these lesions are often intraosseous expansile lytic lesions that can envelope or displace teeth. Extraosseous components might be better visualized on magnetic resonance imaging, demonstrating an enhancing iso- or hypointense mass on T1- and/or T2-weighted imaging. MNTIs have a distinctive biphasic cell population composed of large pigmented epithelial cells and small blue neuroblastic cells. Many immunohistochemical markers have also been identified. The large cell population often expresses cytokeratins, HMB-45, and vimentin; S100 is much less common. The small cell population typically expresses synaptophysin but will be negative for another neuroendocrine marker, chromogranin A. Rarely, patients will have elevated levels of urine vanillylmandelic acid, similar to findings from other tumors of neuroectodermal origin, such as neuroblastomas. First-line treatment of these lesions should be surgery with the goal of complete local excision. Radiotherapy and chemotherapy have been described but have been largely used as adjuvant or neoadjuvant therapy and for metastatic disease. We present a case of MNTI in an 8-week-old male, who had presented with a nonpigmented mass of the mandible associated with a pathologic fracture. In addition to a review of the data, our case serves to highlight potential prognostic factors, current clinical management, and local complications of this rare tumor.

Rescue of Premature Coronal Suture Fusion with TGF-ß2 Neutralizing Antibody in Rabbits with Delayed-Onset Synostosis.

OBJECTIVES: An overexpression of Tgf-ß2 leads to calvarial hyperostosis and suture fusion in individuals with craniosynostosis. Inhibition of Tgf-ß2 may help rescue fusing sutures and restore normal growth. The present study was designed to test this hypothesis. DESIGN: Twenty-eight New Zealand White rabbits with delayed-onset coronal synostosis had radiopaque markers placed on either side of the coronal sutures at 10 days of age. The rabbits were randomly assigned to: (1) sham control rabbits (n = 10), (2) rabbits with control IgG (100 µg/suture) delivered in a collagen vehicle (n = 9), and (3) rabbits with Tgf-ß2 neutralizing antibody (100 µg/suture) delivered in a collagen vehicle (n = 9). Longitudinal growth data were collected at 10, 25, 42, and 84 days of age. Sutures were harvested at 84 days of age for histomorphometry. RESULTS: Radiographic analysis showed significantly greater ( P < .05) coronal suture marker separation, craniofacial length, cranial vault length, height, shape indices, cranial base length, and more lordotic cranial base angles in rabbits treated with anti-Tgf-ß2 antibody than in controls at 42 and 84 days of age. Histologically, rabbits treated with anti-Tgf-ß2 antibody at 84 days of age had patent and significantly ( P < .05) wider coronal sutures and greater sutural area compared to controls. CONCLUSIONS: These data support our hypothesis that antagonism of Tgf-ß2 may rescue fusing coronal sutures and facilitate craniofacial growth in this rabbit model. These findings also suggest that cytokine therapy may have clinical significance in infants with progressive postgestational craniosynostosis.

Juvenile Trabecular Ossifying Fibroma.

Benign fibro-osseous lesions within the maxillofacial region represent a heterogeneous group of benign entities with overlapping histologic features. Ossifying fibroma, the rarest of these entities, represents a true neoplasm. Juvenile ossifying fibroma (JOF) is considered an aggressive rapidly growing sub-type. It tends to occur in the first or second decades of life. Based on histological and clinical features it can further be classified into two variants, namely juvenile trabecular ossifying fibroma (JTOF) and juvenile psammomatoid ossifying fibroma (JPOF). JTOF features a proliferation of cellular fibroblastic tissue admixed with woven bone trabeculae with varying histologic presentations. Correlation with clinical and radiographic features is essential to differentiate it from other fibro-osseous lesions. A case of JTOF of the mandible is exemplified in this Sine Qua Non Radiology-Pathology article.

Cystic Lesions of the Jaw in Children: A 15-Year Experience.

IMPORTANCE: Pediatric jaw cysts represent a rarely symptomatic clinical entity and are not well addressed in the otolaryngology literature. It is important that otolaryngologists should be familiar with these lesions, which can manifest as jaw swelling or as paranasal sinus abnormalities. OBJECTIVE: To review the clinical presentation, radiologic features, management, and outcomes of jaw cysts in children treated at a single academic institution. DESIGN, SETTING, AND PARTICIPANTS: Retrospective medical record review at a tertiary care children's hospital among patients 16 years and younger who were seen with a cystic jaw lesion. MAIN OUTCOMES AND MEASURES: Medical records were reviewed for data on symptoms, physical examination findings, imaging, pathology, interventions, and outcomes among children who were seen at the Department of Oral and Maxillofacial Surgery or the Department of Otorhinolaryngology-Head and Neck Surgery at the University of Maryland Medical Center between January 1997 and December 2012 and were diagnosed as having a jaw cyst. RESULTS: Fifty-seven patients were identified who were diagnosed as having a true cystic jaw lesion and whose complete medical records were available for review. The most common cystic lesions were keratocystic odontogenic tumors (n = 19) and dentigerous cysts (n = 17). Fifty-six percent (32 of 57) of all cystic lesions were asymptomatic on presentation and were identified by imaging. The second most common presentation was local swelling (n = 15), followed by dental irregularities (n = 6). All patients, except for 1 with an eruption cyst, required surgical intervention, including biopsy, enucleation, curettage, or ostectomy, with reconstruction as indicated. Keratocystic odontogenic tumors tended to require more treatment (median, 2 procedures) for metachronous lesions or recurrence. CONCLUSIONS AND RELEVANCE: Pediatric jaw cysts are unusual, and data are scarce regarding their presentation and management. Many of these cysts are asymptomatic and are identified incidentally on orthopantomography. Keratocystic odontogenic tumors were the most common lesion seen in our series, followed by dentigerous cysts. Surgical intervention is required in most patients with a cystic lesion of the jaw.

Tumors of the pediatric maxillofacial skeleton: a 20-year clinical study.

IMPORTANCE: Pediatric jaw tumors are a rare clinical entity and are not well addressed in the otolaryngology literature. It is important that otolaryngologists be familiar with the clinical features, management, and outcomes associated with these lesions. OBJECTIVE: To review the clinical presentation, management, and outcomes of jaw tumors in children treated at a tertiary care academic center. DESIGN, SETTING, AND PARTICIPANTS: Retrospective medical record review of children 16 years or younger who presented to the departments of Oral-Maxillofacial Surgery and Otorhinolaryngology at the University of Maryland Medical Center between 1992 and 2012 and were diagnosed as having a jaw tumor. A PubMed review of literature from 1992 to 2013 on jaw tumors in children was also conducted. MAIN OUTCOMES AND MEASURES: Medical records were reviewed for data on symptoms, physical findings, pathologic diagnosis, intervention, and outcomes. RESULTS: The medical records of 76 patients evaluated for a jaw mass were reviewed, and 20 were found to have a diagnosis of a jaw tumor. The 2 most common pathologic diagnoses were ameloblastoma (n = 5) and juvenile ossifying fibroma (n = 4). Two tumors were malignant, a rhabdomyosarcoma and a teratoma. Thirteen patients presented with evidence of a mass or swelling, 5 patients were asymptomatic with a lesion found on surveillance panoramic radiography, and 1 patient presented with epistaxis and 1 with facial weakness and pain. All tumors excluding a lymphangioma and a rhabdomyosarcoma were managed surgically. Eight patients underwent more than 1 procedure including secondary reconstruction prior to a satisfactory outcome. CONCLUSIONS AND RELEVANCE: Pediatric jaw tumors are rare lesions most commonly presenting with a swelling or mass. Patients can be asymptomatic with the lesion identified on routine imaging. Certain clinical features such as age, location of tumor, and presence or absence of bone and soft tissue can narrow the differential diagnosis and identify tumors that may be malignant. Incisional biopsy is an important first step. A majority of jaw tumors are benign but require surgical intervention for eradication of disease. Multiple procedures, including reconstruction, may be required for certain lesions prior to cure.

Blocking bone morphogenetic protein function using in vivo noggin therapy does not rescue premature suture fusion in rabbits with delayed-onset craniosynostosis.

BACKGROUND: Craniosynostosis is defined as the premature fusion of one or more cranial sutures. Bone morphogenetic proteins (BMPs), regulators of ossification, have been implicated in premature suture fusion. Noggin, an extracellular BMP inhibitor, has been shown experimentally to inhibit resynostosis following surgery. The present study was designed to test the hypothesis that BMP inhibition using noggin therapy may rescue sutures destined to fuse by inhibiting initial ossification. METHODS: Twenty-six, 10-day old rabbits with familial, delayed-onset, coronal suture synostosis were randomly divided into three groups: (1) the sham surgical control group, (2) the bovine serum albumin-treated group [10 µg/suture (protein/vehicle controls)], and (3) the noggin therapy group (10 µg/suture; experimental group). Sutural growth was monitored by radiopaque markers implanted at 10 days of age. At 25 days, the bovine serum albumin or noggin was combined with a slow-resorbing collagen vehicle and injected subperiosteally above the coronal suture. Somatic and sutural growth data were collected at 10, 25, 42, and 84 days of age. Coronal sutures were harvested at 84 days to histologically assess fusion. RESULTS: Results showed no significant (p > 0.05) differences in suture separation at any age. Suture fusion assessed by histomorphology did not differ among the three groups. Although previous data showed noggin to inhibit postoperative resynostosis in this craniosynostotic rabbit model, here there was no effect on initial suture fusion. CONCLUSION: These results suggest that in this rabbit model of craniosynostosis, BMPs do not play a role in the pathogenesis of craniosynostosis and only play a role in postoperative bony wound healing.

Reoperative midface trauma.

Reoperative midface surgery can be challenging. Although well-established surgical principles are still the basis of surgical approaches and techniques, the advent of new materials and technologies brings about opportunities to achieve the best possible outcomes with bony reconstruction and more precise results. Soft tissue deformities continue to be some of the most challenging, especially as they relate to the orbit, but continually evolving techniques offer improved results for volume corrections to treat enophthalmos and diplopia. Conventional orthognathic and reconstructive rhinoplasty techniques can also be applied to great effect and with satisfying results to treat posttraumatic malocclusions and nasal deformities.

Challenges associated with regeneration of orbital floor bone.

Orbital floor fractures are a serious consequence of craniofacial trauma and account for ∼60%-70% of all orbital fractures. Unfortunately, the body's natural response to orbital floor defects generally may not restore proper function and facial aesthetics, which is complicated by the thin bone and adjacent sinuses. Current clinical treatments include alloplastic implants and autologous grafts; however, each has associated disadvantages and sequelae. This review has outlined necessary components for a successful tissue-engineered construct for orbital floor repair. In addition, current successes and progress in the literature specific to orbital floors and craniofacial research have been reviewed. Finally, challenges and future directions have been described.

Macroporous hydrogels upregulate osteogenic signal expression and promote bone regeneration.

The objective of this work was to investigate the effects of macroporous hydrogel architecture on the osteogenic signal expression and differentiation of human mesenchymal stem cells (hMSCs). In particular, we have proposed a tissue engineering approach for orbital bone repair based on a cyclic acetal biomaterial formed from 5-ethyl-5-(hydroxymethyl)-beta,beta-dimethyl-1,3-dioxane-2-ethanol diacrylate (EHD) and poly(ethylene glycol) diacrylate (PEGDA). The EHD monomer and PEGDA polymer may be fabricated into macroporous EH-PEG hydrogels by radical polymerization and subsequent porogen leaching, a novel technique for hydrophilic gels. We hypothesized that EH-PEG hydrogel macroporosity facilitates intercellular signaling among hMSCs. To investigate this phenomenon, hMSCs were loaded into EH-PEG hydrogels with varying pore size and porosity. The viability of hMSCs, the expression of bone morphogenetic protein-2 (BMP-2), BMP receptor type 1A, and BMP receptor type 2 by hMSCs, and the differentiation of hMSCs were then assessed. Results demonstrate that macroporous EH-PEG hydrogels support hMSCs and that this macroporous environment promotes a dramatic increase in BMP-2 expression by hMSCs. This upregulation of BMP-2 expression is associated by a more rapid hMSC differentiation, as measured by alkaline phosphatase expression. Altering hMSC interactions with the EH-PEG hydrogel surface, by the addition of fibronectin, did not appear to augment BMP-2 expression. We therefore speculate that EH-PEG hydrogel macroporosity facilitates autocrine and paracrine signaling by localizing endogenously expressed factors within the hydrogel's pores and thus promotes hMSC osteoblastic differentiation and bone regeneration.

Characterization of cyclic acetal hydroxyapatite nanocomposites for craniofacial tissue engineering.

Cyclic acetal hydrogels are a novel group of biomaterials which may facilitate osteogenic differentiation of encapsulated bone marrow stromal cells (BMSCs) because of their neutral degradation products. Here, we have incorporated hydroxyapatite nanoparticles within cyclic acetal hydrogels to create cyclic acetal nanocomposites for craniofacial tissue engineering applications. We hypothesized that inclusion of nanosized hydroxyapatite particles within cyclic acetal hydrogels would upregulate osteogenic signal expression of encapsulated BMSCs, due to enhanced cell adhesion, and therefore promote osteodifferentiation. Experimental nanocomposite groups consisted of lower (5 ng/mL) and higher (50 ng/mL) concentrations of nanoparticles. The nanocomposites were characterized by scanning electron microscopy, transmission electron microscopy, and energy dispersive spectroscopy. Swelling parameters of hydrogels in the presence of nanoparticles was studied. Osteoblastic differentiation was characterized by alkaline phosphatase (ALP) and osteocalcin (OC) expression, whereas endogenous osteogenic signal expression was characterized by morphogenetic protein-2 (BMP-2) expression. Finally, immunohistochemistry was performed to detect the presence of OC at the protein level. Results indicated that hydroxyapatite nanoparticles were uniformly distributed throughout the hydrogels and did not affect material properties of the gels. Viability of cells was not affected by nanoparticle concentration, and BMP-2 and OC mRNA expression was enhanced in the presence of nanoparticles. However, a difference in BMP-2, ALP, and OC mRNA expression was not noted between the lower and higher concentrations of nanoparticles. This work demonstrates that inclusion of hydroxyapatite nanoparticles within a cyclic acetal nanocomposite hydrogel may enhance BMSC differentiation by promoting endogenous osteogenic signal expression.

Cyclic acetal hydroxyapatite nanocomposites for orbital bone regeneration.

We have incorporated hydroxyapatite nanoparticles within cyclic acetal hydrogels to create nanocomposites that can be used to repair surgically created orbital floor defects in a rabbit animal model. Nanosized hydroxyapatite particles may improve tissue engineering scaffold properties because they have similar length scale of many cellular and molecular components and therefore can enhance cellular adhesion and migration. We hypothesize that inclusion of nanosized hydroxyapatite particles (20-70 nm) within cyclic acetal hydrogels would support bone defect repair. The objectives of our study include (1) characterization of nanocomposites in vitro, (2) investigation of tissue response and capsule tissue surrounding nanocomposites in vivo, and (3) investigation of the potential of nanocomposites to facilitate bone formation at 7- and 28-day time points in vivo. Experimental nanocomposite groups consisted of 0, 10, and 50 ng/mL nanosized hydroxyapatite. In vitro results indicated uniform dispersion of nanoparticles within nanocomposites and increased compressive moduli of nanocomposites with increase in nanoparticle concentration and bone marrow stromal cell viability within nanocomposites. In vivo results at day 7 indicated a tissue response of mild to increased inflammatory cells and presence of immature fibrous tissue. At day 28, tissue response consisted of mild inflammatory response and mature tissue. Quantitative results at day 7 indicated no difference in total bone percentage area between groups. The results also indicated that the tissue capsule surrounding the 0, 10, and 50 ng group implants had no clear organization. Quantitative results at day 28 indicated that the tissue capsule surrounding the 0, 10, and 50 ng group implants was an organized layer and the bone percentage for the 50 ng group was significantly higher than that of the remaining groups. Initial results indicated that our nanocomposites initiate a positive in vivo response in terms of bone growth. However, the percentage of bone area compared with the total area was low at both time points. Thus, in our study, even after addition of nanoparticles to cyclic acetal hydrogels, their biocompatible properties were maintained. On the other hand, addition of nanoparticles to cyclic acetal hydrogels did not lead to complete restoration of orbital floor defects.

Tissue response and orbital floor regeneration using cyclic acetal hydrogels.

Orbital floor injuries are a common form of traumatic craniofacial injury that may not heal properly through the body's endogenous response. Reconstruction is often necessary, and an optimal method does not exist. We propose a tissue engineering approach for orbital bone repair based upon a cyclic acetal biomaterial formed from 5-ethyl-5-(hydroxymethyl)-beta,beta-dimethyl-1,3-dioxane-2-ethanol diacrylate (EHD) and poly(ethylene glycol) diacrylate (PEGDA). The EHD monomer and PEGDA polymer may be fabricated into an EH-PEG hydrogel by radical polymerization. The objectives of this work were to study (1) the tissue response to EH-PEG hydrogels in an orbital bone defect and (2) the induction of bone formation by delivery of bone morphogenetic protein-2 (BMP-2) from EH-PEG hydrogels. EH-PEG hydrogels were fabricated and implanted into an 8-mm rabbit orbital floor defect. Experimental groups included unloaded EH-PEG hydrogels, and EH-PEG hydrogels containing 0.25 microg and 2.5 microg BMP-2/implant. Results demonstrated that the unloaded hydrogel was initially bordered by a fibrin clot and then by fibrous encapsulation. BMP-2 loaded EH-PEG hydrogels, independent of concentration, were surrounded by fibroblasts at both time points. Histological analysis also demonstrated that significant bone growth was present at the 2.5 microg BMP-2/implant group at 28 days. This work demonstrates that the EH-PEG construct is a viable option for use and delivery of BMP-2 in vivo.

Deep neck infections: clinical considerations in aggressive disease.

Deep neck infections are common and occur as a consequence of several etiologies. Antibiotic therapy, interventional radiology, and patient support modalities have become increasingly sophisticated, although surgery continues to be the mainstay of treatment for most patients. Today, neck infections are rarely life threatening when sound and timely management is applied.

Cyclic acetal hydrogel system for bone marrow stromal cell encapsulation and osteodifferentiation.

Many systems have been proposed for the encapsulation of bone marrow stromal cells (BMSCs) within degradable hydrogels. Here, we use a novel cyclic acetal-based biomaterial formed from 5-ethyl-5-(hydroxymethyl)-beta,beta-dimethyl-1,3-dioxane-2-ethanol diacrylate (EHD) and poly(ethylene glycol) diacrylate (PEGDA). A cyclic acetal-based hydrogel may be preferred as cyclic acetals hydrolytically degraded into diols and carbonyls as primary degradation products, which may not affect local acidity, unlike other widely investigated polymers. The EHD monomer and PEGDA polymer may be fabricated into a EH-PEG hydrogel by radical polymerization initiated by the ammonium persulfate (APS) and N,N,N',N'-tetramethylethylenediamine (TEMED) system. The objective of this work is to determine whether the components utilized in the fabrication of EH-PEG hydrogels as well as the EH-PEG hydrogels permit BMSC viability, metabolic activity, and osteodifferentiation. Cell viability and metabolic activity were assessed after 30 min, 1 h, and 3 h of exposure to pertinent concentrations of the initiator system (10-20 mM). Osteodifferentiation was assessed by alkaline phosphatase and osteocalcin expression after a short exposure to the initiator system to simulate the encapsulation process. Lastly, cell viability was assessed immediately after encapsulation and after 7 days of culture within the EH-PEG hydrogels. Results indicate that the metabolic activity and viability of BMSCs are minimally affected, and that osteodifferentiation is not significantly affected by the APS-TEMED initiator system. Also, encapsulated BMSCs maintained viability within EH-PEG hydrogels for 7 days. This work demonstrates that the EH-PEG hydrogel is a viable option for the encapsulation and osteodifferentiation of BMSCs.